2

Types of Formulas

The formulas for compounds can be expressed as an empirical formula and as a molecular(true) formula.

Empirical Molecular (true) Name

CH C2H2 acetylene

CH C6H6 benzene

CO2 CO2 carbon

dioxide

CH2O C5H10O5 ribose

3

• An empirical formula represents the simplest whole number ratio of the atoms in a compound.

• The molecular formula is the true or actual ratio of the atoms in a compound.

Formulas…Chemical Formulas tell us-

• Elements that make up the compound

• Ratio of the elements in the compound

• Subscripts –below the element

• Tell you the number of atoms

Example- Water-> H2O-> 2 hydrogen atoms and one oxygen atom

Molecular Formulas tell us-

• Tell you the total number of atoms of each element in 1 molecule of the substance

Example- C2H2 ->Acetylene

Structural Formulas tell us-

• Shows the way the atoms are joined together in a molecule.

Example-

- Carbon always forms 4 bonds

- Molecular Models show orientation in 3 dimensions so are the best molecular models

5

Empirical and Molecular Formulas

molar mass = a whole number = n

simplest mass

n = 1 molar mass = empirical mass

molecular formula = empirical formula

n = 2 molar mass = 2 x empirical mass

molecular formula =

2 x empirical formula

molecular formula = or > empirical formula

Timberlake LecturePLUS 6

Empirical Formula

Empirical Mass

Molecular Formula

MolecularMass

The Empirical Formula• The lowest whole number ratio of elements

in a compound.• The molecular formula the actual ratio of

elements in a compound• The two can be the same.

– CH2 empirical formula

– C2H4 molecular formula

– C3H6 molecular formula

– H2O both

Calculating Empirical• Just find the lowest whole number ratio

– C6H12O6

– CH4N

• It is not just the ratio of atoms, it is also the ratio of moles of atoms

• In 1 mole of CO2 there is 1 mole of carbon and

2 moles of oxygen

• In one molecule of CO2 there is 1 atom of C

and 2 atoms of O

Calculating Empirical

• Pretend that you have a 100 gram sample of the compound.

• That is, change the % to grams.• Convert the grams to mols for each element.• Write the number of mols as a subscript in a

chemical formula.• Divide each number by the least number.• Multiply the result to get rid of any fractions.

Example• Calculate the empirical formula of a compound

composed of 38.67 % C, 16.22 % H, and 45.11 %N.

• Assume 100 g so• 38.67 g C x 1mol C = 3.220 mole C

12.01 gC • 16.22 g H x 1mol H = 16.09 mole H

1.01 gH• 45.11 g N x 1mol N = 3.219 mole N

14.01 gN

• 3.220 mole C • 16.09 mole H • 3.219 mole N

C3.22H16.09N3.219

If we divide all of these by the smallest one, it will give us the empirical formula

3.220 mol C and 3.219 mol N are essentially the same.

Example• The ratio is 3.220 mol C = 1 mol C

3.219 molN 1 mol N• The ratio is 16.09 mol H = 5 mol H

3.219 molN 1 mol N

• C1H5N1 is the empirical formula = CH5N

• A compound is 43.64 % P and 56.36 % O. What is the empirical formula?

• 43.6 g P x 1mol P = 1.4 mole P 30.97 gP

• 56.36 g O x 1mol O = 3.5 mole O 16 gO

P1.4O3.5

Divide both by the lowest one

• The ratio is 3.52 mol O = 2.5 mol O 1.42 mol P 1 mol P

P1.4O3.5

P1O2.5

This doesn’t work!

• Multiply the result by 2 to get rid of any fractions.

P1O2.52 X = P2O5

Solve

• Caffeine is 49.48% C, 5.15% H, 28.87% N and 16.49% O. What is its empirical formula?

Empirical to Molecular

• Since the empirical formula is the lowest ratio the actual molecule would weigh more by a whole number multiple.

• Divide the actual molar mass by the mass of one mole of the empirical formula.

Caffeine has a molar mass of 194 g. what is its molecular formula? (You found Caffeine’s empirical formula earlier, solve for the empirical formula mass.)

Find x if massformulaempirical

massmolarx

194 g

97 g= 2

C4H5N2O1

C8H10N4O2.

2 X

Example

• A compound is known to be composed of 71.65 % Cl, 24.27% C and 4.07% H. Its molar mass is known (from gas density) is known to be 98.96 g. What is its molecular formula?

Example

71.65g Cl

24.27g C

4.07g H

g

mol

5.35

1

g

mol

12

1

g

mol

1

1

= 2.0mol

= 2.0mol

= 4.0mol

Cl2C2H4

Its molar mass is known (from gas density)

is known to be 98.96 g. What is its molecular

formula?

We divide by lowest (2mol )

Cl1C1H2 would give an empirical mass of 48.5g/mol

massformulaempirical

massmolarx

g

g

5.48

96.98= 2

2 X Cl1C1H2 = Cl2C2H4

Rebekah

Becky

Mae

gan

Brian

Alexis

Alex

Amanda

Rachel Lauren

Brendan

David

Mackenzie Victoria

DaniEvan

Samantha

Michelle

Chelsea

BraxtonKaylee

Cole

Susan

na

Jessie

Humpty Dumpty’s Downfall

Eggshells are made of mostly ionic compounds such as calcium phosphate, Ca3(PO4)2, which makes them brittle. When broken, eggshells break into many pieces that can’t be put back together again.

Formulas are the language used to give information about chemicals. As a first step in studying this new language, you will learn how to name and write formulas for ionic compounds.

Sodium chloride (NaCl) contains only sodium and chlorine. Potassium iodide (KI) contains only potassium and iodine. Each is an example of a binary compound, which is a compound that contains only two elements.

Binary ionic compounds can have more than one ion of each element, as in CaF2, but they are not composed of three or more different elements.

To name binary compounds,:

First, write the name of the positively (+) charged ion, usually a metal.

Second, add the name of the nonmetal or negatively (-) charged ion.

Third, change the end of the name to -ide.

For example: NaCl

(+) is Na; (-) is Cl

1st: Na = Sodium 2nd: Cl = Chlorine

Write: Sodium Chlorine

Change: -ine to -ide Chloride

Put them together: Sodium Chloride

Naming cations

Naming anions

Some oddballs: Nitrogen --> Nitride

Sulfur --> Sulfide

Try some:

AlCl3 ________________ ___________________

ZnI2 ________________ ___________________

CaF2 ________________ ___________________

CaO ________________ ___________________

Al2O3 ________________ ___________________

Al2O3 CaO CaF2

Sodium chloride contains sodium ions that have a +1 charge and chloride ions that have a -1 charge.

You have learned that compounds are electrically neutral. This means that the sum of the charges in an ionic compound must always be zero. One Na+ balances one Cl- in sodium chloride.

When you write a formula, you add subscripts to the symbols for the ions until the algebraic sum of the ions’ charges is zero.

Example: Ca + F [Ca]2+ + F- + F - [Ca]2+ + 2F- CaF2

Remember, the +’s and the -’s must cancel each other out.

If you have more than one ion of a given element in a compound, the subscript indicates how many ions are present. The subscript is predicted by the charges on the atoms.

Alumina is the common name for aluminum oxide. Aluminum is in group 3, so it has 5 electrons and will lose 3 to become Al3+. Oxygen has 6 valence electrons, so it will gain 2 electrons to become O2-.

Al + O Al3+ + O 2-

Notice that one of aluminum’s 3 electrons has not been taken up by oxygen. Because all the electrons must be accounted for, more than one oxygen atom must be involved in the reaction. But oxygen cannot going only one electron, so a second aluminum atom must be added to give a second electron to oxygen. In all, two Al3+ ions must bond with three O2- ions to form Al2O3. Remember that the charges in the formula for aluminum oxide must add up to zero.

2Al3+ + 3O2- Al2O3

Al + Al + O + O + O Al3+ + Al3+ + O 2- + O 2- + O 2-

The easy way!

Write the formula for an ionic compound containing sodium and sulfur.

Analyze: Sodium is in Group 1, so it has an oxidation number of +1. Sulfur is in group 6, so it has an oxidation number of -2.

Set up: Write the symbols for sodium and sulfur ions in formula form, placing the positive ion first:Na+S2-

Solve: The formula as written has one positive charge and two negative charges. To keep neutrality, one more positive charge is needed to balance the 2- charge. This is done by adding a second sodium to the formula. The correct formula is then written as Na2S.

Check: Check to be sure that you have not changed the charges of the ions and that the overall charge of the formula is zero.

2(+1) + (-2) = 0 The formula is written correctly.

Try these:

Write the formula for each of the following compounds:

1. Lithium oxide

2. Calcium bromide

3. Sodium oxide

4. Aluminum sulfide

Try these:

Write the formula for the compound formed from each of the following pairs of elements:

• Barium and oxygen

• Strontium and iodine

• Lithium and chlorine

• Radium and chlorine

Some ions contain more than one element. These are called polyatomic ions. In a polyatomic ion, a group of atoms is covalently bonded. Although the individual atoms have no charge, the group as a whole has a charge.

The formulas and names of some common polyatomic ions are shown. Although the charge is shown to the right of the formula, it is the whole ion, rather than the last atom listed, that is charged.

To name a compound containing a polyatomic ion, follow the same rules as used in naming binary compounds. Name the positive ion first, followed by the negative ion. However, do not change the ending of the negative polyatomic ion.

Example: Calcium Carbonate (Ca2+CO3

2-), found in TUMS.

Try these:

1. Na2CrO4 _________________ __________________

2. KOH _________________ __________________

3. Mg(NO3) _________________ __________________

4. Ca(C2H3O2) _________________ __________________

5. (NH4)2SO4 _________________ __________________

6. NH4Br _________________ __________________

Write the formula for the compound that contains lithium and carbonate ions.

Analyze: Lithium is in group 1, so it has a +1 charge. According to the table on the previous slides, the carbonate ion has a -2 charge, and its structure is CO3

2-.

Set up: Write the symbols for lithium carbonate in formula form:

Li+ CO32-

Solve: Decide the correct ratio of lithium ions to carbonate ions by looking at their charges. In this case, the sum of the positive and negative charges does not equal zero. Two lithium ions are needed to balance the carbonate ion. Because you cannot change the charges of the ions, you must ass a subscript of 2 to the Li+. The correct formula for lithium carbonate is Li2CO3.

Check: Check to be sure the overall charge is zero:

2(1) + (-2) = 0 The formula is correct.

Writing the formulas for polyatomic ionic compounds is the same as for binary ionic compounds.

Remember, if there is more than one polyatomic ion, use parentheses () around it. If there is only one, no need for ().

Try these:

1. A compound containing ammonium and sulfite ions.

2. A compound containing barium and nitrate ions.

NH4+ SO3

2-

+1 -2

x2

x2

(NH4)2SO3

Ba NO3-

+2 -1

x2

x2

Ba(NO3)2

3. A compound containing calcium and phosphate ions.

4. Write the formula for sodium phosphate.

5. Write the formula for magnesium hydroxide.

6. Write the formula for potassium dichromate.

7. Write the formula for aluminum sulfate.

Transition elements form positive ions, just like other metals, but most transition elements can form more than one type of positive ion. In other words, transition elements can have more than one oxidation number.

Copper (II) sulfate on the left forms a blue crystal. The oxidation number is +2. Copper (I) sulfate on the right forms a black crystal. The oxidation number is +1.

Naming transition compounds is very easy. Follow the same rules you learned for binary and polyatomic ions. Add in the oxidation number between the 2 names in the form of Roman numerals.

Element Ion Chemical Name

Chromium Cr2+ Chromium (II)

Cr3+ Chromium (III)

Cr6+ Chromium (VI)

Cobalt Co2+ Cobalt (II)

Co2+ Cobalt (III)

Copper Cu+ Copper (I)

Cu2+ Copper (II)

Gold Au+ Gold (I)

Au2+ Gold (III)

Iron Fe2+ Iron (II)

Fe2+ Iron (III)

Manganese Mn2+ Manganese (II)

Mn2+ Manganese (III)

Mn7+ Manganese (VII)

Mercury Hg2+ Mercury (I)

Hg2+ Mercury (II)

Nickel Ni2+ Nickel (II)

Ni2+ Nickel (III)

Ni4+ Nickel (IV)

CrO3

Cr2O3

CrO

Try these:

Write the names of the following compounds:

1. Pb(NO3)2 ____________________________________________

2. Mn2O3 ____________________________________________

3. Ni(C2H3O2)2 ____________________________________________

4. HgF2 ____________________________________________

5. CuBr3 _____________________________

6. Co3P2 _____________________________

7. AuI _____________________________

8. WAt2 _____________________________

9. Pt2Ac3 _____________________________

Writing the formula for transition compounds:

Follow the same rules as you did for writing binary or polyatomic ionic compound formulas. The only

difference is that you have to pay attention to the oxidation number.

Try these:

1. Copper (I) and sulfite

2. Tin (IV) and fluoride

3. Gold (III) and cyanide

4. Lead (II) and sulfide.

Naming covalent (molecular) compounds can seem very complex…bur it is actually very systematic.

Substances are either organic (containing carbon) or inorganic (not containing carbon).

Binary Inorganic Compounds contain 2 nonmetal elements bonded covalently.

To name binary inorganic compounds, write out the name of the first nonmetal and follow it with the name of the second nonmetal with its ending changed to -ide.

How do you know which one is first? Which ever one is farthest to the left on the periodic table.

If both elements are in the same group, the first element is the one closer to the bottom. For example, in sulfur dioxide, sulfur is named first because it is closer to the bottom of the table.

Remember, binary compounds, only contain 2 elements, but may contain many atoms. Many different compounds can be formed by the two same nonmetal elements. Binary inorganic compounds have prefixes added to their names to help identify them.

one mono- Here are some basic prefixes you will

two di- see fairly often. Keep in mind, they

three tri- may go all the way up to 10.

four tetra-

five pent- Formula Name

NO nitrogen monoxide

NO2 nitrogen dioxide

N2O dinitrogen monoxide

N2O5 dinitrogen pentoxide

Try naming these:

1. S2Cl2

2. CS2

3. SO3

4. P4O10

5. H2O

6. C2H6

7. SeI2

8. CH2F2

9. CO2

To write the formula for binary inorganic compounds for which you are given the name, first write the symbols for each element in the order they are given. Then add the appropriate subscript for each prefix. Remember that the prefixes tell how many atoms are present in the compound.

For example: sulfur hexaflouride

S 6 F SF6

Try these:

1. Carbon tetrachloride

2. Iodine heptafluoride

3. Dinitrogen monoxide

4. Sulfur dioxide

• Some compounds contain H2O in their struc-ture. These compounds are called hydrates.

• This is different from (aq) because the H2O is part of the molecule (not just surrounding it).

• The H2O can usually be removed if heated.• A dot separates water: e.g. CuSO4•5H2O is

copper(II) sulfate pentahydrate.• A greek prefix indicates the # of H2O groups.

Hydrates

sodium sulfate decahydrate nickel(II) sulfate hexahydrate

Na2CO3•H2O BaCl2•2H2O

Na2SO4•10H2O NiSO4•6H2O sodium carbonate monohydratebarium chloride dihydrate

For more lessons, visit www.chalkbored.com

Naming Acids

Acids are divided into two groups: Binary and Oxyacids. Binary acids consist of two elements. Oxyacids consist of 3 elements, one of which is oxygen.

1. NAMING BINARY ACIDS: The name of the binary acid consists of two words. The first word has three parts:

the “hydro” prefix the root of the nonmetal element the “ic” ending

The second word is always “acid”

Examples: HCl = hydro chlor ic acid = hydrochloric acid HBr = hydro brom ic acid = hydrobromic acid HF = hydro fluor ic acid = hydrofluoric acid

2. NAMING OXYACIDS: These are more difficult to name because these acids have hydrogen, a nonmetal, and may have varying numbers of oxygen atoms. For example, H2SO5, H2SO4, H2SO3, and H2SO2

are all acids. How do we name them? To begin, we need a point of reference. Our reference point is this: The “ate” ions (sulfate, nitrate, etc) make the “ic” acids (sulfuric acid, nitric acid) Examples: SO4

2- = sulfate ion H2SO4 = sulfuric acid

NO3- = nitrate ion HNO3 = nitric acid

Once we have our point of reference, the acid with one more oxygen than the -ic acid is called the per-_________-ic acid. The acid with one less oxygen then the -ic acid is called the ___________-ous acid. If the acid has one less oxygen than the -ous acid, it is called the hypo-____________-ous acid. Examples: H2SO5

= persulfuric acid HNO4 = pernitric acid

H2SO4 = sulfuric acid HNO3

= nitric acid H2SO3

= sulfurous acid HNO2 = nitrous acid

H2SO2 = hyposulfurous acid HNO = hyponitrous acid

Some compounds have common names. For example, NaCl is salt. Would you go into a restaurant and order a glass of dihydrogen monoxide? Probably not. You would order water.

Acids and bases are also known by common names, rather than by their chemical names. Some examples are below:

Formula Name

HCl Hydrochloric Acid

H2SO4 Sulfuric Acid

H3PO4 Phosphoric Acid

HNO3 Nitric Acid

HC2H3O2 Acetic Acid

NaOH Sodium Hydroxide (base)

KOH Potassium Hydroxide (base)

NH3 Ammonia (base)

1.Naming an organic compound requires several steps. What follows is a minimal outline. Consult your textbook for more details and examples. Find the longest continuous chain of carbon atoms. This longest chain may not be written in a straight line.

2.Name that longest chain with the appropriate alkane name.

3.Find the substituents and name each of them with the appropriate group name.

4.Number the carbons in the chain such that the lowest number is given to the group nearest one end of the chain.

5.List the groups alphabetically in front of the longest chain name.

6.Precede each group name with a prefix indicating how many of them are present in the molecule. In front of the prefix, list the numbers of each group in the molecule and separate the numbers with a hyphen.

Naming Alkanes