Chapter 4 Form 4 : Periodic Table

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PERIODIC TABLE

• Elements are arranged according their increasing proton number.
• Vertical columns = groups(according to their number of valence electron/s
• Horizontal rows = periods (number of electron shells filled by electrons)

GROUP 18 

• Known as noble gases/inert gases(chemically unreactive elements)
• Non-metals that exist as monoatomic colourless gases. 
• Members : Helium(He), Neon(Ne), Argon(Ar), Krypton(Kr), Xenon(Xe), Radon(Ra).

Physical Properties of Group 18

• Very small atomic sizes. 
• Low melting and boiling points (Weak van der Waals’ forces of attraction between atoms)
• Low densities (Very small masses but huge volumes)
• Melting and boiling points of elements increase down the Group 18. 

Chemical Properties of Group 18

1. All Group 18 elements are chemically inert/unreactive. 
2. The outermost electron shell of each member is fully occupied by electrons. 
3. This is a stable electron arrangement which in

• Helium, it is said achieve duplet electron arrangement.
• Other than Helium, it is said achieve octet electron arrangement. 

Uses of Group 18 Elements

Helium : To fill airships and weather balloons. 

Helium : used as artificial atmosphere in oxygen tank for divers.

Neon : Advertising lights

Neon : Used in aeroplane runway lights

Argon : To fill light bulbs.

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

Krypton : To fill photographic flash lamps.

Xenon : Making electron tubes and stroboscopic lamps

Radon : Used to treat cancer

Group 1 Elements

• Consists of lithium(Li), sodium(Na), potassium(K), rubidium(Rb), caesium(Cs) and francium(Fr). 
• They are known as alkali metals because they react with water to produce alkaline solution.

Physical Properties of Group 1 Elements

• Soft 
• Low melting points
• Low densities
• Shiny and silvery surface
• Good conductor of heat
• Good conductor of electricity
• Hardness, melting point and boiling of the elements decrease. 

Chemical Properties of Group 1 Elements

• All react with water to produce alkaline metal hydroxide solution and hydrogen gas. 
• 2X(s) + 2H2O(l) -> 2XOH(aq) + H2(g)

How to test the alkaline solution?

Put the element group 1 in the water. By using forceps or goggle. Do not hold the element by using hand. 

• All burn in oxygen gas to produce white solid metal oxides. 
• 4X(s) + O2(g) -> 2X2O(s)
• The oxide dissolve in water to form alkaline metal hydroxide solution.
• X2O(s) + H2O(l) -> 2XOH(aq)

Why all elements in Group 1 have same chemical properties?

• Chemical reaction is all about the activity of electron/s
• All the elements have one valence electron.
• Each of them reacts by donating one valence electron to form an ion with a charge of +1 to achieve stable electron arrangement.

Why the reactivity of elements increases down the Group 1?

• Atomic size of Group 1 elements increases from lithium to francium./Number of shells occupied by electrons increases.
• Distance between the valence electron in the outermost shell and positive nucleus increases down the Group 1. 
• Attraction between nucleus and valence electron decreases.
• It is easier for the atom to lose the valence electron to achieve stable electron arrangement.

Group 17 Elements

• Members  are fluorine(F2) , chlorine(Cl2), bromine(Br2), iodine(I2), and astatine(At2) 
• The elements are also known as halogens which exist as diatomic molecules.

Physicals properties of Group 17 elements

• They have low melting and boiling points because molecules are attracted to each other by weak van der Waals’ forces of attraction. 
• The melting and boiling points of the elements increases down Group 17.
• This change the states of elements from gas to solid and the colour of elements from lighter colour to darker colour.

1. Fluorine in gas state the colour is PALE YELLOW
2. Chlorine in gas state the colour is GREENISH YELLOW
3. Bromine in liquid state the colour is REDDISH BROWN
4. Iodine in solid state the colour is PURPLISH BLACK

Why the melting and boiling points of elements increases down Group 17?

• Molecular size/relative molecular mass of the elements increases down Group 17.
• Forces of attraction between molecules/Intermolecular forces of attraction increases.
• More heat is needed to overcome the stronger forces of attraction between the molecules.

All members have similar chemical properties but differ in the reactivity.

• React with water to form two acids : X2(g) + H2O(l)  ->   HX(aq) + HOX(aq)
• Example: 

Cl2(g) + H2O(l)    ->      HCl(aq)     +      HOCl(aq)

• Halogens in gaseous state react with hot iron to form brown solid : 2Fe(s) + 3X2(g) -> 2FeX3(s)
• Example: 2Fe(s) + 3Cl2(g) -> 2FeCl3(s) 
• solid iron(III) chloride(brown)

• Halogens react with sodium hydroxide solution to produce sodium halide, sodium halate(I) and water
• X2 + 2NaOH(aq) -> NaX(aq) + NaOX(aq) + H2O(l)
• Example:
• Cl2 + 2NaOH(aq) -> NaCl(aq) + NaOCl(aq) + H2O(l)

Why all halogens possess similar chemical properties?

• Chemical reaction = lose or accept electron/s
• All halogens always gain one electron to achieve stable octet electron arrangement. 
• Therefore, they have similar chemical properties. 

Why chemical reactivity of halogens decreases down Group 17?

• Atomic size/number of electron occupied shells of halogens increases down Group 17.
• The outermost shell becomes further from the nucleus of the atom.
• Strength to attract one electron into the outermost shell by the nucleus becomes weaker.
• Reactivity decreases. 

Period 

• Elements across a period exhibit a periodic change in properties.
• Period 3
• Proton number increases by one unit from one element to the next element
• All the atoms of the elements have three shells occupied with electrons
• The number of valence electrons in each atom increase from 1 to 8
• All the elements exist as solid except chlorine and argon which are gases
• The atomic radius of elements decreases. This is due to the increasing nuclei attraction on the valence electrons.
• The electronegativity of elements increases. This is also due to the increasing nuclei attraction on the valence electrons and the decreases in atomic size. 

• Oxides of elements change from basic to amphoteric and then to acidic across the period towards the right.
• Basic oxides – react with acids to form salt and water
• Acidic oxides – react with alkalis to form salt and water
• Amphoteric oxides – react with both acids and alkalis to form salt and water. 

                              

Transition Elements

• Elements from Group 3 to Group 12 in the Periodic Table.
• Common characteristics :

1. Solid metal with shiny surface. 
2. Good conductor of heat and electricity.
3. High melting and boiling points.
4. Hard, malleable and ductile.

• Special characteristics

1. Show different oxidation numbers in their compounds
2. Form coloured ions or compounds
3. Use as catalysts
4. Form complex ions

• Show different oxidation numbers in their compound
• Form coloured ions or compounds
• As a catalyst