ADDITIONAL SCIENCE FORM 5

CHAPTER 2: CHEMICAL REACTION

2.1 IONIC COMPOUNDS

Ionic compound is formed by the transfer of one or more electrons from the outer shell of a metal atom to the outer shell of a non-metal atom.

2.1 IONIC COMPOUNDS

Positive ion Formula Hydrogen ion H+

Lithium ion Li+

Sodium ion Na+

Potassium ion K+

Magnesium ion Mg2+

Calcium ion Ca2+

Lead (II) ion Pb2+

Copper (II) ion Cu2+

Aluminium ion Al3+

2.1 IONIC COMPOUNDS

Negative ion Formula Fluoride ion F-

Chloride ion CI-

Bromide Br-

Hydroxide ion OH-

Nitrate ion NO3-

Sulphate ion SO42-

Carbonate ion CO32-

Oxide ion O2-

2.1 IONIC COMPOUNDS

The formation of an ionic compound involves a metal atom and a non-metal atom. An ionic bond is the electrostatic force of attraction between 2 oppositely-charged ions.

2.1 IONIC COMPOUNDS

Formation of sodium chloride1. The electron configuration of sodium atom is 2.8.1. 2. Sodium atom loses one valence electron to achieve a stable octet valence electron configuration. Sodium ion, Na+ is formed. Na Na+ + e-

2.1 IONIC COMPOUNDS

3. The electron configuration of chlorine atom is 2.8.7. 4. Chlorine atom accepts the electron that is lost by sodium atom to achieve a stable octet valence electron configuration. Chloride ion, CI- is formed. CI + e- CI-

2.1 IONIC COMPOUNDS

5. The oppositely-charged ions are attracted to each other by an ionic bond. [ Na ] + [ CI ] [ Na ]+ [ CI ]-

2.1 IONIC COMPOUNDS

Formation of magnesium fluoride1. The electron configuration of magnesium atom is 2.8.2. 2. Magnesium atom loses 2 valence electrons to achieve a stable octet valence electron configuration. Magnesium ion, Mg2+ is formed. Mg Mg2+ + 2e-

2.1 IONIC COMPOUNDS

3. The electron configuration of fluorine atom is 2.7. 4. 2 fluorine atoms accept 2 electrons lost by magnesium atom to achieve stable octet valence electron configuration. 2 fluoride ions are formed. F + e- F-

2.1 IONIC COMPOUNDS

5. The oppositely-charged ions are attracted to each other by an ionic bond. [ Mg ] +2[ F ] [ Mg ] 2+ [ F ]-

2

2.1 IONIC COMPOUNDS

To determine the formula of an ionic compound, the charges of the cation and anion are interchanged. Al3+ CI-

Al Cl3

2.2 REDOX REACTION

Redox is a chemical reaction that involves both oxidation and reduction.

Oxidation Reduction In terms of oxygen

Gain of oxygen Loss of oxygen In terms of electron

Loss of electron Gain of electron

2.2 REDOX REACTION

Magnesium is oxidised to magnesium oxide because it has gained oxygen.Carbon dioxide is reduced to carbon because it has lost oxygen.

2 Mg + CO2 2MgO + C Gain of oxygen - Oxidation

Loss of oxygen – Reduction

2.2 REDOX REACTION

Magnesium is a reducing agent.Carbon dioxide is an oxidising agent.

2 Mg + CO2 2MgO + C

Magnesium is a reducing agent because it causes CO2 to be reduced to C

CO2 is an oxidising agent because it causes magnesium to be oxidised to MgO

2.2 REDOX REACTION

Sodium is said to be oxidised because sodium atom has lost one electron in its valence shell to form sodium ion.

2 Na + CI2 2NaCI Loss of electron - Oxidation

Gain of electron - Reduction

2.2 REDOX REACTION

Chlorine is said to be reduced because chlorine molecule has accepted electron in its valence shell to form chloride ion.

2.2 REDOX REACTION

A chemical cell produces electricity from a chemical reaction. It consists of 2 electrodes immersed in an electrolyte. Electrode - the substance that conduct electricity Electrolyte - solution that conducts electricity

2.2 REDOX REACTION

Chemical cell

When the needle of the voltmeter deflects to the left, this indicates that iron plate is the negative terminal and

copper plate is the positive terminal

Copper (II) ion accepts 2 electron and is reduced to copper atom

Half-cell reaction for reduction:Cu2+ + 2e- Cu

Ionic equation for the chemical cell:Fe + Cu2+ Fe2+ + Cu

2.2 REDOX REACTION

K NaCaMgAl ZnFeSn PbCu HgAg Au

Decreasing electropositivity

Easiest to lose electron

Hardest to lose electron

2.2 REDOX REACTION

Application of redox

reactions

Chemical cells- Produces

electricity from a chemical reaction

Electroplating- Coating a

metal with a less

electropositive metal

Electrochemical protection

- Preventing corrosion by attaching a

more electropositive metal to a metal that is needed to be protected

Metal extraction- Process of separating a

metal from its impurities

2.2 REDOX REACTION

Chemical cell

2.2 REDOX REACTION

Types of chemical cell Uses

Lead-acid accumulator Automobiles

Lead (IV) oxide

2.2 REDOX REACTION

Types of chemical cell Uses

Alkaline cell Camera, walkman

Manganese (IV) oxide (positive

terminal)

Separator

Electrolyte

Zinc powder (negative powder)

2.2 REDOX REACTION

Types of chemical cell Uses

Dry cell Radio, torch light

Zinc (negative terminal)

Graphite rod (positive terminal)

Electrolyte

2.2 REDOX REACTION

Types of chemical cell Uses

Mercury cell Calculator

Mercury (II) oxide (positive terminal) Zinc (negative terminal)

Electrolyte

2.2 REDOX REACTION

Types of chemical cell Uses

Nickel-cadmium cell Laptop computers, handphones

Nickel (IV) oxide (positive terminal)

Cadmium (negative terminal)

Separator

Separator