1. Covalent Bonds
Chapter 6.2 Notes

2. Sharing Electrons Sharing Electrons
A covalent bond is a chemical bond in which two atoms share a pair of valence electrons.
When two atoms share one pair of electrons, the bond is called a single bond.

3. Sharing Electrons
Atoms can share more than one valence electron. When they share two it is called a double bond, when they share three it is called a triple bond.

4. Models of Covalent Bonds
Four ways to represent models of covalent bonds are the electron dot diagram, the structural formula, the space-filling model, and the electron cloud model.
In the electron dot model, the bond is shown by a pair of dots in the space between the symbols.

5. Models of Covalent Bonds
In the structural formula, the pair of dots is replaced by a line.
The electron cloud and the space-filling models show the orbitals of atoms overlap when a covalent bond forms.

6. Molecular Models

7. Molecules of Elements Molecules of Elements
A molecule is a neutral group of atoms that are joined together by one or more covalent bonds.
In the formula H2O, the subscript 2 indicates that there are two hydrogen atoms.

8. Molecules of Elements
The H2, hydrogen, molecule is neutral because it contains two protons and two electrons, one from each hydrogen atom in the molecule.
In the H2 molecule, what keeps the hydrogen atoms together?
The attractions between the shared electrons and the protons in each nucleus hold the atoms together in a covalent bond.

9. Molecules of Elements
A chemical formula can be used to describe the molecules of an element as well as a compound.
When atoms join in pairs we call them diatomic molecules.

10. Unequal Sharing of Electrons
Atoms are able to share electrons unequally.
Elements on the right side of the periodic table have a greater attraction for electrons than elements on the left side.

11. Unequal Sharing of Electrons
Elements at the top have a greater attraction for electrons than do elements at the bottom.
For example, fluorine is at the top right of the periodic table and has the strongest attraction for electrons in the non-metal group.

12. Unequal Sharing of Electrons
Ionization energy is the amount of energy needed to remove an electron from an atom.
Ionization energy increases as you move up and to the right on the periodic table.

13. Ionization Energy

14. Polar Covalent Bonds Polar Covalent Bonds
A polar covalent bond is a 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 represented as - ( is the lower case symbol of the Greek symbol delta).

15. Polar Covalent Bonds
The other atom has a partial positive charge represented as +.
When hydrogen and chlorine bond, the shared electron is closer to the chlorine atom, because chlorine has a greater attraction for electrons. This gives the chlorine atom a slightly negative charge and the sodium atom a slightly positive charge.

16. Polar Covalent Bonds (HCl)

17. Polar Covalent Bonds
Attractions between polar molecules are stronger than attractions between nonpolar molecules.

18. Polar VS Non-Polar Molecules
When a molecule contains only two atoms, such as H2, the molecule will always be polar.
Molecules that contain more than one polar bond are not always polar molecules.
The type of atoms in a molecule and its shape are factors that determine whether a molecule is polar or nonpolar.

19. Polar VS Non-Polar Molecules
For example, in the CO2 molecule, there are double bonds between each oxygen atom and the central carbon atom. Since oxygen has a greater attraction for electrons than carbon, each double bond is polar. However, there is an equal pull on the electrons from opposite directions which cancel out and make the molecule nonpolar.

20. CO2 Molecule

21. Polar VS Non-Polar Molecules
In a H2O molecule, the bonds are polar because oxygen has a greater attraction for electrons than hydrogen does. However, since there is not an equal pull on the electrons, the hydrogen atoms are both located on the same side of the oxygen atom and create a polar molecule. The hydrogen side of the molecule has a partial positive charge, and the oxygen side has a partial negative charge.

22. H2O Molecule