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Ionisation Energies p

Ions and electron configuration Li: 1s 2 2s 1 Li + : 1s 2 He: 1s 2 Cl: 1s 2 2s 2 2p 6 3s 2 3p 5 Cl - : 1s 2 2s 2 2p 6 3s 2 3p 6 Ar: 1s 2 2s 2 2p 6 3s 2 3p 6

Ionisation Energy the amount of energy required to remove an electron from a gaseous atom to form a gaseous ion. Q (g)  Q + (g) + e - Second ionisation energy: energy required to remove a second electron Q + (g)  Q 2+ (g) + e -

Energy is required to remove an electron (endothermic) Factors affecting ionisation energy 1.Charge on the nucleus 2.Repulsion (pushing away) or “shielding” of electron from inner orbitals 3.Repulsion on the electron from other electrons in the valence shell

Factors affecting ionisation energy Charge exerted on each electron by the positively charged nucleus Repel Attract

Effective Nuclear Charge Charge exerted on each electron by the positively charged nucleus Charge exerted on each electron by the positively charged nucleus

Successive (next) Ionization Energies The more electrons that have been removed, the greater the energy required to remove the next electron. –because of lower electron-electron repulsions –greater nucleus-electron attraction

Valence electrons repel one another No other electron in 3rd energy level to repel the one remaining electron Remaining valence electron attracted more strongly to nucleus

Successive Ionization Energy of Mg Big Increase! Big increase in ionization energy when the next electron is removed from a filled inner energy level. This electron has a much higher effective nuclear charge on itself.

Big Increase!

Stop.

Ionisation Energy - Groups Going down a group on the periodic table, ionisation energy decreases –successive electrons are lost from higher energy levels further from the nucleus less attraction to nucleus

Ionization Energy Increases

Ionization Energy - Periods Ionisation energy increases across a period –effective nuclear charge increases –not a smooth increase

Ionization Energy Increases

Ionization energy decreases when going from the second to the third element in each period (Be to B, Mg to Al) –Because of which sub-level the electron comes from (2p 1 is higher energy than 2s 2 ) –Lower ionization energy if removing one electron from a doubly-filled orbital

Isoelectronic Species Iso = same Atoms and ions that have the same electronic structure S 2-, Cl -, Ar, K +, Ca 2+