Chapter 3: Chemical Compounds

3.1 Molecular compounds

Two types of compounds: Molecular and ionic

Molecule: a group of two or more nonmetallic atoms held together in a definite spatial arrangement by forces called a covalent bond.

Molecular Compound: a substance composed of molecules.

Inorganic molecular compounds contain no carbon

Organic molecular compounds contain carbon with usually hydrogen and oxygen (and sometimes other elements such as S and P).

Empirical formula: the simplest formula that we can write that describes the smallest whole number ratio of elements forming a molecule.

Molecular formula: exactly describes the number of each type of atom composing a molecule.

Example:

Benzene: Molecular formula is: C₆H₆

Empirical formula is: CH

Glucose: Molecular formula is C₆H₁₂O₆

Empirical formula is CH₂O

Fructose: Molecular formula is C₆H₁₂O₆

Empirical formula is?

These are examples of organic compounds (molecules containing more than one carbon atom.)

Conclusions about molecular and empirical formulas?

Structural formula is a chemical formula that shows how the atoms are attached to one another.

Two types: explicit and condensed

Acetic acid: C₂H₄O₂

ethane: C₂H₆

3.2 Writing formulas and names of binary molecular compounds

Binary compounds = contain two different elements. These elements are nonmetals or metalloids!

1. The element that lies farthest to the left in the periodic table or is lowest in its group is written first.

There are some exceptions: H and O are frequent exceptions.

H is written after after N and before Te (and the elements in those order) see figure 2.9

O is written after Cl, but before F

NH₃, CH₄, but H₂S

SO₃, but Cl₂O

2. The name of a binary molecular compound consists of two words, one for each element in the order in which they appear.

3. The second word is altered by replacing the element ending with -ide.

ie fluorine with fluoride, sulfur with sulfide

4. The number of each element is indicated by adding a prefix to its part of the name. (Table 2.3)

ie N₂O = dinitrogen oxide

NO = nitrogen monoxide - note that mono is not added to the first named element.

CO = carbon monoxide

CO₂ = carbon dioxide

what are: P₄O₁₀

H₂S

BrO₄

Examples: Write the chemical formulas for:

bromine pentafluoride

silicon tetrachloride

carbon disulfide

Write the names for:

I₂O₅

PCl₅

P₂O₃

3.5 Ions and Ionic Compounds

An anion is an element that has more electrons than protons and thus is negatively charged. Usually these are nonmetals and lie to the left on the periodic table.

A cation is an element that has more protons than electrons and thus is positively charged. Usually these are metals and lie to the right of the periodic table.

Ionic compounds – composed of a metal and a nonmetal – may be simple and have only two elements such as salt, NaCl = sodium chloride

or complex with a polyatomic ion which is a groups of elements held together by covalent forces but also carry a charge.

Monoatomic ions – single atoms that are charged.

Usually we can predict the charge based on the element’s position in the periodic table:

figure 2-10

Formula Unit: the simplest collection of cations and anions that represents an electrically neutral unit.

Binary ionic compound formulas:

1. The cation (usually the metal) is always written first, followed by the anion (usually a nonmetal)

2. The numbers of cations and anions must balance to form an electrically neutral compound.

do some examples

NaF vs Na₂O

potassium and sulfur

aluminum and fluorine

nitrogen and magnesium *

3.6 Binary ionic compound names:

similar to binary molecular names

1. write the name of the cation first.

2. If it is a transition metal that can have more than one charge, indicate the charge with a roman numeral in parenthesis.

3. write the name of the anion and add the -ide suffix.

Examples: sodium fluoride

sodium oxide

what are the names of the above formulas that you wrote.

other examples: Fe₂O₃ = iron (III) oxide

CuO = copper (II) oxide

Examples:

Write the chemical formulas for:

cobalt (III) bromide

aluminum chloride

barium iodide

write the names of the following:

MgCl₂

KI

TiBr₄

Polyatomic ions – composed of nonmetals that together carry a charge

Table 3.7 - you must know this table or you will not be able to name compounds or write their formulas properly

Naming compounds and writing compound formulas with polyatomic ions is exactly the same as with binary compounds except that the polyatomic ion or its name is substituted

Examples:

Write the chemical formulas for a compound composed of:

sodium and phosphate (PO₄^3-)

copper (II) and hydroxide (OH^1-)

potassium and permanganate (MnO₄^1-)

Write the names for the following compounds:

NH₄Cl

Na₂SO₄

Cr(NO₃)₃

Mg₂CO₃ – magnesium carbonate

KOH - potassium hydroxide

Ba₃(PO₄)₂ - barium phosphate

Write the formula for the following:

sodium thiocyante: NaSCN

Iron (III) chlorate: Fe(ClO₃)₃

chromium (II) nitrite: Cr(NO₂)₂