Trends & the Periodic Table. Trends see properties change in predictable ways based location of elements on PTsee properties change in predictable ways.

Trends & the Periodic TableTrends & the Periodic Table

TrendsTrends

• see see properties change in predictable waysproperties change in predictable ways based location of elementsbased location of elements on PT on PT

• some properties can be predicted: some properties can be predicted: densitydensity

melting point/boiling pointmelting point/boiling point

* atomic radius* atomic radius

* ionization energy* ionization energy•electronegativityelectronegativity

anyone know where we can find these numbersanyone know where we can find these numbers

TABLE S

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)

When you’re done it will look like this so leave room for writing!

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

Increasing number of energy levels

Atomic RadiusAtomic Radius• atomic radius: defined as ½ distance atomic radius: defined as ½ distance

between neighboring nucleibetween neighboring nuclei in molecule or in molecule or crystalcrystal

• affected byaffected by

1. # energy 1. # energy

levelslevels2. Proton Pulling2. Proton Pulling

Power (PPP)Power (PPP)

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 move atoms get smaller as move across seriesacross series: :

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

Li: group 1 period 2 Cs: group 1 period 6Li: group 1 period 2 Cs: group 1 period 6

Cs has more energy levels, so it’s bigger

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Increasing Atomic Radius

2-8NeVIIIA or 18

2-7FVIIA or 17

2-6OVIA or 16

2-5NVA or 15

2-4CIVA or 14

2-3BIIIA or 132-2BeIIA or 22-1LiIA or 1

ConfigurationElementFamily

As we go across, elements gain electrons, but they are getting smaller! What is happening?

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Decreasing Atomic Radius

Why does this happen..Why does this happen..

• as go from left to right, you gain more as go from left to right, you gain more protons (atomic number increases)protons (atomic number increases)

• results in greater “proton pulling power” results in greater “proton pulling power” – remember: nucleus is (+) and electrons are (-) remember: nucleus is (+) and electrons are (-)

so eso e-- get pulled towards the nucleus 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 as go across row size tends to decrease a bit because of greater PPP bit because of greater PPP ““proton pulling proton pulling powerpower””

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We can “measure” the PPP We can “measure” the PPP by determining the by determining the

effectiveeffective nuclear chargenuclear 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 nuclear charge -- # inner shell electrons # inner shell electrons (doesn’t include valance e(doesn’t include valance e--))

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calculate calculate ““effective nuclear chargeeffective nuclear charge””• # protons minus # inner electrons# protons minus # inner electrons

+7 +1

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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)

NOTHING NOTHING TO TO SHIELD SHIELD THEMTHEM

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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 EnergyIonization Energy

• definition: amount energy required to definition: amount energy required to remove farthest valence eremove farthest valence e-- from atom from atom

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

Trends in Ionization EnergyTrends in Ionization Energy

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

• As go As go across rowacross row??

decreases

increases

ElectronegativityElectronegativity

• ability of atom to attract electrons to itself ability of atom to attract electrons to itself so can form bonds with other elements so can form bonds with other elements (to create cmpds)(to create cmpds)

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

• Fluorine: most electronegative Fluorine: most electronegative element element = 4.0 Paulings= 4.0 Paulings• Francium: least electronegative element Francium: least electronegative element = 0.7 Paulings= 0.7 Paulings

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Decreasing Atomic Radius

Increasing Ionization EnergyIncreasing Electronegativity

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due to PPP

elements in elements in same groupsame group: farther away valence electrons : farther away valence electrons are from nucleus the easier to remove themare from nucleus the easier to remove them

easier for Cs easier for Cs (top of column) (top of column) to lose electrons than to lose electrons than Li Li (bottom of column) (bottom of column) so Cs is a more reactive metal!so Cs is a more reactive metal!

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elements in same row: easier to take away valence elements in same row: easier to take away valence electrons when have less protonselectrons when have less protons

Li has less “proton pulling power” so easier to remove Li has less “proton pulling power” so easier to remove its valence electronsits valence electrons

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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 to form (+) ions

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

• for metals, for metals, reactivityreactivity increasesincreases as as ionization energy goes downionization energy goes down

Trends for Reactivity Trends for Reactivity (Metallic Character) (Metallic Character) of Metalsof Metals

• 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-metals:Trend for Reactivity of Non-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)

How do you know if an atom gains How do you know if an atom gains or loses electrons?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 electrons metals tend to have 1, 2, or 3 valence electrons – it’s it’s easier to loseeasier to lose these than gain extra needed 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 it’s easier to addeasier to add extra needed than to lose these extra needed than to lose these

• noble gases already have 8 so they don’t form ions noble gases already have 8 so they don’t form ions very easilyvery easily

positive ions (positive ions (cationscations))

• formed by formed by loss of electronsloss of electrons

• cationscations always always smallersmaller than than parentparent atomatom

Ca

2e

8e

8e

2e

Ca+2

2e

8e

8e

Ca

negative ions or (negative ions or (anionsanions))

• formed by formed by gain of electronsgain of electrons

• anionsanions always always largerlarger than than parentparent atomatom

AllotropesAllotropes

• different structural forms of different structural forms of element in element in same phasesame phase– different structures and propertiesdifferent structures and properties– examples: C and Oexamples: C and O

Graphite and Diamond: Graphite and Diamond: both carbon in solid formboth carbon in solid form

OO22 (g) and O (g) and O3 3 (g)(g)

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

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