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Lecture 4. Lewis Structures and Chemical Bonds Chapter 7 Suggested HW 7.1, 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.

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Lecture 4
Lecture 4

Lewis Structures and Chemical Bonds

Chapter 7

Suggested HW

7.1, 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


Review
Review

  • 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

Shell

Number of electron in subshell

1s1

subshell

2s22p6

3s23p4

1s2

S 

[Ne]3s23p4


Octet rule and ions
Octet Rule and Ions

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

(or dubletfor H and He).

Valence electrons = outer shell

  • 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


Forming ions
Forming Ions

Noble gas configuration ALWAYS satisfy the octet rule

Na  (Z = 11)  [Ne] 3s1

Mg  (Z = 12)  [Ne] 3s2

S  (Z = 17)  [Ne] 3s23p4

Cl (Z = 17)  [Ne] 3s23p5


Lewis representation
Lewis Representation

  • 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


Compounds

Compound

Bond Type

Inorganic Compound

Organic Compound

Covalent

Composed of Charged components

Ionic Bonds

Contains Carbon

Cations

Anions


Electronegativity
Electronegativity

Some atoms attract electrons more than others

X-Y

Electronegativity difference

 2 Ionic Bond

< 2 Covalent


Electronegativity1
Electronegativity

Predict the type of bond that will form between:

Ca and F

B and H

C and F


Ionic bonds
Ionic Bonds

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

NaCl

Ion Na+Cl-

Electron Configuration [Ne] [Ne]2s22p6

Lewis Symbol

CaCl2

Ion Ca2+Cl-

Electron Configuration [Ar] [Ne]2s22p6

Lewis Symbol


Covalent bonds
Covalent Bonds

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

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

Electrons pair and are shared between both atoms

Octet Rule NOT satisfied!

Commonly represented as:

H H

Solid line represents covalent bond


Covalent bonding
Covalent Bonding

Energy

Energy

1s1

1s1

s bond

Hydrogen

Hydrogen


Covalent bonding fluorine f 2
Covalent Bonding – Fluorine (F2)

Energy

Energy

Atomic Orbitals are NOT optimized for bonding

2p5

2p5

2s2

2s2

sp3

sp3

Fluorine

Fluorine


Covalent bonding1
Covalent Bonding

Energy

Energy

sp3

sp3

s bond

Fluorine

Fluorine



Covalent bonding ch 4
Covalent Bonding – CH4

2p2

2s2

sp3

1s1

Carbon

Hydrogen (x4)


Covalent bonding ch 41
Covalent Bonding – CH4

sp3

1s1

Carbon

Hydrogen (x4)


Covalent bonding ch 42
Covalent Bonding – CH4

sp3

1s1

Carbon

Hydrogen (x4)







Vsepr
VSEPR

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



Molecule polarity
Molecule Polarity

Will each of these molecules be polar?

CH4

CH3F

CH2F2

CHF3

CF4


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