1. Covalent Bonds (6.2)

2. Covalent Bonds
Nonmetals with high ionization energies do not tend to form ionic bonds
Instead of transferring electrons they share them

3. Sharing Electrons
Two atoms of hydrogen can share their electrons to achieve a stable electron configuration
Covalent Bond - a chemical bond in which two atoms share a pair of valence electrons

4. Molecular Models
The electron cloud model and space-filling model show that orbitals of atoms overlap when a covalent bond forms

5. Molecules of Elements
Molecule - a neutral group of atoms that are joined together by one or more covalent bonds
They are neutral because the number of protons and electrons are balanced in the shared molecule
The attractions between the shared electrons and the protons in each nucleus hold the atoms together in a covalent bond

6. Many nonmetal elements exist as diatomic molecules
Diatomic means “two atoms”

7. Multiple Covalent Bonds
A Nitrogen molecule (N2) shares three pairs of electrons, each atom then has eight valence electrons
Each pair of shared electrons is represented by a long dash in the structural formula
When two atoms share three pairs of electrons it is called a triple bond
When two atoms share two pairs of electrons it is called a double bond

8. Unequal Sharing of Electrons
In general, elements on the right of the periodic table have a greater attraction for electrons than elements on the left (except noble gases)
Elements at the top of a group have a greater attraction for electrons than elements at the bottom of a group

9. Polar Covalent Bonds
When hydrogen and chlorine form a covalent bond the chlorine atom has a greater attraction for the electrons than the hydrogen atom
In the hydrogen chloride molecule, the shared electrons spend more time near the chlorine atom than near the hydrogen atom
Polar Covalent Bond- a covalent bond in which electrons are not shared equally
When atoms form a polar covalent bond, the atom with the greater attraction for electrons has a partial negative charge
The other atom has a partial positive charge

10. Polar and Nonpolar Molecules
If a molecule with a polar covalent bond contains only two atoms, it will be polar
But when molecules have more than two atoms, the answer is not as obvious
The type of atoms in a molecule and its shape are factors that determine whether a molecule is polar or nonpolar
Nonpolar
Polar

11. Carbon Dioxide (CO2)
Each double bond in carbon dioxide is polar because oxygen has a grater attraction for electrons than the carbon atom
Because the molecule is linear (all three atoms line up in a row) the pull of the charges cancel out and the molecule as a whole is nonpolar

12. Water (H20)
Water molecule has two single bonds which are polar because oxygen has a greater attraction for electrons that hydrogen
The water molecule has a bent shape so the polar bonds do not cancel out
The two hydrogen atoms are located on the same side of the molecule opposite the oxygen atom
The oxygen side has a partial negative charge and the hydrogen side has a partial positive charge

13. Attraction Between Molecules
Attractions between polar molecules are stronger than attractions between nonpolar molecules
Water boils at 1000C and Methane boils at C even if they are very similar in mass
Because water molecules are polar, the attractions between the molecules are stronger than the attractions between the nonpolar methane molecules
Attractions between nonpolar molecules exist but they are just weaker
Attractions among nonpolar molecules explain why nitrogen can be stored as a liquid at low temperatures and high pressures