Trends in Periodicity

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Atomic Radius:

'Distance from centre of nucleus to outermost electrons'.

Atomic radius decreases across a period.

Each successive element has extra proton in nucleus so greater positive charge.

No additional shielding as electrons added to same principal energy level.

Increasing nuclear charge pulls electrons closer to nucleus, decreases atomic radius.

First Ionisation Energy:

'Energy needed to remove one electron from one mole of gaseous atoms to form one mole of unipositive ions'.

Increase in first ionisation energy across a period.

Electron removed from same principal energy level, still increase in nuclear charge.

More energy required to remove electron from outer shell.

Electronegativity:

'Measure of relative ability to attract a pair of electrons in a covalent bond towards itself' - withdraw electron density.

Electronegativity increases across a period.

Number of protons in nucleus increases and atomic radius decreases.

Attraction between nucleus and pair of electrons in covalent bond increases as number of protons in nucleus increases and atomic radius decreases.