Chem periodicity part 1

a. Describe and explain the acid/base behaviour of oxides and hydroxides, including, where relevant, amphoteric behaviour in reaction with sodium hydroxide (only) and acids
Na2O, MgO, Al2O3
All have giant structures in which the bonding is ionic. Therefore they have high melting points and boiling points and conduct electricity when molten.
Na2O, MgO: basic oxide (soluble, pH= 13)
Al2O3: amphoteric oxide, insoluble in water
SiO2
Silicon is a metalloid and forms the oxide SiO2 which has a giant covalently bonded structure. It is therefore a solid with high melting point and boiling point and does not conduct electricity when molten. Acidic oxide and is insoluble in water.
SiO2(s) + 2NaOH(aq) à Na2SiO3(aq) + H2O(l)
P4O10 , SO2 , SO3 , Cl2O7
The remaining oxides are formed by non-metals. These oxides are built up from molecules within which the bonding is covalent, but between the molecules the bonding is the weak Van der Waals type. These oxides therefore have low melting points and boiling points and do not conduct electricity in the liquid state. Acidic oxide and gives acidic solution (pH = 2)

P4O6(g) + 12NaOH(aq) à 4Na3PO3(aq) + 6H2O(l)
P4O10(g) + 12NaOH(aq)à 4Na3PO4(aq) + 6H2O(l)
SO2(g) + 2NaOH (aq) à Na2SO3(aq) + H2O(l)
SO3(l) + 2NaOH (aq) à Na2SO4(aq) + H2O(l)
Cl2O(g) + 2NaOH(aq) à 2NaClO(aq) + H2O
Cl2O7(g) + 2NaOH(aq) à 2NaClO4(aq) + H2O(l)
describe and explain the reactions of the chlorides with water
Na: NaCl dissolves in water, forming aqueous ions ( hydration), neutral pH=7
Mg: the high charge density in Mg2+ polarizes water molecules, giving H+ (hydration and hydrolysis) slightly acidic, pH = 6.5. MgCl2 undergoes hydration to form Mg2+ and Cl- ions. Mg2+ has a high charge density as it has a high charge and small ionic radius. (Charge density = charge / size of atom or ion). Hence, the Mg2+ forms a attraction force with the negative end of water molecules (polarises the water molecules). This weakens the O-H bond of water molecules and releases H+.
Al: Due to the high charge density of Al3+ ,it tends to form strong bond with oxygen and weakens the O-H bond of water molecules in the [Al(H2O)6]3+ ion. AlCl3 reacts with water to first form [Al(H2O)6]3+ ions . This Al-containing ion has a high charge density. (Charge density = charge / size of atom or ion). Hence, this ion forms a strong attraction force with the negative end of water molecules. (polarises the water molecules). This weakens the O-H bond of water molecules and releases H+.
Si and P: Si & P has vacant d orbitals available for dative bonding with water. Hence SiCl4 PCl3 and PCl5 can be hydrolysed by water.
interpret the variations and trends in (b), (c), (d), and (e) in terms of bonding and electronegativity
Oxides of elements (Bonding)
• Na2O, MgO, Al2O3: Exist as ionic structure. A large amount of energy is required to break the strong electrostatic attraction forces between the ions in the lattice
• SiO2: Exist as giant covalent structure where Si and O atoms are held by covalent bonds. A lot of energy is required to break the strong covalent bonds.
• P4O6 , P4O10, SO2, SO3: Exist as simple discrete molecules with Van der Waals’ forces and/or permanent dipole- permanent dipole between the molecules. Lower energy required to overcome these intermolecular forces.
Oxides of elements (Eletronegativity)
• Na2O, MgO, Al2O3: In molten state, the ions are mobile and therefore can carry charges around freely. Hence these oxides are able to conduct electricity.
• SiO2, P4O6 , P4O10, SO2, SO3: In giant covalent structure or simple discrete molecules, there are no mobile ions or electrons in all states. Hence they do not conduct electricity.







Reaction of elements with oxygen

4Na(s) + O2(g) -> 2Na2O(s)
On heating, burns in oxygen with a yellow flame to give a mixture of white sodium oxide and yellow sodium peroxide[2Na(s) + O2(g) ->Na2O2(s)]

2Mg(s) + O2(g) -> 2MgO(s)
On heating, burns in oxygen with brilliant white flame and a white magnesium oxide is produced.

4Al(s) + 3O2(g) -> 2Al2O3(s)
On heating, burns with white flame to give white aluminium oxide.
An oxide layer is formed to protect the metal against further oxidation under room temperature.

Si(s) + O2(g) -> SiO2(s)
On heating, burns to give white oxide. Does not undergo oxidation at room temperature.

Limited O2: P4(s) + 3O2(g)->P4O6(s)
Excess O2: P4(s) + 5O2(g)-> P4O10(s)
Red phosphorus: burns on heating. While white phosphorus burst into flame in oxygen to give a white oxide.

S(s) + O2(g) -> SO2(g)
On heating, burns with bright blue flame to give colourless gaseous oxide.
With Pt: 2SO2(g) + O2(g) -> 2SO3(g)
In the presence of a Pt catalyst, this oxide further reacts to give SO3.

Reaction of element with chlorine

2Na(s) +Cl2(g) ->NaCl(s)
On heating, reacts quite vigorously.

2Mg(s) +Cl2(g) -> MgCl2(s)
On heating, burns brightly.

3Al(s) +Cl2(g) -> Al2Cl6(s)
On heating under anhydrous conditions, forms solid chloride.

Si(s) +2Cl2(g) -> SiCl4(l)
On heating under anhydrous conditions, forms colourless covalent liquid.

P(s) +6Cl2(g) -> 4PCl3(l)
PCl3(l) + Cl2 (g)-> PCl5(s)
On heating, white phosphorus burns with pale green flame to give PCl3 and further reacts to give PCl5

Oxidation number in element of oxide and chloride
Na2O : +1 NaCl : +1 The variation between
MgO :+2 MgCl2 : +2 oxidation in element of oxide and
Al2O3 :+3 AlCl3 : +3 chloride in their oxidation number is in
SiO2 : +4 SiCl4 : +4accordance to their valance electron.As element Na Mg Al Si P AND S
P4O6 : +3 PCl3 : +3 are across the same period hence an electron is added to the previous
P4O10 : +5 PCl5 : +5 element electron number to be the next element electron number
SO2 : +4 (starting from Na electron number:11)
SO3 : +6





Reaction of element of oxide with water
Na2O + H2O -> 2NaOH
Basic oxides react with water to form alkaline solutions.

MgO + H2O -> Mg(OH)2
Basic oxides react with water to form alkaline solutions.

Al2O3 does not react with water due to high lattice energy.

SiO2 is insoluble in water due to its giant molecular structure.

P4O6 + 6H2O -> 4H3PO3
P4O10 + 6H2O -> 4H3PO4
Acidic oxides react with water to form acidic solutions.

SO2 + 2H2O -> H2SO3 + H2O
SO3 + 2H2O -> H2SO4 + H2O
Acidic oxides react with water to form acidic solutions.










Suggest types of chemical bonding present in chlorides and oxides from observations of their chemical and physical properties.

Elements- Na Mg Al Si P S Cl
O2 Na2O MgO Al2O3 SiO2 P4O10 SO2 /With ppt SO3
Cl2 NaCl MgCl2 Al2Cl6 SiCl4 PCL3/PCL5

Elements- Na2O MgO Al2O3 SiO2 P4O6 P4O10 SO2 SO3
Chem Bond ----------Giant Ionic------------- ---Giant Covalent----- ---------Simple Covalent----------------------
Elements- NaCl MgCl2 Al2Cl6 SiCl4 PCl3 PCL5
Chem Bond -----Ionic Bond----- -------------------Simple Covalent----------------------


Predict characteristic properties of an element in a given group by using knowledge of chemical periodicity.
Group 1 2 3 4 5 6 7 8
Elements- Na Mg Al Si P S Cl Ar
Structure -------Giant Metallic------ Giant Covalent --------------Simple Molecular------------
Bonding ------Metallic Bond------- ------Covalent---- ---------Van Der Waal's Forces----------
Mpt Pt. -----------HIGH-------------- ----- HIGH------- --------------------LOW------------------------
Electrical -----------GOOD------------ ------LOW-------- ---------NON-CONDUCTOR---------------
Electronegativity ------------Increases across a period & decreases down a group---------------------------


Deduce the nature, possible position in the Periodic Table and identity of unknown elements from given information of physical chemical properties.
Group 1 2 3 4 5 6 7 8
Elements- Na Mg Al Si P S Cl Ar
Physical ------------Metal------------ --Metalloid--- --------------Non-Metals--------------
Mpt Pt ---------HIGH--------------- -----HIGH----- ------------------LOW-----------------
Bonding ----Metallic Bond--------- ---Covalent-- ---------Van Der Waal's Forces---
Structure -----Giant Metallic-------- Giant Covalent -------Simple Molecular------------
Electrical ---------GOOD------------ -----LOW------- ----------NON-Conductor-----------