The Octet Rule Ionic Bonding Noble gases are unlike any other group of elements on the periodic table because of their extreme stability ( they don’t want to interact with other elements) Each noble gas has eight valence electrons, except for helium, which has two. The octet rule says that atoms can become stable by having eight electrons in their outer energy level.

Example Sodium is in Group 1, so it has 1 valence electron. Chlorine is in Group 7A and has 7 valence electrons. What will happen if the two want to combine?

Ionic bonding How can the valence electrons of atoms rearrange to give each atom a stable configuration of valence electrons? If the one valence electron of sodium is transferred to the chlorine atom, chlorine becomes stable with an octet of electrons

Electrons Can Be Transferred Because the chlorine atom now has an extra electron, it has a negative charge. Also, because sodium lost an electron, it now has an unbalanced proton in the nucleus and therefore has a positive charge.

Now that each atom has an octet of outer- level electrons, they are no longer neutral atoms; they are charged particles called ions. An ion is an atom or group of combined atoms that has a charge because of the loss or gain of electrons.

A compound that is composed of ions is called an ionic compound.

Ionic Bonding Ionic compounds, like table salt: NaCl, usually form crystals of repeating ion pairs by combining a metal with a nonmetal element. Ex: KI, CaCl 2, BaF 2, NaCl, Li 2 O, Al 2 S 3

Ionic bonding NACL crystals form repeating patterns of positive and negative ions to maximize the distance between like charges When ionic compounds melt or dissolve in water, their three-dimensional structure breaks apart, and the ions are released from the structure.

Covalent bonding Now what if the following atoms want to combine? Cl-Cl N-N O-O C-O

Covalent bonding If two chlorine atoms combine, they share a single pair of electrons, and each atom attains a stable octet configuration.

Covalent bonding Two oxygen atoms share two pairs of electrons to form O2, and two nitrogen atoms share three pairs of electrons to form N2.

Electron Sharing Produces Molecules Notice that in a covalent bond, atoms share electrons and neither atom has an ionic charge. The attraction of two atoms for a shared pair of electrons is called a covalent bond.

Covalent Bonds: Sharing of pairs of valence electrons between nonmetals.