2. Atomic Structure

Atoms of the same element with the same atomic number but different mass number • Same chemical properties (same amount of e-) • Slightly different physical properties (different amount of neutrons)

Isotopes that have unstable nuclei and therefore emit radiation when they break up Uses • carbon dating • radio therapy • medical tracers • nuclear power

The shorter the wavelength the higher the frequency of the wave and the more energy it contains

When electrons are excited to a higher energy level, and then return to a lower energy level, they release a photon of a specific energy, as shown by a specific frequency of light *electrons moving back to the lowest energy states and over longer distances release more energy as the electron moves to higher energy states, the spectral lines converge

U.V. radiation from a higher sublevel to n=1

Visible light radiation From a higher sublevel to n=2

Infrared radiation From a higher sublevel to n=3

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6…. (4s electrons are lost first in transition metals)

The order in which the energy levels are filled 2 exceptions: chromium and copper fill up 3d first / electrons from 4s are lost first

Electrons prefer to occupy orbitals on their own, and only pair up when no empty orbitals of the same energy are available

Paired electrons have the opposite spin as this reduces the mutual repulsion between the paired electrons

The energy required to remove one mole of electrons from one mole of atoms in the gaseous state to form one mole of univalent cations in the gaseous state X(g) –> X+ + e- +ve dH

• Size of the nuclear charge - the larger the nuclear charge, the larger the force of attraction so the greater ionization energy required • Distance of the electron from the nucleus - the farther away the electron is from the nucleus, the smaller the force of attraction

X+(g) –> X2+(g) + e- • Increases because electrons are being removed from increasingly positive ions –> larger nuclear attraction • Large jumps seen when electron is removed from a new sublevel closer to the nucleus

• Size of the 1st I.E. increases - e- comes from the same sublevel but the nuclear charge increases • The first I.E. of Al is less than that of Mg - the e- removed from Al is at a higher sublevel • The first I.E. of S is less than that of P - electron removed from 3p is a paired e- • ​when paired, extra mutual repulsion results in less required energy to remove

• I.E. increases down a group • e- removed is from a higher energy level • nuclear charge increases but the attraction is reduced by the inner electrons which shield the outer ones