inorganic chemistry - chapter 01 period 3, group 2

8/9/2019 Inorganic Chemistry - Chapter 01 Period 3, Group 2

1/21


2/21

Period 3 Elements: Sodium(Na) toArgon(Ar)

Element Na Mg Al Si P S Cl Ar

Group no. 1 2 13 14 15 16 17 18

Name Sodium Magnesium Aluminium Silicon Phosphorus Sulphur Chlorine Argon

Proton no. 11 12 13 14 15 16 17 18

Electronic

configuration

2.8.1 2.8.2 2.8.3 2.8.4 2.8.5 2.8.6 2.8.7 2.8.8

Valence shellelectronic

configuration

3s1 3s2 3s3 3s4 3s5 3s6 3s7 3s8

Physical state Solid Gas

Metallicproperty Metal Metalloid Non-metal

Atomic radius 0.156 0.136 0.125 0.117 0.110 0.104 0.099 0.088

Firstionisationenergy/kJ

mol-1

494 736 577 786 1060 1000 1260 1520


3/21

Physical Properties Across the

PeriodAtomic Radius Definition: The distance between the nucleus and the

outermost electronic shell that is filled with electrons.

Depend primarily on 2 major factors:Nuclear chargeScreening effect

nuclear charge, stronger attraction between nucleus andelectron cloud

Result: Decrease in atomic radius across the Period.


4/21

The screening effect depends on the number of innerelectronic shells that are filled with electrons.

The negatively charged electronic shells will repel oneanother causing the electron cloud to drift further awayfrom the nucleus. This will result in an increase in atomicradius.

Going across Period 3, electrons are added to the 3rd shell.At the same time, protons are added to the nucleus.

Therefore, the nuclear charge but screening effectremains almost constant.

Na Mg SiAl P SCl Ar


5/21

First Ionisation Energy Definition: The minimum energy required to remove an

electron from a gaseous atom to form a unipositive ion, per

mole of the atom, under standard conditions.

It is a measure of the strength of the attractive forcebetween the nucleus and the electron. This depends on the

nuclear charge and the size of the atom.

From left right, atomic radius as nuclear charge(screening effect remains almost constant). The electrons

are held progressively stronger by the nucleus.Hence, there is a general increase in the first ionisationenergy.


6/21

Electronegativity

Definition: The relative strength of an atom to attractelectrons in a covalent bond to which it is bonded.

Electronegativity across the Period.

Element Na Mg Al Si P S Cl

Electronegativity 0.9 1.2 1.5 1.8 2.1 2.5 3.0


7/21

Reaction of the Elements with

Oxygen The general trend of reactivity towards O2 becomes

weaker across Period 3.

Why?Electronegativity and ionisation energy across thePeriod. Therefore, it becomes more difficult to losean electron. Besides that, electron affinity acrossthe Period makes it easier to accept electrons.


8/21

Sodium reacts vigorously with oxygen as it is easier todonate the 3s1 electron. When burning sodium metal islowered in a jar with excess O2, Na glows brightly with a

yellow flame. A yellow substance, Na2O is formed, which is

basic.

Magnesium reacts with O2 when heated. It burns with awhite flame. It forms a white powder, MgO, which is basic.


9/21

Aluminium reacts slowly with air at room temperature. Whenheated strongly, it quickly forms a white oxide, Al2O3 whichis amphoteric.

Na, Mg and Al are all strong reducing agents as they areeasily oxidised by air.


10/21

Silicon reacts with O2 when heated strongly to form SiO2which is acidic.

Phosphorus burns readily in the air to form acidic oxides.White Phosphorus burst into flames in the presence of O2.If there are an excess of O2, phosphorus pentoxide, P4O10 isformed. If the supply of O2 is limited, phosphorus trioxide,

P4O6 is formed. Both oxides are acidic.


11/21

Sulphur burns with a bluish flame in air to form SO2 first.When left in the air, SO2 will slowly turn into SO3. Both

oxides are acidic.

Chlorine does not react with O2 because it is a strongoxidising agent. Cl2O can be prepared by heating Cl2 withmercury(II) oxide, HgO.


12/21

Reaction of the Elements with

Water

Sodium reacts vigorously in water with a hissing sound . An

alkaline solution is formed and H2 is given off.

Magnesium does not react with cold water. When heated it

reacts with steam. Forming MgO and H2.

Aluminium, silicon, phosphorus and sulphur do not react withwater.


13/21

Chlorine reacts slowly with water to form chlorine water,

which is a mixture of hydrochloric acid and chloric(I) acid.

Argon do not react with water.


14/21

Oxides of Period 3 ElementsNa2O MgO Al2O3 SiO2 P4O10 SO2 SO3 Cl2O7 Cl2O

+1 +2 +3 +4 +5 +6 +7 +8 +1

The general trend of the oxides is from basic to amphotericto acidic.

Na2O(s) + H2O(l) 2NaOH(aq)Sodium oxide dissolves in water to form sodium hydroxide, analkaline solution.

MgO(s) + H2O(l) Mg(OH)2(s)MgO(s) + 2HCl(aq) MgCl2(aq) + H2O(l)Magnesium oxide reacts with water very slowly to formmagnesium hydroxide, a white solid suspension called milk of

magnesia.


15/21

Al2O3(s) + 6HCl(aq) 2AlCl3(aq) +3H2O(l)

Al2O3(s) + 2NaOH(aq) + 3H2O(l) 2NaAl(OH)4(aq)

Aluminium oxide is amphoteric. It can react with acid and

base.

SiO2(s) + 2NaOH(aq) Na2SiO3(aq) + H2O(l)

Silicon dioxide react with alkali to form salt and water.

P4O10(s) + 6H2O(l) 4H3PO4(aq)

SO3(g) + H2O(l) H2SO4(aq)

Cl2O7(aq) + H2O(l) 2HClO4(aq)

All oxides of phosphorus, sulphur and chlorine react withwater to form acidic solutions.


16/21

Properties of Nitrates,Carbonates,Hydroxides and

Sulphates of Group 2 ElementsElement Be Mg Ca Sr Ba

Proton number 4 12 20 38 56

Atomic radius(nm) 0.11 0.16 0.20 0.21 0.23

Electronic configuration [He]2s2 [Ne]3s2 [Ar]5s2 [Kr]5s2 [Xe]7s2

Density(g cm-3) 1.86 1.74 1.55 2.60 3.50

Melting point(C) 1280 650 838 770 614First ionisationenergy(kJ mol-1)

899 738 590 548 502

Atomic radius(pm) 112 160 197 215 222

Standard reductionpotential(V)

-1.85 -2.37 -2.87 -2.89 -2.90


17/21

General Trends in the Physical and Chemical

Properties

The melting point and first ionisation energy down thegroup.

Atomic size and density down the group.

All Group 2 Elements are metals with metallic holding theatoms together in the solid state.

The strength of the metallic bond depends on the numberof electrons per atom donated to the delocalized electronsystem of the bond

Generally the larger the size of an atom, the weaker theattractions.


18/21

Thermal Decomposition of Nitrates, Carbonatesand Hydroxides

2M(NO3)2 2MO + 4NO2 + O2 All the nitrates of Group 2 are decomposed by heat to metal

oxides,nitrogen dioxide and oxygen gases.

MCO3 MO + CO2 All the carbonates of Group 2 decompose to metallic oxides

and carbon dioxide upon heating.

M(OH)2 MO + H2O All the hydroxides of Group 2 decompose to metallic oxides

and water vapour upon heating.


19/21

All nitrates, carbonates and hydroxides of Group 2 elementsdecompose to oxides.

Why?

The anion sizes of the carbonates, nitrates and hydroxidesare larger than the oxides. Therefore, their lattice energiesare smaller compared to the oxides. Hence, the oxides aremore stable than the carbonates, hydroxides and nitrates.

The heat of decomposition of the carbonates, nitrates andhydroxides down the group.


20/21


21/21

References

Ace Ahead STPM Text: Chemistry(2010). Tan Yin Toon, LohWai Leng, Kathirasan Muniandy, S. Sumitha, Lim Ming Hui,and Ho Sook Chee. Oxford Fajar Sdn. Bhd..

inorganic chemistry - chapter 01 period 3, group 2

Documents