CHEMICAL BOND I

Сентябрь 15, 2022

Содержание

2. Valence electrons are the outer shell electrons of an atom. The valence electrons are the electrons
4. The Ionic Bond 1s22s1 1s22s22p5 1s2 1s22s22p6 [He] [Ne]
5. A covalent bond is a chemical bond in which two or more electrons are shared by
6. + + Lewis structure of water Double bond – two atoms share two pairs of electrons
7. Lengths of Covalent Bonds Bond Lengths Triple bond
9. Polar covalent bond or polar bond is a covalent bond with greater electron density around one
10. Electronegativity is the ability of an atom to attract toward itself the electrons in a chemical
13. Classification of bonds by difference in electronegativity Difference Bond Type 0 Covalent ≥ 2 Ionic 0
14. Cs – 0.7 Cl – 3.0 3.0 – 0.7 = 2.3 Ionic H – 2.1 S
15. Draw skeletal structure of compound showing what atoms are bonded to each other. Put least electronegative
16. Step 1 – N is less electronegative than F, put N in center Step 2 –
17. Step 1 – C is less electronegative than O, put C in center Step 2 –
18. Two possible skeletal structures of formaldehyde (CH2O) An atom’s formal charge is the difference between the
19. formal charge on C = 4 - 2 - ½ x 6 = -1 formal charge
20. formal charge on C = 4 - 0 - ½ x 8 = 0 formal charge
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Valence electrons are the outer shell electrons of an
atom. The

valence electrons are the electrons that
particpate in chemical bonding.

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The Ionic Bond
1s22s1
1s22s22p5
1s2
1s22s22p6
[He]
[Ne]

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A covalent bond is a chemical bond in which two or

more electrons are shared by two atoms.

Lewis structure of F2

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+
+
Lewis structure of water
Double bond – two atoms share two pairs

of electrons

or

Triple bond – two atoms share three pairs of electrons

or

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Lengths of Covalent Bonds
Bond Lengths
Triple bond < Double Bond < Single

Bond

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Polar covalent bond or polar bond is a covalent bond with

greater electron density around one of the two atoms

electron rich
region

electron poor
region

e- rich

e- poor

δ+

δ-

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Electronegativity is the ability of an atom to attract toward itself

the electrons in a chemical bond.

Electron Affinity - measurable, Cl is highest

Electronegativity - relative, F is highest

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Classification of bonds by difference in electronegativity
Difference
Bond Type
0
Covalent
≥ 2
Ionic
0 < and

<2

Polar Covalent

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Cs – 0.7
Cl – 3.0
3.0 – 0.7 = 2.3
Ionic
H – 2.1
S

– 2.5

2.5 – 2.1 = 0.4

Polar Covalent

N – 3.0

N – 3.0

3.0 – 3.0 = 0

Covalent

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Draw skeletal structure of compound showing what atoms are bonded to

each other. Put least electronegative element in the center.
Count total number of valence e-. Add 1 for each negative charge. Subtract 1 for each positive charge.
Complete an octet for all atoms except hydrogen
If structure contains too many electrons, form double and triple bonds on central atom as needed.

Writing Lewis Structures

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Step 1 – N is less electronegative than F, put N

in center

Step 2 – Count valence electrons N - 5 (2s22p3) and F - 7 (2s22p5)

5 + (3 x 7) = 26 valence electrons

Step 3 – Draw single bonds between N and F atoms and complete
octets on N and F atoms.

Step 4 - Check, are # of e- in structure equal to number of valence e- ?

3 single bonds (3x2) + 10 lone pairs (10x2) = 26 valence electrons

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Step 1 – C is less electronegative than O, put C

in center

Step 2 – Count valence electrons C - 4 (2s22p2) and O - 6 (2s22p4)
-2 charge – 2e-

4 + (3 x 6) + 2 = 24 valence electrons

Step 3 – Draw single bonds between C and O atoms and complete
octet on C and O atoms.

Step 4 - Check, are # of e- in structure equal to number of valence e- ?

3 single bonds (3x2) + 10 lone pairs (10x2) = 26 valence electrons

Step 5 - Too many electrons, form double bond and re-check # of e-

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Two possible skeletal structures of formaldehyde (CH2O)
An atom’s formal charge is

the difference between the number of valence electrons in an isolated atom and the number of electrons assigned to that atom in a Lewis structure.

The sum of the formal charges of the atoms in a molecule or ion must equal the charge on the molecule or ion.

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formal charge on C
= 4 -
2 -
½ x 6 =

-1

formal charge on O

= 6 -

2 -

½ x 6 = +1

-1

+1

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formal charge on C
= 4 -
0 -
½ x 8 =

0

formal charge on O

= 6 -

4 -

½ x 4 = 0

0

0