Home Up E1 E2 E3 E4 Topics - E1 Topics E2 Topics E3 Topics E4 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 27 28 29 30 31

 

Remember ions and the relation between the charges of many ions and their position in the periodic table:

Ionic Compounds - Ions form ionic compounds that are electrically neutral

Na+ + Cl- --> NaCl   ionic compound

Held together by ionic bonds - the force of attraction between positively and negatively charged ions.

Ionic compounds are generally made from metals and nonmetals since cations typically form from metals and anions from non-metals.

Chemical formula for ionic compounds:

Example:  CaCl2

 Write the metal first followed by the nonmetal

Why two chlorines?  Need to maintain charge neutrality - equal number of positive and negative charges

Ca2+ = +2

2Cl- =2( -1) = -2

Total sum of charges = 0

Note: we indicate the charge as a superscript after the element.  Also note that in the above example it is written as 2+ and not +2.

Remember: the charge on an ion can often be rationalized by its electronic configuration and the idea that a noble gas configuration is particularly stable.

What is the chemical formula of the compound formed from Na+ and S2-?

Na2S

Naming Ionic Compounds

"cation" name + "anion" name (with different suffix if a single atom)

For simple ionic compounds between a metallic element and a nonmetallic element this is of the form:

metal name + nonmetal name (with different suffix)

Common elemental cations

common elemental anions

Li+

lithium

F-

fluoride

Na+

sodium

Cl- 

chloride

Rb+

rubidium

Br-

bromide

Cs+ 

cesium

I-

iodide

Mg2+ 

magnesium

O2-

oxide

Ca2+

calcium

S2- 

sulfide

Ba2+

barium

Cu2+

copper

Al3+

aluminum

 

Li+ + Cl-

LiCl

Lithium chloride

K+ + I-

KI

Potassium iodide

Ca2+ + Cl-

CaCl2

calcium chloride (not calcium dichloride)

Ca2+ + O2-

CaO

calcium oxide

Mg2+ + Cl-

MgCl2

magnesium chloride

Al3+ + O2-

Al2O3

aluminum oxide

Some metals form cations with different charges.  For these or whenever we want to emphasize the charge on the cation, a roman numeral is used.  Some ions also have "common" names.

For instance:

Ions

Chemical formula

Name

"Common Name"

Fe3+ + Cl-

FeCl3

iron(III)chloride

ferric chloride

Fe2+ + Cl-

FeCl2

iron(II) chloride

ferrous chloride

Cu2+ + Cl- 

CuCl2

copper(II)chloride

cupric chloride

Cu+ + Cl- 

Cu

copper(I)chrloide

cuprous chloride

Polyatomic ions:  Many common ions are made of several atoms

Some of the most important are:

hydroxide

OH-

KOH potassium hydroxide

nitrate

(NO3)

KNO3  potasium nitrate (ingredient of black powder)

nitrite

(NO2)-

NaNO2 sodium nitrite (common preservative)

sulfate

(SO4)2-

Na2SO4 sodium sulfate

carbonate

(CO3)2-

CaCO3 sodium carbonate (limestone)

bicarbonate

(HCO3)-

sodium bicarbonate NaHCO3 (baking soda)

phosphate

(PO4)3-

sodium phosphate Na3PO4 (phosphates  were major component of detergents, were phased out, and may be phased back in)

ammonium

NH4+

ammonium nitrate NH4NO3 (common fertilizer)

Structure of ionic compounds:

Ionic bonds are strong and ionic compounds are usually solids that melt at high temperatures.  

The structure of solid ionic compounds, in the most simplistic sense, can be thought of as a bunch of hard spheres packing tightly with negative ions near positive ions.  Basically, the atoms are trying to fill space tightly.  

See a small representative unit of sodium chloride.  This structure repeats itself many many many times in a macroscopic sample such as a salt crystal in your salt shaker.  

Making ionic compounds:  Can't just put Na+ in a bottle because of charge neutrality.  Can make ionic compounds by reacting a nonmetal (which prefers to give up its electrons) with a metal (which prefers to gain an electron).

 

Electron Dot Structures - Helpful tools in thinking about bonding.

Pictorial representation of the valence electron configuration around an atom.  We will only consider s and p block elements (main group) and consequently only be concerned with s and p orbitals. 

Carbon - 1s22s22p2  - four valence electrons

 

Electron dot structure - valence electrons are represented by dots placed around the chemical symbol.  Electrons are placed up to two on each side of the elemental symbol for a maximum of eight, which is the number of electrons in a filled s and p shell.  We place a single electron on each side before pairing them up (this is related to Hund's rule)