Lewis Structures and Chemical BondsChapter 7

Suggested HW7.1, 7.3, 7.7, 7.15, 7.17, 7.23, 7.31, 7.37, 7.39, 7.59, 7.61, 7.63,

7.67, 7.69, 7.73, 7.75, 7.77, 7.81, 7.97, 7.99, 7.101, 7.105, 7.107, 7.109, 7.111, 7.115, 7.119, 7.121, 7.125, 7.127, 7.129,

7.139, 7.143, 7.145, 7.147

Lecture 4

1

• Electrons dictate the chemistry of an atom• Electrons fill orbitals in order or increasing energy

1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p …

• We can represent the electron configuration of an element by showing the orbital designation or orbital configuration

Review

2

1s2 2s22p6 3s23p4

[Ne]3s23p4

1s1

Shell

subshell

Number of electron in subshell

S

Octet Rule and Ions

3

• An ion is an atom that has gained or lost electrons– This results in a net charge on the atom

• If an ion has a net (+) charge cation• If an ion has a net (-) charge anion

Ions tend to form such that they satisfy the Octet Rule

The Octet Rule – Atoms prefer to have 8 electrons in their outer shell

(or dublet for H and He).

Valence electrons = outer shell

Forming Ions

4

Na (Z = 11) [Ne] 3s1

Noble gas configuration ALWAYS satisfy the octet rule

Mg (Z = 12) [Ne] 3s2

Cl (Z = 17) [Ne] 3s2 3p5 S (Z = 17) [Ne] 3s2 3p4

Lewis Representation

5

• American chemist G.N. Lewis had a profound impact on our understanding of chemical bonding. One of his many contributions was a simple way to represent chemical bonds. We call these Lewis Symbols.

– Valence Electrons are represented by dots.– A single dot represents an electron– A pair of dots represents two paired electrons sharing an orbital

H He N O

O2- K Mg2+ I-

1s1 1s2 2s22p3 2s22p4

2s22p6 3s1 [Ne] 5s25p6

Compound

6

Compounds

Organic Compound

Inorganic Compound

Contains Carbon

Composed of Charged

components

Cations Anions

Covalent

Ionic Bonds

Bond Type

Electronegativity

7

Some atoms attract electrons more than others

Electronegativity difference

2 Ionic Bond< 2 Covalent

X-Y

Electronegativity

8

Predict the type of bond that will form between:

Ca and F

C and F

B and H

Ionic Bonds

9

Ion Na+ Cl-

Electron Configuration [Ne] [Ne]2s22p6

Lewis Symbol

Ionic bonds do not share electrons – bond forms through charge attraction

NaCl

CaCl2

Ion Ca2+ Cl-

Electron Configuration [Ar] [Ne]2s22p6

Lewis Symbol

Covalent Bonds

10

Covalent bonds electrons shared between two atoms. This involves an overlap of atomic orbitals

Let’s consider H2 - two hydrogen atoms share electrons.

H H

Commonly represented as:

Solid line represents covalent bond

Octet Rule NOT satisfied! Electrons pair and are shared between both

atoms

Covalent Bonding

11

Energy

1s1

Hydrogen

Energy

1s1

Hydrogen

sbond

Covalent Bonding – Fluorine (F2)

12

Energy

2s2

Fluorine

Energy

2s2

Fluorine

Atomic Orbitals are NOT optimized for bonding

2p5 2p5

sp3 sp3

Covalent Bonding

13

Energy

sp3

Energy

sp3

sbond

Fluorine Fluorine

Covalent Bonding

14

Covalent Bonding – CH4

15Carbon Hydrogen (x4)

1s12s2

2p2

sp3

Covalent Bonding – CH4

16Carbon Hydrogen (x4)

1s1

sp3

Covalent Bonding – CH4

17Carbon Hydrogen (x4)

1s1

sp3

Covalent Bonding – CH4

18

Covalent Bonding – NH3

19

Covalent Bonding – NH3

20

Covalent Bonding – NH3

21

Covalent Bonding – NH3

22

VSEPR

23

Valence Shell Electron Pair Repulsion

• Each region of electrons (bond or lone pair) counts as a balloon• Balloons want to spread out as much as possible

Molecular Shapes

24

Molecule Polarity

25

Will each of these molecules be polar?

CH4 CH3F CH2F2 CHF3 CF4