Atomic Structure Ionisation Energies

Ionisation Energy The first ionisation energy of an element is the energy required to remove completely one mole of electrons from one mole of gaseous atoms to form one mole of gaseous ions with a single positive charge. Na (g)  Na + (g) + e -

Ionisation Energy The second ionisation energy of an element is the energy required to completely remove one mole of electrons from one mole of gaseous singly charged ions to form one mole of gaseous ions with two positive charges. Mg + (g)  Mg 2+ (g) + e -

Factors Affecting Ionisation Energy Ionisation energy is a measure of the energy needed to pull a particular electron away from the attraction of the nucleus. A high value of ionisation energy shows a high attraction between the electron and the nucleus.

Factors Affecting Ionisation Energy Li First ionisation energy (kJ/mol) Ionisation energy decreases when the atom becomes larger because the electrostatic attraction between electrons and protons depends on the distance between the two  the larger the distance the weaker the attraction. K

Factors Affecting Ionisation Energy First ionisation energy (kJ/mol) As the atom gets larger it will also have more energy levels that are full of electrons  reduce the electrostatic attraction between protons and electrons.  This is called ELECTRON SHIELDING.  Hence the ionisation energy will decrease Mg Ca

Factors Affecting Ionisation Energy ionisation energy (kJ/mol) Ionisation energy increases as the charge on the nucleus increases because the electrostatic attraction between the electrons and protons increases. 10p p

Successive ionisation energies Na 2,8,1

Successive ionisation energies Na

Successive ionisation energies Na

Successive ionisation energies Na

Successive ionisation energies Na

Successive ionisation energies Na

Successive ionisation energies Na

Successive ionisation energies Na

Successive ionisation energies Na

Successive ionisation energies Na

Successive ionisation energies Na

Successive ionisation energies Na

Successive ionisation energies Na

Successive ionisation energies Na

Successive ionisation energies Na

Successive ionisation energies Na

Successive ionisation energies Na

Successive ionisation energies Na

Successive ionisation energies Na

Successive ionisation energies Na

Successive ionisation energies Na

Successive ionisation energies Na

Successive ionisation energies Na

Successive ionisation energies Na 2,8,1

Successive ionisation energies Si 2,8,4

Successive ionisation energies Si

Successive ionisation energies Si

Successive ionisation energies Si

Successive ionisation energies Si

Successive ionisation energies Si

Successive ionisation energies Si

Successive ionisation energies Si

Successive ionisation energies Si

Successive ionisation energies Si

Successive ionisation energies Si

Successive ionisation energies Si

Successive ionisation energies Si

Successive ionisation energies Si

Successive ionisation energies Si

Successive ionisation energies Si

Successive ionisation energies Si

Successive ionisation energies Si

Successive ionisation energies Si

Successive ionisation energies Si

Successive ionisation energies Si

Successive ionisation energies Si

Successive ionisation energies Si

Successive ionisation energies Si

Successive ionisation energies Si

Successive ionisation energies Si

Successive ionisation energies Si

Successive ionisation energies Si

Successive ionisation energies Si 2,8,4

Factors Affecting Ionisation Energy Li First ionisation energy (kJ/mol) Ionisation energy decreases when the atom becomes larger because the electrostatic attraction between electrons and protons depends on the distance between the two  the larger the distance the weaker the attraction. K

Factors Affecting Ionisation Energy First ionisation energy (kJ/mol) As the atom gets larger it will also have more energy levels that are full of electrons  reduce the electrostatic attraction between protons and electrons.  This is called ELECTRON SHIELDING.  Hence the ionisation energy will decrease Mg Ca

Factors Affecting Ionisation Energy ionisation energy (kJ/mol) Ionisation energy increases as the charge on the nucleus increases because the electrostatic attraction between the electrons and protons increases. 10p p

Factors Affecting Ionisation Energy- Summary The value of the ionisation energy will: ↑ as Z↑because the electrostatic attraction between the electrons and protons increases. ↓ as size of atom ↑because the larger the distance between electrons and protons the weaker the electrostatic attraction. because more full energy levels (ELECTRON SHIELDING).  reduce the electrostatic attraction between protons and electrons.

Variation in 1 st Ionisation Energy Across a Period Question: Predict the trend in value of 1 st IE for period 2 (Li  Ne) by sketching a graph and giving a reason

Variation in 1 st Ionisation Energy Across a Period General Trend: As Z increases the 1 st IE increases as the electrons are being removed from the same shell i.e shielding is constant and the size of the atom decreases due to increased nuclear charge. There are 2 exceptions to the general trend: Be  B and N  O

Variation in 1 st Ionisation Energy Across a Period Be  B due to the existence of SUB- SHELLS within the energy shells. These are known as s,p,d and f sub-shells. The s sub-shell contains a maximum of 2 electrons The p sub-shell contains a maximum of 6 electrons Beryllium has an electronic configuration of 1s 2 2s 2 Boron has an electronic configuration of 1s 2 2s 2 2p 1 The outer electron in boron is removed from a p- orbital which is higher in energy than the s- orbital outer electron in beryllium Note: higher energy electrons require less energy (i.e.are easier) to remove.

Variation in 1 st Ionisation Energy Across a Period N  O Within the sub-shells are found “orbitals” An orbital can only hold a maximum of two electrons The mutual repulsion between the pair of electrons in oxygen means that less energy is required to remove one of them from the atom, hence lowering the first ionisation energy. Nitrogen is 1s 2 2s 2 2p 3 all p electrons are unpaired Oxygen is 1s 2 2s 2 2p 4 pairing occurs for the first time pxpx pypy pzpz ↑↑↑ pxpx pypy pzpz ↑↓↑↑

Variation in 1 st Ionisation Energy Across a Period - Summary General Trend: As Z increases the 1 st IE increases as the electrons are being removed from the same shell i.e shielding is constant and the size of the atom decreases due to increased nuclear charge. Be  B The outer electron in boron is removed from a p-orbital which is higher in energy than the s-orbital outer electron in beryllium, therefore, it is easier to remove and the first ionisation energy is lower. N  O Nitrogen is 1s 2 2s 2 2p 3 Oxygen is 1s 2 2s 2 2p 4 The mutual repulsion between the pair of electrons in the 2p orbitals in oxygen means that less energy is required to remove one of them from the atom than the unpaired 2p electrons in nitrogen, hence lowering the first ionisation energy.

Variation in 1 st Ionisation Energy Across a Period - Summary Period 3 follows the same pattern as period 2 and is explained in the same way Ionisation energies provide evidence for the presence of shells and orbitals in atoms