some properties of noble gases - web.uvic.caweb.uvic.ca/~asirk/222pblock_2.pdf · 1 the noble gases...

1

The Noble Gases

He ArNe

Xe

RnKr

Some Properties of Noble GasesProperty Atomic radius

(A)Density

(g/dm3)

Boiling point (K)

Melting point (K)

Enthalpy of vaporisation (kJ/mol)

Ionisation energy (kJ/mol)

Helium 0.31 0.18 4.4 0.95 0.08 2372

Neon 0.38 0.9 27.3 24.7 1.74 2080

Argon 0.71 1.78 87.4 83.6 6.52 1520

Krypton 0.88 3.71 122 116 9.05 1351

Xenon 1.08 5.85 167 162 12.7 1170

Radon 1.20 9.97 212 202 18.1 1037

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Properties of Noble Gases

Induced Dipole

3

Reactivity of Noble Gases

HalogensF, Cl, Br, I, At

Br2

I2

Br2

F2

Cl2

The only group to exist in all three states of matter at SATP (standard ambient temperature and pressure: 25 C, 100 kPa)

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Some Properties of the HalogensProperty Atomic radius

(A)Boiling point (C)

Melting point (C)

Electronegativity Ionisation energy (kJ/mol)

Electron affinity

Fluorine 0.64 -188.1 -218.6 3.98 1681 -328

Chlorine 0.99 -34.9 -101.0 3.16 1255 -349

Bromine 1.14 59.5 -7.3 2.96 1140 -325

Iodine 1.33 185.2 113.6 2.66 1008 -295

Astatine - (302) (337) 2.20

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Halogen-Halogen compounds

examples only, not for memorisation

Halogen-Oxygen Compounds


6

Halogen-Oxygen Compounds


Some Important Halogenated Compounds

Teflon

HFreon-12

Freon-22

H

H

Prozac

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Number of Oxidation States Available to Each Element

Metals-Review• Properties of metals?

~lustrous surface (shiny) [so are silicon, iodine, fools gold (pyrite, FeS2): metalloid, non-metal, inorganic compound]

~dense [Li density 1/2 that of H2O; osmium - 40 x H2O]

~malleable (can be flattened, deformed) [but some of the TMs are quite brittle]~ductile (can be pulled into wires) [and Hg is a liquid!]

H&S, Fig. 2.10, p. 43

~ high thermal conductivity [diamond (non-metal) has highest of any element]

~ high 3D electrical conductivity [graphite (non-metal) high 2D version]

~hard [alkalis soft, Hg is a liquid!]

…even though two orders of magnitude difference between worst(plutonium) and best(silver) metal conductivities under ambient conditions, plutonium conductivity is 105 higher than best conducting nonmetallic element

• Bonding in metals?~ essentially covalent, but with the bonding (valence) electrons delocalized (free to move) throughout the bulk metal structure. (e.g. electron-sea model)

~ in the solid state, the bulk structure consists of ordered arrays of atoms: these are crystalline materials with lattice structures.

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Radii

• covalent radius:

can only know if:-element X has a stable form containing X-X single bond-experiment is carried out to measure d, such as diffraction techniques;

e.g. X-ray, neutron, or electron diffraction

• van der Waals radius:

internuclear separation (d) 1/2(d) = rcov

e.g. P4, S6 or S8, H2, F2, & can actually get alkali metals as M2 in the vapour phase, but rcov not actually too meaningful for the alkali elements, which are metallic, and their compounds, which are most often ionic and solid

•

•

•

•

•

•

distance = 2rvdw

rvdw > rcov

• metallic radius:

What does a metallic solid look like?

Types of Solids

crystal glass

atomic arrangementorder

name

concept

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Crystals

Temperature dependence of metallic structure

“Napoleon’s retreat from Moscow”by Adolph Northen (see Wikipedia entry on 1812 French invasion of Russia.

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Early Crystallography

7 crystal systems

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3 ways to fill a cubic crystal

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Metallic Crystal Structures of the Elements

13

Lattice Structures of Metallic Solids• Despite our ability to describe the covalent bonding in metals using molecular orbital theory (more later), it is easiest to describe the structures by considering the atoms as hard spheres

H&S, Fig. 6.6, p. 151

• Many different ordered arrangements are possible: we use packing models to describe these crystal lattices

• Next simplest crystal lattice arises from body-centred cubic

• Simplest possible arrangement: simple cubic packing

Lattice Structures of Metallic Solids (cont’d)• Unit cell: smallest repeating unit of a lattice structure

• Coordination number: number of other atoms “touching” each atom in a lattice

• Total number of spheres in each unit cell?

• Relative packing efficiencies (or % occupancy)

12

3

4

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Lattice Structures of Metallic Solids (cont’d)• Total number of spheres in each unit cell?

simple cubic body-centred cubic

Lattice Structures of Metallic Solids (cont’d)

H&S, Ch6; RC&O, Ch4

• Total number of spheres in each unit cell?

simple cubic body-centred cubic

• Relative packing efficiencies (% occupancy) of the different lattices:

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a

a

a

A review of triangles

a

a2 +b2 = c2

if a and b are equal

b

c

a

c

1

3

2 a

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FCC/CCP BCC

a

aa

ca

c

c

d

The calculations (BCC)

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The calculations (FCC)

BCC

ac

d

What is the atomic radius of Barium?

ρ= 7.86 g/cm2 (BCC) aw=55.847 g/mole

ρ=g(grams per cell)/a3 (volume of cell)

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BCC

ac

d

d=√3 a

d

d=4rFe =√3aBCC

2 atoms/cell

What is the packing efficiency of a BCC?

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d

d=4rFe =√3aBCC

2 atoms/cell

EXTRA: Close Packed Lattice Structures

• here are ccp/fcc unit cell diagrams from our four different sources:

• important to remember the layer diagram describes mechanism for packing whole spheres, while the unit cell’s function is only to provide the minimum positional information necessary to reproduce the bulk lattice.

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Lattice Structures of Metallic Solids

• cubic close-packed (face-centred cubic)

• hexagonal close-packed

“ccp” or “fcc”

“hcp”

~ the corners of the unit cell cube are at the nuclei of 8 atoms ~ the faces of the unit cell cube cut four atoms in half

~ the hexagonal corners of the unit cell cube are at the nuclei of 12 atoms ~ the two hexagonal faces of the unit cell cube cut two atoms in half~ three atoms are completely within the unit cell


ρ= 7.86 g/cm2 (BCC) aw=55.847 g/mole

ρ= (grams per cell) =

(volume of cell)

(2 atoms/cell)(55.847 grams/mol)

6.022*1023 atoms/mol

7.86 grams/cm3a3=g/ρ = =2.36*10-23 cm3

aBCC = 2.86* 10-8 cm

4rFe =√3aBCC

rFe =√3aBCC

4

rFe =1.24*10-8 cm

(atoms/cell)(atomic weight)

NA

a3

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The calculations (FCC)

ρ= ? g/cm2 (FCC) aw=55.847 g/mole

ρ=(grams per cell)/a3 (volume of cell)


6.022*1023 atoms/molρ = = 8.57 grams/cm3

rFe =1.24*10-8 cm

(3.51*10-8 cm)3

4rFe =√2aFCC

aFCC= 4rFe

aFCC =3.51*10-8 cm

√2

4*(1.24*10-8 cm)

√2=


ρ= 3.50 g/cm2 (BCC) aw=137.33 g/mole

ρ=(grams per cell)/a3 (volume of cell)


6.022*1023 atoms/mol

3.50grams/cm3a3=g/ρ = =2.36*10-23 cm3

aBCC = 5.07* 10-8 cm

4rBa =√3aBCC

rBa =√3aBCC

4

rBa=2.19*10-8 cm or 2.19*10-10 m or 219 pm or 2.19 A

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To know

Crystal structure

Spheres per unit cell

Number of nearest neighbours

packing efficiency

reproduce structure

SCBCCFCChexagonal

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Metallic radii• to calculate the metallic radius of an element, need to know the lattice type and the density of the metal.

e.g. atoms in bcc structures are eight-coordinate, each at distance x (=2rmetallic), although there are six more neighbours at distances of 1.15x. This gives packing efficiency of 68%, lower than close packing efficiencies of 74% (12 coordinate).~ ratio of interatomic distances for bcc vs cp forms of the same metal is 0.97:1.00~corresponds to a change of coordn # from 12 to 8.

• to compare within a periodic sequence of elements, need rmetal for a consistent number of nearest neighbours.

• rmetal varies with coordination number:coordination number 12 8 6 4relative radius 1.00 0.97 0.96 0.88

• metallic radius, rmetal: half of the distance between the nearest neighbour atoms in a solid state metallic lattice

~ some values listed for rmetal with coordination number of 12 are estimated, since not all metals actually adopt close-packed structures (See table 6.2)

~all adopt body-centred cubic lattices~rmetal in Table 6.2 reported for 12-coordinate atom, in Table 11.1 for 8-

coordinate (see K: rmetal12 = 235 pm, rmetal8 = 227)~regardless, trends are as we would predict based on Zeff arguments.

• for the alkali metals:

Ionic radii relative to metallic (or covalent) radii (in Å)

Brown, LeMay, Bursten & Murphy “Chemistry The Central Science” 11th Ed., Pearson 2009, Fig. 7.8, p. 263

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Lattice structures of ionic solids• Things to keep in mind when thinking about packing arrangements for ionic solids:(1)

(2)

(3)

RC&O, Table 5.5, p. 83

Salt

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Sodium chloride


Cesium chloriderion(Cs+) = 170 pm

rion(Cl–) = 181 pm

r+/r– =

26

Solid-state structures CaF2

Solid-state structures CaF2

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Fluorite and antifluorite structures

Zinc Blende/Diamond

H&S, Fig 6.19, p. 169

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Gauging the strength of ionic bonds

H&S Fig. 12.5, p316

Strength of Ionic Bonds


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Calculating lattice energies

• Obviously, the calculation takes into account the coulombic (charge) interactions of the ions in the lattice: not just the charges of the ions’ nearest neighbours, but also the influence of charges further away in the lattice.

• Lattice energies can be calculated for ionic solids, and these values can be useful, especially for understanding the role of lattice structure in hypothetical compounds.

• Coulombic contributions to lattice energy can be described using convergent mathematical series, in which the Madelung constant (A) varies depending on the lattice type.

Measuring lattice energies?• Very difficult to measure lattice energy directly

H&S Fig. 6.24, p175

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Measuring lattice energies?

• Just as we discussed for ionization energies and electron affinities, the internal energy change at 0K can be approximated by the enthalpy change (at room temperature) for the analogous process.

• Pretty hard to measure a lattice energy directly. (See definition again!)

• Lattice enthalpy values can be measured indirectly using thermochemical cycles: Born-Haber cycles.

H&S Fig. 6.24, p175

Hess’s Law: for a reaction carried out in a series of steps, H for the overall reaction will equal the sum of enthalpy changes for the individual steps

For n >1 must sum IEs

some properties of noble gases - web.uvic.caweb.uvic.ca/~asirk/222pblock_2.pdf · 1 the noble gases...

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