The Periodic TableUnit 3/Chapters 3 & 8 Notes

Chemistry CPA

Periodic Trends

• Many properties of atoms depend on the strength of attraction between the outer shell electrons and the nucleus

• This attraction will depend on:1. The positive charge that attracts the other shell

electrons2. The distance of electrons from the nucleus

Four Periodic Trends

1. Atomic Radius2. Ionization Energy3. Electronegativity4. Electron Affinity

Atomic Radius

What is it? • Diameter of atom What happens down a group?• Increases• since there is an increase in the number of shells.What happens across a period?• Decreases• since there is an increase in core charge, the outer shell electrons are

attracted closer to the nucleus (it’s the same shell but there are more electrons in the shell as you move across the period)

Atomic Radius decreases across a period

Atomic Radius increases down a family/group

Ionization Energy

• What is it?• Amount of energy required toremove the highest energy electron from an atom. (or steal one electron)• What happens down a group?• Decreases; since the size of the atom is increasing, the attraction is weaker

between the outer shell electrons and the nucleus. Therefore electrons are easier to remove. • What happens across a period?• Increases; since there is an increase in core charge, the attraction is greater

between the outer shell electrons and the nucleus. Therefore electrons are harder to remove.

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Ionization Energy

• In other words…• If its easy to steal a electron, it has low ionization

energy• If its hard to steal an electron, it has a high ionization

energy • The smaller the atom, the harder to steal an electron• The larger the atom the easier it is to steal an electron

Ionization Energy

Electronegativity

• What is it?• Measure of the ability of an atom to attract an electron towards itself

or love of electrons!• What happens down a group?• Decreases; since the electrons are further from the nucleus, there is a

weaker attraction• What happens across a period?• Increases; since there is an increase in core charge, there is a greater

attraction of the outer shell electrons to the nucleus.

Electronegativity

Electron Affinity

• What is it?• The energy release when an electron is added to an atom. Most favorable

toward NE corner of PT since these atoms have a great affinity (“love and happiness”) for e-. (Think of “Jumping for Joy”!)• What happens down a group?• Decreases; since the electrons are further from the nucleus, the atom has no

desire to hang on to it’s electron, so it won’t release too much “Happiness” (energy) if it gains one. • What happens across a period?• Increases; the more electrons an atom has in it’s valence shell, the more

“happy” it will become when it gets closer to completing it shell.

Electron Affinity