A report on Atom

Atoms and molecules as depicted in John Dalton's A New System of Chemical Philosophy vol. 1 (1808)
The Geiger–Marsden experiment:
Left: Expected results: alpha particles passing through the plum pudding model of the atom with negligible deflection.
Right: Observed results: a small portion of the particles were deflected by the concentrated positive charge of the nucleus.
The Bohr model of the atom, with an electron making instantaneous "quantum leaps" from one orbit to another with gain or loss of energy. This model of electrons in orbits is obsolete.
The binding energy needed for a nucleon to escape the nucleus, for various isotopes
A potential well, showing, according to classical mechanics, the minimum energy V(x) needed to reach each position x. Classically, a particle with energy E is constrained to a range of positions between x1 and x2.
3D views of some hydrogen-like atomic orbitals showing probability density and phase (g orbitals and higher are not shown)
This diagram shows the half-life (T½) of various isotopes with Z protons and N neutrons.
These electron's energy levels (not to scale) are sufficient for ground states of atoms up to cadmium (5s2 4d10) inclusively. Do not forget that even the top of the diagram is lower than an unbound electron state.
An example of absorption lines in a spectrum
Graphic illustrating the formation of a Bose–Einstein condensate
Scanning tunneling microscope image showing the individual atoms making up this gold (100) surface. The surface atoms deviate from the bulk crystal structure and arrange in columns several atoms wide with pits between them (See surface reconstruction).
Periodic table showing the origin of each element. Elements from carbon up to sulfur may be made in small stars by the alpha process. Elements beyond iron are made in large stars with slow neutron capture (s-process). Elements heavier than iron may be made in neutron star mergers or supernovae after the r-process.

Smallest unit of ordinary matter that forms a chemical element.

- Atom
Atoms and molecules as depicted in John Dalton's A New System of Chemical Philosophy vol. 1 (1808)

115 related topics with Alpha

Overall

Four covalent bonds. Carbon has four valence electrons and here a valence of four. Each hydrogen atom has one valence electron and is univalent.

Valence electron

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Four covalent bonds. Carbon has four valence electrons and here a valence of four. Each hydrogen atom has one valence electron and is univalent.
The periodic table of the chemical elements

In chemistry and physics, a valence electron is an electron in the outer shell associated with an atom, and that can participate in the formation of a chemical bond if the outer shell is not closed; in a single covalent bond, both atoms in the bond contribute one valence electron in order to form a shared pair.

2-dimensional random walk of a silver adatom on an Ag(111) surface

Brownian motion

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Random motion of particles suspended in a medium (a liquid or a gas).

Random motion of particles suspended in a medium (a liquid or a gas).

2-dimensional random walk of a silver adatom on an Ag(111) surface
This is a simulation of the Brownian motion of 5 particles (yellow) that collide with a large set of 800 particles. The yellow particles leave 5 blue trails of (pseudo) random motion and one of them has a red velocity vector.
This is a simulation of the Brownian motion of a big particle (dust particle) that collides with a large set of smaller particles (molecules of a gas) which move with different velocities in different random directions.
Reproduced from the book of Jean Baptiste Perrin, Les Atomes, three tracings of the motion of colloidal particles of radius 0.53 µm, as seen under the microscope, are displayed. Successive positions every 30 seconds are joined by straight line segments (the mesh size is 3.2 µm).
The characteristic bell-shaped curves of the diffusion of Brownian particles. The distribution begins as a Dirac delta function, indicating that all the particles are located at the origin at time t = 0. As t increases, the distribution flattens (though remains bell-shaped), and ultimately becomes uniform in the limit that time goes to infinity.
A single realisation of three-dimensional Brownian motion for times 0 ≤ t ≤ 2
Brownian motion on a sphere

This explanation of Brownian motion served as convincing evidence that atoms and molecules exist and was further verified experimentally by Jean Perrin in 1908.

A covalent bond forming H2 (right) where two hydrogen atoms share the two electrons

Covalent bond

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A covalent bond forming H2 (right) where two hydrogen atoms share the two electrons
Early concepts in covalent bonding arose from this kind of image of the molecule of methane. Covalent bonding is implied in the Lewis structure by indicating electrons shared between atoms.
Lewis and MO diagrams of an individual 2e bond and 3e bond
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A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms.

A beam of cathode rays in a vacuum tube bent into a circle by a magnetic field generated by a Helmholtz coil. Cathode rays are normally invisible; in this demonstration with a Teltron tube, enough gas has been left in the tube that the gas atoms luminesce when struck by the fast-moving electrons.

Cathode ray

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Cathode rays (electron beam or e-beam) are streams of electrons observed in discharge tubes.

Cathode rays (electron beam or e-beam) are streams of electrons observed in discharge tubes.

A beam of cathode rays in a vacuum tube bent into a circle by a magnetic field generated by a Helmholtz coil. Cathode rays are normally invisible; in this demonstration with a Teltron tube, enough gas has been left in the tube that the gas atoms luminesce when struck by the fast-moving electrons.
A diagram showing a Crookes tube connected to a high voltage supply. The Maltese cross has no external electrical connection.
Glow discharge in a low-pressure tube caused by electric current.
Crookes tube. The cathode (negative terminal) is on the right.  The anode (positive terminal) is in the base of the tube at bottom.
Cathode rays travel from the cathode at the rear of the tube, striking the glass front, making it glow green by fluorescence. A metal cross in the tube casts a shadow, demonstrating that the rays travel in straight lines.
A magnet creates a horizontal magnetic field through the neck of the tube, bending the rays up, so the shadow of the cross is higher.
When the magnet is reversed, it bends the rays down, so the shadow is lower. The pink glow is caused by cathode rays striking residual gas atoms in the tube.

To release electrons into the tube, they first must be detached from the atoms of the cathode.

Spontaneous emission

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Spontaneous emission is the process in which a quantum mechanical system (such as a molecule, an atom or a subatomic particle) transits from an excited energy state to a lower energy state (e.g., its ground state) and emits a quantized amount of energy in the form of a photon.

A thermite reaction using iron(III) oxide. The sparks flying outwards are globules of molten iron trailing smoke in their wake.

Chemical reaction

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Process that leads to the chemical transformation of one set of chemical substances to another.

Process that leads to the chemical transformation of one set of chemical substances to another.

A thermite reaction using iron(III) oxide. The sparks flying outwards are globules of molten iron trailing smoke in their wake.
Antoine Lavoisier developed the theory of combustion as a chemical reaction with oxygen.
As seen from the equation CH4 + 2O2 -> CO2 + 2 H2O, a coefficient of 2 must be placed before the oxygen gas on the reactants side and before the water on the products side in order for, as per the law of conservation of mass, the quantity of each element does not change during the reaction
An example of organic reaction: oxidation of ketones to esters with a peroxycarboxylic acid
Isomerization of azobenzene, induced by light (hν) or heat (Δ)
Representation of four basic chemical reactions types: synthesis, decomposition, single replacement and double replacement.
Illustration of a redox reaction
Sodium chloride is formed through the redox reaction of sodium metal and chlorine gas
Ferrocene – an iron atom sandwiched between two C5H5 ligands
Precipitation
In this Paterno–Büchi reaction, a photoexcited carbonyl group is added to an unexcited olefin, yielding an oxetane.
Schematic potential energy diagram showing the effect of a catalyst in an endothermic chemical reaction. The presence of a catalyst opens a different reaction pathway (in red) with a lower activation energy. The final result and the overall thermodynamics are the same.
Solid heterogeneous catalysts are plated on meshes in ceramic catalytic converters in order to maximize their surface area. This exhaust converter is from a Peugeot 106 S2 1100
Mechanism of electrophilic aromatic substitution
E2 elimination
Electrophilic addition of hydrogen bromide
Acid-catalyzed addition-elimination mechanism
The Cope rearrangement of 3-methyl-1,5-hexadiene
Illustration of the induced fit model of enzyme activity
Thermite reaction proceeding in railway welding. Shortly after this, the liquid iron flows into the mould around the rail gap.

Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking of chemical bonds between atoms, with no change to the nuclei (no change to the elements present), and can often be described by a chemical equation.

Avogadro, who inspired the Avogadro constant

Mole (unit)

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SI base unit of amount of substance.

SI base unit of amount of substance.

Avogadro, who inspired the Avogadro constant

Depending on what the substance is, an elementary entity may be an atom, a molecule, an ion, an ion pair, or a subatomic particle such as an electron.

A Crookes tube with a magnetic deflector

History of subatomic physics

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The idea that matter consists of smaller particles and that there exists a limited number of sorts of primary, smallest particles in nature has existed in natural philosophy at least since the 6th century BC. Such ideas gained physical credibility beginning in the 19th century, but the concept of "elementary particle" underwent some changes in its meaning: notably, modern physics no longer deems elementary particles indestructible.

The idea that matter consists of smaller particles and that there exists a limited number of sorts of primary, smallest particles in nature has existed in natural philosophy at least since the 6th century BC. Such ideas gained physical credibility beginning in the 19th century, but the concept of "elementary particle" underwent some changes in its meaning: notably, modern physics no longer deems elementary particles indestructible.

A Crookes tube with a magnetic deflector
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Cloud chambers played an important role as particle detectors in the early days of subatomic physics. Some particles including the positron were even discovered by using this device
Atomic orbitals of Period 2 elements: 
1s 2s 2p (3 items). All complete subshells (including 2p) are inherently spherically symmetric, but it is convenient to assign to "distinct" p-electrons these two-lobed shapes.
Classification of spin-3⁄2 baryons known in 1960s
The Standard Model
One possible signature of a Higgs boson from a simulated proton–proton collision. It decays almost immediately into two jets of hadrons and two electrons, visible as lines.

Increasingly small particles have been discovered and researched: they include molecules, which are constructed of atoms, that in turn consist of subatomic particles, namely atomic nuclei and electrons.

Principal quantum number

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In quantum mechanics, the principal quantum number (symbolized n) is one of four quantum numbers assigned to each electron in an atom to describe that electron's state.

The characteristic reconstruction fringes on the (100) surface of gold are 1.44 nanometers wide<ref>{{cite journal| vauthors = Bengió S, Navarro V, González-Barrio MA, Cortés R, Vobornik I, Michel EG, Mascaraque A |date=2012-07-18|title=Electronic structure of reconstructed Au(100): Two-dimensional and one-dimensional surface states |journal=Physical Review B|volume=86|issue=4|pages=045426|doi=10.1103/PhysRevB.86.045426|bibcode=2012PhRvB..86d5426B}}</ref> and consist of six atomic rows that sit on top of five rows of the crystal bulk. Image size is approximately 10 nm by 10 nm.

Scanning tunneling microscope

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The characteristic reconstruction fringes on the (100) surface of gold are 1.44 nanometers wide<ref>{{cite journal| vauthors = Bengió S, Navarro V, González-Barrio MA, Cortés R, Vobornik I, Michel EG, Mascaraque A |date=2012-07-18|title=Electronic structure of reconstructed Au(100): Two-dimensional and one-dimensional surface states |journal=Physical Review B|volume=86|issue=4|pages=045426|doi=10.1103/PhysRevB.86.045426|bibcode=2012PhRvB..86d5426B}}</ref> and consist of six atomic rows that sit on top of five rows of the crystal bulk. Image size is approximately 10 nm by 10 nm.
Schematic view of an STM.
A 1986 STM from the collection of Musée d'histoire des sciences de la Ville de Genève.
A large STM setup at the London Centre for Nanotechnology.
The real and imaginary parts of the wave function in a rectangular potential barrier model of the scanning tunneling microscope.
Negative sample bias V raises its electronic levels by e⋅V. Only electrons that populate states between the Fermi levels of the sample and the tip are allowed to tunnel.
Tip, barrier and sample wave functions in a model of the scanning tunneling microscope. Barrier width is w. Tip bias is V. Surface work functions are ϕ.
One-atom-thick silver islands grown on terraces of the (111) surface of palladium. Image size is 250 nm by 250 nm.
A 7 nm long part of a single-walled carbon nanotube.
Atoms on the surface of a crystal of silicon carbide (SiC) are arranged in a hexagonal lattice and are 0.3 nm apart.
STM nanomanipulation of PTCDA molecules on graphite to inscribe the logo of the Center for NanoScience (CeNS), Munich.

A scanning tunneling microscope (STM) is a type of microscope used for imaging surfaces at the atomic level.