TOPIC: Trends in the Periodic Table: Atomic Radius Do Now: get out pack and open to p.10

Trends more than 20 properties change in predictable way based location of elements on PTmore than 20 properties change in predictable way based location of elements on PT some properties: - anyone know where we can find these numbers?!some properties: - anyone know where we can find these numbers?! –Density –melting point/boiling point –atomic radius –ionization energy –electronegativity

When you’re done it will look like this so leave room for writing!

Fr Cs Rb K Na3 2-1Li2 1H1 ConfigurationElementPeriod Going down column 1: increasing # energy levels as go down

Increasing number of energy levels

Atomic Radius Atomic radius: defined as ½ distance between neighboring nuclei in molecule or crystalAtomic radius: defined as ½ distance between neighboring nuclei in molecule or crystal Affected byAffected by 1. # of energy levels 2. Proton Pulling Power

Increasing number of energy levels Increasing Atomic Radius

previousprevious | index | nextindexnext Li: Group 1 Period 2 Cs: Group 1 Period 6 Cs has more energy levels, so it’s bigger

2-8NeVIIIA or FVIIA or OVIA or NVA or CIVA or BIIIA or BeIIA or 2 2-1LiIA or 1 ConfigurationElementFamily As we go across, elements gain electrons, but they are getting smaller!

Increasing number of energy levels Increasing Atomic Radius Decreasing Atomic Radius

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Why does this happen.. As you go from left to right, you again more protons (the atomic number increases)As you go from left to right, you again more protons (the atomic number increases) You have greater “proton pulling power”You have greater “proton pulling power” –Remember the nucleus is + and the electrons are - so they get pulled towards the nucleus The more protons your have, the more Proton Pulling PowerThe more protons your have, the more Proton Pulling Power

as go across row size tends to decrease a bit because of greater PPP “proton pulling power” previousprevious | index | nextindexnext

What the inner electrons do…. They Shield the charge felt by the valance electrons.

previousprevious | index | nextindexnext H and He: only elements whose valence electrons feel full nuclear charge (pull) NOTHING TO SHIELDTHEM

Positive ions (cations) Formed by loss of electronsFormed by loss of electrons Cations always smaller than parent atomCations always smaller than parent atom Ca 2e 8e 2e Ca +2 2e 8e Ca

Negative ions or (anions) Formed by gain of electronsFormed by gain of electrons Anions always larger than parent atomAnions always larger than parent atom