Ionisation Energy

How does the number of protons affect ionisation energy

• More protons in nucleus means greater attraction to outer shell electron

• Greater ionisation energy

How does distance of electrons from nucleus affect ionisation energy

• The bigger the atom, the further away the outer electron

• More weakly attracted, ionisation energy is less

How does shielding attract ionisation energy

• Inner electrons repel outer electrons

• More shielding means less ionisation energy

How does number of electrons in each shell affect ionisation energy

• The greater the number of electrons in each shell, the more they repel each other

• The less the electrons, the more the shell shrinks and gets closer to nucleus

• Smaller atoms need more ionisation energy

Down the group…

• Electron removed is further away from nucleus

• Greater shielding from inner shells

• Despite greater number of protons

• Less attraction, less ionisation energy required

Across a period…

• Number of protons increases

• Electrons are removed from the same shell, same shielding

• Radius decreases, electrons closer to protons

• More attraction, more ionisation energy needed

The first ionisation energy

• The energy required to remove one mole of electrons from one mole of gaseous atoms

• Gaseous form means the molecules are separated into single atoms to make it comparable

The second ionisation energy

The energy required to remove one mole of electrons from one mole of gaseous ions to form a 2+ ion

Why is the second ionisation energy always greater than the first?

• When first electron is removed, a positive ion is formed

• Ion increases attraction on remaining electrons

• Fewer electrons reduce repulsion between electrons

• Energy required to lose electrons is greater