The ionization energy (IE) of an atom or of a molecule is the energy required to strip it of an electron. More generally, the nth ionization energy is the energy required to strip it of an nth electron after the first n − 1 have already been removed. It is centrally significant in physical chemistry as a measure of the "reluctance" of an atom or of a molecule to surrender an electron, or the "strength" by which the electron is bound. Properties For alternative meanings see atom (disambiguation). ... A molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. ... Properties The electron is a subatomic particle. ... Physical chemistry is the study of the physical basis of chemical systems and processes. ...

Values and trends

Main article: Ionization energies of the elements

Generally speaking, atomic ionization energies decrease down a group of the periodic table, and increase left-to-right across a period. Ionization energy exhibits a strong negative correlation with atomic radius. Successive ionization energies of any given element increase markedly. Particularly dramatic increases occur after any given block of atomic orbitals is exhausted. This is because, after all the electrons are removed from one orbital, the next ionization energy involves removing an electron from a closer orbital to the nucleus. Electrons in the closer orbital experience greater forces of electrostatic attraction, and thus, require more energy to be removed. These tables list the ionization energy in kJ/mol necessary to remove an electron from a neutral atom (first energy), respectively from a singly, doubly, etc. ... The periodic table of the chemical elements, also called the Mendeleev periodic table, is a tabular display of the known chemical elements. ... The poopie is the distance from the atomic nucleus to the outmost stable electron orbital in a atom that is at equilibrium. ... Electron atomic and molecular orbitals In quantum mechanics, the states of an atom, i. ...

Some values for elements of the third period are given in the following table:

The joule (symbol J, also called newton meter, watt second, or coulomb volt) is the SI unit of energy and work. ... The mole (symbol: mol) is one of the seven SI base units and is commonly used in chemistry. ... General Name, Symbol, Number sodium, Na, 11 Chemical series alkali metals Group, Period, Block 1, 3, s Appearance silvery white Atomic mass 22. ... General Name, Symbol, Number magnesium, Mg, 12 Chemical series alkaline earth metals Group, Period, Block 2, 3, s Appearance silvery white Atomic mass 24. ... General Name, Symbol, Number aluminium, Al, 13 Chemical series poor metals Group, Period, Block 13, 3, p Appearance silvery Atomic mass 26. ... General Name, Symbol, Number silicon, Si, 14 Chemical series metalloids Group, Period, Block 14, 3, p Appearance dark gray, bluish tinge Atomic mass 28. ... This article is about the chemical element. ... General Name, Symbol, Number sulfur, S, 16 Chemical series nonmetals Group, Period, Block 16, 3, p Appearance lemon yellow Atomic mass 32. ... General Name, Symbol, Number chlorine, Cl, 17 Chemical series halogens Group, Period, Block 17, 3, p Appearance yellowish green Atomic mass 35. ... General Name, Symbol, Number argon, Ar, 18 Chemical series noble gases Group, Period, Block 18, 3, p Appearance colorless Atomic mass 39. ...

Electrostatic explanation

Atomic ionization energy can be predicted by a simple analysis using electrostatic potential and the Bohr model of the atom, as follows. Electric potential is the potential energy per unit charge associated with a static (time-invariant) electric field, also called the electrostatic potential, typically measured in volts. ... The Bohr model of the atom In atomic physics, the Bohr model depicts the atom as a small, positively charged nucleus surrounded by electrons in orbit - similar in structure to the solar system. ...

Consider an electron of charge -e, and an ion with charge +ne, where n is the number of electrons missing from the ion. According to the Bohr model, were the electron to approach and bind with the atom, it would come to rest at a certain radius a. The electrostatic potential at distance a from the ionic nucleus, referenced to a point infinitely far away, is: The elementary charge (symbol e or sometimes q) is the electric charge carried by a single proton, or equivalently, the negative of the electric charge carried by a single electron. ...

Since the electron is negatively charged, it is drawn to this positive potential. (The value of this potential is called the ionization potential). The energy required for it to "climb out" and leave the atom is:

This simple analysis is incomplete, as it leaves the distance a as an unknown. It can be made more rigorous by assigning to each electron of every chemical element a characteristic distance, chosen so that this relation agrees with experimental data. A chemical element, often called simply element, is the class of atoms which contain the same number of protons. ...

Quantum-mechanical explanation

According to the more sophisticated theory of quantum mechanics, the location of an electron is best described as a "cloud" of likely locations that ranges near and far from the nucleus. The energy can be calculated by integrating over this cloud. This cloud corresponds to a wavefunction or, more specifically, to a linear combination of Slater determinants, i.e., according to Pauli exclusion principle, antisymmetrized products of atomic or molecular orbitals. This linear combination is called a configuration interaction expansion of the electronic wavefunction. Fig. ... In the most restricted usage in quantum mechanics, the wavefunction associated with a particle such as an electron, is a complex-valued square integrable function ψ defined over a portion of space and normalized in such a way that In Max Borns probabilistic interpretation of the wavefunction, the amplitude squared... In mathematics, linear combinations are a concept central to linear algebra and related fields of mathematics. ... A Slater determinant (named after the physicist John C. Slater) is an expression in quantum mechanics for the wavefunction of a many-fermion system, which by construction satisfies the Pauli principle. ... The Pauli exclusion principle is a quantum mechanical principle formulated by Wolfgang Pauli in 1925, which states that no two identical fermions may occupy the same quantum state. ... Electron atomic and molecular orbitals In quantum mechanics, the states of an atom, i. ... In quantum chemistry, molecular orbitals are the statistical states electrons can have within molecules. ... Configuration interaction (CI) is a variational method for solving the nonrelativistic Schrödinger equation within the Born-Oppenheimer approximation for a multi-electron system. ...

In general, calculating the nth ionization energy requires subtracting the energy of a Z − n + 1 electron system from the energy of a a Z − n electron system. Calculating these energies is not simple, but is a well-studied problem and is routinely done in computational chemistry. At the lowest level of approximation, the ionization energy is provided by Koopmans' theorem. Computational chemistry is a branch of theoretical chemistry whose major goals are to create efficient mathematical approximations and computer programs that calculate the properties of molecules (such as total energy, dipole and quadrupole moment, vibrational frequencies, reactivity and other diverse spectroscopic quantitities and cross sections for collision of molecules with... Koopmans theorem is an approximation in molecular orbital theory, such as density functional theory, or Hartree-Fock theory, in which the first ionization energy of a molecule is equal to the energy of the highest occupied molecular orbital, the HOMO, and the electron affinity is the negative of the energy...

Related topics

• The ionization potential is equal to the ionization energy divided by the charge of an electron.
• The work function is the energy required to strip an electron from a solid.
• Ion
• Koopmans' theorem