Periodic Trends Section 4.3

Ionization Energy The amount of energy needed to remove an outer electron from a specific atom or ion

Ionization Energy

The Trend It decreases down a group e- shielding - The reduction of the attractive force between a + nucleus and its outermost e- b/c of the cancellation of some of the + charge by – charge of the outer e-

Ionization Energy Ionization energy increase across a period Adding e- to same level & p+ can hold it tighter

Atomic Radius/Radii Atomic radius Usually determined for atoms bonded or close together Bond radius – ½ the distance from center to center of two like atoms bonded together

The Trend Atomic radius increases as you move down a group Due to addition of principle E level The e- in the middle E levels shield the outside e- from the force of the nucleus.

Trend Atomic radius decreases as you move across a period Decreases b/c of increased + charge –You are adding an e- and a p+, but the e-’s are going into the same E level and being pulled by the p+

Atomic Radius As charge increases, the effective nuclear charge increases also This pulls e- closer to the nucleus Overall, this reduces the size of the atom

Repulsive Forces Eventually, the e- will get close and repel each other Here, the atom doesn’t get any smaller Similar trend for ionic radius

Atomic Radii

Electronegativity Electronegativity – a measure of the ability of an atom in a chemical compound to attract e-’s The higher the e-neg, the stronger that atom will pull e-’s from other elements

Electronegativity Decreases as you go down a group Adding principle quantum # + nucleus can’t pull e- as much b/c of e- shielding

E-neg Increases across a pd. Effective nuclear charge is more of a factor

Electron Affinity The energy emitted upon the addition of an electron to a neutral atom in the gas phase. Becomes more negative across a period Decreases down a group Similar to e-neg.

Melting and Boiling Point Not as straight forward as the other trends. Change as the different orbitals begin to fill