Unit 8:Periodic Propertiesof the ElementsDr. Jorge L. AlonsoMiami-Dade College Kendall CampusMiami, FLCHM 1045: General Chemistry and Qualitative AnalysisTextbook Reference: Chapter #6Module #10

Dmitry Ivanovich Mendeleyev (1834-1907) noticed a repeating pattern of properties and reactivities, when the elements are ordered by increasing atomic numbers.

Development of Periodic Table

Development of Periodic Table

Development of Periodic TableMendeleyev predicted the discovery and properties of Sc, Ga, Ge

Phy.Prop.CaScTiAt. #202122Mass #40.07844.95647.88m.pt.111218141933b.pt.175731043560Density1.552.994.54

Development of Periodic Table*

Periodic TrendsSize of atoms and ions: Determined by electrons which are both attracted to the nucleus and repelled by other electrons.

Ionization energy: energy required to remove an electron from and atom or ion. (Measure of how strongly an atom holds its own electrons)

Electron affinity: energy released when an atoms accept electrons. (Measure of how strongly an atom wants other electrons)

Metal, Non-metals, Metalloids

Group Trends: reactive characteristics determined by valence electrons.{Intro.Per.Prop*}

Effective Nuclear Charge (Zeff )Attractive Charge felt by valence electronsZeff = Z - SAtomic Number (#p+)Inner Core of Shielding e- = screening constantEffective Nuclear Charge (Zeff)Atomic Number (Z = #p+)Shielding electrons (S)Felt by{Eff.Nuclear.Charge*}

depends on both the fact that valence electrons are both:Effective Nuclear Charge (Zeff ) attracted to the nucleus repelled by the other (shielding) electrons.Effective Nuclear Charge (Zeff.)+1+2+3+4+5+6+7+8+2(2e-)(18e-)(10e-)(0e-)Shielding electronsIncreasing(19e-) (20e-) (21e-) (22e-) (23e-) (24e-) (25e-) (26e-) (27e-) ( 28e-)

Bonding atomic radius tends to decrease from left to right across a row due to increasing Zeff.increase from top to bottom of a column due to increasing value of nincreasing Zeff.increasing value of n{AtomicRadii*}(1) Sizes of Atoms(Atomic Radii)

Sizes of Atoms (Atomic Radii)

Experimental Techniques for determining radii: X-ray crystallography Neutron scatteringSizes of Atoms and Ions

Sizes of AtomsThe bonding atomic radius is defined as one-half of the distance between covalently bonded nuclei.

Sizes of IonsCations are smaller than their parent atoms.The outermost electron is removed and repulsions are reduced.Anions: larger than parent atoms.Electrons are added and repulsions are increased.{SizeOfIons*}{Pink = cation, Grey = atom}{Grey = atom, Blue = anion}

Sizes of IonsIons increase in size as you go down a column.Due to increasing value of n.{Pink = cation, Grey = atom , Blue = anion}Cations largerAnions larger

Sizes of IonsIn an isoelectronic series, ions have the same number of electrons.Ionic size decreases with an increasing nuclear charge.{Pink = cation, Grey = atom , Blue = anion}

(2) Ionization EnergyElectron gun the amount of energy required to remove an electron from the ground state of a gaseous atom or ion. A good measure of how strongly metal ions hold-on to their electrons as they become cations: M M+ + e-

Ionization EnergyFirst ionization energy is that energy required to remove first electron.Second ionization energy is that energy required to remove second electron, etc.{IonizationEnergy}It requires more energy to remove each successive electron.When all valence electrons have been removed, the ionization energy takes a quantum leap (large jump).

Trends in First Ionization EnergiesAs one goes up in a column, more energy is required to remove the first electron.

Zeff is essentially the same, but the valence electrons are closer to the nucleus.+1Zeff+2+3+4+5+6+7+8

Trends in First Ionization EnergiesAs one goes across a row, the Zeff increases, so more energy is required to remove the first electron.Zeff increases, but the valence electrons essentially in the same distance (energy level) from the nucleus.+1Zeff+2+3+4+5+6+7+8

Trends in First Ionization EnergiesGenerally, across a row, the Zeff increases.{IonizationEnergy}

Trends in First Ionization Energiesthere are two apparent discontinuities in this trend.

Trends in First Ionization EnergiesThe first occurs between Groups IIA and IIIA.Electron removed from p-orbital rather than s-orbitalElectron farther from nucleusSmall amount of repulsion by s electrons.

Trends in First Ionization EnergiesThe second occurs between Groups VA and VIA.Electron removed comes from doubly occupied orbital.Repulsion from other electron in orbital helps in its removal.

(3) Electron AffinityEnergy change accompanying addition of electron to gaseous atom:

Cl + e Cl{ElectronAffinity}A good measure of how strongly non-metal atom acquire electrons to become anions: N + e- N-

Trends in Electron AffinityIn general, electron affinity becomes more exothermic as you go from left to right across a row.{PerTrendElectAffinity}

Trends in Electron AffinityThere are again, however, two discontinuities in this trend.

Trends in Electron AffinityThe first occurs between Groups IA and IIA.Added electron must go in p-orbital, not s-orbital.Electron is farther from nucleus and feels repulsion from s-electrons.

Trends in Electron AffinityThe second occurs between Groups IVA and VA.Group VA has no empty orbitals.Extra electron must go into occupied orbital, creating repulsion.

(4) Properties of Metal, Nonmetals,and Metalloids

Metals versus NonmetalsMetals tend to form cations.Nonmetals tend to form anions.

Metals vs. NonmetalsMetals tend to be: lustrousMalleable and ductileGood conductors of heat and electricity.Loose electrons (cations) in reactions with nonmetals in order to acquire noble gas configurationUnreactive with each, instead they mix with each other to form alloys (solutions)Nonmetals tend to be:Dull BrittlePoor conductors of heat and electricity.Gain electrons (anions) in reactions with metals in order to acquire noble gas configuration.Reactive with each other to form molecular (covalent) compounds.

Gold Gold Jewelry 24k =100% Au; 12k =50% Au, usually mixed with Ag, Pd or Ni (white) or Cu (rose); colored alloys coated with Rh or Pt to prevent rusting.Metals do not react with each other to form compounds, instead they mix with each other to form alloys (solutions)24k =100% Au{coated with Rh or Pt to prevent rusting}12k = 50% mixed with Ag, Pdmixed with Cumixed with Ni

Nonmetal oxides tend to be acidic.SO2 + H2O SO3 + H2O CO2(s) Metal oxides vs. Nonmetal oxidesMetal oxides tend to be basic.

CaO + HOH CO2(s) + H2O(l) H2CO3(aq) weak acidBasic H2O + bromthymol blue Indicator

H2CO3(aq) CO2(g) + H2O(l) AcidH2O + bromthymol blue Indicator Amphoteric: capable of behaving as an acid or a base.

Note that the more oxidized the oxide the stronger its acid base strength!{Acid/Base behavior of Oxides}Ca2+ + 2OH-H2SO3(aq) weak acidH2SO4(aq) strong acidMgONa2OCO2SO3

MetalloidsHave some characteristics of metals, some of nonmetals.For instance, silicon looks shiny, but is brittle and fairly poor conductor.

Not a Metalloid: SiliconeAn organic compound made primarily from silicon and oxygenSilicone overdose

(5) Group TrendsAlkali MetalsAlkaline Earth MetalsNobel GasesHalogens

Alkali MetalsSoft, metallic solids.Name comes from Arabic word for ashes.So reactive, that they are found only as compounds in nature.Have low densities and melting points.Also have low ionization energies.

Alkali MetalsTheir reactions with water are famously exothermic.

Alkali MetalsAlkali metals (except Li) react with oxygen to form peroxides (O22-) 2K + O2 K2O2K, Rb, and Cs also form superoxides (O2-):K + O2 KO2

Produce bright colors when placed in flame.2.{ox # = -1}{ox # = -}Alkali metals react with oxygen to form oxides (O2-) 4K + O2 2K2O

Alkaline Earth MetalsHave higher densities and melting points than alkali metals.Have low ionization energies, but not as low as alkali metals.

Group 4A: The Carbon FamilyAllotropes of Carbon:a) Diamond b) Graphite c) Lonsdaleite d) C60 (Buckminsterfullerene) e) C540 (see Fullerene) f) C70 (see Fullerene) g) Amorphous carbon h) single-walled carbon nanotube

Group 6A: The Oxygen FamilyOxygen, sulfur, and selenium are nonmetals.Tellurium is a metalloid.The radioactive polonium is a metal.

OxygenTwo allotropes:O2O3, ozoneOxidizing agent: Tends to take electrons from other elementsThree anions:O2, oxideO22, peroxideO21, superoxideWeaker oxidizing agent than oxygen.Most stable allotrope is S8, a ringed molecule.SulfurOO

Group VIIA: HalogensPrototypical nonmetalsName comes from the Greek halos and gennao: salt formers{PhyPropHalogens}

Group VIIA: HalogensLarge, negative electron affinitiesTherefore, tend to oxidize other elements easilyReact directly with metals to form metal halidesChlorine added to water supplies to serve as disinfectant

Group VIIIA: Noble GasesAstronomical ionization energiesPositive electron affinitiesTherefore, relatively unreactiveMonatomic gases

Group VIIIA: Noble GasesXe forms three compounds:XeF2XeF4 (at right)XeF6Kr forms only one stable compound:KrF2The unstable HArF was synthesized in 2000.

Metals versus Nonmetals

2006 (B)

2006 (A)

2007 (B)

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