Summary BTEC applied science/forensics unit 1 Chemistry: Periodicity

Periodicity
Periodicity - The repeating patterns of properties of elements concerning atomic number
and position in the periodic table
Atomic radius - Distance of outermost electrons from the nucleus
Shielding - Repulsion effect of inner electrons on outer electrons
Nuclear attraction - The electrostatic attraction between the nucleus and the outer shell
electrons
● Factors change across the period
○ Nuclear charge increases with the number of protons
○ Shielding stays the same
○ Nuclear attraction increases
● Factors change down a group
○ Nuclear charge increases
○ Shielding increases
○ Atomic radius increases
○ First ionisation energy decreases
■ There are more shells
■ Less nuclear attraction
■ Shielding increase
First ionisation energy - The energy required to remove one electron from each atom in a
mole of gaseous atoms
Second ionisation energy
● Always greater than first ionisation energy
● After first electron is removed, the second is pulled closer to the nucleus resulting in
greater attraction
○ This is because the atom is stable now and does not want to lose any more
electrons