Ionic Compounds: Introduction to Bonding
Bonding: the joining of two atoms in a stable arrangement.
There are two different kinds of bonding:
Elements will gain, lose, or share electrons to attain the electron configuration of the noble gas closest to them in the periodic table.
•Ionic bonds result from the transfer of electrons from one element to another.
•Covalent bonds result from the sharing of electrons between two atoms.
During chemical reactions, electrons can be transferred to or from atoms in order to fulfill the octet rule
Example: Na Na+1 + e-
Cl + e- Cl-1
Ionic Bond: Attractive force between oppositely charged particles (electrostatic force); results from transfer of electrons between atoms
Na+ + Cl- NaCl
Ions: Cations and Anions
Cations: positively charged ions (fewer electrons than protons)
Anions: negatively charged ions (more electrons than protons)
Some Things to Know About Ionic Compounds:
Metals tend to lose electrons during ionic bond formation
Nonmetals tend to gain electrons during ionic bond formation
No more than 3 electrons are transferred
Metals lose same number of electrons as their group number
Nonmetals gain the number of electrons equal to their group number subracted from 8 (group number - 8)
Examples: Li. (metal, group IA)
Li Li+ + 1 e-
Cl (nonmetal, group VIIA)
Cl + 1 e- Cl-
Ions Formed by the Main Group Elements
The ratio of positive to negative ions is determined by the charges on the ions (the number of electrons transferred)
The total positive and total negative charges in the final formulas must add up to zero
Example: Na and Cl
Na Na+ + e-
Cl + 1 e- Cl-
These ions will combine in a 1:1 ratio, to give an ionic compound with a net charge of zero:
NaCl
Example: Mg and F
Mg Mg2+ + 2 e-
F + 1 e- F-
Mg2+ + F- MgF2
Practice: K and S
K K+ + 1 e-
S + 2 e- S2-
What is the formula of the ionic compound formed by these 2 ions?
K2S
Practice: Ca and Br
Ca Ca2+ + 2 e-
Br + 1 e- Br-
What is the formula of the ionic compound formed by these 2 ions?
Fe+3 + O2-
CaBr2
Fe2O3
Ionic compounds exist as crystal structures
Crystal lattice: rigid 3-dimensional arrangement of particles
Physical Properties of Ionic Compounds
•Ionic compounds have very high melting points (NaCl = 801 oC) and extremely high boiling points (NaCl = 1413 oC).
•When ionic compounds dissolve in water, they separate into cations and anions. The resulting aqueous solutions conduct an electric current.
NaCl
+
water solution
Naming Ionic Compounds
Name of metallic element comes first, followed by stem of nonmetal with the suffix “ide” appended
compound name = metal + nonmetal stem + ide
Examples: KCl = Potassium chloride
SrO = Strontium oxide
Ca3N2 = Calcium nitride
Names of Single Ions
Names for individual ions follow the same system (metal name is un-changed, non-metal suffix changes to “ide”)
Example: K+ = Potassium ion
Cl- = Chloride ion
Some atoms (such as the transition metals) can form more than one type of charged ion:
Cu Cu+ and Cu2+
Fe Fe2+ and Fe3+
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IonsMetals with Variable Charge
Stock System: Uses Roman numeral in name of chemical formula to indicate the charge on metal atom
Example: CuCl = Copper(I) chloride
CuCl2 = Copper(II) chloride
Older system uses suffixes “-ous” and “-ic” attached to root of metal name (uses non-English stem for elements with non-English names)
-ous = ion of lower charge
-ic = ion of higher charge
Example: Copper (Latin name = cuprum)
CuCl = Cuprous chloride
CuCl2 = Cupric chloride
Example: Iron (Latin name = ferrum)
FeCl2 = Ferrous chloride
FeCl3 = Ferric chloride
Polyatomic ion: cation or anion that contains more than one atom.
