1. Solubility and chemical equations Chapter Two

2. Isotopes Isotopes are atoms of the same element with the same number of protons but different number of neutrons. Isotopes have the same chemical properties as the electrons in isotopes are similar. Isotopes have slightly different physical properties due to differing relative masses. Example : Chlorine-35 and Chlorine-37

3. Cations and Anions Metals from cations (positively charged ions) by losing electrons. Formation of cations : (Sodium) Na [Na] + Non-metals form anions (negatively charged ions) by gaining electrons. Formation of anions : (Oxygen) O [O] 2-

4. Molecules of elements Here are a few common examples Hydrogen – H2 Oxygen – O2 Nitrogen – N2 Chlorine – Cl2 Bromine – Br2 Phosphorus – P 4 Sulphur – S 8

5. Polyatomic Ions Polyatomic ions are ions of grouped atoms Here are a few common examples Nitrate – NO3- Hydroxide – OH - Carbonate – CO32- Sulphate – SO42- Phosphate – PO43- Ammonia – NH3+ Ammonium – NH4+

6. Ionic bonding Ionic bonding between metals and non-metals is formed by electrovalent bonds. Examples : Na ++ Cl-[Na]++ [Cl]-Na Cl Mg 2++ Cl -[Mg] 2++ 2[Cl]- Mg Cl2 Notice that the ions of both elements are swapped to become the chemical formula of the compound. This also applies to covalent compounds.

7. Covalent bonding Non-metals share electrons to create covalent bonding between one other. Examples : H-+ O2-[H]1+1=2 [O]6+2=8 H2O C4-+ H-[C]4+4=8 [H]1+1=2 CH4 Although the formation of the chemical formula is the same as ionic compounds, the method of bonding is different. Both atoms gain electrons through sharing.

8. Chemical Equations Lithium burns in bromine to form lithium bromide. Li + Br Li Br Nickel (II) carbonate decomposes on heating to form nickel (II) oxide and carbon dioxide. Ni CO3Ni O + CO Sometimes, chemical equations have to balanced to be complete.

9. Balancing Equations Nitrogen reacts with oxygen to form nitrogen monoxide. N2+ O2 2 NO Silver nitrate decomposes on heating to form silver, nitrogen dioxide and oxygen. 2 AgNO32 Ag + 2 NO2+ O2 Iron (III) sulphate reacts with sodium hydroxide to form rubidium nitrite and oxygen. Fe (SO4)3+ 6 Na OH 2 Fe (OH) 3+ 3 Na2 SO4

10. Soluble elements Definite solubility Ammonium salts Sodium salts Potassium salts Nitrates

11. Soluble elements Solubility with exceptions Chlorides except Lead (II) and Silver Sulphates except Barium, Calcium and Lead (II)

12. Insoluble salts Carbonates except other soluble salts Hydroxide except other soluble salts and Calcium Oxides except other soluble salts and Calcium