7-1: Chemical Names and Formulas

- Explain the significance of a chemical formula- Determine the formula of an ionic compound formed

between two given ions- Name an ionic compound given its formula- Using prefixes, name a binary molecular compound

from its formula- Using prefixes, name a binary molecular compound

from its formula- Write the formula of a binary molecular compound

given its name

Chemical formula: indicates the relative number of atoms of each kind in a chemical compound For a molecular formula: gives the number of

atoms of each element contained in a single molecule of the compound Ex: hydrocarbon octane

C8H18

Significance of a Chemical Formula

Subscript indicates there are 8 atoms of carbon in a molecule of octane

Subscript indicates there are 18 atoms of hydrogen in a molecule of octane

For an ionic compound: represents one formula unit Formula unit = simplest ratio of the compound’s positive

and negative ions Ex: aluminum sulfate

Al2(SO4)3Subscript 2 refers to 2 aluminum atoms

Subscript 4 refers to 4 oxygen atoms in the sulfate ion

Subscript 3 refers to everything inside the parentheses giving 3 sulfate ions, with a total of 3 sulfur atoms and 12 oxygen atoms

Note: parentheses are used to identify polyatomic ion as one unit

Monatomic ion: ions formed from a single atom Ex: Na+ , Mg2+ , S2- , N3-

By gaining or losing electrons, many main-group elements form ions with noble-gas configurations Ex:

Group 1 lose one electron to give 1+ cation Group 2 lose two electrons to give 2+ cation Group 15, 16, 17 form anions

Not all main-group elements readily form ions Ex: carbon & silicon form covalent bonds

d-block elements form variable charges Ex:

Copper can be Cu+ or Cu2+

Iron can be Fe2+ or Fe3+

Lead can be Pb2+, Pb3+, or Pb4+

Monatomic Ions

Aluminum cation

Strontium cation

Oxide

Bromide

Positive ions (cations) Name of element + cation

Ex: K+ Potassium cationMg2+ Magnesium cationAl3+ ________________Sr2+ ________________

Negative ions (anions) Base of element + -ide ending

Ex: F- FluorideN3- NitrideO2- ________________Br- ________________

Naming Monatomic Ions

Binary compounds: compounds composed of two different elements The total # of positive charges and negative charges

must be equal The formula can be written given the identities of the

compound’s ions Ex: Ions combined = Mg2+ , Br- , Br- Chemical formula =

MgBr2

Binary Ionic Compounds

Writing formulas for ionic compounds:

(Ex: Aluminum bromide) 1. Write the symbols for

the ions (cations first) Al3+ O2-

2. Cross over the charges as subscripts

3+ 2-

Al2 O3

3. Check to make sure total charges are equal.

Al2O3

Calcium sulfide

Ca2+ S2-

Ca2S2

CaS

2 x (+3) = +6 3 x (-2) = -6

Write the formulas for the binary ionic compounds formed between the following elements: 1. Potassium and iodine

KI 2. Magnesium and chlorine

MgCl2 3. Sodium and sulfur

Na2S

You Try!

Nomenclature: naming system Nomenclature of binary compounds involves

combining the names of cations and anions Name cation first, followed by the name of the anion

Ex: Al2O3

1. Name cation first: full name of cation Aluminum

2. Name anion last: base of anion + -ide Oxide

Al2O3 = aluminum oxide

Naming Binary Ionic Compounds

Name the binary ionic compounds indicated by the following formulas: 1. AgCl

Silver chloride 2. ZnO

Zinc oxide 3. CaBr2

Calcium bromide

You Try!

Some elements form two or more cations with different charges Use stock system of naming (usually with d-block elements) Roman numeral represents charge in parentheses

Fe2+ Fe3+

Iron(II) Iron(III)

Ex: Cu2+ + Cl1- CuCl2

Name of cation Name of anion

+ Roman numeral

indicating charge

copper(II) chloride

The Stock System of Nomenclature

Write the formulas and give the names for the following ionic compounds: 1. Cu2+ and Br-

CuBr2 ; copper(II) bromide

2. Pb2+ and Cl-

PbCl2 ; lead(II) chloride

3. Fe3+ and O2-

Fe2O3 ; Iron(III) oxide

You Try!

All but NH4+ (ammonium ion) are negatively charged

Most are oxyanions Oxyanion: polyatomic ions that contain oxygen

Ex: NO3- –nitrate NO2- –nitrite

Most common anions have –ate endings Anion with one less oxygen has –ite ending

Anion with two less oxygen has hypo prefix and –ite ending Anion with one extra oxygen has per prefix and –ate ending

Ex:ClO3

- ClO2- ClO- ClO4

-

chlorate chlorite hypochlorite perchlorate

Compounds Containing Polyatomic Ions

Same as naming for ionic compounds except: Name polyatomic ion as one unit

Ex: AgNO3

silver nitrate

Use parentheses if more than one polyatomic ion present Ex:

Al2(SO4)3 aluminum sulfate

Naming Compounds with Polyatomic Ions

Name the following binary compounds: 1. Na2CO3

Sodium carbonate 2. Ag3PO4

Silver phosphate 3. FeSO4

Iron(II) sulfate

You try!

Recall: Unlike ionic compounds, molecular compounds are composed of individual covalently bonded units, or molecules

Two nomenclature systems to name binary molecules: 1. Stock system for naming

New system– must understand oxidation numbers Oxidation number: a number assigned to an atom in a molecular

compound or molecular ion that indicates the general distribution of electrons among the bonded atoms (7-2)

2. Prefix system Old system – based on numerical prefixes

1. mono- 6. hexa-2. di- 7. hepta-3. tri- 8. octa-4. tetra- 9. nona-5. penta- 10. deca-

Naming Binary Molecular Compounds

Rules for Prefix System of Nomenclature of Binary Compounds:1. Less-electronegative element is given first

First element only gets a prefix if it has more than one Example: P4O10

2. Second element is named by combininga) a prefix indicating the number of atomsb) the root name of the second elementc) the ending -ide

Example: P4O10 = tetraphosphorous decoxide

3. The o or a at the end of a prefix is usually dropped when the word following the prefix begins with another vowel

The Binary Compounds of Nitrogen and Oxygen

Formula Prefix-system name

N2O Dinitrogen monoxide

NO Nitrogen monoxide

NO2 Nitrogen dioxide

N2O3 Dinitrogen trioxide

N2O4 Dinitrogen tetroxide

N2O5 Dinitrogen pentoxide

Name the following molecular compounds: 1. SO3

Sulfur trioxide 2. ICl3

Iodine trichloride 3. PBr5

Phosphorous pentabromide Write formulas for the following molecular compounds:

1. Carbon tetraiodide CI4

2. Phosphorous trichloride PCl3

3. Oxygen difluoride OF2

You Try!

1. Write the formula for the binary ionic compound formed between each of the following pairs of elements:

a) Potassium and sulfurb) aluminum and chlorinec) cesium and sulfur

2. Name the following binary ionic compounds:

a) BaF2

b) AgFc) K3N

3. Write the formula and give the compound name formed between each of the following pairs of ions: (Stock system of nomenclature)

a) Cu+ and O2-

b) Fe3+ and S2-

c) Cu2+ and Cl-

4. Give the names of the following compounds:

a) Ag2S

b) Ba(OH)2

c) NH4NO3

5. Name the following binary molecular compounds:

a) PF5

b) CCl4c) N2O3

6. Write the formulas for the following compounds:

a) Carbon dioxideb) Dinitrogen pentoxidec) Sulfur hexafluoride

Practice Problems