Periodic Trends

What is a trend? A predictable change in a particular direction. Allow you to make predictions about the chemical properties of an element They are actually based on the electron configuration of the element.

Atomic Radius The radius of an atom Hard to calculate because the edge of the e- cloud is fuzzy and not well defined Increases down group- energy levels are added which increase the radius Decrease left to right across a period- nuclear charge increases and pulls the e- tighter to the nucleus

Ions Charged atoms Atoms can gain or loose electrons When they do they become + (have lost electrons) or – (have gained electrons)

Ionic Size Increases down period Decreases from left to right across a period

Ionization Energy The energy required to remove an electron from an atom. Decreases down a group- as you go down a group there are more levels of e-, so the pull of the nucleus on the outer e- is less Called electron shielding Increases from left to right across a period- the addition of p+ increases the nuclear charge and holds the e- tighter

Electronegativity How much an atom in a molecule pulls the e- Highest value on the scale is 4.0 and is given to F When e- are shared between 2 atoms the one with the larger electronegativity will win and the e- spend more time around that nucleus Decreases down a group- due to e- shielding Increases across a period- due to less e- shielding

Electron Affinity Energy change when an atom gains an e- Decreases down a group because of e- shielding Increases left to right across a period because of increase in nuclear charge

Melting and Boiling Points Left to right across a period, increase and then decrease twice