Trends & the Periodic TableTrends & the Periodic Table

TrendsTrends

• more than 20 more than 20 properties change in predictable wayproperties change in predictable way based location of elementsbased location of elements on PTon PT

• some properties: some properties: – DensityDensity–melting point/boiling pointmelting point/boiling point– atomic radiusatomic radius– ionization energyionization energy– electronegativityelectronegativity

Atomic RadiusAtomic Radius

• Atomic radius: defined as ½ distance between neighboring nucleiAtomic radius: defined as ½ distance between neighboring nuclei in in molecule or crystalmolecule or crystal

• ““size” varies a bitsize” varies a bit from substance to substance from substance to substance

X-ray X-ray diffraction diffraction pinpoints pinpoints nuclei – then nuclei – then measures measures distance distance between thembetween them

Cannot measure Cannot measure electron cloudelectron cloud

Trends:Trends:

Atoms get larger as go Atoms get larger as go down columndown column::

↑↑## principal energy levels principal energy levels

Atoms get smaller as Atoms get smaller as move across seriesmove across series: :

↑↑ PPPPPP““proton pulling power”proton pulling power”

2-8-18-32-18-8-12-8-18-32-18-8-1FrFr77

2-8-18-18-8-12-8-18-18-8-1CsCs66

2-8-18-8-12-8-18-8-1RbRb55

2-8-8-12-8-8-1KK44

2-8-12-8-1NaNa33

2-12-1LiLi22

11HH11

ConfigurationConfigurationElementElementPeriodPeriod

Going down column 1:Going down column 1:

increasing # energy levels as go down - makes sense that increasing # energy levels as go down - makes sense that atoms get larger in sizeatoms get larger in size

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Li: Group 1 Period 2 Cs: Group 1 Period 6Li: Group 1 Period 2 Cs: Group 1 Period 6

2-8NeVIIIA or 18

2-7FVIIA or 17

2-6OVIA or 16

2-5NVA or 15

2-4CIVA or 14

2-3BIIIA or 13

2-2BeIIA or 2

2-1LiIA or 1

ConfigurationElementFamily

Going across row 2:Going across row 2:

size atoms actually get a bit smaller as go across row left to size atoms actually get a bit smaller as go across row left to right - what’s going on?right - what’s going on?

What do you remember about What do you remember about charge?charge?

•opposites attract opposites attract •like charges repellike charges repel

•largest influence on atomic size in order:largest influence on atomic size in order:•# principal energy levels# principal energy levels•““proton pulling power (PPP)proton pulling power (PPP)””

EffectiveEffective nuclear chargenuclear charge• Charge actually felt by valence electronsCharge actually felt by valence electrons

• = Atomic Number minus # inner shell electrons= Atomic Number minus # inner shell electrons

• Not same as nuclear charge or # protons in nucleusNot same as nuclear charge or # protons in nucleus

• Charge felt by valence electrons isCharge felt by valence electrons is attenuated attenuated ((shielded) by inner shell electronsshielded) by inner shell electrons

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H and HeH and He: : only elements only elements whose whose valence valence electrons feel electrons feel full nuclear full nuclear charge (pull)charge (pull)

Li’s valence eLi’s valence e-- feels effective nuclear charge of +1 feels effective nuclear charge of +1

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Calculate “effective nuclear charge”Calculate “effective nuclear charge”• # protons minus # inner electrons# protons minus # inner electrons

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

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• sizesize as you go as you go columncolumn• sizesize as you go as you go rowrow

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Ionization EnergyIonization Energy

• = amount energy required to remove valence electron from atom in gas = amount energy required to remove valence electron from atom in gas phasephase

• 1st ionization energy = energy required to remove most loosely held 1st ionization energy = energy required to remove most loosely held

valence electron (evalence electron (e-- farthest from nucleus) farthest from nucleus)

Trends in ionization energyTrends in ionization energy

• What do you think happens to the ionization energy as What do you think happens to the ionization energy as go down columngo down column of of PT?PT?

• As go As go across rowacross row??decreases

increases

•Valence electrons in atoms: effective nuclear charge of +1Valence electrons in atoms: effective nuclear charge of +1

•Cs valence electronCs valence electron lot lot farther away from nucleus than Li farther away from nucleus than Li •electrostaticelectrostatic attraction much weaker attraction much weaker so easier to steal so easier to steal electron away from Cselectron away from Cs

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•easier to steal electron from Li than from Neeasier to steal electron from Li than from Ne

•Li: Li: smaller smaller effective nuclear charge effective nuclear charge - - valence electron valence electron farther away from nucleusfarther away from nucleus

•Li has less “proton pulling power” than NeLi has less “proton pulling power” than Ne

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Trends in ionization energyTrends in ionization energy

•Ionization energy Ionization energy decreasesdecreases as go as go downdown a a columncolumn –gets easier to remove valence electrongets easier to remove valence electron

•Ionization energy Ionization energy increasesincreases as go as go acrossacross a a rowrow –more difficult to remove valence electronmore difficult to remove valence electron

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

ElectronegativityElectronegativity

• 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 noble gases tend not to form bonds, so don’t have electronegativity valuesvalues

• Unit = Pauling Unit = Pauling • Fluorine: most electronegative Fluorine: most electronegative element element = 4.0 Paulings= 4.0 Paulings

Trends in electronegativityTrends in electronegativity

• Related to PPPRelated to PPP• IncreasesIncreases as go as go across rowacross row• DecreasesDecreases as go as go down columndown column

• Remember: Remember: FF most electronegative element!most electronegative element!

Reactivity of MetalsReactivity of Metals

•Metals are Metals are loserslosers!!•judge reactivity of metals by how easily judge reactivity of metals by how easily give up electronselectrons

•most active metals: most active metals: FrFr (then (then Cs)Cs)

•For metals, For metals, reactivityreactivity increasesincreases as ionization as ionization energy goes downenergy goes down

Trends for Reactivity of MetalsTrends for Reactivity of Metals or or Metallic CharacterMetallic Character

•Increases as go down columnIncreases as go down column–easier to lose electrons!easier to lose electrons!

•Decreases as go across rowDecreases as go across row–more difficult to lose electrons!more difficult to lose electrons!

Reactivity of Non-metalsReactivity of Non-metals

•Non-metals are Non-metals are winnerswinners!!•judge reactivity of non-metals by how judge reactivity of non-metals by how easily easily gain electronselectrons

•F: most active non-metalF: most active non-metal•For non-metals: For non-metals:

– reactivity ↑ as electronegativity ↑reactivity ↑ as electronegativity ↑

Trend for Reactivity of Non-Trend for Reactivity of Non-metals:metals:

Depends on PPPDepends on PPP

•IncreasesIncreases as go as go across rowacross row•DecreasesDecreases as go as go downdown columncolumn–(shielded by more inner-shell electrons)(shielded by more inner-shell electrons)

Ionic Size Relative to Parent Ionic Size Relative to Parent AtomAtom

•Depends if (+) ion or (-) ionDepends if (+) ion or (-) ion•How do you make a positive ion?How do you make a positive ion?

•How do you make a negative ion?How do you make a negative ion?

Remove electronsRemove electrons

Add electronsAdd electrons

How do you know if an atom How do you know if an atom gains or loses electrons?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 electrons Metals tend to have 1, 2, or 3 valence electrons –It’s It’s easier to loseeasier to lose them them

•Nonmetals tend to have 5, 6, or 7 valence electronsNonmetals tend to have 5, 6, or 7 valence electrons–It’s It’s easier to addeasier to add some some

•Noble gases already have 8 so they don’t form ions very Noble gases already have 8 so they don’t form ions very easilyeasily

Positive ions (Positive ions (cationscations))

•Formed by Formed by loss of electronsloss of electrons

•CationsCations always always smallersmaller than than parentparent atom atom

Negative ions or (Negative ions or (anionsanions))

•Formed by Formed by gain of electronsgain of electrons

•AnionsAnions always always largerlarger than than parentparent atom atom

AllotropesAllotropes

•Different Different forms of element in same phaseforms of element in same phase–different structures and propertiesdifferent structures and properties

OO22 and O and O33 - both gas - both gas phasephase

OO2 2 (oxygen) - necessary for life (oxygen) - necessary for life

OO33 (ozone) - toxic to life (ozone) - toxic to life

Graphite, diamond:Graphite, diamond: both carbon in solid formboth carbon in solid form

Graphite and DiamondGraphite and Diamond