PAL (IGCSE) – CHEMISTRY
Section 3 Atoms, Elements and Compounds
Atoms, Elements and
Compounds
PAL (IGCSE) Chemistry
Revision Book - Section 3
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PAL (IGCSE) – CHEMISTRY
Section 3 Atoms, Elements and Compounds
Syllabus Content_______________________________
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Section 3 Atoms, Elements and Compounds
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Section 3 Atoms, Elements and Compounds
Syllabus Details________________________________
3. Atoms, elements and compounds
3.1 Atomic structure and the Periodic Table
Core
• State the relative charges and approximate relative masses of protons, neutrons and
electrons
Relative Mass
Charge
Protons
1
+1
Neutrons
1
Neutral
Electrons
1/2000
-1
• Define proton number and nucleon number
Nucleon Number (Mass Number) = Number of protons and neutrons in the nucleus
Proton Number (Atomic Number) = Number of protons in the nucleus
Nucleon Number (Mass number)
A
Z
NOTATION
Chemical Symbol
X
Proton Number (Atomic number)
12 nucleons
EXAMPLE
12
6 protons
6
C
Carbon
The Atom
Nucleus: Protons + Neutrons
Electrons
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Section 3 Atoms, Elements and Compounds
NOTES PAGE
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PAL (IGCSE) – CHEMISTRY
Section 3 Atoms, Elements and Compounds
• Use proton number and the simple structure of atoms to explain the basis of the Periodic
Table (see section 9), with special reference to the elements of proton number 1 to 20
Period table
• Structure based on Proton Number
• Elements ordered by increasing
PROTON NUMBER
• Define isotopes
Isotopes: Elements with the same number of protons but different numbers of neutrons
Example.
Carbon 12 – 6 protons + 6 neutrons
Carbon 14 – 6 protons + 8 neutrons
• State the two types of isotopes as being radioactive and non-radioactive
Two types of isotopes…
Radioactive – will decay to give a new element + an orparticle
Non - radioactive – doesn’t decay
• State one medical and one industrial use of radioactive isotopes
Industrial Usage
Quality Control
Food Sterilization
Sheet metal
Beta Source
unsterilised
Gamma Source
sterilised
detector
Hydraulic
ram


Electronic instructions
to adjust rollers.
Food sterilization to prolong shelf life
Quality control – measuring the thickness of materials in production
Medical Usage

Treatment of cancer - the emitted radiation kills cancer cells
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Section 3 Atoms, Elements and Compounds
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PAL (IGCSE) – CHEMISTRY
Section 3 Atoms, Elements and Compounds
• Describe the build-up of electrons in ‘shells’ and understand the significance of the noble
gas electronic structures and of valency electrons (the ideas of the distribution of electrons in
s and p orbitals and in d block elements are not required.) Note: a copy of the Periodic Table,
as shown in the Appendix, will be available in Papers 1, 2 and 3)
Electron Configuration
Electron configuration up to 20
electrons
1st Shell: 2 electrons
2nd Shell: 8 electrons
3rd Shell: 8 electrons
4th Shell: 2 electrons
Nucleus
1st
2nd
3rd
4th
Electrons
Shells
Noble gas electron structure: The most stable configuration of electrons when
bonding
Valence electrons: The electrons in the outer shell
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Section 3 Atoms, Elements and Compounds
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Section 3 Atoms, Elements and Compounds
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Section 3 Atoms, Elements and Compounds
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PAL (IGCSE) – CHEMISTRY
Section 3 Atoms, Elements and Compounds
3.2 Bonding: the structure of matter
Core
• Describe the differences between elements, mixtures and compounds, and between metals
and non-metals
Element:
Mixture:
Compound:
Metals:
Non-Metals:

Consists of only one type of atom



Easily separated
No chemical bonds between different parts of the mixture
Properties of mixtures are a mixture of the properties of the
separate parts




Two or more elements
Chemically bonded
Very difficult to separate into original components
Properties of compounds are completely different to their
original elements



Shiny
Good conductors of heat and electricity
Metallic bonding



Don’t conduct electricity (except carbon – graphite)
Dull
Poor conductors of heat
Elements
Mixture
Compounds
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Section 3 Atoms, Elements and Compounds
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PAL (IGCSE) – CHEMISTRY
Section 3 Atoms, Elements and Compounds
• Describe an alloy, such as brass, as a mixture of a metal with other elements
ALLOYS:
EXAMPLES:

Mixtures of metal with other elements




Steel = Iron + Carbon
Bronze = Copper + Tin
Solder = Tin and Lead
Brass = Copper + Zinc
3.2 (a) Ions and ionic bonds
Core
• Describe the formation of ions by electron loss or gain
Ion Formation
Gaining Electrons
+
Cl
Cl-
Losing Electrons
+
Na
Na+
• Describe the formation of ionic bonds between elements from Groups I and VII
Ionic Bonding
Cl
Cl
x
x
+
Na
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Na
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Section 3 Atoms, Elements and Compounds
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PAL (IGCSE) – CHEMISTRY
Section 3 Atoms, Elements and Compounds
3.2 (b) Molecules and covalent bonds
Core
• Describe the formation of single covalent bonds in H2, Cl2 , H2O, CH4 and HCl as the sharing
of pairs of electrons leading to the noble gas configuration
Covalent Bonding
Chlorine Gas: Cl2
xx
x
Cl
Hydrogen Gas: H2
xx
Cl
xH
H
xx
1 pair of shared electrons
= single covalent bond
1 pair of shared electrons
= single covalent bond
Methane Gas: CH4
Hydrochloric Acid: HCl
Water: H2O
H
x
H
x
C
x
Cl
O
x
H
H
H
x
H
H
2 pairs of shared electrons
=2 x single covalent bond
4 pairs of shared electrons
=4 x single covalent bond
1 pair of shared electrons
=1 x single covalent bond
• Describe the differences in volatility, solubility and electrical conductivity between ionic and
covalent compounds
Property
Volatility
Solubility
Electrical conductivity
Ionic compound
Very low
Soluble in water
Conduct when molten or in
solution
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Covalent compound
Normally high
Normally insoluble in water
Insulators
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Section 3 Atoms, Elements and Compounds
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PAL (IGCSE) – CHEMISTRY
Section 3 Atoms, Elements and Compounds
Conduction in Ionic Materials
+ - +
-
ol
i ss
D
+
Ions FREE to move
CAN conduct electricity
n
vi
g
Ions fixed in Position
Ions can NOT move
Can NOT conduct Electricity
+
- + - - + +
+
+
Molten
Melting
Solid
-
+
+
O
H
O
H
H
H
- +
H
-
-
-
O
+
-
+
Solution
H
+
-
Supplement
• Describe the formation of ionic bonds between metallic and non-metallic elements
Ionic Bonding
2-
NON-METAL
O
x
O
x
2+
x
Mg
x
Mg
METAL
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Section 3 Atoms, Elements and Compounds
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PAL (IGCSE) – CHEMISTRY
Section 3 Atoms, Elements and Compounds
• Describe the lattice structure of ionic compounds as a regular arrangement of alternating
positive and negative ions
Ionic Giant Structure
-ve ion (e.g. Cl-)
Non-metal
+ve ion (e.g. Na+)
Metal
3.2 (c) Macromolecules
Core
• Describe the giant covalent structures of graphite and diamond
Giant Covalent Structures
Diamond
Graphite
• Relate their structures to the use of graphite as a lubricant and of diamond in cutting
Diamond:
 One giant covalent structure with very strong bonds between all carbon atoms
 Very hard substance – so suitable for cutting
Graphite:
 Weak bonds between the covalently bonded layers
 Layers can easily slide over each other – so suitable as a lubricant
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Section 3 Atoms, Elements and Compounds
NOTES PAGE
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PAL (IGCSE) – CHEMISTRY
Section 3 Atoms, Elements and Compounds
Supplement
• Describe the electron arrangement in more complex covalent molecules such as N2, C2H4,
CH3OH and CO2
Ethene: C2H4
Methanol: CH3OH
H
H
H
C
C
H
C
O
H
x
H
H
C
x x
x x
Carbon Dioxide: CO2
O
x
x
x
O
H
Nitrogen Gas: N2
N
x
x
x
N
xx
• Describe the macromolecular structure of silicon(IV) oxide (silicon dioxide)
Silicon (IV) Oxide (Silicon Dioxide)
Silicon (IV) oxide:
 Giant covalent structure
 Each silicon or oxygen atom bonded to a number of other atoms
 Substance is hard
3.2 (d) Metallic bonding
Supplement
• Describe the similarity in properties between diamond and silicon(IV) oxide, related to their
structures
Similar properties
 Very high melting point
 Very hard
Similar structure
 Giant covalent
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Section 3 Atoms, Elements and Compounds
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PAL (IGCSE) – CHEMISTRY
Section 3 Atoms, Elements and Compounds
• Describe metallic bonding as a lattice of positive ions in a ‘sea of electrons’ and use this to
describe the electrical conductivity and malleability of metals
Metals GIANT Structure
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
Free electrons (-ve)
Metal Atoms (+ve ions)
Conduction in Metals:
 Free electrons (sea of electrons) surround the metal lattice
structure
 These electrons are free to move when a potential difference is
applied
 Metals are therefore good conductors of electricity
Malleability of metals:
 Metals are very malleable – they can be easily rolled into thin
sheets
 This is because the regular array of metal atoms can easily slide
over one another
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