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Covalent bonding

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How does H2 form? The nuclei repel

++

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How does H2 form?

++

The nuclei repel But they are attracted to electrons The hydrogen atoms share the

electrons

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Covalent bonds Nonmetals hold onto their valence

electrons. They can’t give away electrons to bond.

– But the atoms still want noble gas configuration

Nonmetals get a noble gas configuration by sharing valence electrons with each other.

– By sharing both atoms count the shared electrons toward noble gas configuration.

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Covalent bonding Fluorine has seven valence electrons

F

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Covalent bonding Fluorine has seven valence electrons A second atom also has seven

F F

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Covalent bonding Fluorine has seven valence electrons A second atom also has seven By sharing electrons

F F

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Covalent bonding Fluorine has seven valence electrons A second atom also has seven By sharing electrons

F F

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Covalent bonding Fluorine has seven valence electrons A second atom also has seven By sharing electrons

F F

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Covalent bonding Fluorine has seven valence electrons A second atom also has seven By sharing electrons

F F

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Covalent bonding Fluorine has seven valence electrons A second atom also has seven By sharing electrons

F F

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Covalent bonding Fluorine has seven valence electrons A second atom also has seven By sharing electrons Both end with full orbitals

F F

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Covalent bonding Fluorine has seven valence electrons A second atom also has seven By sharing electrons Both end with full orbitals

F F8 Valence electrons

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Covalent bonding Fluorine has seven valence electrons A second atom also has seven By sharing electrons Both end with full orbitals

F F8 Valence electrons

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Covalent bonding Fluorine has seven valence electrons A second atom also has seven By sharing electrons Both end with full orbitals Instead of dots, we use a “–” for the bond

F F

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Single Covalent Bond The sharing of two valence electrons.

– Only nonmetals and metalloids form covalent bonds

• Do not forget about Hydrogen!

Different from an ionic bond because they actually form molecules.

– Ionic bonds are a matrix of ions

– In an ionic solid you can’t tell which atom the electrons moved from or to.

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How to show how they formed I have to tell you what the final formula

is or you cannot write the structure

– Ionic compounds you can write the formula based on charges

You put the pieces together to end up with the right formula.

For example- show how water is formed with covalent bonds.

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Water

H

O

Each hydrogen has 1 valence electron

Each hydrogen wants 1 more

The oxygen has 6 valence electrons

The oxygen wants 2 more

They share to make each other satisfy the octet

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Water Put the pieces together The first hydrogen is good The oxygen still wants one more electron

H O

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Water The second hydrogen attaches Every atom has full energy levels

H OH

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Water The second hydrogen attaches Every atom has full energy levels Change the dots to lines

H OH

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Multiple Bonds Sometimes atoms share more than one

pair of valence electrons. A double bond is when atoms share two

pair (4) of electrons. A triple bond is when atoms share three

pair (6) of electrons.

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Carbon dioxide CO2 - Carbon is central atom

– Assume the first atom is central Carbon has 4 valence

electrons

– Carbon wants 4 more Oxygen has 6 valence electrons

– Oxygen wants 2 moreO

C

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Carbon dioxide Attaching 1 oxygen leaves the oxygen 1

short and the carbon 3 short

OC

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Carbon dioxide Attaching the second oxygen leaves

both oxygen 1 short and the carbon 2 short

OCO

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Carbon dioxide The only solution is to share more

OCO

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Carbon dioxide The only solution is to share more

OCO

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Carbon dioxide The only solution is to share more

OCO

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Carbon dioxide The only solution is to share more

OCO

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Carbon dioxide The only solution is to share more

OCO

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Carbon dioxide The only solution is to share more

OCO

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Carbon dioxide The only solution is to share more Requires two double bonds Each atom gets to count all the atoms in

the bond

OCO

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Carbon dioxide The only solution is to share more Requires two double bonds Each atom gets to count all the atoms in

the bond

OCO8 valence electrons

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Carbon dioxide The only solution is to share more Requires two double bonds Each atom gets to count all the atoms in

the bond

OCO8 valence electrons

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Carbon dioxide The only solution is to share more Requires two double bonds Each atom gets to count all the atoms in

the bond

OCO

8 valence electrons

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How to draw them1. Add up all the valence electrons. (to keep

track)

2. Draw the central atom (or connect multiple central atoms by single bonds)

3. Connect the outer atoms to the central atom using a single bond

4. Complete the octet of the outer atoms

5. Place all extra electrons on the central atom(s)

6. Complete the octet of the central atom by making multiple bonds

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Practice NH3

H2O HCN H2CO

C5H10 (multiple possible structures)

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Structural Examples

H C N

C OH

H

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What about resonance? Resonance is when you can create

more than one structure that “appear” to be the same

– Only the position of the number of bonds connecting atoms is switched.

– But all the bonds must originate from the same central atom

Draw O3

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What about Exceptions to the Octet?

Sometimes a central atom will not complete an octet

– Draw BF3 Sometimes the central atom will need to

have more than an octet to satisfy the octet of the other atoms.

– Draw XeF4

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What about ions? When drawing a polyatomic ion, you will

need to add or subtract the appropriate number of electrons.

– Draw NH4+

– Draw CO-2

– Draw OH-