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Chapter 4 : Periodic Table Of Elements

1) Antoine Lavoisier (1743 1794)

Classified groups into 4 groups

Limitation wrong information (light & heat consider as elements)

2) Johann Dobereiner (1780 1849)

Classified groups = Triad (group of 3)

Limitation few elements were classified

3) John Newlands (1837 1898)

Arranged horizontally in ascending order of their atomic masses

Law of Octaves same properties repeated at every 8 element

4) Lothar Meyer (1830 1895)

Properties of the elements were in a periodic pattern with their atomic masses

Similar chemical properties occupied the same relative positions on the curve

5) Dmitri Mendeleev (1834 1907)

Elements were arranged in ascending order of their atomic masses

Elements with similar chemical properties were placed in a group

Gap for undiscovered elements

Prediction: gallium, scandium and germanium (discover later)

Separate groups for certain elements: transition elements

Meedeleevs Periodic Table was used as a basis for the formation of the Periodic

Table

6) H. J. G. Moseley (1887 1915)

Elements were arranged horizontally in ascending order proton numbers

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Elements with the same number valence electrons same group

Group 18 ( Noble Gases ) monoatomichas achieved stable electron duplet / octet confugirationwill not react with other element

Physical properties

a) colourless gas at room temperature b) insoluble in water

c) cannot conduct electricity d) poor conductors of heat

Physical properties, as it going down the group

a) MP & BP increase- atomic size increases & force of attraction between atoms become strongerb) Density increase- increase of mass is higher than the increase of volume

c) Size increase- increase of shell for each element

Chemical properties

a) inert b) not reactive c) non- flammable

Uses

1) He Helium

airships, weather balloons, cool down metals

2) Ne Neon

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advertising light bulb

3) Ar - Argon

welding, filled light bulbs

4) Kr - Krypton

used in laser, filled photographic flash lamps

5) Xe Xenon

used for watch tower lighting

6) Rn - Radon

treat cancer

Group 1 ( alkali metal ) 1 valance electron

Li , Na , K , Rb , Cs

solid (room temperature) & very reactive

Physical properties

a) Grey solid with shiny silvery surfaces b) Good conductors of electricity

c) Good conductors of heat d) Low MP & BP

e) Low density (Li, Na & K float/Rb, Cs & Fr sink)

Physical properties as it going down the group

a) MP & BP decrease

atomic size increases

number of shells occupied with electrons increases

metallic bonding between atoms becomes weaker

less heat energy is required to overcome the weaker metallic bonding

b) Density increase mass is higher than volume

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c) Size increase number of shell increase

Chemical properties

1) Very reactive & react rapidly with O2 n water vapour in the air (kept in paraffin oil)

2) Reactivity increases (down the group) lose one valence electron to achieve stableoctet/duplet electron arrangement

3) React vigorously with cold water produce alkaline metal hydroxide solutions andhydrogen gas

4) React with oxygen produce white solid metal oxides & metal oxides can dissolve inwater to form alkaline metal hydroxide solutions

5) React with halogens produce white solid metal halides

Safety precautions

a) Cannot hold with bare hands b) Wear safety goggles and gloves

c) No flammable substance nearby d) Avoid the fire

Group 17 ( Halogens ) diatomic (F2, Cl2, Br2, I2 and At2)

non metal

quiet reactive

Physical properties

a) Non-metals b) Insulators of electric c) Poor conductors of heat

d) Low melting point and boiling point e) Low density

f) Colour: F2 (pale yellow gas), Cl2 (greenish-yellow gas), Br2 (reddish-brown liquid),

I2 (purplish-black solid) and At2 (black solid rarest naturally occurring

element and extremely radioactive)

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Physical properties as it going down the group

a) MP & BP increases molecular size increases

forces of attraction between molecules become stronger

more heat energy is required to overcome the stronger forces of attraction (Van derwalls forces of attraction between molecules).

b) Density increases d) Electronegative decreases atomic mass increase

c) Reactivity decreases e) Atomic radius increases gain more valence electron to achieve

stable (octet) electron arrangement

f) Has a pungent & irritating smell g) Colourless & poisonous

Chemical properties

1) React with water produce two acids

2) React with hot iron produce brown solids iron(III) halides

3) React with sodium hydroxide NaOH solution produce water and two types of sodium salts [sodium halide and sodium halite(I)]

Safety precautions

a) Poisonous gas b) Wear safety goggles & gloves c) Handle in the fume of cupboard

Elements in a period

Periodic Table 7 periods (Period 1 - 7)

Proton number increases 1 (across a period from left to right)

No of valence electron increases (across a period from left to right)

Across Period 3

1) Atomic size decreases

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increasing number of electrons / attraction by nucleus on the valence

electrons becomes stronger (pulled closer to the nucleus)

2) Proton number increases

positive charge of the nucleus increases

3) Electronegativity increases proton number increases / positive charge of the nucleus increases

4) Change from solid to gas

Left solid metals

Right non-metals gases

5) Electropositive / metallic properties decreases

6) Na, Mg, Al (metals): good conductor / Si (semi-metal): weak conductor of

electricity / P, S, Cl (non-metals): cannot conduct electricity

7) Na, Mg (metals): form oxides with basic properties

8) Al (metal): form oxides with both basic and acidic properties = amphoteric oxides

9) Si (semi-metal): forms oxides with acidic propertiesP, S, Cl (non-metals): forms oxides with acidic properties

Uses of semi-metals (metalloids)

Semiconductor (flow in one direction)

Microchip

Transition elements

Group 3 to Group 12

Metals

Atomic radius same

Solids with shiny surfaces

Very hard

High density

Ductile (ability to stretched into wires without breaking)

Malleable (ability to be bent into new shape)

High tensile strength (ability to stay in their shape without breaking)

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High melting and boiling points

High density

Good conductors of electricity

Good conductors of heat

Electronegativity is low but increases (across the series)

Special characteristics

Form coloured ions (Cu2+: blue / Fe2+: pale green / Fe3+:yellow)

Form coloured compound (cobalt chloride crystal: pink)

Different oxidation numbers in their compound

Useful catalysts (nickel hydrogenation of vegetable oil, copper(II) sulphate reaction of zinc with dilute sulphuric acid to liberate hydrogen

gas, manganese(IV) oxide decomposition of hydrogen peroxide to liberate

oxygen gas, iron Haber process,vanadium(V) oxide Contact process, platinum

Ostwald process)

Form complex ions (bigger-sized polyatomic ion) (Hexacyanoferrate(III) ion /

[Fe(CN)6]3- )

Uses

1) Iron used as steel

2) Chromium coating corroded metals, heat-resisting alloys and make stainless steel

3) Copper making cables, pipes and electrical wires

4) Titanium metal pipes and tanks, wings of supersonic aircraft