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Chemical Bonding Chapter 4 Section 1

Chemical Bonding Chapter 4 Section 1. A chemical bond is: a force of attraction between any two atoms in a compound. Bonding between atoms occurs because

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Page 1: Chemical Bonding Chapter 4 Section 1. A chemical bond is: a force of attraction between any two atoms in a compound. Bonding between atoms occurs because

Chemical BondingChapter 4 Section 1

Page 2: Chemical Bonding Chapter 4 Section 1. A chemical bond is: a force of attraction between any two atoms in a compound. Bonding between atoms occurs because

• A chemical bond is: a force of attraction between any two atoms in a compound.

• Bonding between atoms occurs because it creates a more stable arrangement for the atoms.

Page 3: Chemical Bonding Chapter 4 Section 1. A chemical bond is: a force of attraction between any two atoms in a compound. Bonding between atoms occurs because

Lewis Symbols – Dot Diagrams

• Convenient way to show the valence electrons

Page 4: Chemical Bonding Chapter 4 Section 1. A chemical bond is: a force of attraction between any two atoms in a compound. Bonding between atoms occurs because

Three types of bonding• Metallic bonding – results from the

attraction between metal atoms and the surrounding sea of electrons

• Ionic bonding – results from the electrical attraction between large numbers of cations and anions

• Covalent bonding – results from the sharing of electron pairs between two atoms

Page 5: Chemical Bonding Chapter 4 Section 1. A chemical bond is: a force of attraction between any two atoms in a compound. Bonding between atoms occurs because

Ionic Bonding• Many atoms transfer electrons

and other atoms accept electrons, creating cations (positive metal ions) and anions (negative nonmetal ions).

• The resulting ions are attracted to each other by electrostatic force.

Page 6: Chemical Bonding Chapter 4 Section 1. A chemical bond is: a force of attraction between any two atoms in a compound. Bonding between atoms occurs because

Ionic bonding between Na and Cl

Sodium atom Chlorine atom 1s2 2s2 2p6 3s1 1s2 2s2 2p6 3s2 3p5 1s2 2s2 2p6 3s1 1s2 2s2 2p6 3s2 3p5 Sodium ion Na1+ Chlorine ion Cl1- 1s2 2s2 2p6 1s2 2s2 2p6 3s2 3p6

Page 7: Chemical Bonding Chapter 4 Section 1. A chemical bond is: a force of attraction between any two atoms in a compound. Bonding between atoms occurs because
Page 8: Chemical Bonding Chapter 4 Section 1. A chemical bond is: a force of attraction between any two atoms in a compound. Bonding between atoms occurs because

Covalent bonding

• In many cases electrons do not completely transfer from one atom to another.

• The electrons between atoms are shared.

Page 9: Chemical Bonding Chapter 4 Section 1. A chemical bond is: a force of attraction between any two atoms in a compound. Bonding between atoms occurs because

Covalent bonding between H2

• Hydrogen’s electron configuration is 1s1

• Because both H atoms need 1 more electron to become isoelectronic with He, it is unlikely that either will give up an electron.

• They share the two electrons.

H· + H · H : H

Page 10: Chemical Bonding Chapter 4 Section 1. A chemical bond is: a force of attraction between any two atoms in a compound. Bonding between atoms occurs because

Types of Covalent Bonds• When electrons are shared equally the

bond is called a NONPOLAR covalent bond. (i.e. H2)

• Sometimes the electrons between two atoms are NOT shared equally. The bond created is called a POLAR covalent bond.

. . . .

H· + ·Cl: H:Cl:

. . . .

Page 11: Chemical Bonding Chapter 4 Section 1. A chemical bond is: a force of attraction between any two atoms in a compound. Bonding between atoms occurs because

How to classify bond types• Electronegativity – measure of the ability

of an atom to attract electrons in a chemical bond

• Each element on the periodic table is assigned an electronegativity value (see page 87) that ranges from 0.7 to 4.0.

• The difference in the electronegativity determines the bonding type (ionic, polar covalent, or nonpolar covalent).

Page 12: Chemical Bonding Chapter 4 Section 1. A chemical bond is: a force of attraction between any two atoms in a compound. Bonding between atoms occurs because

If the electronegativity difference is:

1.7 and higher ionic

0.3 to 1.7 polar covalent

0.0 to 0.3 nonpolar covalent

Page 13: Chemical Bonding Chapter 4 Section 1. A chemical bond is: a force of attraction between any two atoms in a compound. Bonding between atoms occurs because

Practice ProblemsWhat type of bond will occur between

iodine and the following elements: cesium, iron, and sulfur?

The electronegativities of each are:

Iodine 2.5

Cesium 0.7

Iron 1.8

Sulfur 2.5

Page 14: Chemical Bonding Chapter 4 Section 1. A chemical bond is: a force of attraction between any two atoms in a compound. Bonding between atoms occurs because

Answers to problems

Bonding between I and:

Electronegativity difference

Bond Type

Cesium 2.5 – 0.7 = 1.8 Ionic

Iron 2.5 – 1.8 = 0.7 Polar covalent

Sulfur 2.5 – 2.5 = 0.0 Nonpolar covalent

Page 15: Chemical Bonding Chapter 4 Section 1. A chemical bond is: a force of attraction between any two atoms in a compound. Bonding between atoms occurs because

What if I get an electronegativity difference that is 0.3 or 1.7?

• These cut-off numbers are guidelines.

• It is a gradual change not stair-step.

Page 16: Chemical Bonding Chapter 4 Section 1. A chemical bond is: a force of attraction between any two atoms in a compound. Bonding between atoms occurs because

Determine the type of bond between the following pairs.

Bonding between

Electronegativity difference

Bond type

Li & Cl

S & O

Ca & Br

P & H

Si & Cl

S & Br

Page 17: Chemical Bonding Chapter 4 Section 1. A chemical bond is: a force of attraction between any two atoms in a compound. Bonding between atoms occurs because

AnswersBonding between

Electronegativity difference

Bond type

Li & Cl 3.0 – 1.0 = 2.0 Ionic

S & O 3.5 – 2.5 = 1.0 Polar covalent

Ca & Br 2.8 – 1.0 = 1.8 Ionic

P & H 2.1 – 2.1 = 0.0 Nonpolar covalent

Si & Cl 3.0 – 1.8 = 1.2 Polar covalent

S & Br 2.8 – 2.5 = 0.3 Nonpolar covalent