Chapter 2: Chemical Formulas and Composition Stoichiometry

What do chemical formulas show?

The chemical composition of the substance

What are chemical formulas?

Ratio of the elements present in the molecule or compound

Monatomic elements

Elements made of single atoms not connected to each other

Example of a monatomic element

Helium (He), Gold (Au), Sodium (Na)

What are the diatomic elements?

Pure elements that naturally form molecules made of two identical atoms bonded together

diatomic elements

hydrogen (H2), nitrogen (N2), oxygen (O2), fluorine (F2), chlorine (Cl2), bromine (Br2), iodine (I2)

Complex Elements

elements that contain other elements

Examples of complex elements

Ozone (O3), Tetraphosphorus (P4), Octasulfur (S8)

Compound

A substance made up of atoms of two or more different elements joined by chemical bonds

Examples of compounds

Water (H2O) and carbon dioxide (CO2), Sucrose (C12H22O11)

HCl

1 hydrogen atom and 1 chloride atom

H20

2 hydrogen atoms and 1 oxygen atom

NH3

1 nitrogen atom and 3 hydrogen atoms

C3H8

3 carbon atoms and 8 hydrogen atoms

What are the classifications of the periodic table (3)

Metals, Nonmetals, and Metaloids

covalent compound

Non-metals and non-metals

ionic compound

metal and nonmetal

metallic compound

metal + metal

Ions

Atoms or groups of atoms that possess an electric charge

What are the two types of ions?

cations (+) and anions (-)

Cation

A positively charged ion

Cations has

one or more electrons less neutral

Do cations gain or lose electrons?

They lose electrons

What are cations formed by?

metals

What are examples of cations?

Sodium (Na+)

Potassium (K+)

Calcium (Ca++)

Magnesium (Mg++)

Polyatomic Cations

NH4+ (ammonium)

Anions

negatively charged ions

Anions has

one or more electrons more than neutral

Do anions gain or lose electrons?

They gain electrons

What are anions formed by?

nonmetals

Anion examples

Fluoride (F-), Oxygen (O2-), Nitride (N3-)

Polyatomic anions

Sulfate (SO4^2-), Phosphate (PO43-)

Type I Cations

metal atoms that form only one type of charge

What main group of metals are in type I cations?

IA, IIA, IIIA, and some exceptions from the transition metals (Ag, Cd, Zn)

Type II Cations

metal atoms that can form more than one type of positive charge (most of the transition metals)

How do non-metals form anions?

With only one charge commonly found in nature

Polyatomic Ions

ions that are made of more than one atom

Ammonium

NH4 charge +1

Acetate

C2H3O2 -1

Nitrate

NO3 charge -1

Nitrite

NO2 charge -1

Perchlorate

ClO4 charge -1

Chlorate

ClO3 charge -1

Chlorite

ClO2 charge -1

Hypochlorite

ClO charge -1

Permanganate

MnO4 charge -1

Sulfate

SO4 charge -2

Sulfite

SO3 charge -2

Hydroxide

OH charge -1

Cyanide

CN charge -1

Phosphate

PO4 charge -3

Phosphite

PO3 charge -3

Carbonate

CO3 charge -2

Bicarbonate (hydrogen carbonate)

HCO3 charge -1

Peroxide

O2 charge -2

Empirical formula

the smallest whole number ratio of the atoms in a compound

Molecular formula

The actual number of atoms of each element present in a molecule in a compound

Ionic Compounds

Neutral compounds made up of a cation and anion (usually metal)

What type of charge does an ionic compound have?

Neutral (equal to zero) because it's formed at a ratio

What is an example of an ionic compound?

Sodium chloride (NaCl).

Ionic Formula

total positive charge+total negative charge = 0

Chemical formula with the charge

What is an example of an ionic formula?

Sodium chloride (Na 1+, CI 1-)

For every sodium, you need one chloride

What is the naming convention for Type I compounds?

Name of cation (metal) + Base name of anion (nonmetal) + -ide

What do you do if the anion in a Type I compound is a polyatomic ion?

Do not use the -ide ending.

What is the naming convention for Type II compounds?

Name of cation (metal) charge of cation (metal) in Roman numerals in parentheses) + Base name of anion (nonmetal) + -ide

What do you do if the anion in a Type II compound is a polyatomic ion?

If the anion is a polyatomic ion, then you do not use the -ide ending

What are hydrates?

Ionic compounds containing a specific number of water molecules associated with each formula unit

1 water molecule

mono

2 water molecules

di

3 water molecules

tri

4 water molecules

tetra

5 Water Molecules

penta

6 water molecules

hexa

7 water molecules

hepta

8 water molecules

octa

9 water molecules

nona

10 water molecules

deca

Avogadro's number

number of representative particles in a mole, NA = 6.022 X 10^23

What is a mole?

amount of substance

How much is one mole?

6.022 x 10^23

Relative atomic mass

The weighted average of the masses of the constituent isotopes of an element

Amu

atomic mass unit

How much is 1 amu?

1/12 the mass of a carbon-12 atom

Mole = grams/mass

12.0 grams C = 1 mole C

Subscript in Formula: H20

2 mole H = 1 mole H2O

Coefficients in balanced chemical equations: 2 Na + Cl2

2 NaCl; 2 sodium atoms react with one molecule of chlorine to form 2 molecules of salt

How do we calculate the molar mass of a compound?

Add atomic mass numbers together = molar mass g/mol

percent composition

The mass of an individual that would be in 100 grams of a pure sample of a compound

Is percent composition an extrinsic or intrinsic property?

Intrinsic property

percent composition formula

mass of element/mass of compound x 100

What can the percent composition be determined from?

Empirical and molecular formula

What can the empirical formula be determined from?

Percent composition

How do you start finding the empirical formula from percent composition?

Assume 100 g of sample so mass of each element is equal to the percent composition of that element.

What is the next step after determining the mass of each element in the sample?

Apply molar mass to get moles of each element.

How do you find the mole ratio of each element?

Use the element with the smallest number of moles in the denominator.

What do you do with the mole ratio to build the empirical formula?

Use the mole ratio to build the empirical formula, and multiply by an integer if necessary to get whole numbers for each element.

What do you do if there is not a whole number?

We multiply by 2 to get the smallest whole-number ratio.

How do you determine the molecular formula?

1. Write the given empirical formula and molecular formula molar mass

2. Put the molecular formula molar mass on top of the empirical formula and divide

3. Round the answer to the nearest whole number

4. Answer = n

5. Molecular formula= n x empirical formula

molecular formula equation

n = molecular mass / empirical mass

Purity of Sample formula

Percent of purity = mass of pure substance/mass of sample X 100%

- Mass of sample includes impurities