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Chapter 4
THE PERIODIC TABLEOF ELEMENTS
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Historical developmenty Antoine Lavoisier (1743 1794)
- he drew up a list of simple substances, or elements
- he classified elements into 4 groups
- table Lavoisier not accepted because it contains:
a) Non-elements such as heat and light
b) Compounds such as silica, magnesia, chalk, barita
and alumina
Group I Group II Group III Group IV
Heat Carbon Silver Silica
Oxygen Sulphur Lead Magnesia
Hydrogen Chlorine Tin Chalk
Nitrogen Fluorine Cobalt Barita
Phosphorus Bismulth Alumina
Zinc
Nickel
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y Johann W. Dobereiner (1780 1849)
he observed that certain elements had similarproperties
These elements occur in triads, or groups of three
Each triad, the atomic mass of the middle element is
equal to the average mass of the first and last element
Triad table was not accepted because the table only
true for a few elements only
Triads Lithium Sodium Calcium
Atomic
weight
7 23 39
Average
weight
( 7 + 39 ) 2 = 23 = weight of Sodium
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y John Newlands (1837 1898)
He arranged the elements in order of increasing
nucleon number in horizontal rows
He found that the chemical properties of every eighth
element are similar ( law of octaves )
His pattern not successful because :
a) The law of octaves was only accurate for the first 16
elements ( from Li to Ca )
b) There were no positions allocated for elements yet to be
discovered
Li Be B C N O F
Na Mg Al Si P S Cl
K Ca
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y Lother Meyer (1830 1895)
He stated that the properties of the elements areperiodic. They follow their atomic weights
He devised a method to calculate the atomic volume
of an atom :
Atom volume = mass of t
h
e atom of th
e elementdensity of the element
From the value of the atomic volume, he was able to
plot a graph
of atomic volume against atomic massFrom the graph, he conclude that elements with
similar properties occupy similar positions in their
graphs.
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y Dmitri Mendeleev
He arranged the elements in order of increasing
atomic mass
He was more successful for several reasons :a) He left gaps for elements yet to be discovered. He even
used the table to predict the existence and properties if
undiscovered elements.
b) He changed the order if the chemical properties are not
similar
I II III IV V VI VII VIII
1 H
2 Li Be B C N O F
3 Na Mg Al Si P S Cl
4 K Ca ( ) Ti V Cr Mn Fe,Co,Ni
5 Cu Zn ( ) ( ) As Se Br
6 Rb Sr Y Zr Nb Mo ( ) Ru,Rh,Pd
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y Henry G.J.Moseley (1887-1915)
Afterhe obtaining the proton number of the elements,
he arranged the elements according to the increase
proton numbers
Just like Mendeleev did, he left gaps ( ) for elements
yet to be discovered.Moseley work proved that elements should be
arranged by proton number and not by atomic weight.
This is the way the elements of the Periodic Table are
arranged today
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Modern Periodic Tabley
The elements are arranged in order of increasing protonnumber.
y This order is also related to the electron arrangement of
the elements
y Elements wit
hthe same c
hemical properties are placedin the same group
y Refer to you Periodic Table
y The vertical columns are called group. there are 18
groups in the Periodic Table
y Each member of a group shows similarchemical
properties.
y Physical properties such as density, melting point and
colour may show a gradual change when descending the
group
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y Group 1 elements are called alkali metals
y Group 2 elements are called alkaline earth metalsy Group 17 elements are called halogens
y Group 18 elements are called noble gases
y A block of elements called transition elements
separates Group 2 and Group 13
y The horizontal rows are called periods. There are
seven periods
a) Period 1 has two elements only
b) Periodic 2 and 3 have eight elements each. The first
three periods are called the short periods
c) Periods 4 and 5 have 18 elements each. They
called the long periods
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d) Period 6 has 32 elements. Not all the elements can
be listed on the same horizontal row. These
elements are separated below (Lanthanide Series)
e) Period 7 has 31 elements. Not all the elements can
be listed on the same horizontal row. These
elements are separated below ( Actinide Series )
y All members of the same group have the samenumber of valence electrons.
y Valence electrons are electrons in the outermost
shell
a) Group 1 elements have one valence electron
b) Group 2 elements have two valence electrons
c) Group 17 elements have seven valence electrons
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y The number of valence electrons of Group 1 and
Group 2 elements is the same as its group number
y Except forHelium.
y Elements with more than 2 valence electrons
(groups 13 to 18), the group number = 10 + number
of valence electronsPeriods 1 have one electron shell
Periods 2 have two electron shells
Periods 3 have three electron shells
Periods 4 have four electron shells
y So all elements in the same period have the same
number of filled electron shells
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Group 18 Elementsy
Physical properties
Called noble gas and make up almost 1% of the air
All noble gas do not
a) Dissolve in water
b) Conduct electricityc) Conduct heat
They are monoatomic gases at room temperature
a) Boiling point increase down the group
b) Melting point increase down the group
c) Atomic radius increase down the group
d) Density increase down the group
All noble gas have low melting point and boiling
point compare to other gas because intermolecular
force of attraction is low
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y Chemical properties
Noble gas are unreactive because they have filledouter shells of electrons which are a stable electron
arrangement
He have attained the stable duplet electron
arrangementThe other noble gas have attained the stable octet
electron arrangement
Therefore the noble gases do not need to accept,
donate orshare electrons with other elements
All chemical reactions involve either gaining, losing or
sharing electrons
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Uses of Group 18 Elements
y Helium
Used as super-conductors
Fill airships and weather balloons
y Neon
Used in advertising light
y Argon
Used to fill in light bulbs
y KryptonUsed in laser surgery during eye surgery
y Xenon
Used in lighthouse lamps. It gives a beautiful blue light
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Group 1 Elements
y All element in this group are metals which react with
water to form alkaline solutions
Physical properties
y They are all conductors of electricity
y They have low boiling point and melting point
y - Melting point decrease down the group
- Boiling point decrease down the group
- Electropositivity increase down t
he group
( is a measure of the ability of an atom to lose its valence
electron )
- Hardness decrease down the group
-Density increase down t
he group
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Chemical properties
y The alkali metals are the most reactive group of metals in
the Periodic Table
y The alkali metals atoms achieve the stability of a duplet
or octet by giving away its valence electron and form
positive ion
example: Li Li+ + e
2.1 2
Na Na+ + e
2.8.1 2.8
y The reactivity of alkali metal elements increase down the
group
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y Reaction with Oxygen
1) Alkali metals react with oxygen gas to form metal
oxides
example : Na(s) + O2(g) Na2O
2) Alkali metals react with water to form alkaline metal
hydroxide solutions and hydrogen gas
example : 2K(s) + 2H2O(l) 2KOH(aq) + H2(g)
3) Alkali metal react easily with oxygen and water. To
prevent this, alkali metals are kept in oil
4) The alkali metals become more reavtive down the
group
5) Reaction of K, Rb, Cs, Fr with water is explosive.
Thus ,a very small piece should be used during
experiment
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y Reaction with Halogen
1)R
eaction with
halogen will produce colourless,crystalline ionic salts called halides. Example :-
2Na(s) + Cl2(g) 2NaCl(s)
Sodium + chlorine sodium chloride
2) In the above reaction, every alkali atom will donateone electron to the halogen atom. Every halogen
atom will receive one electron from the alkali atom
Li Li+ + e
Br + e Br -
Li+ + Br- LiBr
3) The increase in reactivity is because.
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Group 17 Elementsy Group 17 elements are also known as halogens
y Halogens exist as diatomic molecules(F2, Cl2, Br2, I2 and
At2)
y Halogens are very reactive elements and naturally exist
as halide salts.
Physical properties
y - melting point increase down the group
- boiling point increase down the group
- density increase down the group- size increase down the group
- electronegativity decrease down the group
(electronegativity measures the ability of an element to
accept electrons)
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y At room temperature.
a) Chlorine is a gas
b) Bromine is a liquidc) Iodine is a solid
y Chlorine, bromine and iodine are
a) Not conductors ofheat
b) Not conductors of electricity
Chemical properties
y Reaction withAluminium
a) no reaction was seen until aluminium was heated
b) Whitish, powdery solid halides were produced
2Al(s) + 3Cl2(g) 2AlCl3(s)
Aluminium chloride
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y Reaction with Other Metals
halogens react with almost all metals in the Periodic
Table to yield metal halides
2Al(s) + 3Br2(g) 2AlBr3(s) aluminium bromide
y Reaction with Hydrogen
halogens react withhydrogen to form halides
H2(g) + Br2(g) 2HBr(g) hydrogen bromide
y Reaction with Other Halogens
the halogen also react among themselves
I2(s) + Cl2(g) 2ICI(s) iodine chloride
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y Reactivity decrease down the group
Safety precautions in handling Halogeny the vapor of fluorine, chlorine and bromine are
poisonous
y Astatine is a hazardous material because it is
radioactivey The following precaution should be taken when handling
halogen:
a) halogen gas and liquid should be handled inside a fume
chamber
b) Safety goggles should be used when handling halogen
fumes
c) Gloves should be used when handling halogen materials
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Elements In A Period
y The horizontal rows of elements in the Periodic Table
are called periods
y The elements are arranged from left to right. Each step
will involve an increase in
a) 1 proton particleb) 1 proton number
c) 1 valence electronElements in
Period 3Na Mg Al Si P S Cl Ar
Protonnumber 11 12 13 14 15 16 17 18
Electron
configuration2.8.1 2.8.2 2.8.3 2.8.4 2.8.5 2.8.6 2.8.7 2.8.8
Valence
electron1 2 3 4 5 6 7 8
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Changes in Properties Across
Period 3y The following properties increase from left to right of each
period
a) Proton numberb) The number of valence electron
c) Electronegativity
y The following properties decreases from left to right
a) Electropositivityb) Radius
c) Melting point
d) Boiling point
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y The elements changes from
a) Solid to gas
b) Metallic to non-metallic
c) Conductor to non-conductor
y Uses of Semi-metals(metalloid) in Industry
1) Silicon is a semi-metal. It is widely used in the
semiconductor industry
2) Silicon is used to make
a) Transistor
b) Diode
c) Electric componentsd) Microchips
3) Germanium is another semi-metal. It is also used
extensively in the electronic industry
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Transition Elements
y The transitional elements lie in between group 2 andgroup 13 in the Periodic Table
y All elements in this block of Periodic Table have similar
properties
Physical propertiesy The transition elements are.
a) Hard
b) Shiny
c) Densey They are good.
a) Conductors ofheat
b) Conductors of electricity
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y They.
a) Are malleable and ductile
b) Have high tensile strength
y The radius of all the transition elements is almost
constant
y The following properties decrease from left to right
a) Boiling point
b) Melting point
y The following increase from left to right
a) Proton number
b) Density
y Electronegativity is low for all the elements. However, it
increase slowly from left to right in the Periodic Table
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Special Characteristic ofTransition Elements
1. Majority of the transition elements have more than one
oxidation number in their compound
Elements Compound Formula Oxidation number
Chromium Potassium dichromate(IV) K2Cr2O7 +6
Chromium(III) chloride CrCl3 +3
Iron Iron(II) chloride FeCl2 +2
Iron(III) chloride FeCl3 +3
Nickel Nickel(II) sulphate NiSO4 +2
Nickel(III) bromide NiBr 3 +3
Copper Copper(I) ch
loride CuCl +1Copper(II) oxide CuO +2
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2. Most transition elements form coloured ions
3. Many of the transition elements are able to form
complex ions
Ions Formula of the ions Colour (aqueous)
Chromate(VI) CrO42- Yellowish
Dichromate(VI) Cr 2O72- Orange
Iron(II) Fe2+ Greenish
Iron(III) Fe3+ Brownish
Copper(II) Cu2+ Bluish
Cobalt(II) Co2+ Pale reddish
Manganate(VII) MnO4- Purple
Elements Complex ion Formula
Copper Copper(II) tetra amine Cu(NH3)42+
Chromium Chromium(III) hexa amine Cr(NH3)63+
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4. Many of the transition elements can act as a catalyst
5. Catalysts are used in chemical reaction to speed up
the rate of a reaction
Precious Stones1. All precious stones have brilliant colours
2. These colours are due to the present of transition
elements in the stones
Transition elements Catalyst used in (process)
Nickel Used in hydrogenation of alkenes to produce alkane and
hydrogenation of margarine
Vanadium(
V) oxide
Used in Contact process to produce sulp
huric acid
Iron Used in Haber process to produce ammonia
Platinum Used in Ostwald process to produce nitrogen oxide and
finally to produce nitric acid
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Uses ofTransition Elements in IndustriesWe use catalysts in industries to speed up manufacturing
processes
Precious stones Colour Transition elements
Emerald Green Nickel, Iron
Ruby Red Chromium
Sapphire Deep blue Iron, Titanium
Turquoise Blue-green, blue, or green Copper
Amethyst Violet Manganese, Iron
Manufacture of Catalyst
A
mmonia IronMargarine Nickel
Sulphuric acid Vanadium(V) oxide
Nitric acid Platinum, Rhodium
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The Importance of Diverse
Elements and Compoundsy The uses of elements in our everyday lives
Elements Uses
Hydrogen, H2 Used to cut or weld metals
Used to hydrogenate palm oil to make margarine
Helium, He Used to fill up weather balloons and air ships
Oxygen, O2 Used during respiration of all living things
Use during the burning or oxidation of materials
Nitrogen, N2 Used to make ammonia
Aluminium,Al Used to make electric cables, alloys, windows and doors
Silicon, Si Used to make microchips
Phosphorus, P Used to make matches
Iron, Fe Used to produce steel which is used to make metal
objects such as cars
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y The uses of compounds
Compounds Uses
Ammonia, NH3 Fertilisers, nitric acid
Silver bromide, AgBr Photographic film
Carbon dioxide, CO2 Fire extinguisher, carbonated drinks
Chlorofluorocarbon,
CFC
Freon in air conditioner and
refrigerator
Ethanol, C2H5OH Liquor and Flavour
Iron(II) sulphate, FeSO4 Iron pills for anaemic patientsMagnesium oxide, MgO Antacid for gastric patients