Chemical formulas indicate the relative number and type of atoms in a chemical compound or molecule. A chemical formula for an ionic compound represents one formula unit and uses the simplest whole number ratio of ions present. Binary ionic compounds are composed of two elements and the total positive charges must equal the total negative charges. Molecular compounds use a prefix system to indicate the number of atoms of the less electronegative element present. Polyatomic ions are named as units within chemical formulas.

1. Chemical Formulas and chemical compoundsChapter 7.1

2. Objectives: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.Write the formula of a binary molecular compound given its name.

3. Chemical names and FormulasThere are millions of natural and synthetic chemical compoundsCalcium carbonate – limestoneSodium chloride – table saltDihydrogen monoxide – waterThese are their chemical and common namesChemical names help to describe the atomic makeup of the compounds

4. Significance of a Chemical FormulaChemical formulaIndicates the relative number of atoms of each kind in a chemical compound.Molecularformula

5. Indicates the relative number of atoms of each kind in a molecule. (Covalently bonded)C8H18Subscript indicates there are 8 atoms of carbon in a molecule of octaneSubscript indicates there are 18 atoms of hydrogen in a molecule of octane

6. Chemical formula for ionic compoundIonic compound consists of lattice of positive and negative ions held together by mutual attraction.Chemical formula represented by one formula unitSimplest ratio of the compounds positive and negative ionsAluminum sulfate below consists of aluminum cations and sulfate ionsAl2(SO4)3Subscript 3 refers to everything inside the parentheses giving 3 sulfate ions, with a total of 3 sulfur atoms and 12 oxygen atomsSubscript 2 refers to 2 Aluminum atomsSubscript 4 refers to 4 oxygen atoms in the sulfate ionNote: when you only have one of an atom, no subscript is usedNote: parentheses are used to identify polyatomic ion as one unit

7. Monatomic ionsIons formed from a single atomExamplesNa+1 lose one electronMg2+ S2- gain two electronsN-3Cl1-Not all main-group elements readily form ions

8. Examples

9. Carbon & Silicon form covalent bonds

10. d-block elements form variable charges

11. examples

12. Copper, can be Cu+1 or Cu+2

13. Iron, can be Fe+2 or Fe+3

14. Lead, can bePb+2, Pb+3, or Pb+4Naming Monatomic ionsPositive ionsName of elementEx: K+ Potassium Mg+2 Magnesium Al+3 __________ Sr+2 __________Negative ions

15. Base of element + -ide ending

16. Ex: F-1 Fluoride N-3 Nitride O-2 _______ Br-1 _______

17. Binary Ionic CompoundsCompounds composed of two different elementsTotal # of positive charges must be equal to total # of negative chargesWriting formulas, Ex: Aluminum oxideWrite the symbols for ions (Cation first) Al+3 O-2Cross over the charges as subscripts Al2O3Check to make sure total charges are equal, divide by largest number, to give smallest whole-number ratio Al2O3+3-22 x (+3) = +63 x (-2) = -6

18. Naming binary ionic compoundsNomenclatureNaming systemName Al2O3