PeriodicProperties

of the Elements

Unit 8:Periodic Properties

of the Elements

Dr. Jorge L. AlonsoMiami-Dade College –

Kendall CampusMiami, FL

CHM 1045: General Chemistry and Qualitative Analysis

Textbook Reference:

•Chapter #6

•Module #10

PeriodicProperties

of the Elements

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

PeriodicProperties

of the Elements

Development of Periodic Table

PeriodicProperties

of the Elements

Development of Periodic TablePhy.

Prop. Ca Sc TiAt. # 20 21 22

Mass # 40.078 44.956 47.88

m.pt. 1112 1814 1933

b.pt. 1757 3104 3560

Density 1.55 2.99 4.54

Mendeleyev predicted the discovery and properties of Sc, Ga, Ge

PeriodicProperties

of the Elements

Development of Periodic Table

*

PeriodicProperties

of the Elements

Periodic Trends

Size 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*}

PeriodicProperties

of the Elements

Effective Nuclear Charge (Zeff )

Attractive Charge felt by valence electrons

Zeff = Z - SAtomic Number

(#p+)

Inner Core of Shielding e- = screening

constant

Effective Nuclear Charge (Zeff)

Atomic Number (Z = #p+)

Shielding electrons (S) Felt by

{Eff.Nuclear.Charge*}

PeriodicProperties

of the Elements

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 electrons

Increasing

(19e-) (20e-) (21e-) (22e-) (23e-) (24e-) (25e-) (26e-) (27e-) ( 28e-)

PeriodicProperties

of the Elements

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 n

increasing Zeff .

increasin

g value of n

{AtomicRadii*}

(1) Sizes of Atoms(Atomic Radii)

PeriodicProperties

of the Elements

Sizes of Atoms (Atomic Radii)

PeriodicProperties

of the Elements

PeriodicProperties

of the Elements

PeriodicProperties

of the Elements

PeriodicProperties

of the Elements

PeriodicProperties

of the Elements

Experimental Techniques for determining radii:

(1) X-ray crystallography

(2) Neutron scattering

Sizes of Atoms and Ions

PeriodicProperties

of the Elements

Sizes of Atoms

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

PeriodicProperties

of the Elements

Sizes of Ions• Cations 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}

PeriodicProperties

of the Elements

Sizes of Ions

• Ions increase in size as you go down a column.Due to increasing

value of n.

{Pink = cation, Grey = atom , Blue = anion}

Cations larger

Anions larger

PeriodicProperties

of the Elements

Sizes of Ions

• In an isoelectronic series, ions have the same number of electrons.

• Ionic size decreases with an increasing nuclear charge.

{Pink = cation, Grey = atom , Blue = anion}

PeriodicProperties

of the Elements

(2) Ionization Energy

Electron 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-

PeriodicProperties

of the Elements

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).

PeriodicProperties

of the Elements

Trends in First Ionization Energies

• As 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.

+1

Zeff+2

+3 +4 +5 +6 +7

+8

PeriodicProperties

of the Elements

Trends in First Ionization Energies

• As 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.

+1

Zeff+2

+3 +4 +5 +6 +7

+8

PeriodicProperties

of the Elements

Trends in First Ionization Energies• Generally, across a row, the Zeff increases.

{IonizationEnergy}

PeriodicProperties

of the Elements

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

PeriodicProperties

of the Elements

Trends in First Ionization Energies

• The 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.

PeriodicProperties

of the Elements

Trends in First Ionization Energies

• The second occurs between Groups VA and VIA.Electron removed

comes from doubly occupied orbital.

Repulsion from other electron in orbital helps in its removal.

PeriodicProperties

of the Elements

(3) Electron Affinity

Energy 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-

PeriodicProperties

of the Elements

Trends in Electron Affinity

In general, electron affinity becomes more exothermic as you go from left to right across a row.

{PerTrendElectAffinity}

PeriodicProperties

of the Elements

Trends in Electron Affinity

There are again, however, two discontinuities in this trend.

PeriodicProperties

of the Elements

Trends in Electron Affinity

• The 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.

PeriodicProperties

of the Elements

Trends in Electron Affinity

• The second occurs between Groups IVA and VA.Group VA has no

empty orbitals.Extra electron must

go into occupied orbital, creating repulsion.

PeriodicProperties

of the Elements

(4) Properties of Metal, Nonmetals,and Metalloids

PeriodicProperties

of the Elements

Metals versus Nonmetals

• Metals tend to form cations.• Nonmetals tend to form anions.

PeriodicProperties

of the Elements

Metals vs. Nonmetals

Metals tend to be: • lustrous• Malleable and ductile• Good conductors of heat and electricity.• Loose electrons (cations) in reactions

with nonmetals in order to acquire noble gas configuration

• Unreactive with each, instead they mix with each other to form alloys (solutions)

Nonmetals tend to be:

• Dull

• Brittle

• Poor 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.

PeriodicProperties

of the Elements

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, Pd mixed with Cu mixed with Ni

PeriodicProperties

of the Elements

Nonmetal oxides tend to be acidic.

SO2 + H2O

SO3 + H2O

CO2(s)

Metal oxides vs. Nonmetal oxides

Metal oxides tend to be basic.

CaO + HOH

CO2(s) + H2O(l) H2CO3(aq) weak acid

Basic 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 acid

H2SO4(aq) strong acid

MgONa2O

CO2

SO3

PeriodicProperties

of the Elements

Metalloids

• Have some characteristics of metals, some of nonmetals.

• For instance, silicon looks shiny, but is brittle and fairly poor conductor.

PeriodicProperties

of the Elements

Not a Metalloid: Silicone

• An organic compound made primarily from silicon and oxygen

Silicone overdose

PeriodicProperties

of the Elements

PeriodicProperties

of the Elements

(5) Group TrendsAlkali Metals

Alkaline Earth Metals

Nobel Gases

Halogens

PeriodicProperties

of the Elements

Alkali Metals• Soft, 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.

PeriodicProperties

of the Elements

Alkali Metals

Their reactions with water are famously exothermic.

PeriodicProperties

of the Elements

Alkali Metals

• Alkali metals (except Li) react with oxygen to form peroxides (O2

2-)

2K + O2 K2O2

• K, Rb, and Cs also form superoxides (O2-):

K + O2 KO2

• Produce bright colors when placed in flame.

2.{ox # = -1}

{ox # = -½}

• Alkali metals react with oxygen to form oxides (O2-)

4K + O2 2K2O

PeriodicProperties

of the Elements

Alkaline Earth Metals

• Have higher densities and melting points than alkali metals.

• Have low ionization energies, but not as low as alkali metals.

PeriodicProperties

of the Elements

Group 4A: The Carbon Family

Allotropes 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

PeriodicProperties

of the Elements

Group 6A: The Oxygen Family

• Oxygen,

sulfur, and

selenium are nonmetals.• Tellurium is a metalloid.• The radioactive polonium is a metal.

PeriodicProperties

of the Elements

Oxygen• Two allotropes:

O2

O3, ozone• Oxidizing agent: Tends to take electrons

from other elements• Three anions:

O2−, oxide O2

2−, peroxide O2

1−, superoxide

• Weaker oxidizing agent than oxygen.

• Most stable allotrope is S8, a ringed molecule.

Sulfur

O O

PeriodicProperties

of the Elements

Group VIIA: Halogens• Prototypical nonmetals• Name comes from the Greek halos and gennao: “salt formers”

{PhyPropHalogens}

PeriodicProperties

of the Elements

Group VIIA: Halogens

• Large, negative electron affinitiesTherefore, tend to oxidize

other elements easily

• React directly with metals to form metal halides

• Chlorine added to water supplies to serve as disinfectant

PeriodicProperties

of the Elements

Group VIIIA: Noble Gases

• Astronomical ionization energies• Positive electron affinities

Therefore, relatively unreactive

• Monatomic gases

PeriodicProperties

of the Elements

Group VIIIA: Noble Gases

• Xe forms three compounds:XeF2

XeF4 (at right)

XeF6

• Kr forms only one stable compound:KrF2

• The unstable HArF was synthesized in 2000.

PeriodicProperties

of the Elements

Metals versus Nonmetals

PeriodicProperties

of the Elements

2006 (B)

PeriodicProperties

of the Elements

PeriodicProperties

of the Elements

2006 (A)

PeriodicProperties

of the Elements

PeriodicProperties

of the Elements

2007 (B)

PeriodicProperties

of the Elements