For this purpose, a dimensionless quantity, the Pauling scale, symbol χ, is the most commonly used. ElectronegativityĮlectronegativity, symbol χ, is a chemical property that describes the tendency of an atom to attract electrons towards this atom. The electron affinities of the noble gases have not been conclusively measured, so they may or may not have slightly negative values. Chlorine most strongly attracts extra electrons. Nonmetals like to gain electrons to form anions to have a fully stable electron shell.
This affinity is known as the first electron affinity, and these energies are negative. When an electron is added to a neutral atom, energy is released. To use electron affinities properly, it is essential to keep track of signs. Molecules with high electron affinity form very stable negative ions which are important in the chemical and health industry as they purify the air, lift mood, and most importantly, act as strong oxidizing agents. Electron affinities are more difficult to measure than ionization energies.Īn atom of Beryllium in the gas phase, for example, gives off energy when it gains an electron to form an ion of Beryllium.īe + e – → Be – – ∆H = Affinity = - kJ/molĮlectron affinity is one of the most important parameters that guide chemical reactivity. Note that ionization energies measure the tendency of a neutral atom to resist the loss of electrons. In other words, it can be expressed as the neutral atom’s likelihood of gaining an electron. The change in energy (in kJ/mole) of a neutral atom or molecule (in the gaseous phase) when an electron is added to the atom to form a negative ion. In chemistry and atomic physics, the electron affinity of an atom or molecule is defined as: *Fluorine's electron affinity is smaller than chlorine's because of the higher electron - electron repulsions in the smaller 2p orbital compared to the larger 3p orbital of chlorine.Electron Affinity and Electronegativity of BerylliumĮlectron Affinity of Beryllium is - kJ/mol.įirst Ionization Energy of Beryllium is 9.3226 eV. (More negative energy = greater affinity) Element Obviously, the halogens, which are one electron away from a noble gas electron configuration, have high affinities for electrons: Since a half-filled "p" subshell is more stable, carbon has a greater affinity for an electron than nitrogen. This occurs because of the same subshell rule that governs ionization energies. The change is small and there are many exceptions.Įlectron affinity decreases or increases across a period depending on electronic configuration. (An unbound electron has an energy of zero.)Īs with ionization energy, there are two rules that govern the periodic trends of electron affinities:Įlectron affinity becomes less negative down a group.Īs the principal quantum number increases, the size of the orbital increases and the affinity for the electron is less. A more negative electron affinity corresponds to a greater attraction for an electron. This is because energy is usually released in this process, as opposed to ionization energy, which requires energy. Notice the sign on the energy is negative.