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:
Period Element Configuration 1 H
1 2 Li 2-1
3 Na 2-8-1 4 K
2-8-8-1 5 Rb 2-8-18-8-1
6 Cs 2-8-18-18-8-1 7 Fr
2-8-18-32-18-8-1 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: Family IA or 1 IIA or 2 IIIA or 13 Element
Li Be B Configuration 2-1 2-2 2-3
IVA or 14 C 2-4 VA or 15 N
2-5 VIA or 16 O 2-6 VIIA or 17
F 2-7 VIIIA or 18 Ne
2-8 You are still adding electrons shouldnt they get larger?! Atoms actually get a bit smaller as you go across a row Whats 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) 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 its 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 dont 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? Remove electrons How do you create a negative ion?
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 dont 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
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