PERIODIC TRENDS

Diatomic Molecules- BrINClHOF twins

Shielding Effect

Kernel electrons block the attractive force of the nucleus from the valence electrons

+nucleus

Valence

Electrons--

--

Electron

Shield

“kernel”

electrons

++

Decreasing Atomic Size Across a Period

• As the attraction between the (+) nucleus and the (–) valence electrons , the atomic size .

• From left to right, size decreases because there is an increase in nuclear charge

+++ +

Li Be B1s22s1 1s22s2 1s22s22p1

Li Be B

Atomic Radius

Atomic Radii

Li

Na

K

Rb

Cs

ClSPSiAl

BrSeAsGeGa

ITeSbSnIn

Tl Pb Bi

Mg

Ca

Sr

Ba

Be FONCB

1.52 1.11

1.86 1.60

2.31 1.97

2.44 2.15

2.62 2.17

0.88 0.77 0.70 0.66 0.64

1.43 1.17 1.10 1.04 0.99

1.22 1.22 1.21 1.17 1.14

1.62 1.40 1.41 1.37 1.33

1.71 1.75 1.46

IA IIA IIIA IVA VA VIA VIIA

= 1 Angstrom

Relative Size of Atoms

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 350

Ionic Radius

Formation of Cation

11p+

sodium atomNa

e-

loss of one valence

electron

e-

e-

e-

e-e-

e-

e-

e- e-

e-

sodium ionNa+

11p+e-

e-

e-

e-e-

e-

e-

e-

e-

e-

e-

Formation of Anion

17p+

chlorine atomCl

e-

e-

e-

e-

e-e-

e-

e-

e- e-

e-

e-

e-

e-

e-

e-

e-

e-

gain of one valence

electron

chloride ionCl1-

17p+e-

e-

e-

e-e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

Sizes of ions: electron repulsion

• Valence electrons repel each other.

9 +

• When an atom becomes a anion (adds an electron to its valence shell) the repulsion between valence electrons increases

• Thus, F– is larger than F

Fluorine atomF

1s22s22p5

9+-

--

-

--

--

-

F1-

1s22s22p6

+1e+1e-- 9+-

--

-

--

--

-

-

Fluorine ionFluoride ion

Atomic Radii

Li

Na

K

Rb

Cs

ClSPSiAl

BrSeAsGeGa

ITeSbSnIn

Tl Pb Bi

Mg

Ca

Sr

Ba

Be FONCB

1.52 1.11

1.86 1.60

2.31 1.97

2.44 2.15

2.62 2.17

0.88 0.77 0.70 0.66 0.64

1.43 1.17 1.10 1.04 0.99

1.22 1.22 1.21 1.17 1.14

1.62 1.40 1.41 1.37 1.33

1.71 1.75 1.46

IA IIA IIIA IVA VA VIA VIIA

= 1 Angstrom

0.60 0.31

0.95 0.65

1.33 0.99

1.48 1.13

1.69 1.35

1.71 1.40 1.36

0.50 1.84 1.81

0.62 1.98 1.85

0.81 2.21 2.16

0.95

IA IIA IIIA IVA VA VIA VIIA

= 1 Angstrom

Li1+ Be2+

Na1+ Mg2+

Ba2+

Sr2+

Ca2+K1+

Rb1+

Cs1+

Cl1-

N3- O2- F1-

S2-

Se2- Br1-

Te2- I1-

Al3+

Ga3+

In3+

Tl3+

Ionic Radii

Trends in Atomic and Ionic Size

152

186

227

Li

Na

K

60

Li+

95

Na+

133

K+

e

e

e

F-

136

Cl-

181

Br-

195

F

Cl

Br

64

99

114

e

e

e

Metals NonmetalsGroup 1

Al

143

50

ee

e

Group 3 Group 7

Cations are smaller than parent atoms Anions are larger than parent atoms

Al3+

IA IIA IIIA IVA VA VIA VIIA

0.60 0.31

0.95 0.65

1.33 0.99

1.48 1.13

1.69 1.35

1.71 1.40 1.36

0.50 1.84 1.81

0.62 1.98 1.85

0.81 2.21 2.16

0.95

Li1+ Be2+

Na1+ Mg2+

Cl1-

N3- O2- F1-

S2-

Se2- Br1-

Te2- I1-

Al3+

Ga3+

In3+

Tl3+

Ca2+K1+

Sr2+Rb1+

Cs1+ Ba2+

Li

Na

K

Rb

Cs

ClSPSiAl

BrSeAsGeGa

ITeSbSnIn

Tl Pb Bi

Mg

Ca

Sr

Ba

1.52 1.11

1.86 1.60

2.31 1.97

2.44 2.15

2.62 2.17

0.88 0.77 0.70 0.66 0.64

1.43 1.17 1.10 1.04 0.99

1.22 1.22 1.21 1.17 1.14

1.62 1.40 1.41 1.37 1.33

1.71 1.75 1.46

Be B C N O F

= 1 Angstrom

AtomicRadii

IonicRadii

Cations: smaller than parent atoms

Anions: LARGERthan parent atoms

Electronegativity

Electronegativity

The ability of anatom in a compound to attract sharedelectrons to itself.

Linus Pauling1901 - 1994

1

2

3

4

5

6

1

2

3

4

5

6

Electronegativities

7

Be

1.5

Al

1.5

Si

1.8

Ti

1.5

V

1.6

Cr

1.6

Mn

1.5

Fe

1.8

Co

1.8

Ni

1.8

Cu

1.9

Zn

1.7

Ga

1.6

Ge

1.8

Nb

1.6

Mo

1.8

Tc

1.9

Ag

1.9

Cd

1.7

In

1.7

Sn

1.8

Sb

1.9

Ta

1.5

W

1.7

Re

1.9

Hg

1.9

Tl

1.8

Pb

1.8

Bi

1.9

1.5 - 1.9

N

3.0

O

3.5

F

4.0

Cl

3.0

3.0 - 4.0

C

2.5

S

2.5

Br

2.8

I

2.5

2.5 - 2.9

Na

0.9

K

0.8

Rb

0.8

Cs

0.7

Ba

0.9

Fr

0.7

Ra

0.9

Below 1.0

H

2.1

B

2.0

P

2.1

As

2.0

Se

2.4

Ru

2.2

Rh

2.2

Pd

2.2

Te

2.1

Os

2.2

Ir

2.2

Pt

2.2

Au

2.4

Po

2.0

At

2.2

2.0 - 2.4

Per

iod

Actinides: 1.3 - 1.5

Li

1.0

Ca

1.0

Sc

1.3

Sr

1.0

Y

1.2

Zr

1.4

Hf

1.3

Mg

1.2

La

1.1

Ac

1.1

1.0 - 1.4

Lanthanides: 1.1 - 1.3

1A

2A

3B 4B 5B 6B 7B 1B 2B

3A 4A 5A 6A 7A

8A

Hill, Petrucci, General Chemistry An Integrated Approach 2nd Edition, page 373

8B

Ionization Energy

Ionization Energies

• Energy is required to remove an electron from an atom to form a cation.

• Ionization energy () is the amount of energy needed to remove an electron from the gaseous atom E in its ground state:

E (g) + E+(g) + e-- energy required for reaction = .

• Ionization energy is always positive ( > 0).

• Larger values of mean that the electron is more tightly bound to the atom and is harder to remove.

• Units for ionization energies are kilojoules/mole (kJ/mol) or electron volts (eV) - 1 eV = 96.49 kJ/mol.

Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

First Ionization Energies(kJ/mol)

H1312.1

Li520.3

Na495.9

K418.9

Be899.5

Mg737.8

Ca589.9

B800.7

Al577.6

Ga578.6

C1086.5

Si786.5

Ge761.2

N1402.4

P1011.8

As946.5

O1314.0

S999.7

Se940.7

F1681.1

Cl1251.2

Br1142.7

Ne2080.8

Ar1520.6

Kr1350.8

He2372.5

Rb402.9

Sr549.2

In558.2

Sn708.4

Sb833.8

Te869.0

I1008.7

Xe1170.3

Smoot, Price, Smith, Chemistry A Modern Course 1987, page 188

s p

Multiple Ionization Energies

Al Al+ Al2+ Al3+

578

kJ/m

ole

-

1817

kJ/

mol

e-

2745

kJ/

mol

e-

The second, third, and fourth ionization energies of aluminum are higher than the first because the inner electrons are more tightly held by the nucleus.

1st Ionizationenergy

2nd Ionizationenergy

3rd Ionizationenergy

Smoot, Price, Smith, Chemistry A Modern Course 1987, page 190

Ionization Energies (kJ/mol)

Element

Na

Mg

Al

Si

P

S

Cl

ArHerron, Frank, Sarquis, Sarquis, Cchrader, Kulka, Chemistry 1996, Heath, page

1st

498

736

577

787

1063

1000

1255

1519

2nd

4560

1445

1815

1575

1890

2260

2295

2665

3rd

6910

7730

2740

3220

2905

3375

3850

3945

4th

9540

10,600

11,600

4350

4950

4565

5160

5770

5th

13,400

13,600

15,000

16,100

6270

6950

6560

7320

6th

16,600

18,000

18,310

19,800

21,200

8490

9360

8780Shaded area on table denotes core electrons.

Metallic Characteristicsmetallic character increases

nonmetallic character increases

met

allic

cha

ract

er in

crea

ses

non

met

allic

cha

ract

er in

crea

ses

Summary of Periodic Trends

Ionic size (cations) Ionic size (anions)decreases decreases

Shielding is constantAtomic radius decreasesIonization energy increasesElectronegativity increasesNuclear charge increases

Nu

clea

r ch

arg

e in

crea

ses

Sh

ield

ing

in

crea

ses

Ato

mic

rad

ius

incr

ease

sIo

nic

siz

e in

crea

ses

Ion

izat

ion

en

erg

y d

ecre

ases

Ele

ctro

neg

ativ

ity

dec

reas

es

1A

2A 3A 4A 5A 6A 7A

0