Unit 04
Chemical Bonding
Valence e-
– Valence e- - e- in the highest occupied energy level of an element’s atom
– Same as group # for groups 1 & 2– Subtract 10 from groups 13-18
• electrons used in chemical bonding
Lewis Dot Structure – shows number of valence e-
Ex: bromine
Br● ●
●●●
● ●
Valence e-
White Board Practice
K C
O Ar
● ●
●
●
●
●
●
●
●
●
●
● ●
●●
●●
●●
Learning Check
Which Lewis Dot Structure is incorrect?A.
Mg B
S Xe
● ●
●
●
●
●
●
●
●
●
●
● ●
●●
●●
●●
●
B. D.
C.
Octet Rule:
- when forming compounds atoms want to have 8 e- (s2p6) like the noble gases (except He)
Na (atom)
1s22s22p63s1
●
lose 1 e-
Na (cation)
+1s22s22p6
octetUsing the Dot Structure
Na (neutral
atom)
Na (cation)
lose 1 e- +
●
Mg (neutral
atom)
Mg (cation)
lose 2 e-2+
●
Cations (metals): positively charged ion, tend to lose e-
●
B
(neutral atom)
B (cation)
lose 3 e- +3●
●
Cations ca+ion
+1
+2 +3
gain 2e-
Cl
(neutral atom)
O (neutral
atom)
Cl (atom)
1s22s22p63s23p5
●
gain 1 e-
Cl (chloride ion)
-1s22s22p63s23p6
octetUsing the Dot Structure
Cl
(chloride ion)
-
●
O
(oxide ion)
2-●
●●
●
● ●
●gain 1e-
●
●●●
●
●●
●●
●
valence
● ●
●●●
● ●
●
●
●
Anions (Nonmetals) – negatively charged ions, gain e-
gain 3e- N
(neutral atom)
●
N
Nitride ion)
●●
●●
●
●●
●●
●●
●
-3
-2
Anions
-1-3
White Board Practice
N
I
Li
Ca
●
●
●
●
●
N
(nitride ion)
3-gain 3e-
●
●●
●●●
●
●
●
●
●
●
●
●●
I
(chloride ion)
gain e-
●
●●
●●
●●
●
-
●
LiLose 1 e- +
CaLose 2e- +2
●
●
Ionic Compound:
1. ionic compounds form crystals2. high melting and boiling points3. hard and brittle4. conduct electricity when dissolved in water
or melted
Properties
•Composed of a metal (cation) and nonmetal (anion)•Ionic bond – oppositely charged ions attract•Electrically neutral (+) = (-)•Generally called salts
Ionic Bonding
Na Cl
1. Sodium and Chlorine
●● ●
●●
●
●
●
donates e-
Na+ ● Cl●
●●
●
●
●
●
2. Potassium and Oxygen
K O● ●
●
●
●●
donates e -
K+● O
●●●
●●
●
●
●
+
+
K●
donates e-
K+
-2
+1 -2
-
K2O
NaCl
+1 -1
Does O have 8?
Al
3. Aluminum and Bromine
Mg N●
●●
●●
Mg+2● N
●●●
●●
●
●●
+● Mg+2
-3
● ●●●
●●
●
●
Al+3
● Br●
●●
●
●
●
●
+
●
●
Br● ●
●●
●●
●Br
● ●●●
●●
●Br
+3 -1
● Br●
●●
●
●
●
●
● Br●
●●
●
●
●
●
-
-
-+2 -3
Mg
4. Magnesium and Nitrogen
Mg●
●
●
●
N●
●
●●
●
Mg+2● N
●●●
●●
●
● -3
AlBr3
Mg3N2
Does Al have moreelectrons?
Does N have 8 yet?
What about Mg’s other e-?
Does N have 8 yet?
Ionic Bonding– Title left side of spiral Ionic Bonding– Copy the problem– Draw the Lewis Structure for ea. element used in
bonding– CATION = RED– ANION = BLUE/GREENISH– Show donated e- with an arrow– Show New ions charges– Put a BOX around the Formula
EXAMPLE:
1. Potassium & Fluorine
K●
F● ●
●●
●●+ ● K + F● ●
●●
●●●●
KF
-
Bonding in Metals
• Metallic bonds – the attraction between positive ions and surrounding mobile electrons
Sea of ElectronsMetal cations
• Good conductors of electrical current, ductile (wires), malleable (forced into shapes)
Covalent Compounds
• Also called MOLECULAR COMPOUNDS• Formed from 2 or more nonmetals
• Low melting and boiling point
CharacteristicCovalent compoundMolecular compound
Ionic compound
Representative unit MoleculeFormula unit (balance
of oppositely charged ions)
Type of elements Nonmetallic Metallic combined with nonmetallic
Melting & Boiling point
Low High
Important differences between covalent and ionic compounds
Covalent Bonds– Forms when 2 atoms share a pair of valence e-
Types of Covalent Bonds1. Single Covalent Bond – two atoms share a pair of e-
Ex: F2
F F● ●
●●
●●
● ●●●●
●● ●F F● ●
●●
●●
● ●●●●
●● ●and F F
● ●●●
●
●●●●
●● ●
Unshared pair – e- not shared between atoms
What makes this bonding work?Atoms have 8 e- in their outer level to make them stable
Ex: H2
H● H● H H
Why does H2 only need 2 e- to be stable?first energy level only contains 2 e-
Covalent Bonds
2. Double Covalent Bond – 2 pairs of e- are shared between atomsEx: O2
O●●
●●●
●●O
●●●●●
●O● ●
● O and●●●
● ● ●
● ●O● ● O
● ●
● ●●
●
Covalent Bonds
3. Triple Covalent Bond – 3 pairs of e- are shared between atomsEx: N2
NN●●
●●
●N●●
●●
●N●
● N●● and N●
●●●● ●● ●● ●
Covalent Bonds
Covalent Lewis Dot Structures
1. Draw each atom’s Lewis Structure2. Connect single electrons until each atom has 8 e- (H
only 2)3. The central atom is often the first atom written & is
usually the atom w/the least # of e-. (Exception – H can’t be the central atom)
4. Place the unshared pairs around the atoms so ea. is stable (8 around it, except H – only 2)
Examples:1. Br2
Br● ●
● ●●
●
●Br● ●
●●
●
●
●Br● ●
●●
●
●Br● ●
●
●●
●
Covalent Lewis Dot Structures
2. NH3
N●
● ●
●
●
H●
H●
H●
N● ●
HH
H
3. CO2
C●
●
●
●
O
O● ●
● ●●●
●●●
●
●●
CO O● ●
●●
● ●
●●
4. CCl4
C ●
●
●
Cl●
Cl●
Cl●C ClCl
Cl
5. H2O
H●
O● ●●
●●
●
●
Cl
● ●
● ●● ●
● ●
● ●● ●
● ●
●●
●●
●●
●●●
● ●
Cl● ●
● ●● ●
●●
● ●
● ●
●●
● ●
●●
●●
●●
●●
H●
O
H
H● ● ●
●
White Board Practice Problems:
1. CH4
C●
●
●
●
H●
H●
H●
H●
C H
H
HH
2. H2
White Board Practice Problems:
H HHH● ●
3. PH3
White Board Practice Problems:
P ●
● ●
●
●
H●
H●
H●
P● ●
HH
H
4. OF2
White Board Practice Problems:
O● ●●
●●●
F●
F
● ●
● ●● ●
● ●
●●
●●●
O● ●
● ● F● ●
● ●
●●F● ●
●●
● ●
5. CHI3
White Board Practice Problems:
C●
●
●
●
H●
I●
I
● ●
● ●● ●
● ●●
●●
●●
I●
● ●
● ●
●● C I
II
●●
H● ●● ●
●●
● ●
● ●● ●
●●
●●
Title Left Side: Covalent Bonding Practice
Draw the molecule then tell me how many double bonds does it have?
1. CO2
Draw the molecule then tell me what kind of covalent bond is formed.
2. P2
Draw the following molecules.3. SiO2
4. CH4
VSEPR Theory
• Explains the shapes of molecules. • The VSEPR theory states: b/c electrons repel each
other, molecules adjust their shapes so that the valence e- pairs are as far apart from each other as possible.
• These are called electrostatic balanced positions
Shape Formula Bond Angle ElectronsLinear AX2 180o 4 shared
0 unshared
Linear AX 180o 1 shared3 unshared
Bent AX2 105o 2 shared2 unshared
Trigonal Pyramidal
AX3 107o 3 shared1 unshared
Tetrahedral AX4 109.5o 4 shared0 unshared
Trigonal Planar AX3 120o 4 shared0 unshared
Contains a double bond
Bond Polarity
Polar Covalent Bond – when 2 atoms are joined by a covalent bond and the bonding electrons are not shared equally
Nonpolar Covalent Bond – when 2 atoms are joined by a covalent bond and the bonding electrons are shared equally
Bond Polarity
Differences between polar, nonpolar, and ionic bonds
How do you determine if a bond is polar, nonpolar, or ionic?
Subtract the electronegativities of the bonding atoms (p. 265 in textbook)
Electronegativity Differences & Bond Type
Type of BondElectronegativity Difference Range
Nonpolar Covalent Bond 0.0 – 0.4
Polar Covalent Bond 0.5 – 1.67
Ionic Bond greater than 1.67
Determine if the bonds between the following atoms are polar, nonpolar, or ionic:
H 2.2C 2.55 0.35 Nonpolar
1. Hydrogen and Carbon
2. Oxygen and Carbon
3. Potassium and Chlorine
4. Fluorine and Fluorine
O 3.44C 2.55 0.89 Polar
K 0.82Cl 3.16 2.34 Ionic
F 3.98F 3.98 0.0 Nonpolar
Polar Molecule – a molecule with a positive and negative end. Polar bonds must be present.
• Take into account if the molecule is symmetrical and if polar bonds are present.
Polarity of Molecule
Polarity of Molecule
It is possible to have polar bonds but not a polar molecule!• Carbon dioxide has 2 polar bonds and is linear (symmetrical).• Bond polarities cancel out b/c they are in opposite directions.
CarbonOxygen Oxygen
Draw the dot structure of the following molecules – then predict the shape and polarity
1. I2
2. H2S
3. CHCl3
4. CO2