A periodic trend is a tendency in the properties in elements on the periodic table.
Trends may have exceptions however.
- Elements in the same period have the same number of occupied electron shells.
- Elements in the same group have similar reactivity.
- Atomic radius increases left and down.
- First ionisation energy increases up and right. - Going up the eletrons are closer to the nucleus so hard to remove, going right there is more core charge so hard to remove.
- Metallic character increases down and left.
- Reactivity for metals (groups 1 and 2) is they want to lose electrons. Group 1 is more reactive because they have just 1 electron to lose. Reactivity for non-metals (like groups 16 and 17) is they want to lose electrons. Group 17 is more reactive because they need just 1 electron more.
- Reactivity in a group increases down for metals and increases up for non-metals. For metals, atomic radius bigger as you go down, less core charge, easier to lose electrons, more reactive. For non-metals, the atomic radius smaller as you go up, more core charge, more attract electrons, more reactive.
- Electronegativity increases up and right, except for group 18.