form 4 chap 3 exercise w ans

1. Periodic Table of Elements
Historical
Development of the
Periodic Table
Electron Arrangement
& Arrangement of
Elements
Group
Characteristics
Period
Transition
Elements
Group 1 Group 17 Group 18

2. Scientists Discoveries
1 Atoinne
Lavoiser
(1743 – 1794)
-In 1789, first Chemist try to classify the substance, include the light &
heat into metals & non-metals.
-Unsuccessful bcoz light, heat & a few other compounds were also
considered as elements
2 Johann W
Dobereiner
(1780 – 1849)
-In1829,he divided the elements into the groups of 3 elements with
similar chemical properties
-Known as Dobereiner’s Traid
-The atomic mass of the middle element was approximately the
average atomic mass of the other 2 elements in each traid.
-Traid system was confined to some elements only.
-Led chemists to realise that there was a relationship between the
chemical properties & the atomic mass of each element.
3 John Newlands
( 1837-1898)
-From 1864 – 1865, he arranged the elements in order of increasing
atomic mass.
-Elements with similar properties recurred at every 8 element.

3. -known as the Law of Octaves.
-Failure bcoz the Law of Octaves was obeyed by the 17 first elements
only.
-Shows the existence of a periodic pattern for the properties of
elements.
4 Lothar Meyer
(1830-1895)
-In 1870 , he plotted graph of the atomic volume against the atomic
mass.
-Realised that elements with similar chemical properties occupied
equivalent positions on the curve.
-He found that the properties of the elements formed a periodic pattern
against their atomic masses.
5 Dmitri
Mendeleev
(1834-1907)
-In 1869, he arranged the elements in order of increasing atomic mass
& grouped them according to similar chemical properties in vertical
coloum.
-He left gaps (empty spaces) in the table to be filled by undiscovered
elements.

4. -He was able to predict the properties of undiscovered elements.
6 Hendry J.G.
Moseley (1887-
1915)
-In 1914,he studied the X-ray spectrum of elements.
-From experiment, he concluded that proton number should be the
basic for the periodic change of chemical properties instead of the
atomic mass.
-He arranges the elements in order of increasing proton number in the
Periodic Table. Thus, he confirmed the works / Mendeleev.
-The modern Periodic Table based on the foundation of Henry J.G
Moseley.

5. 1) Arranged according to ascending proton number of the element.
2) 1-18 called Group. 1-7 called periods

6. Group
1) Group arranged according to the number of valence electron in the outermost
shells.
2) All elements in a group
a) Have the same valence electrons
b) Have the same chemical properties
c) Physical properties will change as we go down the group.
3) Groups have special names.
Group Name
1 Alkali metals
2 Alkaline earth metals
17 Halogens
18 Inert (noble) gases
3-12 Transition metals
4) Group 1,2,13 & transition elements are metals. Group 15-18 are non-metals.
Group 14 has 2 non-metals ( carbon& silicon)

7. Period
1) Period arranged according to the number of shells occupied with electron in an
atom.
2) Elements in period 1 – 7
Period Number of elements
Period 1 2 elements
Period 2 & 3 8 elements
Period 4 & 5 18 elements
Period 6 32 elements
Period 7 23 lements

8. Electrons Arrangement
1) Number of filled electron shells increases, as we go down the group.
2) By knowing the proton number of the element, we can determine the group &
period it’s placed in.
3) Relationship between number of valence electrons with the group number of an
element.
No.of valence
electrons
1 2 3 4 5 6 7 8 (second 8. First 8 is in
transition elements
except helium)
Group 1 2 3 14 15 16 17 18
9) Number of electrons = number of protons
10) The number of shells = period
11) Valence electron = group

9. 12) Maximum number of electron which occupy each shell
Shell number Maximum number of electrons
1 2
2 8
3 8/18
4 46
Exp:
Electron arrangement =2.4
Carbon
Valence electron 4 so it is
placed in group 14
First shell has 2 electrons &
second shell has 4
electrons. So it has 2 shells
& it is in period 2.
Shell
Electron

10. Element Proton
number
Electron
arrangement
Number of
electron valence
Group Number of
shell
Period
H 1 1 1 1 1 1
He 2 2 2 (duplet) 18 1 1
Li 3 2.1 1 1 2 2
Be 4 2.2 2 2 2 2
B 5 2.3 3 13 2 2
C 6 2.4 4 14 2 2
N 7 2.5 5 15 2 2
O 8 2.6 6 16 2 2
F 9 2.7 7 17 2 2
Ne 10 2.8 8(octet) 18 2 2
Na 11 2.8.1 1 1 3 3
Mg 12 2.8.2 2 2 3 3
Al 13 2.8.3 3 13 3 3

11. Group 18
- Helium(He),Neon(Ne),Argon(Ar),Krypton(Kr),Xenon(Xe) & Radon(Rn)
- Noble/inert gases that exists in monoatomic gases.
Physical properties
1) Can’t dissolve in water , can’t conduct electricity & heat
2) Low densities
3) Colorless gaseous state at room temperature & pressure
4) Melting & boiling point is low.

12. 5) Changes of physical properties when going down group 18:
Properties Changes Explanation
Atomic size increases Bcoz the number of occupied shells increases.
Melting &
boiling point
increase Bcoz
1)the atomic size increaseswhen going down the group
2)The force of attraction between particles become stronger
3)Thus, more heat is needed to overcome the stronger force
Density increase because the mass increases

13. Chemical Properties
1) Unreactive/inert
2) Atoms don’t need to donate, accept/share electrons bcoz the electron
arrangement of the noble gas atoms are stable.
Uses
Elements Uses
Helium -Fill air ships/weather balloons
-Gas in diving tank
Neon -Light up advertising boards/lights
Argon -Fill in filament bulbs
Krypton -Used in flash bulbs & lasers
Randon -For cancer treatments
Xenon -Used in flash bulbs & lasers

14. Group 1
- Lithium (Li) , Sodium (Na) , Potassium (K) , Rubidium (Rb) , Caesium (Cs) &
Francium (Fr)
- Known as alkali metals.
Physical properties
1) Conduct heat & electricity
2) High melting point & boiling point
3) All alkali metals are grey in colour with shiny surfaces but they are soft, can cut
easily

15. 4) Changes in physical properties going down the group:
Properties Changes Explanation
Atomic size Increases Because the number of occupied shells increases
Melting &
boiling point
Decreases Because
1)The atomic size increases when going down the
group.
2)The metal bond between atoms become weaker
3)Thus,less heat is needed to overcome the weaker
bond.
Density increases Because increase in atomic size so it became heavier.
Chemical Properties
1) Very reactive elements.
2) The reactivity increases when going down the group. The valence electron in the
outermost shell become further from the nucleus. The forces of attraction of
nucleus on the valence electron become weaker. The valence electron becomes
easier to release.

16. Chemical properties Chemical equations
Reacts with water to produce alkaline metal,
hydroxide solutions & hydrogen gas
2 X + 2 H2O 2 XOH + H2O
Burns in oxygen gas to produce white, solid metal
oxides
4 X + O2 2 X2O
Burns in chlorine gas to form white solid, metal
chloride.
2 X + Cl2 2 XCl
X= metals in group 1 (Li,Na,K,Rb,Cs,Fr)
Safety Precautions when handling Alkali metals
1) Kept in paraffin oil
2) Use forceps to take the metal
3) Wear safety goggles & gloves

17. Group 17
1) Fluorine (F) , Chlorine (Cl) , Bromine (Br) , Iodine (I) & Astatine (At)
2) Known as halogens
3) Exists in Diatomic molecules, which F2,Cl2,Br2,I2,At2
4) Non-metals
Physical properties
1) Doesn’t conduct heat & electricity bcoz they consist of covalent molecules.
2) Low melting point & boiling point bcoz their molecules r attracted to each other
by intermolecular force.
Force of attraction & intermolecular force
are the same.
Means the forces between 2 molecules

18. 3) Changes of properties when going down the group 17.
Properties Changes Explanation
Atomic size Increases Because the number of shells increases
Melting & boiling
point
Increases Because
1)The atomic size increases when going down the
group.
2)The force of attraction between particles become
stronger.
3)Thus,more heat is needed to overcome the
stronger force.
Colour Darker Flourine = pale yellow gas
Chlorine = Greenish-yellow gas
Bromine = Reddish-brown liquid
Iodine = purplish-black solid
Density Increases Because increase in atomic size so it became
heavier.
Physical changes change from
a gas (fluorine & chlorine)
to liquid (bromine)
to solid (iodine & astatine)

19. Chemical Properties
1) Same chemical properties bcoz all halogen atoms have 7 valence electrons but
their physical properties are different.
2) Reactivity decreases down the group
Chemical properties Chemical equations
Reacts with water to produce 2 acids X2 + H2O HX + HOX
Reacts with hot iron to form a brown solid
iron halides
3 X2 + 2Fe 2FeX3
Reacts with sodium hydroxide solution,NaOH
to form sodium halite(I) & water
X2 + 2NaOH NaOX + H2O
X = halogens (F,Cl,Br,I,At)

20. Elements across the period
1) Horizontal rows = periods
2) Consists of 7 periods which periods 1,2 & 3 are short periods. Others are long
periods
3) The number of protons in the elements increases across the period from left to
right. They increase by 1 proton
Element Na Mg Al Si P S Ci Ar
Proton number 11 12 13 14 15 16 17 18
Electron
arrangement
2.8.1 2.8.2 2.8.3 2.8.4 2.8.5 2.8.6 2.8.7 2.8.8
Metallic properties Metals Semi metal Non-metals
Physical properties Solid
Electrical
conductivity
Good Average Poor
Element oxide base amphoteric acid

21. Across Period 3
- Atomic size of elements increases
- Electropositivity(accept) of elements increases
- Electropositivity(easy to donate) of elements decreases
- Electronegativity increases
- Metallic properties decreases
- Non-metallic properties increases
Element Sodium Magnesium Aluminum Silicon Phosphorus Sulphur Chlorine
Acid-base
properties
Base Base Amphoteric Acid Acid Acid Acid
Reaction
with
acidic /
alkaline
solution
Acid
X Alkali
Acid
X Alkali
Acid
Alkali
X Acid
Alkali
X Acid
Alkali
X Acid
Alkali
X Acid
Alkali
X = Insoluble
= Soluble

22. Transition elements
1) Transitions elements have
a) Shiny surface
b) Ductile
c) Malleable ( can easily shaped into different shapes)
d) Hard
e) High melting point & boiling point
f) High density
g) Conducts electricity & heat
2) a) Transition elements form coloured compounds & ions
Element Ion Colour
Chromium (Cr) Cr3+
CrO2
-4
Cr2O2-7
Green
Yellow
Orange
Manganese (Mn) Mn2+
MnO-
4
Pale pink
Purple
Iron (Fe) Fe2+
Pale green

23. Fe3+
Yellowish brown
Cobalt ( Co) Co2+
Pink
Nickel (Ni) Ni2+
Green
Copper (Cu) Cu2+
Blue( CuSO4)
Green (CuCO3)
b) Precious stones are coloured bcoz of the presence of these coloured ions in them
Gemstone Transition metal Colour
Emerald
Amethyst
Sapphire
Ruby
Topaz
Ni & Fe
Fe & Mn
CO & Ti
Cr
Fe
Green
Purple
Blue
Red
Yellow

24. c) They form complex ions which are coloured,such as:
Hexacyanoferrate (II) ion , [Fe(CN)6]4-
Hexacyanoferrate(II) ion , [Fe(CN)6]3-
Hexaamina chromium(II) ion , [Cr(NH3)6]3+
Tetraamina copper(II) ion , [Cu(NH3)4]2+
Tetrachlorocuprate(II) ion , [CuCl4]2-
d) All transition elements except scandium & zinc have more than 1 oxidation
numbers.
Compound Formula Oxidation number
Chromium (III) chloride
Potassium (VI) dichromate
Manganese (II) sulphate
Manganese (IV) oxide
Potassium (VII) manganate
Iron (II) sulphate
Iron (III) chloride
Copper (I) oxide
Copper (II) sulphate
CrCl3
K2Cr2O7
MnSO4
MnO2
KmNo4
FeSO4
FeCl3
Cu2O
CuSO4
+3
+6
+2
+4
+7
+2
+3
+1
+2

25. e) Transition metals are good catalysts. A specific catalyst is used for a specific
reaction,as in,
Process Catalyst To manufacture
Haber process Iron filings , Fe Ammonia
Contact process Vanadium (V) oxide (
V2O5)
Sulphuric acid
Ostwald process Platinum , Pt Nitric acid
Hydrogenation Nickel , Ni Margarine
Uses of transition elements in industry
1) Mercury used in thermometer bcoz the melting & boiling point & liquid state are
high
2) Tungsten used to make filament bulb as it doesn’t melt easily
3) Iron used to make vehicles, electrical appliances & other products
4) Chromium used to coat iron to prevent rusting of iron substances.