Electrons

a plus ion (+) has an overall positive charge

they have less electrons than protons

a minus ion (-) has an overall negative charge

they have more electrons than protons

X(g) ---> X(g)+ (+) e-

The energy required to remove one electron from each ion in one mole of gaseous atoms to form one mole of gaseous 1+ ions.

X(g)+ ---> X(g)2+ (+) e-

The energy required to remove one electron from each ion in one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions.

X(g)2+ ---> X(g)3+ (+) e-

The energy required to remove one electron from each ion in one mole of gaseous 2+ ions to form one mole of gaseous 3+ ions

• how close electrons are to the nucleus

- protons in the nucleus attract outer electrons

• the smaller the atomic radius the closer the electrons are to the nucleus

- stronger they are attracted

• "electron sheilding"

- electrons in the core energy levels repel each other and the outer electrons

nuclear charge- down a group and across a period it increases, this makes it harder to ionise the first electron

sheilding by core electrons- down a group it increases, this makes it easier, across a period it stays the same, this makes no difference to the effect of the first ionisation energy

atomic radius- down a group it expands, this makes it easier, across a period it contracts, this makes it harder, to ionise the first elecron