Atom | Definition, Structure, Nuclear Properties, History & Facts



What is an Atom?

An atom is the tiniest unit of matter that forms a chemical element. Each and every type of solid, liquid, gas, and form of plasma is composed of neutral or ionized atoms. In general, atoms are 100 picometers across. Due to quantum effects, they are so small that it is impossible to predict their behavior with sufficient accuracy using classical physics, as would be the case, for example, if they were tennis balls.

A nucleus and one or more electrons connected to it make up each atom. The nucleus is composed of one or more protons and a sizable number of neutrons. Only the most common kind of hydrogen has no neutrons. More than 99.94% of the mass of an atom is found in its nucleus. The electric charges of the protons are positive, those of the electrons are negative, and those of the neutrons are zero. The atom is electrically neutral if the number of protons and electrons is equal. An atom has an overall charge of positive or negative if it contains more electrons than protons; these atoms are known as ions.

The electromagnetic force pulls an atom's electrons toward the protons in its atomic nucleus. The nuclear force draws the protons and neutrons in the nucleus together. The electromagnetic force that keeps positively charged protons apart is typically weaker than this force. The electromagnetic force that repels objects can occasionally outweigh the nuclear force. The nucleus breaks in this instance, leaving behind several parts. This type of nuclear decay exists.

The atomic number, which designates which chemical element the atom belongs to, is determined by the quantity of protons in the nucleus. For instance, a copper atom is any atom with 29 protons. The element's isotope is determined by the number of neutrons in it. For instance, a copper atom with 34 neutrons is copper-63 (29+34), and one with 36 neutrons is copper-65; naturally occurring copper is composed of roughly 70% Cu-63 and the remaining 30% Cu-65.

Atoms can create chemical compounds like molecules or crystals by joining up with one or more other atoms through chemical bonds. For instance, the Statue of Liberty in New York City was initially built of pure copper, but over time, oxygen, carbon, and Sulphur atoms reacted with the surface to give the copper a green patina. The majority of the physical changes seen in nature are caused by atoms' capacity to bind and detach. The science that investigates these changes is chemistry.

In philosophy

Many ancient societies, including those of Greece and India, adopted the fundamental notion that matter is composed of tiny, inseparable components. The ancient Greek term Atomos, which meaning "uncuttable," is the source of the word atom. Modern atomic theory is not based on these antiquated ideas; rather, it is founded on philosophical reasoning as opposed to scientific reasoning. John Dalton, a scientist who lived in the early 19th century, observed that chemical elements appeared to join with one another in basic weight units. On the idea that these weight units were the basic building blocks of matter, he chose to call these units "atoms." Although it was later found that Dalton's atoms are not truly indivisible, the phrase persisted.

Atom Structure

Although the term "atom" originally referred to a particle that could not be divided into smaller particles, it is now used to refer to a group of subatomic particles that make up an atom. The electron, proton, and neutron are the building blocks of an atom.

Using a mass of 9.11 10-³¹ kg, the electron is by far the least massive of these particles. It also has a negative electrical charge and is too tiny to be measured with current methods. Prior to the discovery of neutrino mass, it was the lightest particle with a positive measured rest mass. Under normal circumstances, the attraction between the positively charged nucleus's positively and negatively charged electrons binds them to it. An atom becomes positively or negatively charged overall if it has more or less electrons than its atomic number; such an atom is referred to as an ion. J.J. Thomson had a major role in the discovery of electrons in the late 19th century; for further information, see the history of subatomic physics.

With a mass of 1.6726 10-²⁷ kg, protons are 1,836 times heavier than electrons and have a positive charge. The atomic number of an atom is the sum of all of its protons. Ernest Rutherford noted in 1909 that nitrogen emits what looked to be hydrogen nuclei when subjected to an alpha particle bombardment. He recognized the hydrogen nucleus as a separate particle within the atom in 1920 and gave it the name proton.

The free mass of a neutron is 1.6749 10⁻²⁷ kg, or 1,839 times that of an electron. Neutrons have no electrical charge. Although neutrons are the heaviest of the three component particles, the nuclear binding energy can diminish their mass. Nucleons, which are made up of protons and neutrons, are similar in size—on the order of 2.5 10⁻¹⁵ m—but their'surfaces' are not clearly defined. James Chadwick, an English physicist, discovered the neutron in Year 1932..

In the Standard Model of physics, protons and neutrons are composite particles made up of genuinely elementary particles called quarks, whereas electrons are truly elementary particles with no intrinsic structure. Atoms contain two different types of quarks, each of which has a little electric charge. Two up quarks (each having a charge of +2/3) and one down quark (with a charge of 1/3) make up protons.

One up quark and two down quarks make up neutrons. The two particles' different masses and charges are explained by this disparity.

The strong interaction (also known as the strong force), which is mediated by gluons, holds the quarks together. The nuclear force, a remnant of the strong force with somewhat modified range-properties, holds the protons and neutrons to one another in the nucleus (see the article on the nuclear force for more). The gluon is an elementary particle that mediates physical forces. It belongs to the family of gauge bosons.


Nucleus of an Atom

Nucleons are the collective name for the bonded protons and neutrons that make up the small atomic nucleus of an atom. A nucleus's radius is about equivalent to 1.07 3√ A femtometers, where 1.07 3√ A is the sum of all its nucleons. This is substantially less than the atom's radius, which is approximately 105 fm. The residual strong force, a short-range attractive potential, holds the nucleons together. This force is substantially stronger than the electrostatic force that prevents positively charged protons from repelling one another at distances lower than 2.5 fm.

The atomic number, or number of protons in an atom, is the same for all atoms of the same element. The isotope of an element can differ depending on the amount of neutrons in that element. The nuclide is determined by the total amount of protons and neutrons. The stability of the nucleus is determined by the ratio of neutrons to protons, with some isotopes undergoing radioactive decay.

Fermions are defined as the proton, electron, and neutron. The Pauli exclusion principle, which applies to fermions, forbids identical fermions—such as multiple protons—from existing in the same quantum state simultaneously. As a result, each proton in the nucleus must exist in a distinct quantum state from every other proton, and the same holds true for each neutron in the nucleus and each electron in the electron cloud.

Through a radioactive decay that brings the number of protons and neutrons closer together, a nucleus with a different number of protons than neutrons may be able to transition to a lower energy state. As a result, atoms with equal numbers of protons and neutrons are more resistant to decay. However, as the atomic number increases, an increasing proportion of neutrons are needed to maintain the stability of the nucleus due to the mutual repulsion of the protons.

It is possible to change the proportion of protons and neutrons in the atomic nucleus, albeit the strong force may make this need extremely high energy. When several atomic particles combine to form a heavier nucleus, such as when two nuclei collide energetically, this process is known as nuclear fusion. Protons, for instance, need energy between 3 and 10 keV to break through the coulomb barrier and combine into a single nucleus at the center of the Sun. The opposing process, known as nuclear fission, causes a nucleus to split into two smaller nuclei, typically by radioactive decay. High energy subatomic or photon bombardment of the nucleus is another way to alter it. The atom transforms into a different element if this changes the number of protons in a nucleus.

According to Albert Einstein's mass-energy equivalence formula, E=mc2, where m is the mass loss and c is the speed of light, if the mass of the nucleus after a fusion reaction is less than the sum of the masses of the separate particles, then the difference between these two values can be emitted as a type of usable energy (example gamma ray or the kinetic energy of a beta particle). The non-recoverable loss of the energy is what keeps the fused particles together in a state that calls for this energy to separate them. This deficit is a component of the binding energy of the new nucleus.

In most cases, the fusing of two nuclei that results in bigger nuclei with atomic numbers less than those of iron and nickel—a total nucleon number of roughly 60—occurs as an exothermic process that releases more energy than is necessary to bring the nuclei together. Because of this process of energy release, nuclear fusion in stars is a self-sustaining reaction. The binding energy per nucleon in the nucleus starts to decline for heavier nuclei. Therefore, fusion events that result in nuclei with atomic weights more than about 60 and atomic numbers greater than about 26 are endothermic reactions. These more powerful nuclei are unable to undertake an energetic fusion reaction that would maintain a star's hydrostatic stability.

Through a radioactive decay that brings the number of protons and neutrons closer together, a nucleus with a different number of protons than neutrons may be able to transition to a lower energy state. As a result, atoms with equal numbers of protons and neutrons are more resistant to decay. However, as the atomic number increases, an increasing proportion of neutrons are needed to maintain the stability of the nucleus due to the mutual repulsion of the protons.

Electron cloud

The electromagnetic force pulls the electrons of an atom toward the protons in the nucleus. The electrons are constrained by this force inside an electric potential well surrounding the smaller nucleus, therefore an external energy source is required for the electron to escape. The attractive force between an electron and the nucleus increases with proximity. As a result, electrons trapped close to the potential well's core need more energy to free themselves than electrons trapped farther apart.

Like other particles, electrons exhibit both wavelike and particle like characteristics. Inside the potential well, there is an area known as the electron cloud, where each electron creates a particular kind of standing wave in three dimensions that is stationary with respect to the nucleus. An atomic orbital, a mathematical function that describes the likelihood that an electron would appear to be at a specific location when its position is measured, defines this behaviour. Around the nucleus, there is only a definite (or quantized) collection of these orbitals since all other potential wave patterns quickly decay into a more stable form. Orbitals vary from one another in size, shape, and orientation, and they can have one or many ring or node structures.

Each atomic orbital corresponds to a specific electron energy level. A photon with enough energy to propel it into the new quantum state can be absorbed by an electron to change its state to one at a higher energy level. Similar to how a photon can emit extra energy as a photon, an electron in a higher energy state can drop to a lower energy level spontaneously. Atomic spectral lines are caused by these distinctive energy values, which are determined by the variations in the energies of the quantum states.

The electron binding energy is much smaller than the binding energy of nucleons since it is required to remove or add an electron. For instance, splitting a deuterium nucleus only requires 2.23 million eV, whereas stripping a ground-state electron from a hydrogen atom only needs 13.6 eV. If protons and electrons are distributed equally across the atom, the atom is electrically neutral. Ions are defined as atoms with either a surplus or a shortage of electrons. The electrons that are most distant from the nucleus may be shared or transferred to other neighboring atoms. Atoms can form molecules and other kinds of chemical compounds, such as ionic and covalent network crystals, by this method.

Properties of Atom

Nuclear properties

Any two atoms that have the same number of protons in their nuclei are said to be members of the same chemical element. Differing isotopes of the same element are atoms that have different numbers of neutrons but equal quantities of protons. For instance, all hydrogen atoms can accept exactly one proton, but there are other isotopes of hydrogen that can have one, two, or more neutrons. Hydrogen-1 is the isotope that is most prevalent and is also known as protium. From the single proton element hydrogen through the 118 proton element oganesson, the known elements are grouped by their atomic numbers. The radioactivity of element 83 (bismuth) is so minute as to be essentially nonexistent, while all isotopes of known elements with atomic numbers greater than 82 are radioactive.

The term "stable isotopes" refers to the 339 nuclides that naturally occur on Earth, of which 252 (or around 74%), have not been seen to decay. Only 90 nuclides have been observed to decay, despite the fact that another 162 (for a total of 252) are theoretically capable of doing so. Additionally, they are formally categorized as "stable" Another 34 radioactive nuclides are long-lived enough to have existed since the Solar System's formation, with half-lives more than 100 million years. Primordial nuclides are the 286 nuclides in this group. Last but not least, there are 53 more short-lived nuclides that are known to be produced naturally, either as daughter products of primordial nuclide disintegration (such as radium from uranium) or as byproducts of the Earth's natural energetic processes, such as cosmic ray bombardment (for example, carbon-14).

There is at least one stable isotope for each of the 80 chemical elements. For each of these elements, there are often just a few stable isotopes, with an average of 3.2 stable isotopes per element. While ten stable isotopes have been found for the element tin, which has the most stable isotopes of any element, 26 other elements have only one. There are no stable isotopes for elements 43, 61, or 83 or above.

The ratio of protons to neutrons and the presence of specific "magic numbers" of protons or neutrons, which stand for closed and filled quantum shells, both influence the stability of isotopes. The filled shells, like the filled shell of 50 protons for tin, confer remarkable stability on the nuclide. These quantum shells correspond to a set of energy levels within the shell model of the nucleus of an atom. Only four of the 252 known stable nuclides—hydrogen-2 (deuterium), lithium-6, boron-10, and nitrogen-14—have odd numbers of both protons and neutrons. Additionally, only four naturally occurring radioactive odd-odd nuclides—potassium-40, vanadium-50, lanthanum-138, and tantalum-180m—have a half-life of over a billion years. Due to nuclear pairing effects, most odd-odd nuclei are extremely unstable to beta decay because the decay products are even-even and thus more tightly bonded.

Atomic Mass

The protons and neutrons that make up an atom account for a significant portion of its mass. The mass number refers to the total number of these particles (also known as "nucleons") in an atom. Because it expresses a count, it is a positive integer and dimensionless (rather than having a dimension of mass). The mass number "carbon-12," which possesses 12 nucleons, is an illustration of its utilization (six protons and six neutrons).

Daltons (Da), commonly known as the unified atomic mass unit, are frequently used to express the actual mass of an atom at rest (u). This quantity is equal to one-twelfth of a carbon-12 free neutral atom's mass, or around 1.66×10−27 kg The atomic weight of hydrogen-1, the lightest isotope of hydrogen and the nuclide with the lowest mass, is 1.007825 Da. The atomic mass is the value of this number. A given atom has an atomic mass that is generally equal (within 1%) to its mass number times the atomic mass unit (for instance, the mass of a nitrogen-14 is around 14 Da), although this value won't be an exact integer unless it's carbon-12 (by definition). Lead-208 has the heaviest stable atom, with a mass of 207.9766521 Da.

Chemists employ the mole instead of working directly with atoms since even the most massive ones are far too light. Any element's mole of atoms always has the same amount of atoms (about 6.022×10²³). This value was set so that a mole of atoms of an element with an atomic mass of 1 u would have a mass close to that of 1 gramme. Because each carbon-12 atom has an exact atomic mass of 12 Da according to the definition of the unified atomic mass unit, a mole of carbon-12 atoms weighs precisely 0.012 kg.

Shape and size of Atom

Since an atom's outer boundary isn't clearly defined, its dimensions are typically expressed in terms of an atomic radius. This is a measurement of how far the electron cloud may be seen to stretch from the nucleus. This presupposes that the atom has a spherical shape, which only holds true for atoms in free space or a vacuum. The distances between two nuclei when two atoms are linked together in a chemical bond can be used to calculate atomic radii. The radius is dependent on an atom's position on the atomic structure diagram, the kind of chemical bond, the number of nearby atoms (coordination number), and a quantum mechanical characteristic called spin. Atom size tends to increase while travelling down columns but decrease when moving across rows on the periodic table of the elements (left to right). As a result, helium has the smallest atom, with a radius of 32 pm, whereas caesium has one of the largest, with a radius of 225 pm.

An atom's form can depart from spherical symmetry when subjected to outside pressures, such electrical fields. Group-theoretical analysis demonstrates that the deformation is dependent on the field strength and the orbital type of the outer shell electrons. For instance, in crystals, where strong crystal-electrical fields may develop at low-symmetry lattice locations, aspherical deviations may be induced. It has been demonstrated that Sulphur ions and chalcogen ions in pyrite-type compounds experience significant ellipsoidal deformations.

Although individual atoms can be seen using a scanning tunneling microscope, individual atoms cannot be seen with an optical microscope because their dimensions are hundreds of times smaller than the wavelengths of light (400-700 nm). Consider that an average human hair is around 1 million carbon atoms wide to get an idea of how tiny an atom is. About 2 sextillion (2×10²¹) hydrogen atoms and 2 sextillion (2×10²¹) oxygen atoms make up each individual drop of water. The average number of carbon atoms in a single carat diamond, which has a mass of 2×10⁻⁴ kg, is 10 sextillion (10²²). The atoms in an apple would be around the same size as the original apple if it were enlarged to the size of the Earth.

Radioactive decay

Every element has one or more isotopes with radioactively unstable nuclei that can decay, releasing electromagnetic radiation or nuclear particles. When a nucleus' radius exceeds that of the strong force, which only functions across distances of the order of one fm, radioactivity can result.

The most common forms of radioactive decay are as below:

When a helium nucleus with two protons and two neutrons emits an alpha particle, the process of alpha decay is initiated. With a lower atomic number, a new element is produced as a result of the emission.

The weak force controls the processes of beta decay (and electron capture), which are caused by the conversion of a neutron into a proton or a proton into a proton. Proton to neutron transitions (with the exception of electron capture) result in the emission of a positron and a neutrino, while neutron to proton transitions are accompanied by the emission of an electron and an antineutrino. The discharges of electrons or positrons are known as beta particles. The atomic number of the nucleus is altered by one during beta decay. Because electron capture uses less energy than positron emission, it is more frequently used. Instead of a positron being released from the nucleus, an electron is instead taken up by the nucleus in this form of decay. In the course of this process, a proton turns into a neutron while still emitting neutrinos.

Gamma decay: this process, which causes the emission of electromagnetic radiation, happens when the energy level of the nucleus changes to a lower state. The excited nucleus state that causes gamma emission often happens after the emission of an alpha or beta particle. Gamma decay consequently frequently follows alpha or beta decay.

Ejection of neutrons, protons, nucleon clusters, or more than one beta particle from a nucleus are some of the other, more uncommon types of radioactive decay. Internal conversion is a process that generates high-speed electrons that are not beta rays, followed by the generation of high-energy photons that are not gamma rays, and is an analogue of gamma emission that permits excited nuclei to lose energy in a different way. In a process known as spontaneous nuclear fission, a few big nuclei explode into two or more charged pieces of various masses and a number of neutrons.

The half-life, or characteristic decay time period for any radioactive isotope, is defined by how long it takes for half of a sample to decay. Every half-life, this exponential decay mechanism gradually reduces the amount of the remaining isotope by 50%. Thus, only 25% of the isotope is present after two half-lives, and so on.

Magnetic moment of Atom

Spin is a fundamental quantum mechanical feature of elementary particles. Although these particles are thought to be point-like and cannot be considered to be rotating strictly speaking, this is equivalent to the angular momentum of an object that is spinning around its centre of mass. The reduced Planck constant (ħ) is used to measure spin, and electrons, protons, and neutrons all have spin 1⁄2 ħ, or "spin-1⁄2"," respectively. In an atom, the nucleus itself has angular momentum because of its nuclear spin, whereas electrons moving around the nucleus have orbital angular momentum in addition to their spin.

Just as a revolving charged item produces a magnetic field conventionally, the magnetic field created by an atom—its magnetic moment—is governed by these several types of angular momentum, although electron spin makes the most significant contribution. Bound electrons couple up with each other as a result of the Pauli exclusion principle, which states that no two electrons may exist in the same quantum state. In each pair, one electron is in a spin-up state while the other is in a spin-down state. As a result, in some atoms with an even number of electrons, these spins cancel one another out, bringing the total magnetic dipole moment to zero.

An unpaired electron and a net overall magnetic moment result from an odd number of electrons in ferromagnetic materials like iron, cobalt, and nickel. When the spins of unpaired electrons are aligned with one another, a spontaneous process known as an exchange contact, it results in the orbitals of nearby atoms overlapping and a lower energy state. A quantifiable macroscopic field can be produced by the substance when the magnetic moments of ferromagnetic atoms are lined up. When there is no magnetic field, the magnetic moments of the individual atoms in paramagnetic materials line up in random directions, but when there is a field, they line up.

When both neutrons and protons are present in even amounts, the nucleus of an atom will not have a spin; however, the nucleus may have a spin in other situations. Because of thermal equilibrium, spin-aligned nuclei typically face random orientations, but for some elements, such as xenon-129, it is feasible to polarise a sizable fraction of the nuclear spin states, causing them to face the same direction. This phenomenon is known as hyperpolarization. Magnetic resonance imaging will benefit greatly from this.

Energy levels of Atom

When the distance from the nucleus reaches infinity, the potential energy of an electron in an atom is negative; the dependency on the electron's position reaches its minimum inside the nucleus, roughly in inverse proportion to the distance. A bound electron can only inhabit a limited range of states in the quantum-mechanical model, each of which corresponds to a distinct energy level; for a theoretical justification, see the time-independent Schrödinger equation. The amount of energy required to release an electron from an atom can be used to determine an energy level, which is often expressed in electronvolts (eV). The ground state, or stationary state, of a bound electron is its lowest energy level, while an electron transitioning to a higher level produces an excited state. Due to a rise in the (average) distance from the nucleus, the energy of the electron also increases along with n. The electrostatic potential of the nucleus does not contribute to the energy's dependence on ℓ, rather, electron interaction does.

According to the Niels Bohr model, which can be precisely calculated by the Schrödinger equation, for an electron to transition between two states, such as from the ground state to the first excited state, it must absorb or emit a photon at an energy matching the difference in the potential energy of those levels. Electrons move like particles when they hop between orbitals. For instance, just one electron will change states in response to a single photon striking the electrons; for further information, see Electron characteristics.

These particular energy levels manifest as separate bands in the electromagnetic spectrum because the energy of a photon is proportional to its frequency when it is emitted. Each element has a distinctive spectrum, which can vary depending on the nuclear charge, the electron subshells it occupies, how the electrons interact electromagnetically, and other things.

Some photons are absorbed by atoms when a continuous spectrum of energy is conveyed through a gas or plasma, changing the energy state of the electrons. Excited electrons that are still attached to their atom spontaneously release their energy as a photon, which travels in an arbitrary direction. As a result, they lose energy and fall to lower energy levels. In order to create a sequence of dark absorption bands in the energy output, the atoms act as a filter. (An observer looking at the atoms from a perspective that excludes the background continuous spectrum sees a series of emission lines from the photons the atoms emit.) The strength and width of atomic spectral lines can be measured using spectroscopy in order to determine a substance's composition and physical characteristics.

Some of the spectral lines have a fine structural splitting, as may be seen by closely examining them. The interaction between the spin and velocity of the outermost electron, known as spin-orbit coupling, is what causes this. The Zeeman effect is a phenomenon whereby spectral lines break into three or more components when an atom is exposed to an external magnetic field. This results from the magnetic field's interaction with the atom's and its electrons' magnetic moment. A single spectral line can be seen when an atom has numerous electron configurations at the same energy level. Multiple spectral lines are produced as a result of the atom's shifting of these electron configurations to slightly different energy levels as a result of the magnetic field's interaction with it. The Stark effect, which modifies the electron energy levels, can result in a similar splitting and shifting of spectral lines when an external electric field is present.

An interacting photon with the right energy can promote the emission of a photon with the right energy level if a bound electron is in an excited state. To make this happen, the electron must transition to a state with a lower energy and an energy difference that matches the energy of the photon that is interacting with it. The photons that were released and those that had interacted move away in parallel and with synchronized phases. In other words, the two photons' wave patterns are coordinated. With the help of this physical characteristic, lasers may produce coherent light beams with a specific frequency range.

Valence and bonding behavior of Atom

An element's valency is its capacity for combination. The amount of bonds it can establish with other atoms or groups is what determines its size. The valence shell and the electrons that reside in it are referred to as an atom's outermost electron shell and its valence electrons, respectively. The bonding behaviour with other atoms is governed by the quantity of valence electrons. Chemical interactions between atoms frequently result in the filling (or emptying) of their outer valence shells. For bonds that form between atoms with one more electron than a filled shell and others that are one electron short of a full shell, such as occurs in the compound sodium chloride and other chemical ionic salts, a transfer of one electron between atoms is a suitable approximation. Multiple valences, or propensities to share different numbers of electrons in various compounds, are characteristics of several elements. Thus, there are numerous types of electron-sharing that go beyond straightforward electron transfers in the chemical bonds formed between these components. Examples include organic compounds and the atom carbon.

A periodic table, which is designed to show recurrent chemical features, is frequently used to illustrate the chemical elements. Elements with the same amount of valence electrons form a group and are arranged in the same column of the table. The elements at the extreme right of the chart have their outer shell entirely filled with electrons, resulting in chemically inert substances known as the noble gases. (The horizontal rows correspond to the filling of a quantum shell with electrons.)

States of Atom

Amounts of atoms are present in various states of matter, which depend on external physical factors like pressure and temperature. Materials can change between solids, liquids, gases, and plasmas by adjusting the circumstances. A material can also exist in many allotropes withing a state. Solid carbon, which can be found as graphite or diamond, is one illustration of this. Additionally, there are gaseous allotropes like ozone and dioxygen.

Atoms can create a Bose-Einstein condensate at temperatures very close to absolute zero, at which point quantum mechanical effects that are typically only seen at the atomic scale become visible on a macroscopic scale. The behaviour of this group of supercooled atoms therefore resembles that of a single super atom, which would allow for important verifications of quantum mechanical behaviour.

Identification of Atom

Atoms are so small that they cannot be seen, but tools like the scanning tunnelling microscope (STM) allow us to see them at the surfaces of materials. The quantum tunnelling phenomenon, which is used in the microscope, enables particles to pass through a barrier that would be impossible from a classical perspective. Between two biassed electrodes, electrons can tunnel through the vacuum and produce a tunnelling current that depends exponentially on the distance between the electrodes. One electrode is ideally an atom-containing sharp tip. The tip's height is changed at each point of the surface scan in order to maintain a constant tunnelling current. The height profile is determined by how close to the surface the tip moves and how far it moves away. For low bias, the microscope captures the local density of the electronic states close to the Fermi level by averaging electron orbitals across densely clustered energy levels. Due to the distances involved, both electrodes must be exceedingly stable; only then can periodicities that are specific to individual atoms be recognized. The technique is not chemically specialised and is unable to distinguish between the atomic species that are present at the surface.

The mass of an atom can be used to quickly identify it. A magnetic field will cause an atom's route to bend if one of its electrons is removed, creating an ion. The mass of the atom determines the radius by which the magnetic field rotates an ion's trajectory. This idea is the basis for the mass spectrometer's measurement of the mass-to-charge ratio of ions. By monitoring the strength of the several ion streams, the mass spectrometer can calculate the percentage of each isotope present in a sample if it contains multiple isotopes. Both inductively coupled plasma mass spectrometry and atomic emission spectroscopy, which use a plasma to evaporate materials for analysis, are methods for vaporizing atoms.

Using time-of-flight mass spectrometry, the atom-probe tomograph can chemically detect individual atoms with sub-nanometer resolution in three dimensions.

Non-destructively identifying the atomic species present in a sample involves the use of electron emission techniques like X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES), which measure the binding energies of the core electrons. Both of these can be made area-specific with the right emphasis. Electron energy loss spectroscopy (EELS), which analyses the energy loss of an electron beam inside a transmission electron microscope when it comes into contact with a part of a material, is another such technique.

The atomic makeup of far-off stars can be examined using excited state spectra. It is possible to isolate and tie particular light wavelengths present in the observed light from stars to the quantum transitions in free gas atoms. A gas-discharge lamp made of the same substance can reproduce these hues. This method allowed for the discovery of helium 23 years before it was identified on Earth.

Origin and current state of Atom

With an average density of roughly 0.25 particles/m3, baryonic matter makes up about 4% of the observable universe's total energy density (mostly protons and electrons). Particles are far more concentrated within galaxies like the Milky Way, where the interstellar medium (ISM) has a matter density of 105 to 109 atoms/m3. The Local Bubble is thought to contain the Sun, making the density in the area around the Sun merely 103 atoms/m3. The ISM undergoes constant enrichment with elements more massive than hydrogen and helium as a result of the formation of stars, which arise from thick clouds in the ISM.

Up to 95% of the baryonic substance in the Milky Way is confined inside stars, which are hostile environments for atomic matter. About 10% of the galaxy's mass is made up of dark matter, the balance being entirely made up of total baryonic material. Most "atoms" get totally ionised, or have all of their electrons detached from their nuclei, as a result of the high temperatures found inside stars. Electron shells are not conceivable in stellar remnants, with the exception of their surface layers, due to extreme pressure.

Formation of Atom

It is believed that electrons have existed in the universe since before the Big Bang. Atomic nuclei forms in nucleosynthesis reactions. In about three minutes Big Bang nucleosynthesis produced most of the helium, lithium, and deuterium in the Universe, and perhaps some of the beryllium and boron.

Atoms' ubiquity and stability depend on their binding energy, which is lower than the energy of a nucleus and electrons in an unbound system. Plasma is a gas of positively charged ions (perhaps even bare nuclei) and electrons that exists where the temperature is substantially higher than the ionization potential. Atoms become statistically advantageous when the temperature falls below the ionization potential. 380,000 years after the Big Bang, during a period known as recombination, the expanding Universe cooled enough for electrons to connect to nuclei, atoms (complete with bound electrons) overtook charged particles.

Since the Big Bang, which did not result in the production of carbon or heavier elements, atomic nuclei have been fused in stars to form additional helium and the series of elements from carbon to iron (via the triple alpha process).

Through cosmic ray spallation, isotopes like lithium-6, as well as some beryllium and boron, are produced in space. This happens when a high-energy proton collides with an atomic nucleus, ejecting a significant number of nucleons.

The r-process, which involves the capture of neutrons by atomic nuclei in supernovae and colliding neutron stars, and the s-process, which occurs in AGB stars, both entail the production of elements heavier than iron. Lead is an example of an element that was primarily created through the radioactive decay of heavier elements.


The majority of the atoms that make up the Earth and its inhabitants were present in the nebula that formed when the Solar System broke out from a molecular cloud. Radiometric dating can be used to calculate the age of the Earth by comparing the relative proportions of the remaining elements, which are the product of radioactive decay. Because of its lower abundance of helium-3, the majority of the helium in the Earth's crust (about 99% of the helium from gas wells) is a byproduct of alpha decay..

There are a few trace atoms on Earth that are neither products of radioactive decay nor were there in the beginning (i.e., not "primordial"). Cosmic rays cause ongoing atmospheric production of carbon-14. On Earth, some atoms have been produced artificially, either on purpose or as a byproduct of nuclear reactions or explosions. The only naturally occurring transuranic elements—those with atomic numbers more than 92—on Earth are plutonium and neptunium. With the exception of residues of plutonium-244, which may have been left behind by cosmic dust, all detectable amounts of transuranic elements have long since decayed because their radioactive lives are less than the Earth's age today. Neutron capture in uranium ore results in the production of natural reserves of plutonium and neptunium.

There are roughly 1.33 x 1050 atoms on Earth. 99% of the atmosphere is made up of molecules, including carbon dioxide as well as diatomic oxygen and nitrogen, despite the fact that a few isolated atoms of noble gases like argon, neon, and helium do exist in minute quantities. The vast majority of atoms mix near the Earth's surface to create a variety of compounds, including water, salt, silicates, and oxides. Crystals, liquid, and solid metals are examples of materials made up entirely of atoms rather than distinct molecules. This atomic matter develops networked arrangements without the specific kind of molecular matter's small-scale disrupted order.

Rare and theoretical forms

It is known that all nuclides with atomic numbers greater than 82 (lead) are radioactive. On Earth, there is no primordial nuclide with an atomic number greater than 92 (uranium), and heavier elements typically have shorter half-lives. Even yet, moderately stable isotopes of super heavy elements with atomic numbers 110 to 114 may exist as a "island of stability." The half-life of the island's most stable nuclide has been estimated to be anywhere from a few minutes to millions of years. In any event, in the absence of any stabilizing effects, super heavy atoms (with Z > 104) would not exist due to growing Coulomb repulsion (which causes spontaneous fission with progressively shorter half-lives).

Exotic matter

There is an antimatter particle with the opposing electrical charge for every matter particle. As a result, the antiproton is a negatively charged counterpart to a proton, while the positron is a positively charged antielectron. A matter particle and its matching antimatter particle destroy one another when they collide. Antimatter particles are therefore uncommon in the cosmos, along with an imbalance between the numbers of matter and antimatter particles. Although hypotheses of baryogenesis may provide an explanation, the underlying origins of this imbalance are still not entirely understood. Therefore, no antimatter atoms have been found in the natural world. At the CERN laboratory in Geneva, antihydrogen—the hydrogen atom's antimatter counterpart—was created in 1996.

By substituting another particle with the same charge for one of the protons, neutrons, or electrons, other unusual atoms have been made. For instance, a more powerful muon can take the place of an electron to create a muonic atom. These atoms can be used to test the basic physics hypotheses.

Conclusion to Atoms

Numerous meticulous physicists, chemists, and mathematicians conducted a number of experiments that led to the development of the quantum model of the atom. The nucleus of the atom, which is a concentrated region of positive charge, is surrounded by an electron-filled, largely empty void. The electrons are in orbitals, which represent likely locations depending on energy, and the protons and neutrons make up the dense nucleus. The electron clouds are another name for the orbitals. All hues and emission spectra are the result of electrons changing energy levels.

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