Ch. 7: Ionic Compounds & Metals

Sec. 7.1: Ion Formation

Forming Chemical Bonds

• Objectives– Define chemical bond.– Relate ionic bond formation to electron

configuration.– Describe the formation of positive and negative

ions.

Forming Chemical Bonds

• How do thousands of compounds form from the relatively few elements known to exist?

Forming Chemical Bonds

• Valence electrons are the electrons involved in the formation of chemical bonds between two atoms.

Forming Chemical Bonds

• A chemical bond is the force that holds two atoms together.

• Chemical bonds are due to:– the attraction between a positive nucleus of

one atom and the negative electrons of another (covalent), OR

– The attraction between a positive ion and a negative ion (ionic)

Forming Positive Ions

• Recall the octet rule ….• Recall: metals have low ionization energy

& electronegativity (meaning…?)• Recall: metals form positive ions• A positive ion forms when an atom loses

one or more valence electrons in order to attain a noble gas configuration.

Example• Neon 1s22s22p6

• Sodium atom 1s22s22p63s1

• Sodium ion 1s22s22p6

• A positively charged ion is called a cation.

Forming cations

• Sodium atom (Na)– 11 protons

– 12 neutrons

– 11 electrons

• Sodium ion (Na+)– 11 protons

– 12 neutrons

– 10 electrons

SAME electron configuration as neon but it is NOT neon.

Reactivity of metals

• Depends on how easily they lose their valence electrons– Group 1A (1+ ions): very easily ---> highly

reactive– Group 2A (2+ ions): relatively easy ---> very

reactive– Group 3A (3+ ions): easily ---> reactive

Transition Metals

• When forming positive ions, transition metals commonly lose their two “s” electrons, forming 2+ ions.

• It is also possible for the d electrons to be lost, forming other relatively stable electron arrangements. These are referred to as pseudo-noble gas configurations.

• Therefore, most transition elements can form more than one kind of ion– For example, Fe can form a 2+ OR 3+ ion.

Forming Negative ions

• Recall octet rule; Recall the high ionization energy and electronegativity of nonmetals

• Nonmetals form a stable outer electron configuration by gaining 1 or more electrons.

Forming Anions

Argon 1s22s22p63s23p6

Chlorine 1s22s22p63s23p5

Cl- 1s22s22p63s23p6

• By gaining a single electron, a chlorine atom attains the electron configuration of argon.

• With the addition of one electron, chlorine becomes a negatively charged ion called an anion.

Forming Anions

• To name an anion, the ending –ide is added to the root name of the element.

• The anion of chlorine is called chloride.

• What is the anion of nitrogen called? arsenic?

Let’s look at nitrogen . . .

• Nitrogen atom (N)– 7 protons

– 7 neutrons

– 7 electrons

• Nitride ion (N3-)– 7 protons

– 7 neutrons

– 10 electrons

SAME electron configuration as neon but it is NOT neon

General Trends

• Group 5A/15: gain 3 e-’s and become 3- ions

• Group 6A/16: gain 2 e-’s and become 2- ions

• Group 7A/17: gain 1 e- and become 1- ions