Trends in Periodic Table Chapter 7

Atomic Radii Atomic Radii-Half the distance between the nuclei of the 2 atoms of the same element that are joined by a single covalent bond.

Trends in Atomic Radii Trends in Atomic Radii Decrease across a group due to 1.Increased nuclear charge 2. No screening effect Increase down a group due to 1. New Shell 2. Screening effect

Ionisation Energies Ionisation Energies-Energy required to remove the most loosely bound electron from a neutral gaseous atom in its ground state. Na---Na+ + e-

Trends in Ionisation Energy Increase across a group due to 1. Increased nuclear charge 2. Decreased Atomic Radius Decrease down a group due to 1. Increased atomic Radius 2. Screening Effect.

Trends in Ionisation Energy

Exceptions Exceptions Be -- 1s2 2s2 B -- 1s2 2s2 2p1 N -- 1s2 2s2 2pX1 2pY1 2pZ1 O -- 1s2 2s2 2pX2 2pY1 2pZ1

Why The Exceptions? Irregularities due to the fact that any sublevel that is completely filled (Be) or exactly half filled (N) has extra stability. The Ionisation energies are therefore higher.

Evidence for existence of Energy levels

Ionisation energies of Chlorine

Note: There is a large increase in ionisation energies when an electron is removed from a new shell. This is due to: New shell is closer to the nucleus. Less shielding Filled shell, therefore extra stability

Electronegativity Electronegativity-Relative attraction that an atom in a molecule has for a shared pair of electrons in a covalent bond.

Trends in Electronegativity Increase across a group due to 1. Nuclear charge 2. Decreased atomic radii Decrease due to 1. Increased atomic Radius 2. Screening effect

Trends within Groups Trends within Groups Li F Na Increased Reactivity Cl K Br Rb I Cs At

Reactivity of Halogens There is a steady increase in the boiling points of the nobel gases down the group from Helium to Radon. As atoms increase in size, temporary dipoles are more easily created. Therefore Van der Waal’s forces are stronger between bigger atoms and give rise to higher boiling points. This explains why Iodine is a grey solid,Bromine a red liquid and Chlorine and fluorine are gases at room Temp.