Chapter 4.3

Trends in the Periodic Table

Describe periodic trends in ionization energy, atomic radius, electronegativity, and ionic size; and relate and relate them to atomic structures of the elements.

Trend : predictable change in a particular direction

Trends in reactivity down a group of Alkali Metals

Objective 1:

Atomic RadiiDefined as one-

half the distance between the nuclei of identical atoms that are bonded together

Period trendsDecrease from left

to right

Group trends Increase down a

group

Atomic Radii

Ionization EnergyDefined as

energy required to remove one electron from a neutral atom of an element (IE)

A + energy A+ + e-

Ion – atom or group of bonded atoms that has a positive or negative charge.

Ionization EnergyPeriod trends

Generally increase across a period

Group trends Generally decrease

down a group

Ionic radiiCation – positive ion

Formed by loss of one or more electrons

Ionic Radii

Anion– negative ion Formed by gain of

one or more electrons

Valence ElectronsDefined as the electrons available to be

lost, gained, or shared in the formation of chemical compounds

Sodium atom

Chlorine atom

Valence electron

ElectronegativityDefined as the measure of

the ability of an atom in a chemical compound to attract electronsWant to gain electrons!!

Noble gases have very low electronegativity

Alkali metals are low as wellHalogens have the highest Electronegativi

ty Period trends Tend to increase

across a period Group trends

Tend to decrease down a group