Chemistry Topic 2
Topic 2: Microscopic World (1)
Topic 2.1 Atomic Structure
A. Elements
1. An element is a substance which cannot be broken down into anything
simpler by chemical methods.
2. ___________________________ is the most abundant element in the Earth’s crust.
3. ___________________________ is the most abundant metal in the Earth’s crust.
B. Details for some common elements
Elements needed to familiarize in detail:
Name
Hydrogen
Helium
Lithium
Beryllium
Boron
Carbon
Nitrogen
Oxygen
Fluorine
Neon
Sodium
Magnesium
Aluminium
Silicon
Phosphorus
Sulphur
Chlorine
Argon
Potassium
Calcium
Iron
Copper
Bromine
Iodine
Mercury
Symbol Atomic
no.
H
1
He
2
Li
3
Be
4
B
5
C
6
N
7
O
8
F
9
Ne
10
Na
11
Mg
12
Al
13
Si
14
P
15
S
16
Cl
17
Ar
18
K
19
Ca
20
Fe
Cu
Br
I
Hg
Types
Non-metal
Non-metal
Metal
Metal
Semi-metal
Non-metal
Non-metal
Non-metal
Non-metal
Non-metal
Metal
Metal
Metal
Semi-metal
Non-metal
Non-metal
Non-metal
Non-metal
Metal
Metal
Metal
Metal
Non-metal
Non-metal
Non-metal
State
(r.t.p.)
Gas
Gas
Solid
Solid
Solid
Solid
Gas
Gas
Gas
Gas
Solid
Solid
Solid
Solid
Solid
Solid
Gas
Gas
Solid
Solid
Solid
Solid
Colour
Yellow
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Chemistry Topic 2
Elements just need to memorize the symbols only:
Name
Chromium
Nickel
Cadmium
Platinum
Symbol
Cr
Ni
Cd
Pt
Name
Manganese
Zinc
Tin
Gold
Symbol
Mn
Zn
Sn
Au
Name
Cobalt
Silver
Barium
Lead
Symbol
Co
Ag
Ba
Pb
C. Structure of atoms
1. An atom consists of protons(s) ____, electron(s) ____ & neutron(s) ____.
Particle
Relative mass
Charge
Position
Proton
Neutron
Electron
2. In atoms, electrons move in the shells around a positive nucleus.
(Nucleus contains both protons and neutrons.)
3. The closer the distance between the electrons and the nucleus, the stronger
is the attraction between the electrons and the nucleus.
Electron diagram of Mg atom (12 electrons) is:
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Chemistry Topic 2
D. Electronic arrangement of elements
1. Electrons are filled from the shell nearest to the nucleus and then to the
outermost shell.
2. The arrangement of the first 20 elements are as follows:
Name
Symbol
Atomic no.
Hydrogen
Helium
Lithium
Beryllium
Boron
Carbon
Nitrogen
Oxygen
Fluorine
Neon
Sodium
Magnesium
Aluminium
Silicon
Phosphorus
Sulphur
Chlorine
Argon
Potassium
Calcium
H
He
Li
Be
B
C
N
O
F
Ne
Na
Mg
Al
Si
P
S
Cl
Ar
K
Ca
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Electronic
arrangement
3. For elements having 8 electrons in the outermost shell (octet structure,
except for He, having only _________________________ in the outermost shell), the
elements rarely react to form compounds. They are called _____________________.
4. The atoms of each element try to make their outermost shell
_________________________ in order to gain extra stability.
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Chemistry Topic 2
E. Atomic structure
1.
2. A (mass no.) = no. of protons + no. of neutrons
Z (atomic no.) = no. of protons/ no. of electrons in a neutral atom.
F. Isotopes
1. Definition: Isotopes are atoms of the same element having the same no. of
protons and electrons, but different no. of neutrons.
2. Isotopes of the same elements have:
i. The _________________________________________________ (same no. of protons &
electrons)
(Note: Not the same no. of outermost shell electrons)
ii. _____________________________________________________ (e.g. Different masses)
G. Relative isotopic mass and relative atomic mass
1. Relative isotopic mass
i. The carbon-12 scale: The mass of a 12C atom is defined to have a relative
mass of 12.0000.
ii. A 12C atom is regarded as having a mass of 12 atomic mass unit (a.m.u.)
iii. Mass of 1 H atom = 1 a.m.u. = 1/12 mass of a 12C atom.
2. Relative atomic mass
i. The relative atomic mass of an element is the weighted average of the
relative isotopic masses of all the naturally occurring isotopes of that
element on the 12C = 12.00 scale.
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Chemistry Topic 2
ii. RAM= MA ´ a% + MB ´ b% + MC ´ c%
MA , MB , MC = relative isotopic masses of isotopes A, B & C
a%, b%, c% = relative abundance of isotopes A, B & C
iii. Example:
20 Ne
Isotopes
% Abundance
90.52%
The average atomic mass of Ne:
= (20)(90.52%)+(21)(0.31%)+(22)(9.17%)
= 20.19
Ne
0.31%
21
Ne
9.17%
22
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Chemistry Topic 2
Topic 2.2 Periodic Table
A. The periodic table
1. The periodic table is arranged in the order of _____________________________________
(or increasing no. of protons)
2. Group
The vertical column of elements in the periodic table.
Elements in the same group have _________________________________________________
because they have the ______________________________________________________________.
3. Period
The horizontal row of the elements in the periodic table. Elements in a
period have different chemical properties. Across the period,
i. The _____________________________________ of elements decreases.
(metal ® non-metal)
ii. The _________________________________________ increases. (From forming
cations to anions)
iii. The no. of electron shells remains the same.
B. Group I elements (Alkali metals)
1. They have one electron in the outermost shell.
2. They form __________________________ with charge __________.
3. They easily react with ________________________________________________, so they
must be stored under paraffin oil.
4. They will ___________________________________ because of the low density.
5. Example:
K atom
Na atom
Atomic state:
Attraction
between nucleus
& outermost e- :
React by _______________
C. Group II elements (Alkaline earth metals)
1. They have two electrons in the outermost shell.
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Chemistry Topic 2
2. They form cations with charge ____________.
3. Example:
Ca atom
Mg atom
Atomic state:
Attraction
between nucleus
& outermost e- :
React by _________________
4. Group I metal atoms lose electrons easier than group II metal atoms.
5. For Na & Ca, their reactivity difference cannot be predicted just based on
theory as which the effect of losing less number of electrons or longer
distance between nucleus and outermost shell electrons is the dominant
factor unless we know the result.
D. Group VII elements (Halogens)
1. They have seven electrons in the outermost shell.
2. They form ____________________ anion with charge __________.
3. They are ______________________ and ______________________.
4. Colour become more ____________________ when going down the group.
5. They exist as ___________________________ molecules.
6. Example:
F atom
Cl atom
Atomic state:
Attraction
between nucleus
& outermost e- :
React by _______________
7. At room temp and pressure, fluorine and chlorine are gases, bromine is a
______________________ and iodine is a ___________________.
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Chemistry Topic 2
E. Group 0 elements (Noble gases)
1. They usually have 8 electrons in the outermost shell, except Helium, it
only has 2 electrons in the outermost shell.
2. They are inert because each member has a
_______________________________________.
3. The melting points and boiling points ________________________ down the
group.
4. They are _________________________.
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Chemistry Topic 2
Topic 2.3 Ionic bonding
A. Ionic bonding
1. An ionic bond is formed when ____________________________________________________.
Ionic bond is formed by the ________________________________________________________.
The metal atoms lose electrons to form ________________ while the non-metal
atoms gain electrons to form __________________.
2. It is a _____________________________________________________________ between the
__________________________________. (so ionic compounds have high m.p. / b.p.)
3. Ionic bond is non-directional.
4. Ionic compounds can conduct electricity only when in ________________________
state. It is because in solid state, there are ________________________________________
for the conduction of electricity.
5. Molten state: _________________________________________________________
6. Aqueous state: _______________________________________________________
7. The molten form or the aqueous form of an ionic compound can be used as
an electrolyte (conduct electricity and decomposed at the same time.)
B. Deduction of formulae (ionic compounds)
1. To deduce the formula of an ionic compound, the charges of the ions must be
memorized.
2. For any ionic compounds, overall +ve = overall -ve.
3. The charges and names of common cations:
Charges
Formula
H+
Na+
K+
Name
Hydrogen ion
Sodium ion
Potassium ion
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Chemistry Topic 2
+1
+2
+3
Ag+
NH4+
Li+
Mg2+
Ca2+
Cu2+
Zn2+
Fe2+
Pb2+
Hg2+
Mn2+
Al3+
Fe3+
Cr3+
Silver ion
Ammonium ion
Lithium ion
Magnesium ion
Calcium ion
Copper (II) ion
Zinc ion
Iron (II) ion
Lead (II) ion
Mercury (II) ion
Manganese (II) ion
Aluminium ion
Iron (III) ion
Chromium (III) ion
4. The charges and names of common anions:
Charges
-1
-2
-3
Formula
ClBrOHNO3NO2HCO3MnO4O2S2SO42SO32CO32Cr2O72CrO42PO43N3-
Name
Chloride ion
Bromide ion
Hydroxide ion
Nitrate ion
Nitrite ion
Hydrogencarbonate ion
Permanganate ion
Oxide ion
Sulphide ion
Sulphate ion
Sulphite ion
Carbonate ion
Dichromate ion
Chromate ion
Phosphate ion
Nitride ion
C. Naming ionic compounds
1. Cation is named first before anion, e.g. KOH = potassium hydroxide.
2. For the elements which form cations in 2 or more forms, the charge must be
listed in brackets. E.g. iron(II), iron(III).
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Chemistry Topic 2
D. Drawing electronic diagram
Only need to draw the outermost shell electrons, since outermost shell
electrons are involved in bond forming.
E. Colours of ions in aqueous solution
Name
Copper (II) ion
Iron (II) ion
Chromium (III) ion
Nickel (II) ion
Iron (III) ion
Manganese (II) ion
Permanganate ion
Dichromate ion
Formula
Cu2+
Fe2+
Cr3+
Ni2+
Fe3+
Mn2+
MnO4Cr2O72-
Colour
Blue green
Green
Yellow brown
Very pale pink/colourless
Purple
Orange
F. Migration of ions
1. Dichromate ions (-ve) move to the +ve terminal while copper (II) ions
(+ve) move to the -ve terminal due to electrostatic attraction. (not diffusion)
2. If the polarities of the battery are reversed, the direction of movement of
ions will also be reversed.
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Chemistry Topic 2
Topic 2.4 Covalent bonding
A. Covalent bonding
1. A covalent bond is formed ________________________________________________________.
It is formed by the __________________________________________________________________,
then exist as molecules.
2. Covalent bond is directional.
3. The molecules formed can be an element or a compound.
4. To melt or boil a molecular substance, only the ___________________________________
___________________________ are removed. (not the strong covalent bond)
5. Compounds made of molecules do not conduct electricity, since no
__________________________________.
B. Drawing electronic diagram
1. Only need to draw the outermost shell electrons, since outermost shell
electrons are involved in bonding forming.
2. The atom which requires forming more covalent bonds is drawn as central
atom.
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Chemistry Topic 2
C. Naming covalent compounds
1. The non-metal with smaller group no. or the central atom of a covalent
compound named first before the one with larger group no., e.g. NO =
nitrogen monoxide.
2. Hydrogen is usually named first, such as hydrogen sulphide (H2S), except
ammonia (NH3)
3. For covalent oxides, the no. of oxygen must be shown:
i. 1 O = monoxide
ii. 2 O = dioxide
iii. 3 O = trioxide
D. Formula mass and relative molecular mass
1. Relative molecular mass of a molecule = sum of RAM of all atoms present in
the molecule.
2. Relative formula mass of a pure substance = sum of RAM of all elements in 1
formula unit of the substance.
Note: since all relative masses are just ratio, so no units (g)!
E. Dative covalent bond
1. A dative covalent bond is a covalent bond, but the electron pair is supplied by
one of the bonding atom only.
2. The atom that donates the electron pair is called the electrons pair donor. It
should have at least one unshared electron pair.
3. The atom that gains the electron pair is called the electron pair acceptor.
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Chemistry Topic 2
Topic 2.5 Structure
A. Substances having giant ionic structure
1. All ionic compounds exist as giant lattice (NEVER form molecules)
2. Have high m.p. and b.p. due to ____________________________________________________.
3. Good conductor of electricity in molten and aqueous state, but not in
solid state since there are no _________________________________.
4. Hard (∵ ionic bond is strong between cation and anion), but brittle.
(can be broken easily by mechanical method)
5. ___________________ in water (because H2O molecules are polar), but insoluble in
organic solvents, e.g. CCL4, 1,1,1-trichloroethane, methylbenzene, etc.
B. Ionic crystal
1. Crystals refer to a solid with particles in regular arrangement.
2. Factors affecting the structure of ionic crystal
i. The arrangement of ions within an ionic crystal (lattice) in governed by
a) The ratio of cation to anion to become electrically neutral.
b) Relative sizes of the ions.
ii. Each ion tends to be surrounded by max. number of oppositely charged
ions, so that max. amount of energy can be releases to obtain max.
stability.
3. Structure of NaCl and CsCl
i. Since caesium ion is larger than sodium ion, it can allow greater no. (8) of
Cl- ion to come in closer contact
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Chemistry Topic 2
ii. If caesium chloride has the sodium chloride type of ionic lattice, there
would be a great wastage of space, i.e. less efficient packing.
iii. The caesium chloride lattice consists of two interpenetrating cubic
lattices of Cs+ and Cl- ions.
C. Substances having giant covalent structure
1. Exist in a _______________________ bonded by _________________________ (NEVER form
molecule)
2. Hard (since covalent bond is strong) but brittle.
3. High m.p. and b.p.
4. No mobile electrons or ions to conduct electricity in all states. (except
____________, which has mobile electrons)
5. 3 substances have this type of structure:
i. Diamond
Each carbon atom is bonded to 4 other carbon atoms. Thus breaking
these substances require the breaking of the covalent bonds.
ii. Quartz
Each silicon atom is bonded to 4 oxygen atoms while each oxygen
atom is bonded to 2 silicon atoms.
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Chemistry Topic 2
iii. Graphite
a) Each carbon atom is bonded trigonally to 3 other carbon atoms in
the same layer by identical and directional C-C covalent bonds to
give a planar structure of hexagonal rings.
b) Weak van der Waals’ forces attract planes of carbon atoms
together. Hence, the planes are widely spaced. This accounts for the
lubricating properties of graphite.
c) Electrons are delocalized in between the layers and account for the
electrical conductivity of graphite.
6. ________________ in all solvents.
D. Substances having simple molecular structure
1. Exist in form of ___________________.
2. Low m.p. and b.p., because although the atoms are bonded by strong
covalent bond, the __________________________________________________________
____________________. Changing states just requires the breaking of the weak van
der Waals’ forces.
3. Soft, due to weak van der Waals’ forces.
4. _______________________________________ to conduct electricity at all states.
5. Solubility is higher in ___________________________ than in water (aqueous).
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Chemistry Topic 2
6. The structures of iodine and dry ice (solid CO2) are shown below:
E. Metallic bond (giant metallic structure)
1. When metal atoms lose its outermost shell electrons, the electrons move
around the positive ions.
2. The ______________________________________________________________ hold the structure
together.
3. Metals can conduct electricity in both solid and molten state due to
_______________________________________________.
4. When size of metal atoms decrease, strength of metallic bond _______________.
5. The more the no, of outermost shell electrons involves in metallic bond,
the ______________ is the strength of the bond.
6. Properties of metals
i. High density and hardness – atoms are packed closely together.
ii. High melting point & strength – strong electrostatic attraction between
delocalized electrons and positive ions.
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Chemistry Topic 2
iii. Good conductor of heat and electricity – transferred by delocalized eiv. Malleable and ductile – the layers of atoms can _______________________________
without breaking the metallic bond.
v. Metals have lustre – many metals have shinny appearance, except those
which are reactive, because ____________________________________________________
____________________________________________________________________________________.
F. Comparison of properties between substances if various
structure
Structure
Giant ionic
structure
Giant covalent
structure
Simple
molecular
structure
Giant metallic
structure
Examples
All ionic
compound
SiO2, diamond,
graphite, B, Si
H2O, CO2, I2
All metals
High
Very high
Low
Relatively high
Usually soluble
Insoluble
Usually
insoluble
insoluble
Insoluble
Insoluble
Usually soluble
Insoluble
Hard but brittle
Hard but brittle
Soft
Good in both
molten/
aqueous state
Poor conductor
(except graphite)
Poor conductor
Particles
Types of
bonding /
forces
m.p. and
b.p.
Solubility in
water
Solubility in
organic
solvent
Hardness of
soild
Electrical
conductivity
Only group I
metals are soft
Good in
molten/solid
state
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