Chemistry form 4 chapter 4

7/28/2019 Chemistry form 4 chapter 4

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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


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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 alsoconsidered as elements

2 Johann W

Dobereiner

(1780 1849)

-In1829,he divided the elements into the groups of 3 elements withsimilar chemical properties

-Known as Dobereiners 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 thechemical properties & the atomic mass of each element.

3 John Newlands

( 1837-1898)-From 1864 1865, he arranged the elements in order ofincreasingatomic mass.-Elements with similar properties recurred at every 8 element.


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-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 ofelements.

4 Lothar Meyer

(1830-1895)-In 1870 , he plotted graph of the atomic volume against the atomicmass.-Realised that elements with similar chemical properties occupiedequivalent positions on the curve.-He found that the properties of the elements formed a periodic patternagainst 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 propertiesin verticalcoloum.-He left gaps (empty spaces) in the table to be filled by undiscoveredelements.


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-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 thebasic for the periodic change ofchemical properties instead of theatomic mass.

-He arranges the elements in order of increasing proton number in thePeriodic Table. Thus, he confirmed the works / Mendeleev.

-The modern Periodic Table based on the foundation of Henry J.G

Moseley.


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1)Arranged according to ascending proton number of the element.

2)1-18 called Group. 1-7 called periods


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Group

1)Group arranged according to the number of valence electron in the outermostshells.

2)All elements in a groupa)Have the same valence electronsb)Have the same chemical propertiesc)Physical properties will change as wego down the group.3)Groups have special names.Group Name

1 Alkali metals

2 Alkaline earth metals

17 Halogens

18 Inert (noble) gases3-12 Transition metals

4)Group 1,2,13& transition elementsare metals. Group 15-18are non-metals.Group 14has 2 non-metals( carbon& silicon)


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Period

1)Period arranged according to the number of shells occupied with electron in anatom.

2)Elements in period 1 7Period Number of elements

Period 1 2 elements

Period 2 & 3 8 elements

Period 4 & 5 18 elementsPeriod 6 32 elements

Period 7 23 lements


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Electrons Arrangement

1)Number offilled electron shells increases, as we go down the group.2)By knowing the proton number of the element, we can determine the group &

period its placed in.

3)Relationship between number of valence electrons with the group number of anelement.

No.of valenceelectrons

1 2 3 4 5 6 7 8 (second 8. First 8 is intransition 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


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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


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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


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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)Cant dissolve in water , cant conduct electricity& heat2)Low densities3)Colorless gaseous state at room temperature& pressure4)Melting & boiling point is low.


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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


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Chemical Properties

1)Unreactive/inert2)Atoms dont need to donate,accept/share electronsbcoz the electron

arrangement of the noble gas atoms are stable.

UsesElements 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 & lasersRandon -For cancer treatments

Xenon -Used in flash bulbs & lasers


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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 point3)All alkali metals are grey in colourwith shiny surfacesbut they are soft, can cut

easily


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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.


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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 oil2)Use forceps to take the metal3)Wear safety goggles & gloves


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Group 17

1)Fluorine (F) , Chlorine (Cl) , Bromine (Br) , Iodine (I) & Astatine (At)2)Known as halogens3)Exists in Diatomic molecules, which F2,Cl2,Br2,I2,At24)Non-metals

Physical properties

1)Doesnt 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


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3)Changes of properties when going down the group 17.Properties Changes Explanation

Atomic size Increases Because the number of shells increasesMelting & 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 thestronger 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)


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Chemical Properties

1)Same chemical properties bcoz all halogen atoms have 7 valence electrons buttheir 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)


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Elements across the period

1)Horizontal rows = periods

2)Consists of7 periods which periods 1,2 & 3 are short periods. Others are longperiods

3)The number of protons in the elements increases across the period from left toright. 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


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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 ChlorineAcid-base

properties

Base Base Amphoteric Acid Acid Acid Acid

Reaction

with

acidic /

alkalinesolution

Acid

X Alkali

Acid

X Alkali

Acid

Alkali

X Acid

Alkali

X Acid

Alkali

X Acid

Alkali

X Acid

Alkali

X = Insoluble

= Soluble


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Transition elements

1)Transitions elements havea)Shiny surfaceb)Ductilec)Malleable ( can easily shaped into different shapes)d)Harde)High melting point & boiling pointf)

High density

g)Conducts electricity & heat2)a) Transition elements form coloured compounds & ions

Element Ion Colour

Chromium (Cr) Cr3+

CrO2-4Cr2O2

-7

Green

YellowOrange

Manganese (Mn) Mn2+

MnO-4

Pale pink

Purple

Iron (Fe) Fe2+

Pale green


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Fe3+

Yellowish brown

Cobalt ( Co) Co2+

Pink

Nickel (Ni)Ni

2+

Green

Copper (Cu) Cu2+

Blue( CuSO4)Green (CuCO3)

b)Precious stones are coloured bcoz of the presence of these coloured ions in themGemstone Transition metal ColourEmerald

Amethyst

Sapphire

Ruby

Topaz

Ni & Fe

Fe & Mn

CO & Ti

Cr

Fe

Green

Purple

Blue

Red

Yellow


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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 oxidationnumbers.

Compound Formula Oxidation number

Chromium (III) chloride

Potassium (VI) dichromate

Manganese (II) sulphate

Manganese (IV) oxidePotassium (VII) manganate

Iron (II) sulphate

Iron (III) chloride

Copper (I) oxide

Copper (II) sulphate

CrCl3

K2Cr2O7

MnSO4

MnO2KmNo4

FeSO4

FeCl3

Cu2O

CuSO4

+3

+6

+2

+4+7

+2

+3

+1

+2


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e) Transition metals are good catalysts. A specific catalyst is used for a specificreaction,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 arehigh

2)Tungsten used to make filament bulb as it doesnt melt easily3)Iron used to make vehicles, electrical appliances & other products4)Chromium used to coat iron to prevent rusting of iron substances.

Chemistry form 4 chapter 4

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