Periodic Table of Elements
Analyse the Periodic Table of ElementsAnalyse Group 18 elementsAnalyse Group 1 elementsAnalyse Group 17 elementsAnalyse elements in a periodUnderstand transition elements
Antoine Lavoisier (1743 – 1794)Classify substances into
metals and non-metalsUnsuccessful because light,
heat and some other compounds where not elements.
Johann Dobereiner (1780 - 1849)Introduced triads. Elements were classified
into groups of three elements with same chemical properties
The atomic mass of middleelements was approximately the average atomic mass of the other two elements
Lothar Meyer (1830 - 1895)Plotted a graph of the
atomic volume against atomic mass.
Elements with similar chemical properties occupied same positions.
Successful in showing the properties of elements formed a periodic pattern against their atomic masses.
John Newlands (1837 - 1898)Arranged elements in order of
increasing atomic mass.Elements with similar properties
recurred at every eight element.This was known as the Law of
OctavesFailed because only obeyed by
first 17 elements only
Dimetri Mendeleev (1839 – 1907) Arranged elements in order of
increasing atomic massElements with similar chemical
properties are grouped togetherHe left empty spaces in the table
for undiscovered elements
Henry J. G. Moseley (1887-1915)Concluded that proton
number should be the bases for the periodic change of chemical properties
Arranged the elements in order of increasing proton number in the Periodic Table.
Elements are arranged according their increasing order of proton number.
Vertical columns = groups(according to their number of valence electrons)
Horizontal rows = periods (number of electron shells filled by electrons)
Known as noble gases/inert gases(chemically unreactive elements)
Non-metals that exist as monoatomic colourless gases.
Members : Helium(He) Neon(Ne) Argon(Ar) Krypton(Kr) Xenon(Xe) Radon(Rn).
Very small atomic sizes. Low melting and boiling points
Weak van der Waals’ forces of attraction between atoms.
Low densitiesVery small masses but huge volumes.
Melting and boiling points of elements increase down the Group 18.
All Group 18 elements are chemically inert/unreactive.
The outermost electron shell of each member is fully occupied by electrons.
This is a stable electron arrangement which inHelium, it is said achieve duplet electron
arrangement.Other than Helium, it is said achieve octet
electron arrangement.
HeliumTo fill airships and weather
balloons.
used as artificial atmosphere in oxygen tank for divers.
NeonAdvertising lights
Used in aeroplane runway lights
ArgonTo fill light bulbs.
KryptonUsed in lasers to
repair the retina of the eye.
To fill photographic flash lamps.
XenonMaking electron tubes
and stroboscopic lamps
Used in bubble chambers in atomic energy reactors.
RadonUsed to treat
cancer
Consists of lithium(Li), sodium(Na), potassium(K), rubidium(Rb), caesium(Cs) and francium(Fr).
Li Na K Rb Cs Fr
They are known as alkali metals because they react with water to produce alkaline solution.
Soft Low melting pointsLow densitiesShiny and silvery surfaceGood conductor of heatGood conductor of electricity
Hardness, melting point and boiling point of the elements decreases going down the group.
When go down Group 1, size of atom becomes larger. The positive nucleus gets further away from the negative sea of electrons.
The force of attraction between the metal ions and the sea of electrons gets weaker down the group. Less energy is needed to overcome this weakening force of attraction.
1. All react with water to produce alkaline metal hydroxide solution and hydrogen gas.
2X(s) + 2H2O(l) 2XOH(aq) + H2(g)
2. All burn in oxygen gas to produce white solid metal oxides.
4X(s) + O2(g) 2X2O(s)
The oxide dissolve in water to form alkaline metal hydroxide solution.
X2O(s) + H2O(l) 2XOH(aq)
3. All burn in chlorine gas to produce white solid metal chlorides.
2X(s) + Cl2(g) 2XCl(s)
Why the reactivity of elements increases down the Group 1?Atomic size of Group 1 elements increases from
lithium to francium//Number of shells occupied by electrons increases.
Distance between the valence electron in the outermost shell and positive nucleus increases down the Group 1.
Attraction between nucleus and valence electron decreases.
It is easier for the atom to lose the valence electron to achieve stable electron arrangement.
Why all elements in Group 1 have same chemical properties?Chemical reaction is all about the activity of electronsAll the elements have one valence electron.Each of them reacts by donating one valence electron
to form anion with a charge of +1 to achieve stable electron
arrangement.
Members are fluorine(F2) , chlorine(Cl2), bromine(Br2), iodine(I2), and astatine(At2)
F Cl Br I At
The elements are also known as halogens which exist as diatomic molecules.
They have low melting and boiling points because molecules are attracted to each other by weak van der Waals’ forces of attraction.
The melting and boiling points of the elements increases down Group 17.
This change the states of elements from gas to solid and the colour of elements from lighter colour to darker colour.
Elements State Colour
Fluorine Gas Pale yellow
Chlorine Gas Greenish-yellow
Bromine Liquid Reddish-brown
Iodine Solid Purplish-black
Why the melting and boiling points of elements increases down Group 17?
Molecular size/relative molecular mass of the elements increases down Group 17.
Forces of attraction between molecules/Intermolecular forces of attraction increases.
More heat is needed to overcome the stronger forces of attraction between the molecules.
All members have similar chemical properties but differ in the reactivity.
1. React with water to form two acidsX2(g) + H2O(l) HX(aq) + HOX(aq)
Example: Cl2(g) + H2O(l) HCl(aq) + HOCl(aq)
hydrochloric hypochlorous acid acid
Hypochlorous acid is a bleaching agent (bleach both blue and red litmus paper)
2. Halogens in gaseous state react with hot iron to form brown solid.
2Fe(s) + 3X2(g) 2FeX3(s)
Example: 2Fe(s) + 3Cl2(g) 2FeCl3(s)
solid iron(III) chloride(brown)
3. Halogens react with sodium hydroxide solution to produce sodium halide, sodium halate(I) and water
X2 + 2NaOH(aq) NaX(aq) + NaOX(aq) + H2O(l)
Example: Cl2 + 2NaOH(aq) NaCl(aq) + NaOCl(aq) + H2O(l)
Sodium chlorate(I)
Why all halogens possess similar chemical properties?
Chemical reaction = lose or accept electrons All halogens always gain one electron to achieve
stable octet electron arrangement. Therefore, they have similar chemical properties. Why chemical reactivity of halogens decreases down
Group 17? Atomic size/number of electron occupied shells of
halogens increases down Group 17. The outermost shell becomes further from the nucleus
of the atom. Strength to attract one electron into the outermost
shell by the nucleus becomes weaker. Reactivity decreases.
Elements across a period exhibit a periodic change in properties.
Proton number increases by one unit from one element to the next element
All the atoms of the elements have three shells occupied with electrons
The number of valence electrons in each atom increase from 1 to 8
All the elements exist as solid except chlorine and argon which are gases
The atomic radius of elements decreases. This is due to the increasing nuclei attraction on the valence electrons.
The electronegativity of elements increases. This is also due to the increasing nuclei attraction on the valence electrons and the decreases in atomic size.
Uses of metalloidMake diodes and transistorsA diode A transistor
Both are commonly used in the making of microchipsMicrochips are widely used in the manufacture of
computers, mobile phones, televisions, video recorders, calculators, radio and etc.
Metalloid – semi-metal, reacts with acid only, weak conductor, brittle and not malleable and ductile.
Oxides of elements change from basic to amphoteric and then to acidic across the period towards the right.
Basic oxides – react with acids to form salt and waterAcidic oxides – react with alkalis to form salt and
waterAmphoteric oxides – react with both acids and alkalis
to form salt and water.
Elements from Group 3 to Group 12 in the Periodic Table.
Common characteristicsSolid metal with shiny surface. Good conductor of heat and electricity.High melting and boiling points.Hard, malleable and ductile.
Special characteristics;
Show different oxidation numbers in their compounds
Form coloured ions or compoundsUse as catalystsForm complex ions
Show different oxidation numbers in their compound
Compound Formula Oxidation number
Chromium(III) chloride CrCl3 +3
Potassium dichromate(VII) K2Cr2O7 +6
Manganese(II) sulphate MnSO4 +2
Manganese(VI) oxide MnO2 +4
Potassium manganate(VII) KMnO4 +7
Iron(II) sulphate FeSO4 +2
Iron(III) chloride FeCl3 +3
Copper(I) oxide Cu2O +1
Copper(II) sulphate CuSO4 +2
Form coloured ions or compounds
Element Ion Colour
Chromium
Cr3+ Green
CrO42- Yellow
Cr2O72- Orange
ManganeseMn2+ Pale pink
MnO4- Purple
IronFe2+ Pale green
Fe3+ Yellowish brown
Cobalt Co2+ Pink
Nickel Ni2+ Green
Copper Cu2+ Blue Green
Form coloured ions or compoundsGemstone Transition metal Colour
EmeraldNi and Fe Green
AmethystFe and Mn Purple
SapphireCo and Ti Blue
RubyCr Red
TopazFe Yellow
As catalyst
Process CatalystTo
manufacture
Haber Process
Iron fillings, Fe
Ammonia
Contact Process
Vanadium(V) oxide, V2O5
Sulphuric acid
Ostwald Process
Platinum, Pt Nitric acid
Hydrogenation
Nickel, Ni Margarine
HAI
CSV
ONiP
To form complex ions
Element Complex ions Formula
Iron
Hexacyanoferrate(II) ion
[Fe(CN)6]4-
Hexacyanoferrate(III) ion
[Fe(CN)6]3-
Chromium
Hexaamina chromium(III) ion
[Cr(NH3)6]3+
Copper
Tetraamina copper(II) ion
[Cu(NH3)4]2+
Tetrachlorocuprate(II) ion
[CuCl4]2-
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