Periodic Properties of Periodic Properties of ElementsElements

Chemistry 100

Chapter 7

The Modern Periodic Table

Atomic sizeAtomic size

Atoms do not have a well defined size. As the distance from the nucleus increases, it

becomes less probable that an electron will be found there.

Examine a molecule of A2 the distance between one nucleus and the other

is d, then the radius of an A atom is ½d

An “Atomic Size” CalculationAn “Atomic Size” Calculation

Atomic radiiAtomic radii

The C-C bond in diamond is 1.54Å, so we assign 0.77Å as the radius of the carbon atom.

The bond in Cl2 is 1.99Å long, so we give the Cl atom a radius of 0.99Å.

We predict that the C-Cl bond should be 0.77 + 0.99 = 1.76Å long. Experimental result is 1.77Å.

Atomic Radii and Periodic Atomic Radii and Periodic TableTable As you descend a group, the atoms get

larger. This seems to be intuitive - the atoms lower in a

group have more electrons and these fill higher shells.

As you cross a row, radius decreases. The electrons are in the same shell but the

nuclear charge increases as you cross a group - electrons attracted to centre.

Li1.52

Be1.13

B0.88

C0.77

N0.75

O0.73

F0.71

Ne0.69

Na1.86

Cl0.99

K2.27

Br1.14

Rb2.47

I1.33

Ionization energyIonization energy

The first ionization energy I1, is the energy required to remove one electron from the neutral atom. Example Na (g) Na+ (g) + e-

The second ionization energy I2, is the energy required to remove the second electron. Example Na+(g) Na2+ (g) + e-

IE (Cont’d)IE (Cont’d)

The greater the value of I, the more difficult it is to remove an electron

The first electron is more readily removed than the second, etc. I1 < I2 < I 3 < I4

Na [Ne]3s1 Si [Ne]3s23p2 Cl [Ne]3s23p5

Mg [Ne]3s2 P [Ne]3s23p3 Ar [Ne]3s23p6 = [Ar]Al [Ne]3s23p1 S [Ne]3s23p4

1) More difficult to remove electron from smaller atom2) I1 < I2 < I 3 < I4 First electron easiest to remove3) Inner-shell electrons “impossible” to remove

Electron AffinityElectron Affinity

Ionization energy measures the energy change associated with the removal of an electron.

Cl (g) Cl+(g) + e- E = 1251 kJ/mol Positive value means energy must be added to atom to

remove electron Electron Affinity measures the energy change related to

the addition of an electron

Cl (g) + e- Cl-(g) E = -349 kJ/mol

Electron Affinity (cont)Electron Affinity (cont)

The Cl- ion is more stable than the Cl atom Cl configuration [Ne]3s23p5

Cl- configuration [Ne]3s23p6

The ion has the same electron configuration as Ar - a closed shell

The Cl- ion is readily formed

Electron Affinity ValuesElectron Affinity Values

Metals, Non-metals & Metals, Non-metals & MetalloidsMetalloids Elements which ionize (lose electrons)

readily are metals: Sodium, Iron, Lead Elements which readily gain electrons are

non-metals: Chlorine, Sulphur, Argon Separating them are the metalloids: Boron,

Silicon, Arsenic

Metals v Non-metalsMetals v Non-metals

Shiny luster, often silveryNo luster, many colours

Solids are malleable (can be shaped with hammer) and ductile (can be drawn into wires)Solids often brittle; some are hard, some soft

Metals vs. Nonmetals (Round Metals vs. Nonmetals (Round 2)2) Good conductors of heat and electricity

Poor conductors (graphite is an exception) Most metal oxides are basic

Most non-metallic oxides are acidic Tend to form cations (+ve charge) in solution

Tend to form anions or oxyanions in solutions

MetalsMetals

All but Hg are solids are 25ºC. (What is the other liquid element?)

Low ionization energies; form positive ions Oxides are basic

CaO(s) + H2O(l) Ca(OH)2 (aq)Metal oxide + acid salt + water

MgO(s) + 2HCl(aq) MgCl2(aq) + H2O(l)

Non-metalsNon-metals

Vary greatly in appearance. Seven exist as diatomic atoms.

H2 (colourless gas) F2 (yellowish gas) Cl2 (green gas) Br2 (red liquid) I2 (purple volatile solid)

Diamond (C) is hard, sulphur is soft.

Nonmetals (Round 2)Nonmetals (Round 2)

Tend to gain electrons to form anions Oxides are acidic

non-metal oxide + water acidCO2 + H2O H2CO3 (aq)

non-metal oxide + acid salt + waterSO3 + 2KOH K2SO4 (aq) + H2O(l)

AluminumAluminum

Al2O3 amphoteric oxide

(can act as either an acid or a base).Al2O3(s) + 6 HCl (aq) 2 AlCl3 (aq) + 3 H2O (l) (basic)

Al2O3 (s) + 2 NaOH (aq) + 3 H2O (l) 2 NaAl(OH)4

(acidic oxide)

MetalloidsMetalloids

Generally hard, non-malleable solids In pure state they are non-conductors but

with controlled impurities they form semi-conductors Computer chips are made of Si

AllotropyAllotropy

Carbon can exist as carbon black (soot), graphite, buckyballs, or diamond.

These are called allotropes - same element, different physical appearances.

Carbon is said to exhibit allotropy

Allotropy (Cont’d)Allotropy (Cont’d)

Tin is a metal at 25ºC. Below 13ºC it can turn into a white, non-metallic powder.

At extremely high pressures, there is a metallic form of hydrogen.