2 Group 18 Elements Updated

8/8/2019 2 Group 18 Elements Updated

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PERIODIC TABLE OF ELEMENTS

B. GROUP 18 ELEMENTS

1. The elements in Group 18 are

Helium 2Neon 2.8

Argon 2.8.8 Krypton 2.8.18.8

Xenon 2.8.18.18.8

Radon 2.8.18.32.18.8

2. They are also known as noble gases, which are chemicallyunreactive. Noble gases are monoatomic.

3. Helium has two valence electrons. This is called dupletelectron arrangement.

4. Other noble gases have eight valence electrons. This is calledoctetelectron arrangement.

5. Duplet and octet electron arrangements are very stablebecause the outermost occupied shells are full.

6. All nobles gases are inertwhich means chemically unreactive.

BECAUSE THE OUTERMOST OCCUPIEDSHELLS ARE FULL

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Why noble gases exist as monoatomic

gases and are chemically unreactive?


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Argon To fill light bulbs, it can last longer

To provide inert atmosphere for welding at high

temperature.

Krypton Used in lasers to repair the retina of the eye.

To fill photographic flash lamps.

Radon

Used in treatment of cancer.

Xenon

Used in bubble chambers in atomic energy reactors.

Hw: QR B pg. 65 no. 1,2


C. GROUP 1 ELEMENTS

7. The elements in Group 1 are

Lithium 2.1Sodium 2.8.1Potassium 2.8.8.1

Rubidium 2.8.18.8.1Caesium 2.8.18.18.8.1Francium 2.8.18.32.18.8.1

8. They are also known as alkali metals which react with water toform alkaline solutions.

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9. All Group 1 elements have one valence electron in theiroutermost occupied shells.

Physical Properties of Group 1 Elements1. Group 1 elements are soft metals with lowdensities and

lowmelting points as compared to other metals such as ironand copper.

2. They have silvery and shiny surfaces.

3. They are goodconductor of heat and electricity.

Table 1: Physical Properties of Group 1 Elements

6. From Table 1, when going down the group, atomic size anddensity increase.

7. When going down the group, melting points and boiling points

decrease

Chemical Properties of Group 1 Elements

Elements/symbol

Electronarrangement

Atomicradius(nm)

Meltingpoints(C)

Boilingpoints(C)

Density(g cm-3)

Lithium, Li 2.1 0.15 180 1336 0.57

Sodium, Na 2.8.1 0.19 98 883 0.97

Potassium, K 2.8.8.1 0.23 64 756 0.86

Rubidium, Rb 2.8.18.8.1 0.25 39 701 1.53

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Lithium, sodium and potassium have similar chemicalpropertiesbut differ in reactivity.

Let us carry out this Experiment!Practical Book Experiment 4.1, page 35Activity 4.3, page 38

1. Alkali metals react vigorously with water to produce alkalinemetal hydroxide solutions and hydrogen gas.

Chemical equation;

2Li + 2H2O 2LiOH + H2Lithium Water Lithium Hydrogen

hydroxide gas

2Na + 2H2O 2NaOH + H2

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Sodium Water Sodium Hydrogenhydroxide gas

2K + 2H2O 2KOH + H2

Potassium Water Potassium Hydrogenhydroxide gas

2. Alkali metals react rapidly with oxygen gas, to produce whitesolid metal oxides.

Chemical equations;

4Li + O2 2Li2OLithium Oxygen Lithium

gas oxide

4Na + O2 2Na2OSodium Oxygen Sodium

gas oxide

4K + O2 2K2OPotassium Oxygen Potassium

gas oxide

3. Alkali metals burn in chlorine gas to form white solid metalchlorides.

Chemical reaction;

2Li + Cl2 2LiClLithium Chlorine Lithium

gas chloride

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2Na + Cl2 2NaClSodium Chlorine Sodium

gas chloride

2K + Cl2 2KClPotassium Chlorine Lithium

gas chloride

4. Alkali metals burn in bromine gas to form metal bromides.

For example,

2Li + Br2 2LiBrLithium Bromine Lithium

gas bromide

2Na + Br2 2NaBrSodium Bromine Sodium

gas bromide

2K + Br2 2LiBrPotassium Bromine Potassium

gas bromide

5. Therefore, alkali metals have similar chemical properties.

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Whyalkali metals have similarchemical properties?


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Alkali metals have one valence electron in their outermostoccupied shells.

Each of them reacts by donating one electron from its

outermost occupied shell to form an ion with a charge of+1,thus achieving the stable electron arrangement of the atom ofnoble gas.

Li Li+ + 1e-

2.1 2

Na Na+ + 1e-2.8.1 2.8

K K+ + 1e-

2.8.8.1 2.8.8

6. The reactivity of Group 1 elements increases down the group.

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WhyThe reactivity of Group 1elements increases down the group?


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Going down Group 1, the atomic size (atomic radius)increases.

The single valence electron in the outermost occupied shell

becomes furtheraway from the nucleus

Hence, the attraction between the nucleus and the valenceelectron becomes weaker

Therefore, it is easier for the atom to donate the single valenceelectron to achieve the stable electron arrangement.

Safety precautions in handling Group 1 elementsAlkali metals are very reactive. Safety precautions must be taken whenhandling alkali metals.

The elements must be stored in paraffin oil in bottles Do not hold alkali metals with your bare hands Use forceps to handle them Wear safety goggles

Wear safety gloves Use a small piece of alkali metal when conducting experiments

Hw: QR C pg. 69 no. 1,2,3


D. GROUP 17 ELEMENTS

1. The group 17 elements are:

Flourine 2.7

Chlorine 2.8.7

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Bromine 2.8.18.7

Iodine 2.8.18.18.7

Astatine 2.8.18.32.18.7

2. Group 17 elements are known as halogens

3. Halogens exist as diatomic molecules.

4. Halogens have seven valence electrons.

Physical Properties of Group 17 Elements

1. All Group 17 elements are non-metals.

Element SymbolProton

Number

Physicalstate atroom

temperature

ColourMeltingpoint

Boilingpoint

Flourine F 9 Gas Pale yellow

Increase IncreaseChlorine Cl 17 Gas

Greenish-yellow

Bromine Br 35 LiquidReddish-

brown

Iodine I 53 SolidPurplish-

black

2. Halogen have low melting and boiling points becausetheir molecules are attracted to each other by weakforces. Less energy is needed to overcome the forces .

3. When going down the group, the melting and boilingpoints increases. This is because the molecular sizeincreases.

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Diagram:


1. Group 17 elements react with water, metal and alkali.

a) Halogen react with waterto form 2 acids

In general:

X2 + H2O HX + HOX ; X is halogen

HX and HOX solutions are acidic. HOX solution exhibits bleaching

properties.

Example:

Cl2 + H2O HCl + HOCl

Chlorine Water Hydrochloric Hypochlorus

Cl2

Cl2

Cl2

Cl2

van derWaalsforces

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What is physicalstate of astatine?

Practical book Carry out anexperiment 4.2 page 39

HW: Draw diagram and answerthe question


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acid acid

Br2 + H2O HBr + HOBr

Bromine Water Hydrobromic Hypobromus

acid acid

I2 + H2O HI + HOI

Iodine Water Hydrobromic Hypoiodus

acid acid

b) Halogens in gaseous state react with hot iron

To form a brown solid , iron(III) halides.

In general:

2Fe + 3X2 2FeX3 ; X is halogen

Example :

2Fe + 3Br2 2FeBr3Iron Bromine Iron(III) bromide

2Fe + 3Cl2 2FeCl3Iron Chlorine Iron(III) chloride

2Fe + 3I2 2FeI3

Iron Iodine Iron(III) iodide

c) Halogens react with sodium hydroxide solution , NaOH.

To form sodium halide, sodium halate and water

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The halogens are decolourised during these reaction.

In general:

X2 + NaOH NaX + NaOX + H2O

[X is halogen]

Example:


Fluorine is the mostelectronegative element

Elelctronegativity of an element refers to the measurement of the

strength of an atom in its molecule to attract electrons towards itsnucleus.

WHY they have similar chemical properties???

Halogens have 7 valence electrons.

When halogens take part in chemical reactions, their atomalways gain one electron to achieve a stable octet electronarrangement.

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2 NaOH + I2 NaI + NaOI + H2O

Chlorine, Bromine and Iodine have similar

chemical properties but differ in reactivity.

The Reactivity of Halogens decrease down the group.

Do You Know WHY???


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The explanation

a) The atomic size increases down the group.

b) The distance of the outermost shell becomesfurther from the nucleus.

c) The force of attraction of the nucleus on the electronsof the outermost shell decrease.

d) The tendency of an atom to receive one electron toachieve an octet electron arrangement decrease

Safety Precautions in handling Group 17 elements

1. The vapour of Flourine, Chlorine and Bromine arepoisonous.

2. The following precaution should be taken when handlinghalogen:

a) Halogen gas and liquid should be handled inside afume chamber

b) Wear safety goggles when handling halogen fumes.

c) Wear safety gloves when handling halogen materials.

Do It Yourself

Element X Y Z

Proton number 9 17 35

1. Elements X, Y and Z are same group in the periodictable.

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a. What is the valence electron of the elements X,Y andZ?

seven(7)

b. Which group in the periodic table can you find theelements X,Y and Z?

group 17

c. Element Y can react with water. What are the

properties of the solution produced?

Acidic and bleaching properties

d. Write an equation for the reaction between element Zand hot iron.

2Fe + 3Z2 2FeZ3

3. List all halogen elements from the top to the bottom ofgroup 17.

Flourine, Chlorine, Bromine, Iodine and Astatine

4. Which are the most reactive and least reactivehalogen?

Most reactive: Flourine least reactive : Astatine

4. Write the chemical equations for the following reaction:a) Chlorine with water

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Cl2 + H2O HCl + HOCl

b) bromine with iron

2 Fe + 3Br2 2FeBr3

c) iodine with sodium hydroxide

2 NaOH + I2 NaI + NaOI + H2O

5. Explain the changes to the reactivity of halogens when

going down group 17.

The atomic size of halogen increases down the group.

The distance of the outermost shell becomes furtherfrom the nucleus.

Therefore, the force of attraction of the nucleus on the

electrons of the outermost shelldecrease.

The tendency of an atom to receive one electron toachieve an octet electron arrangement decrease. Thiscauses the reactivity to decrease down the group.


E. Elements in a PERIOD 3

Elements in period 3

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Na Mg Al Si P S Cl Ar

2.8.1 2.8.2 2.8.3 2.8.4 2.8.5 2.8.6 2.8.7 2.8.8

Physical properties

symbol Na Mg Al Si P S Cl Ar

Proton number 11 12 13 14 15 16 17 18

Atomic radius (pm) 186 160 143 118 110 104 100 94

electronegativity 0.9 1.2 1.5 1.8 2.1 2.5 3.0 -

Melting point (oC) 98 650 660 1411 44 115 -101 -189

Boiling point (oC) 892 1105 2517 3231 280 444 -34 -186

Metal properties- element in period 3 can be classified into three type

metal : Na, Mg, Al

semi-metal : Sinon-metal : P, S, Cl, Ar

- the metal oxides are usually basic

- non-metallic oxides are acidic oxide

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The oxide of the elements changes from basic to amphoteric and

then acidic across the eriod.

SO2 (p) + H2O (ce) H2SO3 (ak)

Na2O (p) + H2O (ce) 2NaOH (ak)


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- Aluminium oxide, Al2O3 is an amphoteric

i. Aluminium oxide is a bases/alkaly when reacted with acid.

ii. Aluminium oxide is an acid when react with alkali.

Proton number

Size of atom

why?- All the element in period 3 have three filled electron shell butthe proton is increasing by one unit across the period

- As a result, the increase of proton number is increasing theelectrostatic force between the nucleus and the valenceelectron

- The valence electron are pulled closer to the nucleus,causing the atomic radius to decrease

Electronegativity

why?

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Amphoteric oxides is oxide that had acidic and basic properties

Al2O3 (p) + 6HCl (ak) 2AlCl (ak) + 3H2O (ce)

Al2O3 (p) + 2NaOH (ak) + 3H2O (ce) 2NaAl(OH)4 (ak)

Proton number is increasing at one unit when across the period

The atomic radius is decreasing when across the period

The electronegativity increases across the period


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- Electronegativity is a measurement of the tendency of anelement to attract the electrons

- The force of attraction of the nucleus is increase whenacross the period because the size of atomic radius is

decreasing and the proton number is increasing.

Uses of semi-metals- Silicon is a semi-metal, known as metalloid.- Silicon is use in microelectronic industry like transistor,diode

and another electronic component.- Silicon can be built onto a crystal of silicon to make a

microchip.


E. Transitions Elements

Transitions elements are elements from group 3 to Group 12.

Character:

- solid with shiny surfaces- ductile- malleable- high tensile strength- high melting and boiling points- high densities- good conductors of heat and electricity

(typical character of metals)

How to differentiate transition metal from other metal?

Three special characteristic for transition elements

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1. Transition elements show different oxidation number intheir compounds.

2. Transition elements form coloured ions or compounds.3. Transition elements and their compounds are useful

catalyst.1. Transition elements show different oxidation number in their

compounds.

They exhibit a wide range ofoxidation states or positively chargedforms. The positive oxidation states allow transition elements toform many different ionic and partially ionic compounds.

All the transition elements except scandium and zinc havemore than one oxidation number.

For example iron. Iron have 2 oxidation number as iniron(II), Fe2+ and iron(III), Fe3+

Example:

Compound Formula Oxidation number

Iron(II) sulphate FeSO4 +2Iron(III) chloride FeCl3 +3

Copper(I) oxide Cu2O +1

Copper(II) sulphate CuSO4 +2

Manganese(II) sulphate MnSO4 +2

Manganese(IV) oxide MnO2 +4

2. Transition elements form coloured ions or compounds

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Do you know why the gemstoneshave different colour?
http://chemistry.about.com/library/weekly/aa122002a.htmhttp://chemistry.about.com/library/weekly/aa122002a.htm


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Gemstones

Transition metals solutions

http://chemistry.about.com

3. Transition elements and their compounds are useful catalyst

Ruby Emerald Sapphire Amethyst

cobalt(II) nitrate(red)

potassium dichromate(orange)

potassium chromate(yellow)

nickel(II) chloride(light blue)

copper(II) sulfate(blue)

potassium permanganate(purple)

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Catalyst: Chemical substance use to speed up the chemicalreactions

A specific catalyst is used for a specific reaction.

Example

Process Catalyst To produce

Haber Process Iron filling, Fe Ammonia

Contact Process Vanadium(v) oxide, V2O5 Sulphuric acid

Ostwald Process Platinum, Pt Nitric acid

Hydrogenation Nikel, Ni Margarine

Transitions elements are widely used in our daily lives.

Chapter 4 : Periodic Table of Elements

Exercise :

1. Below is a list of elements represented by the symbols as shown:

P11 , Q

12

6 , R19

9 , S27

13 , T35

17 , U39

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(a) Pick a pair of elements that belongs to the same Group in the Periodic Table.

Explain your answer.

[2 m

(b) State the

Group in which element Q belongs to.

[

Period in which element Q belongs to.

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[

(c) State elements which are

(i) metals :

(ii) non-metals :

[2

(d) Which element will form amphoteric oxide?

Which element reacts with cold water?

Write a balanced chemical equation for the reaction.

(f) Write the formula of the ion formed by element S.

Explain the meaning of the term electronegativity.

Which of the two elements R and T is more electronegative?

Explain your answer in (g)(ii).

[2

Which of the two elements S and T has smaller atomic size?

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