Trends the Periodic Table Trends More than 20
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 – 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)
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? 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 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
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