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Chemical formulas – a group of chemical symbols and numbers that represent the number of atoms of each element that make up a compound . ( H2O)

In a chemical formula, the element with the positive charge is always written first.

Chemical Formulas

Subscript – the number that shows how many atoms of an element are in the compound.Examples H20, CO2

The number 2 is the subscript in each.

Subscripts

Valence number – The number of electrons an atom needs to gain, lose, or share to become stable.

(Gain electrons – negative valence)

(Lose electrons – positive valence.)

Valence Numbers

Binary Compound – a compound composed of ONLY2 elements.

Polyatomic Ion- a group of positively or negatively charged covalently bonded atoms.

How to Write Formulas1. Write the symbol correctly for both elements.2. Write the valence number above each symbol. Make sure you have a positive first, and then a negative.3. Criss-cross valences to make a subscript.4. NEVER write 1 as a subscript. (It is understood to be 1 if there is no number.)5. Reduce to lowest terms.

• Sodium Chloride Aluminum Oxide

• Copper (I) Sulfide Iron (III) Iodide

Examples

Aluminum Bromide Magnesium Nitride

Calcium Iodide Potassium Sulfide

Copper (I) Chloride Barium Fluoride

Hydrogen Oxide Lead Bromide

Practice Problems

Aluminum Bromide Magnesium Nitride AlBr3 Mg3N2Calcium Iodide Potassium Sulfide CaI2 K2SCopper (I) Chloride Barium Fluoride CuCl Ba F2Hydrogen Oxide Lead Bromide H2O PbBr2

Check your Work

1. Lead Iodide 2. Barium Fluoride

3. Tin (II) Nitride 4. Lithium Chloride

5. Sodium Bromide 6. Iron (II) Oxide

• 7. Potassium Fluoride 8. Silver Bromide• 9. Calcium Chloride 10. Copper (I) Iodide• 11. Aluminum Nitride 12. Cobalt (II) Sulfide

Practice Problems

7. Potassium Fluoride 8. Silver Bromide

9. Calcium Chloride 10. Copper (I) Iodide

11. Aluminum Nitride 12. Cobalt (II) Sulfide

Calcium Phosphate

Tin (IV) Chromate

Ammonium Oxide

Magnesium Sulfate

1. Change the ending of the second element to – “ide”.

(Do not change the names of polyatomic ions.)

2. Check to see if Roman numeral is needed.Ex: NaCl - Sodium Chloride

Fe2O3 – Iron (III) Oxide

Naming Compounds

• 1. PbI2 2. BaF2• 3. Sn3N2 4. LiCl• 5. NaBr 6. FeO• 7. KF 8. AgBr• 9. CaCl2 10. CuI• 11. AlN 12. CoS

Practice Problems

Homework Check1. K2O 6. Ca3(PO4)2

2. NaC2H3O2 7. FeBr2

3. Ag2SO4 8. HClO3

4. ZnCO3 9. MgSO3

5. CrS 10. (NH4)3PO4

Homework CheckCd CrO4 Cu(ClO3)2Al2O3 PbC2O4FePO4 KClO3AgNO3 SnS2NaClO2 SbCl5ZnI2 Li3PO4

Homework Check

1.Ammonium Phosphate 2. Iron (ll) Bromide 3. Hydrogen Chlorate 4. Sodium Acetate 5. Silver Sulfate 6. Chromium (lll) Sulfide 7. Potassium Oxide 8. Tin (ll) Oxide 9. Hydrogen Oxide10. Antimony (III) Phosphate

Predicting Reactions between Elements

To form an ionic bond, a metal bonds to a non-metal.

Metals to the left of stair-step line except H.Non-metals to the right of stair-step line, except H

Metalloids along stair-step except Al which is a metal.

Properties of compounds.

• See handout and p. 288 in textbook.

Naming Compounds Examples

• Zn3N2 ______________________

• K2SO3 ______________________

• CuO ______________________

• Ba(C2H3O2)2 _____________________

Homework check1.Iron (ll) Hydroxide 2. Aluminum Perchlorate 3. Chromium (ll) Acetate 4. Tin (lV) Chloride 5. Lead Chromate 6. Copper (ll) Sulfide 7. Potassium Hypochlorite 8. Mercury (ll) Dichromate 9. Calcium Hydroxide10. Tin (ll) Sulfite

Homework check11. Zinc Phosphate12. Barium Fluoride13. Sodium Nitrate14. Cadmium Carbonate15. Mercury (ll) Peroxide 16. Iron (lll) Sulfite17. Antimony (V) Oxide 18. Copper(l) Permanganate19. Chromium (lll) Oxalate20. Ammonium Sulfate

Homework checkChlorine - nonmetal Aluminum - metalBoron - metalloid Calcium - metalZinc - metal Hydrogen - nonmetalNeon - nonmetal Nickel - metalSodium - metal Magnesium - metalSilver - metal Fluorine - nonmetalSilicon - metalloid Potassium - metalHelium - nonmetal Uranium - metalBromine - nonmetal Carbon - nonmetalFrancium - metal Argon - nonmetal

1.Ammonium Phosphate 11. Manganese(ll) Oxide2. Iron (ll) Bromide 12. Tin (lV) Iodide3. Hydrogen Chlorate 13. Calcium Oxide 4. Sodium Acetate 14. Potassium Chloride5. Silver Sulfate 15. Copper (l) Hydroxide6. Chromium (lll) Sulfide 16. Ammonium Sulfide7. Potassium Oxide 17. Aluminum Carbonate8. Tin (ll) Oxide 18. Hydrogen Sulfite9. Copper (ll) Phosphate 19. Iron (lll) Sulfate10. Zinc Sulfate 20. Aluminum Nitride