Trends & the Periodic Table

Trends see properties change in predictable ways based location of elements on PTsee properties change in predictable ways based location of elements on PT some properties can be predicted:some properties can be predicted: density density melting point/boiling point melting point/boiling point * atomic radius * ionization energy electronegativityelectronegativity anyone know where we can find these numbers TABLE S

Periodic properties: Graph shows a repetitive pattern (Note: Doesn’t have to be a straight line)

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 - makes sense that atoms get larger in size

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. # energy levels levels 2. Proton Pulling Power (PPP)

TRENDS: atoms get larger as go down column: ↑ # principal energy levels atoms get smaller as move across series: ↑ PPP “proton pulling power”

Li: group 1 period 2 Cs: group 1 period 6 Cs has more energy levels, so it’s bigger

Increasing number of energy levels Increasing Atomic Radius

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! What is happening?

Increasing number of energy levels Increasing Atomic Radius Decreasing Atomic Radius

Why does this happen.. as go from left to right, you gain more protons (atomic number increases)as go from left to right, you gain more protons (atomic number increases) results in greater “proton pulling power”results in greater “proton pulling power” –remember: nucleus is (+) and electrons are (-) so e - get pulled towards the nucleus more protons you have, the stronger PPPmore protons you have, the stronger PPP

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

We can “measure” the PPP by determining the effective nuclear charge this is charge actually felt by valence electronsthis is charge actually felt by valence electrons equation to calculate effective nuclear charge:equation to calculate effective nuclear charge: nuclear charge - # inner shell electrons 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

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 definition: amount energy required to remove farthest valence e - from atomdefinition: amount energy required to remove farthest valence e - from atom 1st ionization energy: energy required to remove most loosely held valence electron (valence e - farthest from nucleus)1st ionization energy: energy required to remove most loosely held valence electron (valence e - farthest from nucleus)

Trends in Ionization Energy What do you think happens to the ionization energy as go down column of PT?What do you think happens to the ionization energy as go down column of PT? As go across row?As go across row? decreases increases

Electronegativity ability of atom to attract electrons to itself so can form bonds with other elements (to create cmpds)ability of atom to attract electrons to itself so can form bonds with other elements (to create cmpds) 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 Fluorine: most electronegative elementFluorine: most electronegative element = 4.0 Paulings = 4.0 Paulings Francium: least electronegative elementFrancium: least electronegative element = 0.7 Paulings = 0.7 Paulings

Increasing number of energy levels Increasing Atomic Radius Decreasing Atomic Radius Increasing Ionization Energy Increasing Electronegativity Increasing electron shielding due to  PPP

elements in same group: farther away valence electrons are from nucleus the easier to remove them easier for Cs (top of column) to lose electrons than Li (bottom of column) so Cs is a more reactive metal! previousprevious | index | nextindexnext

elements in same row: easier to take away valence electrons when have less protons Li has less “proton pulling power” so easier to remove its valence electrons previousprevious | index | nextindexnext

Reactivity of Metals metals are losers!metals are losers! judge reactivity of metals by how easily electronsjudge reactivity of metals by how easily give up electrons to form (+) ions most active metals: Fr (then Cs)most active metals: Fr (then Cs) for metals, reactivity increases as ionization energy goes downfor metals, reactivity increases as ionization energy goes down

Trends for Reactivity (Metallic Character) of Metals Trends for Reactivity (Metallic Character) of Metals increases as go down columnincreases as go down column –easier to lose electrons! decreases as go across rowdecreases as go across row –more difficult to lose electrons!

Reactivity of Non-metals non-metals are winners!non-metals are winners! judge reactivity of non-metals by how easily electronsjudge reactivity of non-metals by how easily gain electrons F: most active non-metalF: most active non-metal for non-metals:for non-metals: –reactivity ↑ as electronegativity ↑

Trend for Reactivity of Non-metals: depends on PPP increases as go across rowincreases as go across row decreases as go down columndecreases as go down column –(shielded by more inner-shell electrons)

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 8 (or 2 for H)atoms form ions to get a valence # of 8 (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 these than gain extra needed non-metals tend to have 5, 6, or 7 valence electronsnon-metals tend to have 5, 6, or 7 valence electrons –it’s easier to add extra needed than to lose these 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 structural forms of element in same phasedifferent structural forms of element in same phase –different structures and properties –examples: C and O

Graphite and Diamond: both carbon in solid form

O 2 (g) and O 3 (g) O 2 (oxygen) - necessary for life O 3 (ozone) - toxic to life