1. Unit 1 Lesson 2 Chemical Compounds

2.  Valency: It is the number of electrons that an atom gained, lost or even shared during a chemical reaction

3. Metal Valency Metal Valency Metal Valency Lithium(Li) Potassium (K) Sodium (Na) Silver(Ag) Copper I(Cu) Monovalent Calcium(Ca) Magnesium (Mg) Iron П (Fe) Lead(Pb) CopperП (Cu) Mercury(Hg) Divalent Aluminium (Al) Gold (Au) Iron III (Fe) Trivalent The Valency of Metals

4. Non-metalValencyNon-metalValency Hydrogen H Chlorine Cl Flourine F Bromine Br Iodine I Monovalent Sulphur S Carbon C Tetravalent Sulphur S Oxygen O Divalent Nitrogen N Phosphorous P Pentavalent Nitrogen N Phosphorous P Trivalent Sulphur S Hexavalent The Valency of Non- Metals

5. The valency of nobel gases is zero because their outer electron shell is completely filled with electrons (have 8 electrons) [except (2 He) has 2 electrons]. Sulphur (S) is divalent, tetravalent and Hexavalent. Nitrogen (N) is trivalent and pentavalent. Phosphorus (P) is trivalent and pentavalent.  Some non-metals have more than one valency such as

7. MonovalentDivalentTrivalent Hydroxide (OH) - Bicarbonate (HCO 3 ) - Nitrate (NO 3 ) - Nitrite (NO 2 ) - Ammonium (NH 4 ) + Sulphate (SO 4 ) -2 Carbonate (CO 3 ) -2 Phosphate (PO 4 ) - 3 The Valency of Atomic group

8. Chemical formula: It is a formula that represents the number and the type of the atoms in the molecule.

9.  How to write a chemical formula for a compound ? 1. Write the name of the compound in words. 2. Write the symbol of each element or atomic group down to the name. 3. Write the valency down to each symbol. 4. Exchange their valencies and simplify them (shortened as much as possible) 5. You don't have to write the one (1)

10. Types of compounds: 1- Acids 2- Bases (alkalis) 3- Oxides 4 - Salts

11. 1- Acids: Substances dissociate in water producing positive hydrogen ions (H + ) Examples: Hydrochloric acid (HCl) Sulphuric acid (H 2 SO 4 ) Nitric acid (HNO 3 ) - properties of acids: They have a sour taste They change the colour of litmus paper into red due to the presence of the positive hydrogen ions(H + ) The chemical formula off all minerals acids begin with hydrogen

12. 2- Bases: Substances dissociate in water producing negative hydroxide ions (OH-) Examples: Sodium hydroxide (NaOH) Potassium hydroxide (KOH) Calcium hydroxide Ca(OH)2 -properties of bases: Their aqueous solutions have bitter taste They change the colour of litmus paper into blue due to the presence of the negative hydroxide ions (OH-) The chemical formula off all bases end with (OH-)

13. 3- Oxides: They are compounds resulted from the combination between oxygen and element even though it’s metal or non metal. Metal oxidesNonmetal oxides Sodium oxide (Na 2 O)Carbon dioxide (CO 2 ) Calcium oxide (CaO)Sulphur trioxide (SO 3 ) Aluminium oxide (AL 2 O 3 )

14. Positive ion with negative ion Positive ion with negative atomic group Positive atomic group with negative ion Positive atomic group with negative atomic group Sodium chloride NaClSodium nitrate NaNO 3 Ammonium chloride NH 4 Cl Ammonium carbonate ( NH 4 ) 2 CO 3 Lead bromide PbBr 2 Magnesium carbonate MgCO 3 Ammonium bromide NH 4 Br 4- Salts: They are compounds resulted from the chemical combination of a positive ion (or positive atomic group) with a negative non-metallic ion except oxygen (or negative atomic group)