Chapter 4 The Periodic Table

CHAPTER 4

Periodic Table

of Elements

A. The Periodic Table of Elements

Historical Development of the Periodic Table

Arrangement of elements in the Periodic Table

• Arranged in an increasing order of proton number (from 1 → 113)

• Elements with similar chemical properties are placed in the same vertical column

Each vertical column of elements is called a group.

The vertical columns are known as Group 1 to Group 18.

The number of valance electrons in an atom decides the position of the group of an element in the Periodic Table.

For elements with 1 to 2 valence electrons,

The group of an element

= The number of valence electrons in its atom

For elements with 3 to 8 valence electrons,

The group of an element

= The number of valence electrons in its atom + 10

Each of these horizontal rows of elements is called period.

The horizontal rows are known as Period 1 to Period 7.

The number of shells occupied with electrons in the atom decides the position of the period of an element in the Periodic Table.

B. Group 18 Elements

• Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe) and Radon (Ra).

• The elements are known as noble gases.

• Noble gases are monoatomic.

Physical properties

1. Low melting point/boiling point

2. Low density

3. Colourless gases

4. Very small atomic size

5. Insoluble in water

6. Cannot conduct electricity

7. Poor conductor of heat

Inert property of Group 18

• All noble gases are inert (chemically unreactive)

• 2 valence electron – duplet electron arrangement

• 8 valence electron – octet electron arrangement

Why noble gases exist as monoatomic gases and chemically unreactive?

Ans:

• Because the outermost shell occupied with electron are full / achieve the duplet or octet electron arrangement.

• So, noble gas does not donate, receive or share electron with other elements.

Going down Group 18

Size of atom increase

• Going down Group 18 elements, the numbers of shells occupied with electron in the atom increase.

• The size of atom increase.

Melting & boiling points increase

• Going down the group, size of atom increase / become bigger

• The forces of attraction between the atoms become stronger

• Thus, more heat energy is needed to overcome the stronger forces of attraction

Use of Group 18 elements

Helium

• Used to filled airships and weather balloons

Neon

• Used in advertising light and television tubes

Argon

• Fill light bulbs

• Used to provide inert atmosphere for welding at high temperature

Krypton

• Used in lasers to repair the retina of the eye

• Used to fill photographic flash lamps

Radon

• Used in the treatment of cancer

Xenon

• Used for making electron tubes and stroboscopic lamps

• Used in bubble chambers in atomic energy reactors

C. Group 1 Elements

• Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Caesium (Cs), Francium (Fr)

• The elements are known as alkali metals.

Physical properties:

1. Low melting point/boiling point

2. Low density

3. Surfaces

4. Silvery and shiny surface

5. Good conductor of heat & electricity

Chemical properties:

With water

2M + 2H2O → 2MOH + H2

Example:

• 2Li + 2H2O → 2LiOH + H2

• 2Na + 2H2O → 2NaOH + H2

With oxygen gas

4M + O2 → 2M2O

Example:

• 4Na + O2 → 2Na2O

• 4K + O2 → 2K2O

Metal oxide with water

M2O + H2O → 2MOH

Example:

• Li2O + H2O → 2LiOH

• Na2O + H2O → 2NaOH

With chlorine/bromine gas

2M + Cl2 → 2MCl

2M + Br2 → 2MBr

Example:

• 2K + Br2 → 2KBr

• 2Na + Cl2 → 2NaBr

Going down Group 1

Size of atom increase

• Going down Group 1 elements, the numbers of shells occupied with electron in the atom increase.

• The size of atom increase.

Melting & boiling points decrease

• Going down the group, size of atom increase / become bigger

• The forces of attraction between the atoms become weaker

• Thus, less heat energy is needed to overcome the weak forces of attraction

Reactivity increase • Going down the group, size of atom increase / become

bigger • The single valence electron in the outermost occupied

shell become further away from nucleus • The attraction between the nucleus and valence

electron becomes weaker • It is easier for the atom to release/donate the single

valence electron to achieve the stable electron arrangement

• Reactivity increase

Safety precautions

• Must stored in paraffin oil in bottles

• Do not hold alkali metals with your bare hands

• Use forceps to take alkali metals

• Wear safety goggles and gloves

• Used only small pieces of alkali metal when conducting experiments

D. Group 17 Elements

• Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I), Astatine (At)

• The elements are known as halogens.

• Exist as diatomic molecules.

• They are poisonous.

Physical properties:

• Low melting point/boiling point

• Exist as diatomic molecule

• Change in physical state

Fluorine – pale yellow gas

Chlorine – greenish-yellow gas

Bromine – reddish-brown liquid

Iodine - purplish-black solid

Chemical properties:

Reaction with water to form 2 acids

X2 + H2O → HX + HOX

Example:

• Cl2 + H2O → HCl + HOCl

HX & HOX solution – acidic HOX solution – bleaching properties

Hydrochloric acid

Hypochlorus acid

Reaction with hot iron to form iron(III) halides (brown solid)

2Fe + 3X2 → 2FeX3

Example:

• 2Fe + 3Br2 → 2FeBr3

Reaction with sodium hydroxide solution, NaOH to form sodium halide, sodium halate(I) & water

X2 + 2NaOH → NaX + NaOX + H2O

Example:

• I2 + 2NaOH → NaI + NaOI + H2O Sodium iodide

Sodium Iodate(I)

Going down Group 17

Size of atom

• Going down Group 17 elements, the numbers of shells occupied with electron in the atom increase.

• The size of atom increase.

Melting & boiling points increase

• Going down the group, size of atom increase / become bigger

• The forces of attraction between the atoms become stronger

• Thus, more heat energy is needed to overcome the stronger forces of attraction

Reactivity decrease

• Going down the group, size of atom increase / become bigger

• The attraction between the nucleus and valence electron becomes weaker

• It is difficult for the atom to receive/attract one electron to achieve the stable electron arrangement

• Reactivity decrease

Safety precautions

• Handle the elements in a fume chamber

• Wear safety goggles and gloves when handling halogens

E. Elements in Period (Period 3)

Elements

• Sodium, Magnesium, Aluminium, Silicon, Phosphorus, Sulphur, Clorine, Argon

Acid-base properties of oxides of elements on Period 3

• Metal oxide:

Metal oxide that show basic properties

• Amphoteric oxide:

Metal oxide that show basic and acidic properties

• Non-metal oxide:

Metal oxide that show acidic properties

Elements in:

• Basic metal oxide:

Na, Mg

• Amphoteric oxide:

Al

• Acidic non-metal oxide:

Si, P, S, Cl

Across the period

• The proton number increase by one

• All the atoms have three shells occupied with electrons

• The number of valence electron increase by one

• All element exist as solid except chlorine and argon (gases)

• Size of atom decrease – force attraction between nucleus and valence electron become stronger

• Electronegativity increase:

• Size of atom become smaller

• Force attraction between nucleus and valence electron stronger

• It is easier for nucleus to attract electron into the atom

Use of semi-metal

• Semi-metal (metalloid) – weak conductors of electricity

Used as semiconductor

• Used of semiconductor:

Make diodes and transistors (making microchips for computer, mobile phones, televisions, video recorders etc.)

F. Transition Elements (Metals)

Elements

• Element from Group 3 to Group 12

Physical properties

1. Shiny surfaces

2. Ductile

3. Malleable

4. High tensile strength

5. High melting & boiling points

6. High density

7. Good conductor of heat & electricity

Special characteristics of transition elements

• Shows different oxidation numbers in their compounds

• Form coloured ions or compounds

• Useful as catalyst

Use in industries

Haber process:

• Manufactured of ammonia, NH3

• Catalyst: Iron, Fe

Ostwald process:

• Manufactured of nitric acid, HNO3

• Catalyst: Platinum, Pt

Contact process:

• Manufactured of sulphuric acid, H2SO4

• Catalyst: Vanadium(V) oxide, V2O5

Manufacture of margarine

• Catalyst: Nickel, Ni