Mastering ChemistryMastering Chemistry

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• Course ID:Course ID:

• MCWICKUN89304MCWICKUN89304

Basic Concepts Basic Concepts of Chemical of Chemical

BondingBonding

Chapter 8Chapter 8

What’s Ahead (p 297)What’s Ahead (p 297)

• Three types of bonds

• Lewis symbols

• Ionic bonding

• Octet rule

• Lattice energy in ionic compounds

Three Types of Chemical BondsThree Types of Chemical Bonds

• Ionic bondIonic bond– Transfer of electronsTransfer of electrons– Between metal and nonmetal ionsBetween metal and nonmetal ions

• Covalent bondCovalent bond– Sharing of pairs of electronsSharing of pairs of electrons– Between nonmetal atomsBetween nonmetal atoms

• Metallic bondMetallic bond– Bonding electrons relatively free Bonding electrons relatively free

to moveto move

Valence electrons: outer shell electrons of an atom; valence electrons participate in chemical bonding.

1A 1ns1

2A 2ns2

3A 3ns2np1

4A 4ns2np2

5A 5ns2np3

6A 6ns2np4

7A 7ns2np5

Group # of valence e-e- configuration

Table 8.1

Show only valence electrons!

Ionic Bonding

Na (s) + ½ Cl2 (g) → NaCl (s) ΔHfo = −410.9 kJ

The Crystal Structure of Sodium Chloride

Fig 8.3

Li + F Li+ F -The Ionic Bond

1s22s11s22s22p5 1s21s22s22p6[He][Ne]

Li Li+ + e-

e- + F F -

F -Li+ + Li+ F -LiF(s)

Octet Rule: Atoms tend togain, lose, or share electronsuntil surrounded by 8 valenceelectrons

Lattice energy (E):

• increases as Q increases and/or

• increases as d decreases

Electrostatic (Lattice) Energy

Eel = k Q+Q-d

Q+ is the charge on the cation

Q- is the charge on the aniond is the distance between the ions

Lattice energy (E): the energy required to completely separate one mole of a solid ionic compound into gaseous ions

Eqn. [8.4]

Metal atoms lose electrons so that cation has a noble-gas outer electron configuration

Nonmetal atoms gain electrons so that anion has a noble-gas outer electron configuration

Electron Configurations of Cations and Anions

of Representative Elements

+1 +2 +3 -1-2-3

Cations and Anions Of Representative Elements

Electron Configurations of Cations of Transition Metals

When a cation is formed from an atom of a transition metal, electrons are always removed first from the ns orbital and then from the (n – 1)d orbitals.

Fe: [Ar]4s23d6

Fe2+: [Ar]4s03d6 or [Ar]3d6

Fe3+: [Ar]4s03d5 or [Ar]3d5

Mn: [Ar]4s23d5

Mn2+: [Ar]4s03d5 or [Ar]3d5

“First in, first out”

Three Types of Chemical BondsThree Types of Chemical Bonds

• Ionic bondIonic bond– Transfer of electronsTransfer of electrons– Between metal and nonmetal ionsBetween metal and nonmetal ions

• Metallic bondMetallic bond

– Bonding electrons relatively free to Bonding electrons relatively free to movemove

• Covalent bondCovalent bond– Sharing of electronsSharing of electrons– Between nonmetal atomsBetween nonmetal atoms

Metallic Crystals• Lattice points occupied by metal atoms• Held together by metallic bonds• Soft to hard, low to high melting point• Good conductors of heat and electricity

Cross Section of a Metallic Crystal

nucleus &core e-

mobile “sea”of valence e-

Electron-Sea Model

Covalent BondingCovalent Bonding• Objectives:Objectives:

– Characteristic propertiesCharacteristic properties

– Lewis structuresLewis structures

– Multiple bondsMultiple bonds

– Bond polarity and electronegativityBond polarity and electronegativity

• Atoms share pairs of electrons

• Several electrostatic interactions in these bonds:

Attractions between electrons and nuclei

Repulsions between electrons

Repulsions between nuclei

Covalent Bonding

Change in electron density as two hydrogen

atoms approach each other

Covalent Bond

Why should two atoms share electrons?

F F+

7e- 7e-

F F

8e- 8e-

F F

F F

Lewis structure of F2

lone pairslone pairs

lone pairslone pairs

single covalent bond

single covalent bond

H HO+ + OH H O HHor

Lewis structure of water

Double bond – two atoms share two pairs of electrons

single covalent bonds

O C O or O C O

double bonds

Triple bond – two atoms share three pairs of electrons

N N N N

triple bond

or