Periodic tablePeriodic table: trends in chemical and : trends in chemical and physical properties that occur within the physical properties that occur within the same groups and periodssame groups and periods First attempt (Mendeleev and Meyer) elements First attempt (Mendeleev and Meyer) elements

arranged in order of increasing atomic weightarranged in order of increasing atomic weight Modern periodic tableModern periodic table: elements arranged : elements arranged

in order of increasing atomic numberin order of increasing atomic number

Effective nuclear charge (Effective nuclear charge (ZZeffeff): ): positive positive charge felt by a valence electron in a charge felt by a valence electron in a many-electron atommany-electron atom Depends on its distance from the nucleus and Depends on its distance from the nucleus and

the number of core electronsthe number of core electrons Core electrons block, or screen, valence eCore electrons block, or screen, valence e-- from the from the

full attraction of the nucleusfull attraction of the nucleus As average number of screening/core electrons (As average number of screening/core electrons (SS) )

increases, effective nuclear charge decreasesincreases, effective nuclear charge decreases As distance from the nucleus increases, As distance from the nucleus increases, SS increases and increases and

ZZeffeff decreases decreases

Mg: [Ne]3sMg: [Ne]3s22 ZZ = 12 = 12 S S = core e= core e-- = 10 = 10 ZZ – – SS = 12 – 10 = = 12 – 10 =

22

Effective nuclear charge…Effective nuclear charge…› Increases as you move across a periodIncreases as you move across a period

Number of core e-, Number of core e-, SS, remains the same, remains the same Atomic number increases; higher nuclear Atomic number increases; higher nuclear

charge, charge, ZZ Valence e- added to counter charge of p+, but Valence e- added to counter charge of p+, but

valence e- don’t shield one anothervalence e- don’t shield one another

› Decreases as you go down a groupDecreases as you go down a group Large e- cores (think atomic radius) aren’t Large e- cores (think atomic radius) aren’t

able to screen valence e- from the nuclear able to screen valence e- from the nuclear chargecharge

Bounce two of the same atoms off each Bounce two of the same atoms off each other (B)other (B)

The distance between two nuclei is the The distance between two nuclei is the nonbonding atomic radiusnonbonding atomic radius (aka: van (aka: van der Waals radius)der Waals radius)

++

--

----

--

-- ++

--

--

--

----

BBradrad

BBradrad

Homonuclear Homonuclear diatomic moleculediatomic molecule

Distance between 2 Distance between 2 nuclei is nuclei is bond lengthbond length

Half the bond length Half the bond length is the is the bonding bonding atomic radiusatomic radius

Decrease in atomic radius across a periodDecrease in atomic radius across a period› Effective nuclear charge increases, drawing the Effective nuclear charge increases, drawing the

electrons in towards the nucleus very tightlyelectrons in towards the nucleus very tightly Increase in atomic radius down a groupIncrease in atomic radius down a group

› As the principal quantum number increases, the As the principal quantum number increases, the probability of finding the electrons further from the probability of finding the electrons further from the nucleus increasesnucleus increases

Arrange the following atoms in order of Arrange the following atoms in order of increasing atomic size:increasing atomic size:› Mg, Ca, SrMg, Ca, Sr› B, F, Ge, PbB, F, Ge, Pb

Ionic radius: Ionic radius: distance between ions in an distance between ions in an ionic compoundionic compound

When atoms form ions, they tend to When atoms form ions, they tend to achieve a full valence shell by either achieve a full valence shell by either losing e- or gaining e-losing e- or gaining e-

Cations are smaller than parent atomCations are smaller than parent atom› Outermost orbital is emptied - decreasing Outermost orbital is emptied - decreasing

radius of the ionradius of the ion Anions are larger than parent atomAnions are larger than parent atom

› Outermost orbital fills up, taking up more Outermost orbital fills up, taking up more spacespace

For ions of the same charge, ion size For ions of the same charge, ion size increases down a groupincreases down a group

Ion size decreases across a periodIon size decreases across a period

ASIDE: ASIDE: Transition metals lose Transition metals lose electrons in outermost orbital first!electrons in outermost orbital first!› Ex.: Fe(3dEx.: Fe(3d664s4s22) ) Fe Fe3+3+(3d(3d55) + 3e) + 3e--

Isoelectric series: Isoelectric series: group of ions containing group of ions containing the same number of electronsthe same number of electrons

Ex: SeEx: Se2-2-, Br, Br--, Rb, Rb++, Sr, Sr2+2+, Y, Y3+3+

› SeSe2-2- = atomic # 34 (36 e = atomic # 34 (36 e--) ) › BrBr-- = atomic # 35 (36 e = atomic # 35 (36 e--) ) › RbRb++ = atomic # 37 (36 e = atomic # 37 (36 e--) ) › SrSr2+2+ = atomic # 38 (36 e = atomic # 38 (36 e--) ) › YY3+3+ = atomic # 39 (36 e = atomic # 39 (36 e--))

Ionic size in isoelectric series decreases Ionic size in isoelectric series decreases with increasing atomic number due to with increasing atomic number due to increasing effective nuclear chargeincreasing effective nuclear charge

Ionization energy Ionization energy ((II)): : minimum energy minimum energy required to remove an erequired to remove an e-- from a gaseous from a gaseous atom or ionatom or ion› The larger the ionization energy, the harder it The larger the ionization energy, the harder it

is to remove the eis to remove the e--

First ionization energy First ionization energy ((II11)): : energy needed energy needed to remove 1to remove 1stst e- from neutral atom e- from neutral atom› NaNa(g)(g) Na Na++

(g)(g) + e + e--(g)(g) II11 = +496 kJ/mol = +496 kJ/mol

Second ionization energy (Second ionization energy (II22): ): energy energy needed to remove 2needed to remove 2ndnd e e--

› NaNa++(g)(g) Na Na2+2+

(g)(g) + e + e--(g)(g) II22 = +4562 kJ/mol = +4562 kJ/mol

Each successive ionization energy is Each successive ionization energy is higher than the previoushigher than the previous

Sharp increase in ionization energy Sharp increase in ionization energy when a core ewhen a core e-- is removed is removed

Decreases as you move down a group Decreases as you move down a group and atomic number gets largerand atomic number gets larger› Outermost eOutermost e-- is easier to remove as you go is easier to remove as you go

down a group and atom gets biggerdown a group and atom gets bigger Increases as you move across a periodIncreases as you move across a period

› Outermost eOutermost e-- is harder to remove as you go is harder to remove as you go across a period and atom gets smalleracross a period and atom gets smaller

Electron affinity (E):Electron affinity (E): energy change energy change associated with adding an eassociated with adding an e-- to a to a gaseous atom or iongaseous atom or ion› II(g)(g) + e + e--

(g)(g) I I--(g)(g) ΔΔE = -295 kJ/molE = -295 kJ/mol

For most atoms, energy is usually For most atoms, energy is usually released when an ereleased when an e-- is added is added› Negative valueNegative value

Puts an e- in a new (higher energy) Puts an e- in a new (higher energy) subshell (unfavorable)subshell (unfavorable)

NeNe(g)(g) = e = e--(g)(g) Ne Ne--

(g)(g) ΔΔE > 0E > 0

To determine whether eTo determine whether e-- affinity is (+) or affinity is (+) or (-), look at e(-), look at e-- configuration: configuration:› Do you have to add the eDo you have to add the e-- to a higher energy to a higher energy

orbital or subshell?orbital or subshell?› Ne = 1sNe = 1s222s2s222p2p66

› NeNe-- = 1s = 1s222s2s222p2p663s3s1 1

How easily an atom or ion loses an eHow easily an atom or ion loses an e--

Forms consecutively more (+) speciesForms consecutively more (+) species Measure of how tightly an eMeasure of how tightly an e-- is held on is held on

toto Usually requires energy [(+) value]Usually requires energy [(+) value]

How easily an atom or ion gains an eHow easily an atom or ion gains an e--

Forms consecutively more (-) speciesForms consecutively more (-) species Measure of attraction for an outside eMeasure of attraction for an outside e--

Usually releases energy [(-) value]Usually releases energy [(-) value]

What is the ionization energy for FWhat is the ionization energy for F--(g)(g) if if

the electron affinity for Fthe electron affinity for F(g)(g) is -328 is -328 kJ/mol?kJ/mol?

Which member of each ion pair has the Which member of each ion pair has the higher ionization energy? Why?higher ionization energy? Why?› Sodium or rubidiumSodium or rubidium› Silicon or phosphorousSilicon or phosphorous

Which element has the higher electron Which element has the higher electron affinity, sulfur or chlorine?affinity, sulfur or chlorine?

Shiny lusterShiny luster Various colors, but most are silveryVarious colors, but most are silvery Malleable and ductileMalleable and ductile Good conductorsGood conductors Metal oxides form bases in HMetal oxides form bases in H22OO Form cations in solutionForm cations in solution All are solids at RT (except Hg) All are solids at RT (except Hg)

No lusterNo luster Various colorsVarious colors BrittleBrittle Poor conductorsPoor conductors Nonmetal oxides form acids in HNonmetal oxides form acids in H22OO Form anions in solutionForm anions in solution Solids, gases, and liquid at RTSolids, gases, and liquid at RT

Metals form cationsMetals form cations Low ionization energiesLow ionization energies Metallic character:Metallic character:

› Increases down a groupIncreases down a group› Decreases across a periodDecreases across a period

When metals are oxidized they form When metals are oxidized they form characteristic cations:characteristic cations:› Group 1A metals: Group 1A metals:

1+ ions1+ ions

› Group 2A metals: Group 2A metals: 2+ ions2+ ions

› Most transition metals have variable chargesMost transition metals have variable charges

Form anionsForm anions› When nonmetals react with metals, nonmetals gain e- When nonmetals react with metals, nonmetals gain e-

and metals lose e-and metals lose e- Metal + Nonmetal Metal + Nonmetal Salt Salt 2Al2Al(s)(s) + 3Br + 3Br22(l)(l) 2AlBr 2AlBr33(s)(s)

When nonmetals are reduced they form When nonmetals are reduced they form characteristic anionscharacteristic anions› Group 7A nonmetalsGroup 7A nonmetals

1- ions1- ions

› Group 6A nonmetalsGroup 6A nonmetals 2- ions2- ions

› Group 5A nonmetalsGroup 5A nonmetals 3- ions3- ions

SoftSoft Chemistry dominated by loss of single Chemistry dominated by loss of single

e-e-› M M M M++ + e + e--

Reactivity increases down the group b/c Reactivity increases down the group b/c easier to lose e-easier to lose e-

Alkali metals react with water to form Alkali metals react with water to form MOH and HMOH and H22 gas gas

› 2M2M(s)(s) + 2H + 2H22OO(l)(l) 2MOH 2MOH(aq)(aq) + H + H22(g)(g)

Alkali metal ions are reduced to metal gas atoms that emit Alkali metal ions are reduced to metal gas atoms that emit characteristic colors when placed in a high temp flamecharacteristic colors when placed in a high temp flame

““s”s” e e-- is excited by flame and jumps to “p” sublevel and is excited by flame and jumps to “p” sublevel and then emits light energy when it returns to ground statethen emits light energy when it returns to ground state

Na line (589 nm): 3p 3s transition

Li line: 2p 2s transition

K line: 4p 4s transition

Harder and more denseHarder and more dense Chemistry dominated by loss of 2 e-Chemistry dominated by loss of 2 e-

› M M M M2+2+ + 2e + 2e--

Reactivity increases down the group b/c Reactivity increases down the group b/c easier to lose e-easier to lose e-

Very unique element that formsVery unique element that forms› Colorless diatomic gas, HColorless diatomic gas, H22

› Metallic solid at high pressuresMetallic solid at high pressures› Can behave as a cation or anion:Can behave as a cation or anion:

2Na2Na((ss)) + H + H2(2(gg)) 2NaH 2NaH((ss)) less common (Hless common (H--; hydride); hydride)

HH2(2(gg)) + Cl + Cl2(2(gg)) 2HCl 2HCl((gg))

most common (Hmost common (H++; proton); proton)

Metallic character increases down the Metallic character increases down the groupgroup› OO22 colorless gas; others are solids colorless gas; others are solids› Te is a metalloid, Po is a metal, etc.Te is a metalloid, Po is a metal, etc.

Gain e- to form 2- anionsGain e- to form 2- anions 2 important forms of oxygen: O2 important forms of oxygen: O22 & O & O33

3O3O22(g)(g) 2O 2O3(3(gg)) HH = +284.6 kJ = +284.6 kJ OO22: potent oxidizing agent: potent oxidizing agent

› Two oxidation states for oxygen:Two oxidation states for oxygen:› 2- (Ex. H2- (Ex. H22O)O)› 1- (Ex. H1- (Ex. H22OO22))

All form diatomic moleculesAll form diatomic molecules› FF22 and Cl and Cl22 gases; Br gases; Br22 liquid; I liquid; I22 solid solid

Gain an eGain an e-- to form an anion to form an anionXX22 + 2e + 2e-- 2X 2X--

Fluorine is one of the most reactive substances Fluorine is one of the most reactive substances knownknown

2F2F22(g)(g) + 2H + 2H22OO(l)(l) 4HF 4HF(aq)(aq) + O + O22(g)(g) HH = -758.7 kJ = -758.7 kJ All react with metals to produce ionic halide saltsAll react with metals to produce ionic halide salts

MgMg(s)(s) + Cl + Cl22(g)(g) MgCl MgCl22(s)(s)

All react with hydrogen gas to form gaseous All react with hydrogen gas to form gaseous hydrogen halide compoundshydrogen halide compounds

ClCl22(g)(g) + H + H22(g)(g) 2HCl 2HCl(g)(g)

All monatomicAll monatomic Notoriously unreactiveNotoriously unreactive Have completely filled Have completely filled ss and and pp

subshellssubshells In 1962 the first compound of the In 1962 the first compound of the

noble gases was prepared: XeFnoble gases was prepared: XeF22, , XeFXeF44, and XeF, and XeF66

› Why these particular compounds?Why these particular compounds?