How do you find the number of bond pairs?

Answer 1

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Bond pairs

1. Determine the column each element is in.

2. That is the number of valence electrons each atom has available for bonding.

3. Add up the valence electrons for all the atoms on the compound to determine the number of electrons available for bonding. For polyatomic ions such as sulfate with a negative 2 charge, the negative 2 means there 2 more electrons available for bonding.

4. Each atom needs 8 electrons to have an octet, 8 electrons in the outer shell, so multiply the number of atoms by 8 (except H by 2) to determine the number electrons needed. (except Hydrogen which only needs 2 electrons to fill its 1s orbital)

5. Subtract the number of electrons available from the number electrons needed. (Step#4 - Step#3) This answer is the number of electrons involved in bonding.

6. Divide this number by 2 to determine the number of bonds pairs needed.

7. You place the least electronegative atom in the center

8. Place these bonds pairs between the atoms. One line represents a bond (2e-'s)

9. Place enough electron pairs around each atom to make an octet(except hydrogen only needs 2e-'s). One line represents a pair of e-'s.

10. Check to make sure the number of electrons used equals the number of valance electrons available .(#3)

11. Check the shape. Electron pairs repel each other, so make sure the bonds are as far away from each as possible.

Example #2 Sulfur dioxide SO2

1. Column #'s S = 6, O = 6.

2. 6 + (2 * 6) = 18 electrons available for bonding.

3. 3 atoms * 8 = 24 electrons needed in total.

4. 24 - 18 = 6 electrons involved in bonding.

5. 6 ÷ 2 = 3 bond pairs.

6. S in center, O's on the outside.

7. 3 bonds between bonding 2 O's to an S. That means a single and a double bond.

8. The S has 1 nonbonding pair, 1 O has 1 nonbonding pair, the other O has 2 nonbonding pairs.

9. Count 18 electrons.

10. The shape will be Y-shaped.

Example #1 Phosphate ion, PO4, -3 charge

1. Column #'s P = 5, O = 6.

2. 5 + (4 * 6) + 3(-3 charge) = 32 electrons available for bonding.

3. 5 atoms * 8 = 40 electrons needed in total.

4. 40 - 32 = 8 electrons involved in bonding.

5. 8 ÷ 2 = 4 bond pairs.

6. P in center, O's on the outside.

7. 4 bonds between bonding 2 O's to an P. That means 4 single bonds.

8. Each O atom will need 3 nonbonding pairs.

9. Count 32 electrons.

10. The shape will be Tetrahedral-shaped.