1. Using symbols to write formulas Chapter 7
Chemical Formulas
Using symbols to write formulas Chapter 7

2. Chemical formula Two purposes:
1. To indicate the composition of a compound
2. To indicate the number of atoms in one molecule of an element

3. Monatomic vs Diatomic
Monatomic-one atom molecules eg He, Ne, Ar, Kr, Xe, Ra
Diatomic- two atom molecules eg H2, O2, N2, Cl2, F2, Br2, I2

4. Kinds of Formulas
Empirical formula-indicates the simplest whole-number ratio in which the atoms of the elements are present in the compound
Molecular formula-shows the number of atoms of each element in one molecule of the substance

5. Kinds of Formulas(cont)
Structural formula- shows the way in which atoms are joined together in a molecule.

6. Types of compounds Ionic compound- transfer of valence electrons
Molecular compound- two kinds covalent compounds sharing of electrons and metallic compounds a bond between two metals

7. Ionic signs
Superscript- defines charge or how many more protons than electrons if it is a positive charge; and how many more electrons than protons if it is a negative charge
Cations- are positive ions
Anions- are negative ions

8. Ionic signs cont
Subscripts- tell the number of ions in the compound of each element
May not always be there may be understood to be one
Are the only thing to be changed in writing a formula

9. Rules for binary ionic compounds
1. Write the symbols for the two elements in the compound placing the symbol for the cation first
2. Determine the charge on the atoms of each element. Two sources of this information A. The charges can be obtained from a table B Infer charge from its position on PT

10. Rules (cont)
3. From the known charges on the ions select subscripts that will make the total positive charge equal to the total negative charge so that the compound as a whole is electrically neutral

11. Rules (cont)
4. When using subscripts with polyatomic ions, the formula of the ion is placed in parentheses and the subscript is placed outside the parentheses

12. Naming Ionic Compounds
Cation name is usually simply the name of the metal
The name of the anion is the name of the nonmetal altered by adding suffix of -ide to a root word
Cation is named first then anion

13. Two naming systems Traditional system- makes use of suffixes.
Suffix –ous is added to the latin root of the metallic ion that has the lower charge
Suffix-ic to the latin root of the metallic ion that has the higher charge

14. Examples for Traditional system
Copper, iron, mercury, lead, tin,

15. Stock System of Naming
Is a newer system for naming ions of metals that form two kinds of ions. With the stock system the name of the ion is simply the name of the metal followed by a Roman numeral in parenthesis.

16. Naming Molecular Compounds
Usually the positive charge comes first
Two systems again
Traditional uses prefixes to separate the names: Mono=1; Di = 2; Tri =3; Tetra = 4 penta = 5; hexa= 6; hepta = 7 ;
Octa = 8; Nona(o) = 9; deca = 10

17. Naming molecular compounds
Stock system- the roman numeral is used to show the apparent charge on the atom with the positive oxidation number

18. Assignment Copy down figure 7-20 page 163 And column F page 164
Copy table 7-22 page 165
Figure 7-23 page 167
Figure page 167