Unit 5: Chemical Bonding

Q: How do atoms interact with each other?•Ionization Energy•Ions: Cations & Anions

The Smallest Atoms

• Small atoms have more attraction between the positively-charged nucleus and the negative electrons, so the ionization energy is greater in small atoms. – It requires more energy for an electron to

be removed from a small atom.

• Ionization energy: amount of energy needed to remove an electron from an atom.

The Largest Atoms

• In large atoms, valence electrons are far from the nucleus, so there is a weak attraction between the electrons and the (+)-charged nucleus.– Its valence electrons can be easily plucked

off.

• It does not require much energy for electrons to be removed from a large nucleus, yielding LOW ionization energy.

Periodicity of Ionization Energy

• Ionization energies increase across each period because atoms with 8 valence electrons (or close to) have a “tighter grip.” It’s more difficult to remove an electron from an atom with 7 valence electrons than an atom that only has 1 valence electron.

• Ionization energies decrease down each group. As the size of the atom increases, less energy is required to remove an electron.

Removing/Adding Electrons Produce Charged Atoms –

IONS!• Ionization (removing e-) always pro

duces positively-charged ions, cations.

• Ion: an atom or group of bonded atoms that has a positive or negative charge

Cations: Positive Ions• Cations are positive ions.

•Number of p+ > number of e-

• When an atom loses an electron, they lose one negative charge and become a positive ion.

• Cations are formed when energy is used to remove an electron (ionization energy)

Formation of Cation

11p+

e-

e-

e-

e-

e-e-

e-

e-

e- e-

e-

11p+e-

e-

e-

e-e-

e-

e-

e-

e-

e-e-

Sodium Cation = Na+

11 p+

10 e-

________

1+

Sodium atom: Na11 p+

11 e-

______

0 neutral

LOSE one valence

electron

Anions

• Negative Ions = Anions•Number of p+ > number of e-

When an atom gains an electron, they gain one negative charge and become a negative ion.

Formation of Anions

17p+

Chlorine atomCl

17 p+

17 e-

(7 valence e-, 10 core e-)

e-

e-

e-

e-

e-e-

e-

e-

e- e-

e-

e-

e-

e-

e-

e-

e-

e- gain one valence

electron

17p+e-

e-

e-

e-e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

Chlorine anion = negative ion

Cl-

17 p+

18 e-

_____________________

1-(8 valence e-, 10 core e-)

Li+

e

e

e

e

Li

Lithium atom

Lithium ion

+Li

First Ionization

Energy

Ionization Energy

Ionization energy leads to the formation of positive ions, cations.

A + Energy A+ + e-

Driving Force

• Atoms behave in ways to achieve full orbitals.– Full orbitals give the atom the most stability.– Noble gases have the most stability (Except

Helium)• “Stability” = Lowest energy = Unreactive

• Octet Rule: Atoms lose, gain, or share electrons in order to have 8 valence electrons.

Successive Ionization Energy

• Unit: Kilojoule (kJ) 1 kJ = 1000 J

• First ionization energy, I1 = energy to remove the first electron.

• Second ionization energy, I2 = energy to remove another (2nd) electron

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

Successive Ionization Energies (IE)

• Each successive ionization requires MORE energy than the previous one.

A + 1st IE A+ + e-

A+ + 2nd IE A2+ + e-

A2+ + 3rd IE A3+ + e-

A: Neutral atomIonization always produces cations.

Successive Ionization Energies (KJ/mol)

Element

H

He

Li

Be

B

C

Al

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

1st

1312.1

2372.5

520.3

899.5

800.7

1086.5

577.6

2nd

5250.7

7298.5

1752.2

2427.2

2352.8

1816.7

3rd

11815.6

14849.5

3660.0

4620.7

2744.8

4th

21007.6

25027.0

6223.0

11577.5

5th

32828.3

37832.4

14831.0

6th

47279.4

18377.9

Successive Ionization Energies (KJ/mol)

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