Trends & the Periodic Table

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

previousprevious | index | nextindexnext

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

We can “measure” the Proton Pulling Power by determining the Effective nuclear charge It is the charge actually felt by valence electronsIt is the charge actually felt by valence electrons The equationThe equation Nuclear charge - # inner shell electrons (doesn’t include valance e - )

previousprevious | index | nextindexnext Calculate “effective nuclear charge” # protons minus # inner electrons # protons minus # inner electrons +7+1

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

Increasing number of energy levels Increasing Atomic Radius Decreasing Atomic Radius Increased Electron Shielding

Look at all the shielding Francium's one valance electron has. It barely feels the proton pull from the nucleus. No wonder it will lose it’s one electron the easiest. No wonder it’s the most reactive metal

Ionization Energy = amount energy required to remove a valence electron from an atom in gas phase= amount energy required to remove a valence electron from an atom in gas phase 1st ionization energy = energy required to remove the most loosely held valence electron (e - farthest from nucleus)1st ionization energy = energy required to remove the most loosely held valence electron (e - farthest from nucleus)

Cs valence electron lot farther away from nucleus than LiCs valence electron lot farther away from nucleus than Li electrostatic attraction much weaker so easier to steal electron away from Cselectrostatic attraction much weaker so easier to steal electron away from Cs THEREFORE, Li has a higher Ionization energy then CsTHEREFORE, Li has a higher Ionization energy then Cs previousprevious | index | nextindexnext

Increasing number of energy levels Increasing Atomic Radius Decreasing Atomic Radius Increased Electron Shielding Decreased Ionization Energy (easier to remove an electron) Increased Ionization Energy (harder to remove an electron)

Electronegativity ability of atom to attract electrons in bondability of atom to attract electrons in bond noble gases tend not to form bonds, so don’t have electronegativity valuesnoble gases tend not to form bonds, so don’t have electronegativity values Unit = PaulingUnit = Pauling Fluorine: most electronegative elementFluorine: most electronegative element = 4.0 Paulings = 4.0 Paulings

Increasing number of energy levels Increasing Atomic Radius Decreasing Atomic Radius Increased Electron Shielding Decreased Ionization Energy (easier to remove an electron) Increased Ionization Energy (harder to remove an electron) Decreased Electronegativity Increased Electronegativity

Reactivity of Metals judge reactivity of metals by how easily electronsjudge reactivity of metals by how easily give up electrons (they’re losers)

Increasing number of energy levels Increasing Atomic Radius Decreasing Atomic Radius Increased Electron Shielding Decreased Ionization Energy (easier to remove an electron) Increased Ionization Energy (harder to remove an electron) Decreased Electronegativity Increased Electronegativity Most reactive metal = Fr (the most metallic) More metallic

Reactivity of Non-metals judge reactivity of non-metals by how easily electrons (they are winners)judge reactivity of non-metals by how easily gain electrons (they are winners)

Increasing number of energy levels Increasing Atomic Radius Decreasing Atomic Radius Increased Electron Shielding Decreased Ionization Energy (easier to remove an electron) Increased Ionization Energy (harder to remove an electron) Decreased Electronegativity Increased Electronegativity Most reactive metal = Fr (the most metallic) More metallic Most Reactive Nonmetal = F Nonreactiv e BACK

How do you know if an atom gains or loses electrons? Think back to the Lewis structures of ionsThink back to the Lewis structures of ions Atoms form ions to get a valence of 8Atoms form ions to get a valence of 8 (or 2 for H) (or 2 for H) Metals tend to have 1, 2, or 3 valence electronsMetals tend to have 1, 2, or 3 valence electrons –It’s easier to lose them Nonmetals tend to have 5, 6, or 7 valence electronsNonmetals tend to have 5, 6, or 7 valence electrons –It’s easier to add some Noble gases already have 8 so they don’t form ions very easilyNoble gases already have 8 so they don’t form ions very easily

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

Allotropes Different forms of element in same phaseDifferent forms of element in same phase –different structures and properties O 2 and O 3 - both gas phaseO 2 and O 3 - both gas phase –O 2 (oxygen) - necessary for life –O 3 (ozone) - toxic to life Graphite, diamond:Graphite, diamond: –both carbon in solid form