Trends & the Periodic Table

Trends More than 20 properties change in predictable way based on location of elements in PT Ex: density, melting point, atomic radius, ionization energy, electronegativity

Atomic radius Ionization energy Electronegativity

Atomic Radius Atomic radius = 1/2 distance between neighboring nuclei in molecule or crystal “size” varies bit from substance to substance

Cannot measure electron cloud: X-ray diffraction pinpoints nuclei to measure distance

Trends: Atoms get larger as go down a column – ↑ principal energy levels

Going down column 1: 2-8-18-32-18-8-1 Fr 7 2-8-18-18-8-1 Cs 6 2-8-18-8-1 Rb 5 2-8-8-1 K 4 2-8-1 Na 3 2-1 Li 2 1 H Configuration Element Period ↑ energy levels as go down, so makes sense that atoms get larger

previous | index | next                                                                                                                                                                                                                    Li: Group 1 Period 2 Cs: Group 1 Period 6

Going across row 2: 2-8 Ne VIIIA or 18 2-7 F VIIA or 17 2-6 O VIA or 16 2-5 N VA or 15 2-4 C IVA or 14 2-3 B IIIA or 13 2-2 Be IIA or 2 2-1 Li IA or 1 Configuration Element Family You are still adding electrons – shouldn’t they get larger?! Atoms actually get a bit smaller as you go across a row What’s going on?

What do you remember about charge? opposites attract/like charges repel valence electrons are pulled into atom by (+) charge of nucleus the greater the (+) charge, the more pulling power

previous | index | next                                                                                                                                                                                                                    as go L to R across row the size ↓ a bit because of greater “proton pulling power (PPP)”

previous | index | next                                                                                                                                                                                                                    size  as you go  & size  as you go 

Ionization Energy amount energy required to remove electron from an atom Ionization energy = energy required to remove most loosely held valence electron

Trends in ionization energy What do you think happens to the ionization energy as you go down a column of the periodic table? As you go across a row?

previous | index | next                                                                                                                                                                                                                    Same group: Cs’ valence electron farther away from nucleus so electrostatic attraction is much weaker (easier to steal electron away from Cs)

easier to steal electron from Li than Ne Li: less PPP than Ne previous | index | next                                                                                                                                                                                                                    Same row: easier to steal electron from Li than Ne Li: less PPP than Ne

Trends in ionization energy Ionization energy ↓ as go down column – easier to remove valence electron as gets farther away (↑ # electron levels) Ionization energy ↑ as go across row – it’s more difficult to remove valence electron due to ↑ PPP

Electronegativity Ability of atom to attract electrons in a bond Noble gases do not form bonds are inactive don’t have electronegativity values Unit = Pauling Fluorine: most electronegative element (4.0 Paulings)

Trends in electronegativity Related to “proton pulling power (PPP)” ↑left to right across a row ↓top to bottom of a column

Electronegativity increases in direction of arrow from Fr towards F (most electronegative element)

Reactivity of Metals metals are losers! judge reactivity of metals by how easily they give up electrons most active metals: Fr (#1) and Cs (#2) Reactivity metals: ↑ as ionization energy ↓

Trends for Reactivity of Metals (AKA: Metallic Character) Increases as go down column Easier to lose electrons! Decreases as go across row Harder to lose electrons!

Reactivity of Non-metals non-metals are winners! judge reactivity of non-metals by how easily they gain electrons most active non-metal: fluorine reactivity non-metals: ↑ as electronegativity ↑

Trend for Reactivity of Non-metals depends on PPP ↑ as go across row (left to right) ↓ as go down column (top to bottom) shielded by more inner-shell electrons

Ionic Size Relative to Parent Atom Depends on if (+) ion or (-) ion How do you create a positive ion? How do you create a negative ion? Remove electrons Add electrons

How do you know if an atom gains or loses electrons? Octet rule: magic # 8 Metals have 1, 2, or 3 valence electrons easier to lose them Nonmetals have 5, 6, or 7 valence electrons easier to gain more Noble gases: have 8 so don’t form ions

Positive ions or cations Cations always smaller than parent atom lost electrons therefore smaller in size

Negative ions or anions Anions always larger than parent atom gained electrons therefore larger in size