The document summarizes key aspects of the periodic table, including: 1) It describes the historical development of the periodic table by scientists like Lavoisier, Dobereiner, Newlands, Meyer, and Mendeleev. 2) It explains the modern arrangement of elements in the periodic table based on proton number and discusses the properties of elements in the same group and period. 3) It provides examples of properties and reactions of representative elements from groups 1, 17, 18 and period 3 of the periodic table. Transition elements and semimetals are also discussed.

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CHAPTER 4 : PERIODIC TABLE OF ELEMENTS
Historical Development Of The Periodic Table
Antoine Lavoisier
 The first scientist to classify substances
 His classification was unsuccessful because light, heat and a few other
compounds were also considered as elements.
Johann Dobereiner
 Divided the elements into group of three elements with similar
chemical properties
 The atomic mass of the middle element was approximately the average
atomic mass of the other two elements in each triad.
 This classification led chemist to realise that there was a relationship
between the chemical properties and the atomic mass of each
element.
John Newlands
 Arranged the known elements in order of increasing atomic mass.
 The Law of Octaves contributed by him was a failure because the Law
was obeyed by the first 17 elements only.
 He was the first chemist to show the existence of a periodic pattern
for the properties of elements.
Lothar Meyer
 Plotted a graph of the atomic volume against the atomic mass.
 Successful in showing that the properties of the elements formed a
periodic pattern against their atomic masses.
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Dmitri Mendeleev
 Arranged the elements in order of increasing atomic mass and grouped
them according to similar chemical properties
 Left gaps in the table to be filled by undiscovered elements.
Henry J.G.Moseley
 Concluded that proton number should be the basis for the periodic
change of chemical properties instead of the atomic mass.
 Rearranged the elements in order of increasing proton number in the
Periodic Table.
Arrangement Of Elements in the Periodic Table
 Elements are arranged in an increasing order of proton number.
 Elements with similar chemical properties are placed in the same
vertical column
 Vertical column of elements in the table is called Group ( Group 1 to
Group 18 )
 Horizontal row of elements in the table is called Period.
 The Group and Period of an element can be known by the electron
arrangement.
 The number of valence electrons : The position of the Group
 The number of shells : Determine the position of the period.
Example:
X
13
Electron arrangement : 2.8.3
Group : Group 13 and Period : 3
Advantages Of Grouping Elements In The Periodic Table
 The systematic arrangement of elements help us to study the elements
systematically especially in physical and chemical properties.
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GROUP 18 ELEMENTS ( Noble / Inert gas )
 Consists of helium, neon, argon, krypton, xenon and radon
 Noble gases are monoatomic which are very un-reactive and chemically
inert.
 Because the electron arrangement are stable which the outermost
occupied shell are full
 Helium has two valence electrons : Duplet electron arrangement
 Other noble gases has 8 valence electrons : Octet electron
arrangement.
Physical Properties Of Group 18 Elements
 Colourless gases at room temperature & pressure.
 Low melting and boiling point
 Low density
The Changes Of The Physical Properties Going Down The Group
 Atomic size increases
 The number of occupied shell in the atom increases from helium to
radon
 The melting & boiling points increases
 The atomic size of each element increases down the group causes
the force of attraction between the atom of each element becomes
stronger.
 The density of element increases
Uses Of Group 18 Elements
Name Uses
Helium In airship, weather balloons
Neon In advertising light
Argon An inert gas for electric bulbs
Krypton Gas-filled electronic devices and laser
Xenon Electronic flash guns
Radon Natural radioactive gas
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GROUP 1 ELEMENTS ( The Alkali Metal )
 Consists of Lithium, Sodium, Pottassium, Rubidium, Caesium and Francium.
 With 1 electron in the outermost shell.
Physical Properties Of Group 1
 The elements in Group 1 are metals but they have some unusual physical
properties.
1. Have silvery and shiny surfaces
2. Soft and can be cut by using a cutter
3. Low density and melting point
4. good conductors of heat and electricity.
These physical properties will change gradually when going down the group.
 The atomic size increases
 The number of occupied shell in the atom increases from lithium to
francium
 The hardness, melting point and boiling point decrease.
Chemical Properties Of Group 1 Elements
 Have similar properties but different in reactivity.
 The reactivity increases when going down the Group.
 Chemical properties :
1. React vigorously with water to produce alkaline metal hydroxide
solution and hydrogen gas, H2
Ex: 2 Li + 2 H2O  2 LiOH + H2
2. Burn in oxygen gas rapidly to produce white solid metal oxides.
Ex : 4 Li + O2  2 Li2O
The metal oxide dissolves in water to form alkaline metal hydroxide
solution.
Ex : Li2O + H2O  2 LiOH
3. Burn in chlorine gas, Cl2 to form solid metal chlorides
Ex: 2 Na + Cl2  NaCl2
Also burn in bromine to form metal bromides.
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 Alkali metals have 1 e in their outermost occupied shell. So, they will
react with other elements by donating 1 e from outermost shell to form
ion with charge +1 in order to achieve the stable electron arrangement.
 Reactivity increases going down the group
 Because the increasing of the atomic size. When going down the
group the single valence e in the outermost occupied shell becomes
further away from the nucleus. The attraction between the nucleus
and valence e becomes weaker. So easier for the atom to donate the
single valence e to achieve the stable electron arrangement of the
atom of noble gas.
 All metals G 1 are extremely reactive, so:
1. must be stored in paraffin oil in bottles
2. do not hold the metal with your bare hand, use forceps
3. Only small piece of alkali metal is used when conducting experiments.
GROUP 17 ELEMENTS ( HALOGENS)
 Elements in group 17 are poisonous. Consists of fluorine, chlorine,
bromine, iodine and astatine.
 All halogens exist as diatomic molecules.
 Have 7 electrons valence at the outermost shell.
 In order to achieve the stable electron arrangement, halogens are
required to gain 1 electron to form ion with charge -1.
Physical Properties
 Low melting and boiling point
 Molecules are attracted to each other by weak force.
 Melting and boiling points increase when going down the group. So the
physical state of halogen at room temperature changes from gas to
liquid then to solid.
 The atomic size increases with an increase of electron shell, giving
rise to an increase in density
 The colours of elements ( the colour becomes darker )
Elements Colour
Fluorine Pale yellow gas
chlorine Greenish-yellow gas
Bromine Reddish-brown liquid
Iodine Purplish-black solid
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Why melting and boiling points increase when going down the group?
Because the molecular size increases when going down group which
causes the van der Waals’ forces among the molecules increase.
Chemical properties
 Similar chemical properties but different in reactivity.
 The chemical properties as below:
1. React with water to form 2 acid
Ex : Cl2 + H2O  HCl + HOCl
Q : Can you write the chemical equation when bromine and iodine
react with water
2. In gaseous state, react with hot iron to form a brown solid iron (III)
halides
Ex : 2 Fe + 3 Br2  2 FeBr3
Q : Can you write the chemical equation when bromine and iodine
react with iron?
3. React with sodium hydroxide to form sodium halide, sodium halite and
water.
Ex : I2 + 2 NaOH  NaI + NaOI + H2O
 Reactivity of element decreases when going down group
 The size of atom increasing when going down the group.
Thus, the outermost occupied shell of each halogen atom becomes
further from the molecule. Therefore, the strength to attract one
electron into the outermost occupied shell by the nucleus becomes
weaker.
Safety Precaution
 Handle them in a fume chamber
 Use safety goggles and gloves when using halogens.
 Always use small amounts of substances.
 All the elements are poisonous.
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ELEMENTS IN A PERIOD
Elements of period 3:
Element Na Mg Al Si P S Cl Ar
Proton number 11 12 13 14 15 16 17 18
Electron 2.8.1 2.8.2 2.8.3 2.8.4 2.8.5 2.8.6 2.8.7 2.8.8
arrangement
Atomic radius 0.156 0.136 0.125 0.117 0.110 0.104 0.099 0.095
(nm)
Metallic property Metal Semi- Non-metal
metal
Physical property Solid
Electrical Good Average Non-metal
conductivity
Electronegatively Increase
Across period 3 :
 The proton number increases
 Atom of the elements has 3 shells occupied with electron.
 The number of valence electron in each atom increases.
 The atomic radius of elements decreases due to the increasing nuclei
attraction on the valence electrons.
 The electro negativity of elements increases.
 The increase in nuclei attraction on valence electrons and the
decrease in atomic size.
 Electronegativity : Refer to the measurement of the strength of an
atom in its molecule to attract electron towards its nucleus.
 Elements change from metallic to non-metallic atom across the period.
 The oxides of elements in period change from basic to acidic properties
across period 3.
Na2O MgO Al2O3 SiO2 P4O10 SO2 Cl2O7
Basic Amphoteric Asidic oxides
Oxides oxide
Uses Of Semi-metal In Industry
 Called metalloids
 Weak conductor of electricity
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 Semi-metal such as : silicon, germanium used as semiconductor ( to make
diodes and transistor).
 Silicon and germanium have 4 valence electrons, they need to share 4
other valence electrons to achieve the octet arrangement. Thus, they
form large covalent molecules, which cannot conduct electricity.
However, when heated, covalent bonds breaks and its free valence
electrons can conduct electricity.
TRANSITION ELEMENTS
 These are the elements from group 3 to group 12 in periodic table.
Special Characteristic
1. Transition elements show different oxidation number in their compound.
2. Form coloured ions/compound
3. Elements and their compounds are useful catalysts.
Example:
Platinum --- Ostwald process
Nickel --- Manufacture of margarine
Vanadium (v) oxide --- Contact process
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