Chapter 4 B Periodic Table Of Elements 2f3m32

PERIODIC TABLE OF ELEMENTS

PERIODIC TABLE OF ELEMENTS • Introduction:

• All goods in supermarket are well arranged to ease customer. • They are arranged in particular manner. • So do with the elements around us such as hydrogen, carbon and many more. • They are systematically and orderly arranged in a table called the Periodic Table of Elements.

Historical Development of the Periodic Table

Periodic Table of Elements

Arrangement of Elements in The Periodic Table Basic principle of arrangement in Periodic Table : • Increasing order of proton number. • Range : 1 to 113 proton number. • Elements with similar chemical properties are placed in the same vertical column called GROUP. • There are 18 groups. • 7 horizontal rows of elements called PERIOD. • The number of valence electrons in an atom decides the position of the group of an element in the Periodic Table. • The position of the period of an element in the Periodic Table is determined by the number of shells occupied with electrons in the atom of that element.

For elements with 1 to 2 valence electron: The group number = number of valence For elements with 3 to 8 valence electron: The group number = number of valence + 10 The period number = the number of shells occupied with electrons

• Some element group have been given a special names. For examples, • Group 1 : Alkali metal , • Group 17 : Halogen • Group 18 : Noble gases

Example :

Do it Yourself 1. Element D has a proton number of 19. Where is element D located in the Periodic Table? 2. An atom of element E has 10 neutron. The nucleon number of element E is 19. in which group and period is element E located in the Periodic Table? 3. An atom of element G has 3 shells occupied with electrons. It is placed in Group 17 of the Periodic Table. What is the electron arrangement of atom G?

Do it Yourself …answer

B. Group 18 Elements

Group 18 Elements • Group 18 elements are known as noble gases or inert gases. • Group 18 elements consist of helium, neon, argon, krypton, xenon and radon

Group 18 Elements Element

Proton number

Electron arrangement of atom

Helium, He

2

Neon, Ne

10

Argon, Ar

18

Krypton, Kr

36

2. 8. 18. 8

Xenon, Xe

54

2. 8. 18.18. 8

• The outermost occupied shell is full

Group 18 Elements - Physical properties • Noble gases exist as monoatomic gases (exist as single atom). – They are colourless gases at room temperature. – They cannot dissolve in water. – They cannot conduct electricity and heat.

Group 18 Elements - Physical properties – They have •very small atomic sizes. – Atomic radius increase down the group – The number of filled electron shell increase, the valence electron is further from the nucleus

•low melting and boiling point. – Attracted by very weak van der Waals’ forces of attraction – Increase down the group – As the atomic size increase, the van der Waals’ force of attraction become stronger

• low melting and boiling point.

Group 18 Elements - Physical properties

The inert property of Group 18 elements • The outermost occupied shell of the atom of each element in Group 18 is full of electrons. • Helium has 2 valence electron. This is called a duplet electron arrangement. • Neon, argon and other noble gases have 8 valence electrons. This is called octet electron arrangement (2 .8, 2. 8. 8). • These electron arrangements are very stable. • Therefore, noble gases are chemically unreactive or known as inert. • They do not need to gain, lose or share electrons with other elements.

Uses of Group 18 elements

•Helium gas is used to fill airships and weather balloons. • The diver’s oxygen tank consists of a mixture of helium and oxygen. • Liquid helium is used to cool metals into superconductors.

•Neon gas is used in advertising lights and television tubes.

Uses of Group 18 elements

•Argon gas is used to fill light bulbs.

•Krypton gas is used in laser to repair the retina of the eye. • It is also used to fill photographic flash lamps.

C. Group 1 Elements

Group 1 Elements • The elements in Group 1 are

– Lithium – Sodium – Potassium – Rubidium – Caesium – Fransium

• They are also known as alkali metals which react with water to form alkaline solutions. • All Group 1 elements have one valence electron in their outermost occupied shells.

Group 1 Elements - Physical Properties 1. Group 1 elements are soft metals with low densities and low melting points as compared to other metals such as iron and copper. 2. They have silvery and shiny surfaces.

3. They are good conductor of heat and electricity.

• From Table 1, when going down the group, atomic size and density increases. – The number of filled electron shell increases down the group, the distance between the outermost electron shell and the nucleus inceases.

• When going down the group, melting points and boiling points decrease – The metallic bond between the atoms become weaker

Chemical Properties of Group 1 Elements • Lithium, sodium and potassium have similar chemical properties but differ in reactivity

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

Alkali metals react vigorously with water

Alkali metals react vigorously with water

Chemical Properties of Group 1 Elements 2. Alkali metals react rapidly with oxygen gas, to produce white solid metal oxides.

Chemical Properties of Group 1 Elements 3. Alkali metals burn in chlorine gas to form white solid metal chlorides

Chemical Properties of Group 1 Elements 4. Alkali metals burn in bromine gas to form metal bromides

• Therefore, alkali metals have similar chemical properties • Do you know why ? Alkali metals have one valence electron in their outermost occupied 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 of noble gas.

• The reactivity of Group 1 elements increases down the group. • Do you know why ? i. Going down Group 1, the atomic size increases. ii. The single valence electron in the outermost occupied shell becomes further away from the nucleus iii. Hence, the attraction between the nucleus and the valence electron becomes weaker iv. Therefore, it is easier for the atom to donate the single valence electron to achieve the stable electron arrangement.

D. Group 17 Elements

Group 17 Elements 1. The group 17 elements are: • Flourine • Chlorine • Bromine • Iodine • Astatine 2. Group 17 elements are known as halogens 3. Halogens exist as diatomic molecules. 4. Halogens have 7 valence electrons.

Group 17 Elements - Physical Properties 1. All Group 17 elements are non-metals. 2. They are insulators of heat and electricity. 3. Halogen have low melting and boiling points because their molecules are attracted to each other by weak force. 4. When going down the group, the melting and boiling points increases. This is because the molecular size increases. The van der Waals’ forces of attraction between the molecules become stronger. 5. The colour of the halogen becomes darker down the group

Group 17 Elements - Physical Properties

Element Symbol

Proton Number

Flourine

F

9

Electron Physical Colour Arrangement state at room temperature 2.7 Gas Pale yellow

Chlorine

Cl

17

2.8.7

Bromine

Br

35

2.8.18.7

Liquid

Iodine

I

53

2.8.18.18.7

Solid

Gas

Greenishyellow Reddishbrown Purplishblack

Melting point

Boiling point

Increase

Increase

Group 17 Elements - Chemical Properties a) Halogen react with water • To 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

+

Hydrochloric acid

HOCl hypochlorous(I) acid

Group 17 Elements - Chemical Properties b) Halogens in gaseous state react with hot iron • To form a brown solid , iron (III) halides

In general: 2 Fe +

3X2

Example: 2 Fe +

3Br2

 2FeX3



2FeBr3

; X is halogen

Group 17 Elements - Chemical Properties c) Halogens react with sodium hydroxide solution , NaOH. • To form sodium halide, sodium halate and water • The halogens are decolourised during these reaction

In general: X2 + NaOH

 NaX + NaOX + H2O

Example: 2NaOH + I2



NaI

+

sodium iodide

NaOI

; X is halogen

+

H2O

sodium iodate(I)

• Chlorine, Bromine and Iodine have similar chemical properties but differ in reactivity. Why they have the similar properties?? I.

Halogens have 7 valence electrons.

II. When halogens take part in chemical reactions, their atom always gain one electron to achieve a stable octet electron arrangement.

• The Reactivity of Halogens decrease down the group. WHY? I. The atomic size increases down the group. II. The distance of the outermost shell becomes further from the nucleus. III. The force of attraction of the nucleus on the electrons of the outermost shell decrease. IV. The tendency of an atom to receive one electron to achieve an octet electron arrangement decrease

Do It Yourself Element

X

Y

Z

Proton number

9

17

35

1. Elements X, Y and Z are same group in the periodic table. a. What is the valence electron of the elements X,Y and Z? b. Which group in the periodic table can you find the elements X,Y and Z? c. Element Y can react with water. What are the properties of the solution produced? d. Write an equation for the reaction between element Z and hot iron.

Do It Yourself…answer Element

X

Y

Z

Proton number

9

17

35

1. Elements X, Y and Z are same group in the periodic table. a. What is the valence electron of the elements X,Y and Z? seven or 7 a. Which group in the periodic table can you find the elements X,Y and Z? group 17 a. Element Y can react with water. What are the properties of the solution produced? acidic and bleaching properties a. Write an equation for the reaction between element Z and hot iron. 2Fe + 3Z2 2FeZ3

E. Transition Elements

E. TRANSITION ELEMENTS • Transition elements are elements from Group 3 to Group 12 in the Periodic Table of the elements. • Examples of transition elements are iron (Fe), zinc (Zn), copper (Cu), silver (Ag), gold (Au) and mercury.(Hg).

E. TRANSITION ELEMENTS All transition elements are metals, thus, these elements have the following properties : 1. 2. 3. 4. 5. 6. 7.

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

E. TRANSITION ELEMENTS • Special characteristics of transition elements

1. Different Oxidation Numbers • Transition elements can form ions with different oxidation numbers when forming compounds. Transition Element

Oxidation Numbers

Name of ion

Ionic symbol

Example of compound

+2

Iron(II) ion

Fe2+

FeCl2

+3

Iron (III) ion

Fe3+

FeCl3

+1

Copper(I) ion

Cu+

Cu2O

Cu2+

CuO

Ni2+

NiSO4

Ni3+

NiCl3

Iron, Fe

Copper, Cu +2

+2 Nickel, Ni +3

Copper (II) ion Nickel (II) sulphate Nickel (III) chloride

E. TRANSITION ELEMENTS • Special characteristics of transition elements

2. Coloured Ions or Compounds Name of ion of transition element Chromate ion

Formula of ion of transition element CrO42-

Colour in aqueous solution Yellow

Dichromate ion

Cr2O72-

Orange

Permanganate ion

MnO4-

Purple

Iron (II) ion

Fe2+

Green

Iron (III) ion

Fe3+

Brown

Copper (II) ion

Cu2+

Blue

Cobalt (II) ion

Co2+

Pink

Manganese (II) ion

Mn2+

Pink

Chromium (III) ion

Cr3+

Green

Nickel (II) ion

Ni2+

Green

• Examples of some precious stones and the transition elements present which give their distinctive colours :

Precious stone

Colour

Ruby

Red

Transition element present Chromium

Sapphire

Blue

Iron and Titanium

Emerald

Green

Chromium

Amethyst

Purple

Manganese

E. TRANSITION ELEMENTS • Special characteristics of transition elements

3. Act as catalysts • Transition elements or compounds can act as catalysts in certain reactions. • Catalysts are chemicals which can increase the rate of a chemical reaction Transition element

Process

Product

Iron

Haber Process

Ammonia

Vanadium (V) oxide

Process

Sulphuric acid

Platinum

Ostwald Process

Nitric acid

F. Elements in Period

1. Properties of Elements in Period 3 • Periods are horizontal row in the Periodic Table. • The elements in Period 3 are Sodium (Na), Magnesium (Mg), Aluminium (Al), Silicon (Si), Phosporus (P), Sulphur (S), Chlorine (Cl), Argon (Ar).

1. Properties of Elements in Period 3 Element of Period 3

Na

Mg

Al

Si

P

S

Cl

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

Atomic Radius (pm)

186

160

143

118

110

104

100

94

Physical state at room temperature

Solid

Solid

Solid

Solid

Solid

Gas

Gas

Electronegati vity

0.9

1.2

1.5

2.1

2.5

3.0

-

Solid Hjklh

1.8

Based on the table above, we notice the trends of changes across Period 3, i.

The proton number increases by one unit from one element to the next element. ii. All the atoms of the elements have three shells occupied with electrons. iii. The number of valence electrons in each atom increases from 1 to 8. iv. All the elements exist as solid except chlorine and argon which are gases.

1. Properties of Elements in Period 3 Element of Period 3

Na

Mg

Al

Si

P

S

Cl

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

Atomic Radius (pm)

186

160

143

118

110

104

100

94

Physical state at room temperature

Solid

Solid

Solid

Solid

Solid

Gas

Gas

Electronegati vity

0.9

1.2

1.5

2.1

2.5

3.0

-

Solid Hjklh

1.8

Based on the table above, we notice the trends of changes across Period 3, v.

The atomic radius of elements decreases. This is due to the increasing nuclei attraction on the valence electrons. vi. The electronegativity of elements increases. This is also due to the increasing nuclei attraction on the valence electrons and the decrease in atomic size.

Properties of oxides elements • Elements of periods 3 can be classified into metals or non-metals based on the basic or acidic properties of their oxides. • Metal form oxides with basic properties. • Non- metal form oxides with acidic properties. • Some metals show both acidic and basic properties. • These oxides are known as AMPHOTHERIC OXIDES.

• Na and magnesium form basic metal oxides: Na2O, MgO. • Aluminium ,form amphoteric oxide: Al2O3.\ • Silicon, Phosporus, sulphur and chlorine form acidic non-metal oxides. • Refer figure 4.10(pg 74). • The properties of the oxides of elements in P3 change frm basic properties the acidic properties when going across the period.

2. Acid-base properties of oxides of elements in Period 3.

• Basic oxides reacts with acids to form salts and water. Example : Na2O(s) + 2HNO3(aq)  2NaNO3(aq) + H2O(l)

• Acidic oxides reacts with alkali to form salts and water. Example : SiO2(s) + 2NaOH(aq)  Na2SiO3(aq) + H2O(l)

• Amphoteric oxides can react with both acids and alkalis.

2. Acid-base properties of oxides of elements in Period 3.

• The elements change from metals to metalloid and finally to non-metals across the period

• Therefore Na & Mg are metals, Al is metalloid, Si, P, S & Cl are non-metals.

3. Uses of semi-metals in industry

•Semi-metals or metalloids are weak conductors of electricity. Semi-metals such as silicon and germanium are used as semiconductors.

•Semi conductors are used to make diodes and transistors that widely used in the making of microchips for the manufacture of electrical and microelectronic equipments such as computers, mobile phones, televisions and video recorders.