atomic structure

P orbitals

S orbitals

D orbitals

First ionisation energy

Energy required to remove 1 mole of electrons from 1 mole of gaseous atoms of element to form 1 mole of singly positively charged gaseous ions

Second ionisation energy

Energy required to remove 1 mole of electrons from 1 mole of singly positively charged gases ion to form 1 mole of doubly positively charged gaseous ions

Nuclear charge

Attractive force of protons in nucleus for electrons

Inc protons, inc nuclear charge

Shielding effect

Shielding of valence electrons from electrostatic attraction of positively charged nucleus mainly by inner shell electrons

dec shielding, dec attraction to nucleus, dec IE (energy to remove valence electron)

Trend - across a period

→ first IE generally increases across period

Number of protons increase, nuclear charge increase

Shielding effect remains relatively constant since inner shell electrons remains the same (no change in number of shells)

Effective nuclear charge increases, thus stronger electrostatic forces of attraction between nucleus and valence electrons

Thus more energy needed to remove valence electrons and first IE generally increase

Trend - down a group

→ ionisation energy decreases down the group

Number of protons increase, nuclear charge increase

Number of electron shells also increase, thus shielding effect increases

Weaker electrostatic forces of attraction to nucleus

Less energy to remove valence electron, first IE decreases down the group