Chapter 8 Periodic Relations Among the Elements Classification of the elements Four categories of elements in the Periodic Table

1. Noble gases, elements in which the the outer shell is complete. Group 8A 2. Representative elements (main group) Groups 1A, 2A, 2B, 3A, 4A, 5A, 6A, and 7A. These are elements in which the last electron added enters the outermost shell but the shell but in which the outermost shell is incomplete. The outer most shell for these elements is the valence shell. (Filling the s and p subshells)

3. The Transition elements. Elements in which the second shell counting in from the outside is building from 8 to 18 electrons. The outermost s subshell and d subshell of the second shell form outside contain the valence electrons in these elements. The (n-1)d and ns subshells are regarded as the valence shells in the transition elements. The first transition series runs from scandium (Sc) through copper (Cu). Elements in group 2B (Zn, Cd, Hg) are not considered transition metals.

4. The inner transition elements. Elements in which the third shell counting in from the outside is building from 18 to 32 electrons. The valence shell of the inner transition elements consist of the (n-2)f(n-1)d and ns subshells. The first inner transition series runs from cerium (Ce) through lutetium (Lu); 4f subshell filling.

Chapter 8 Periodic Trends

Ions and Their Electron Configurations Ionic Bonding o Na( s ) + 12 Cl2 (g) → NaCl(s) ∆H f = −410.9 kJ mol

Na +

Cl → Na+ + [ Cl ]– 2s22p6

3s23p6

Lewis Symbols: uses atomic symbol and one dot for each of the valence electrons.

Electron Configurations of Ions of Representative Elements Na 1s22s22p63s1 = [Ne] 3s1 Na+ 1s22s22p6 = [Ne] Cl Cl–

1s22s22p63s23p5 1s22s22p63s23p6

= [Ne] 3s23p5 = [Ne] 3s23p6 = [Ar]

Transition metals In forming ions, transition metals lose the valence shell s electrons first (first in, first out) then as many d electrons as are required to reach the charge on the ion. 6

Fe

[Ar]3d 4s 2+

Fe

3+

Fe

[Ar]3d [Ar]3d

2

6 5

Chapter 8 Periodic Trends

Trends 1. Within each column (group) the atomic radius tends to increase as we proceed from top to bottom 2. Within each row (period) the atomic radius tends to decrease as we move from left to right. •

orbitals increase in size with increasing principle quantum number, n.

•

The effective nuclear charge increases moving from left to right but the principle quantum number stays the same.

•

The effective nuclear charge remains relatively constant while the principle quantum number increases.

•

Increasing ionization energy Decreasing atomic radius Increasing nonmetallic character and electronegativity Decreasing metallic character

B Si Ge

As Sb

Te At

Decreasing ionization energy Increasing atomic radius Decreasing electronegativity Increasing metallic character

Nonmetals

Metals

Most metallic element Most nonmetallic element

Chapter 8 Periodic Trends

Trends in periodic properties depend on several factors including (1) the number of valence electrons, (2) the magnitude of the nuclear charge and the total number of electrons surrounding the nucleus, (3) the number of filled shells lying between the nucleus and the valence shell, and (4) the distances of the electrons in the various shells from each of the other and from the nucleus.

Effective Nuclear Charge: increases from left to right in a period and from bottom to top of a group.

Variations in Covalent Radii Across a period

Atom

Nuclear Charge +11

Electron Configuration

Na

Covalent radius, Å 1.86

Mg

1.60

+12

[Ne]3s2

Al

1.43

+13

[Ne]3s23p1

Si

1.17

+14

[Ne]3s23p2

P

1.10

+15

[Ne]3s23p3

S

1.04

+16

[Ne]3s23p4

Cl

0.99

+17

[Ne]3s23p5

[Ne]3s1

Chapter 8 Periodic Trends

Down a group

Atom F Cl Br I At

Covalent radius, Å 0.64 0.99 1.14 1.33 1.4

Nuclear Charge +9 +17 +35 +53 +85

Number of Electrons in Each Shell 2, 7 2, 8, 7 2, 8, 18, 7 2, 8, 18, 18, 7 2, 8, 18, 32, 18, 7

Ioinic Radii Sizes of Ions Cations are smaller than their parent atoms removal of outermost electrons fewer electron-electron repulsions Anions are larger than their parent atoms increased electron-electron repulsions

Variations in Ionic Radii Species N3O2Radius, Å

1.71

1.40

F1.33

Ne 1.12

Na+ 0.97

Mg2+ Al3+ 0.66 0.50

Electron configuration: 1s22s22p6 increasing nuclear charge 8 O2– 1.40

9

11

12

13

F– 1.33

Na+ 0.97

Mg2+ 0.66

Al3+ 0.50 Å

decreasing radius Isoelectronic series

“same number of electrons”

Chapter 8 Periodic Trends

Ionization energy The ionization energy is the minimum amount of energy required to remove an electron from the ground state of the isolate gaseous atom or ion.

I1 I2

Na(g) → Na + (g) + e − Na

+

(g ) → Na (g ) + e 2+

−

496 kJ mol 4560 kJ mol

Higher Ionization Energies I1 < I2 < I3 < ,,,

Electron affinities Electron affinity is the energy change that occurs when an electron is added to a gaseous atom.

X ( g) + e − → X − ( g)

Cl (g) + e − → Cl − (g ) Ar (g) + e − → Ar − (g)

∆E = − 349 kJ mol ∆E > 0

Chapter 8 Periodic Trends

The Alkali Metals (Group 1A) ( ns1, n ≥ 2) Low ionization energies

With water

With Oxygen

The Alkaline Earth Metals (Group 2A) ( ns2, n ≥ 2) Low ionization energies, tendancy to form M2+ Reaction with water

The Group 3A Elements: (ns2np1, n ≥ 2)

Chapter 8 Periodic Trends

The Group 4A Elements: (ns2np2, n ≥ 2)

The Group 5A Elements: (ns2np3, n ≥ 2)

The Group 6A Elements: (ns2np4, n ≥ 2) The Halogens (Group 7A) (ns2np5, n ≥ 2)

The Noble Gases (Group 8A) (ns2np6, n ≥ 2) All have large ionization energies Relatively unreactive

Xe + nF2 → XeF2 XeF4 XeF6 Group 1A and Group 1B Elements

Chapter 8 Periodic Trends

Properties of Oxides Metal oxides are basic.

metal oxide + water → metal hydroxide + H2 O(l) → Ca(OH )2 ( aq)

CaO(s)

metal oxide + acid → salt + water + 2 HCl ( aq) → CaCl2 ( aq ) + H2O( l)

MgO(s )

Non-metal oxides are acidic Non − metal oxide + water → acid CO2 ( g) P4 O10 (s) SO3 ( g)

+ H2O(l) → H2CO3 (aq ) + 6 H2O(l) → 4H3 PO4 ( aq) + H 2O(l) → H 2 SO4 ( aq)

Metal oxides tend to be ionic. Nonmetal oxides tend to be molecular. Na2O

MgO

Al2O3

SiO2

P4O10

SO3

Cl2O7

Type of Compound Structure

Ionic

Ionic

Ionic

Molecular

Molecular

Molecular

Molecular

Extensive 3-D

Extensive 3-D

Extensive 3-D

Extensive 3-D

Melting point (°C) Boiling point (°C) Acid-base nature

1275

2800

2045

1610

Discrete molecular units 580

Discrete molecular units 16.8

Discrete molecular units -91.5

?

3600

2980

2230

?

44.8

82

Basic

Basic

Amphoteric

Acidic

Acidic

Acidic

Acidic

Amphoteric - displays both acidic and basic properties, depending on the environment.

Chapter 8 Periodic Trends