CHEMISTRY 2010
A. CHEMICAL BONDING
 In elements or compounds, the force holding the particles/atoms together is called a chemical
bond.
 Atoms of elements undergo bonding to achieve an octet configuration, for stability
 3 types of chemical bonds: Ionic bonds, Covalent bonds, Metallic bonds
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IONIC BONDING:
Formed by ions
Atoms lose or gain electrons to form ions – lose electrons to form +ve and -ve ions respectively
All atoms are electrically neutral
Atoms of metals lose electrons to form a positive ion called a CATION [Group I – III]
Atoms of non-metals gain electrons to form a negative ion called an ANION [Group V – VIII]
All ions have the electronic structure of a noble gas.
An ionic bond is a strong electrostatic force of attraction between oppositely charged ions [metal
and non-metal] which hold them close together.
An ionic bond is usually formed when there is transfer of electron(s) from metals to non-metals.
Formula/Nuclide notation of an ion – everything same but put charge at top right hand corner
Drawing of the ionic bond between two or more atoms – different symbols to represent the
electrons, charge at the top right hand and a legend
Ionic compounds: Sodium chloride, Magnesium oxide, Iron (III) oxide
 COVALENT BONDING:
 Formed when electrons are shared between atoms of non-metal
 Difference from ionic bonding: Shared NOT transferred, between NON-METALS not METAL
and NON-METAL :D
 Overlapping of outer electron shells to share electrons, resulting in a covalent bond
 When electrons are shared, both atoms get to count the electrons towards noble gas
configuration.
 Valency is the number of electrons used in bonding.
 When each atom shares ONE electron, a SINGLE covalent bond is formed. H H
Valency: 2
 When each atom shares TWO electrons, a DOUBLE covalent bond is formed and so on. O O
Valency: 4
 Total number of electrons involved = number of bonds x 2
 STRUCTURE OF IONIC COMPOUNDS:
 Studied example – Sodium chloride
 consists of large number of Na+ and Cl- ions arranged in an ORDERLY [alternate] manner
 Ionic compounds have a crystal lattice structure and
 STRONG ionic bonds a.k.a. electrostatic forces of attraction
 Physical properties –
1. HIGH melting and boiling points  solid at r.t.p.
_____ is a giant ionic compound with crystal lattice structure and strong ionic bonds. Thus, large
amounts of energy are needed to break the bonds. Hence, it has high melting and boiling points.
*MUST follow this structure.
2. SOLUBLE in water
Ions ATTRACT the water molecules, hence breaking the crystal lattice structure, causing ions to
separate and dissolve in the solution
3. Conduct electricity in MOLTEN or SOLUTION state
Ions can move freely in the molten state or when in solution and moving ions carry the electric
current. Ionic compounds DO NOT conduct electricity in the solid state as ______ is a giant
ionic compound with crystal lattice structure. Hence, it has no free moving ions to conduct
electricity in the solid state.
Note: Giant ionic compounds with crystal lattice structure and strong ionic bonds has no smell as
large amount of energy is needed to boil and evaporate it, making it non volatile and of no smell.
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1.
STRUCTURE OF COVALENT COMPOUNDS:
Network of atoms held by STRONG covalent bonds
Giant covalent substances have MACROMOLECULAR structure
Example: Diamond; each carbon atom is joined to four others in a tetrahedral arrangement in
diamond. Strong covalent bonds and rigid tetrahedral structure make diamond very hard.
Example: Graphite; carbon atoms are arranged in rings of six on flat layers in graphite.
Intermolecular forces of attraction between layers are weak and so layers can easily slide past
each other, making graphite soft and slippery. Carbon fibre is graphite mixed with other
materials. It is light, stiff and strong. Used to make boats, air/spacecrafts. Carbon nanotube is a
SINGLE layer of graphite rolled into a tube. 50000 times thinner than human hair – extremely
lightweight and strong and conduct electricity better than metals.
Diamond and graphite are allotropes – different forms of the same element
Example: Silicon dioxide/Silicon (IV) oxide, SiO2; also has a tetrahedral structure.
Physical properties –
HIGH melting and boiling points  solid at r.t.p.
_____ is a giant covalent substance was a macromolecular structure and strong covalent bonds.
Hence, large amounts of energy are needed to break these bonds, resulting in high melting and
boiling points.
Diamond melts at 3500oC and boils at 4800oC
2. INSOLUBLE in water
3. DO NO conduct electricity [except graphite]
All outer shell electrons in the atoms are used in bonding and there are no free moving
electrons to conduct electricity. Graphite has ONE extra electron not used in bonding.
 STRUCTURE OF SIMPLE COVALENT MOLECULAR SUBSTANCE:
 Usually liquid or gas or r.t.p.
 Weak intermolecular forces of attraction between molecules and hence, molecules are not held
tightly together
 Physical properties –
1. Usually LOW melting and boiling points
______ is a simple covalent substance with weak intermolecular forces of attraction between
the molecules. Hence, only small amounts of energy are needed to bring the bonds between
them and they have low melting and boiling points.
2. Mostly INSOLUBLE in water
3. DO NOT conduct electricity
Do not have free moving ions OR electrons to conduct electricity.
B. CHEMICAL FORMULAS
C. ACIDS AND BASES
ACIDS
Produce hydrogen ions (H+) when dissolved in
water
Only behave as acids when dissolved in water
ALKALIS
Produce hydroxide ions (OH-) when dissolved
in water
Alkalis are soluble bases [dissolve in water]
Oxides are insoluble bases.
Pure acids are simple covalent molecules
Have a sour taste
Have a bitter taste, soapy feel
IRRITANTS
Turn moist blue litmus paper red
Turn moist red litmus paper blue
Reacts with carbonates and hydrogenReacts with ammonium compounds to
carbonates to produce salt + water + carbon
produce ammonia + salt + water
dioxide. Reacts with MOST metals to produce
hydrogen + salt. (Except silver and gold)
ACID + BASES  SALT + WATER
Hydrochloric acid in stomach, Lactic acid in
Potassium/Sodium hydroxide in soap, Sodium
muscles, Methanoic acid in bee sting/ant bite,
hydroxide in toothpaste, Magnesium hydroxide
Ethanoic/Acetic acid in vinegar
in indigestion relief pills.
Ionization & Concentration
A strong acid/alkali ionizes completely in water while weak acids/alkalis ionize slightly in water.
A concentrated acid/alkali has more acid/alkali molecule in a litre of solution as compared to a
dilute acid/alkali.
Indicators – substances that change colour when put into an acidic or alkali solution.
Universal
pH
Colour
0-2
Red
3-4
Orange
5-6
Yellow
7-9
Green
Methyl Orange
Methyl Orange
0-4: Orange
4-14: Yellow
Methyl Red
0-5: Red
5-14: Yellow
Litmus – changes at pH 7 from blue to red
Phenolphthalein – changes at pH 9 from colourless to pink (fushcia)
pH meter – accurate, objective, fast, precise
10-11
Blue
12-14
Indigo 
purple
pH of common chemicals
pH
Chemical
0-2
Hydrochloric/
Sulfuric acid
3-4
Ethanoic acid
5-6
Rain water
7-9
Pure water
10-11
Ammonia
12-14
Calcium/
Sodium
hydroxide
D. BALANCING CHEMICAL EQUATIONS
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Ensure that there is the same number of atoms on both sides
Check the reaction
When element is a metal, just put one copy of the element
Note: Remember, for non-metals, do not just put one copy, unless they are able to exist as so,
e.g. He.
 Remember the ionic and covalent compounds!