element elements and compounds diagonal relationship and irregularity structure of atom compounds a...

ElementElements and Compounds Diagonal Relationship and IrregularityStructure of Atom

Compounds

A compound is a substance composed of two or more elements, chemically combined with one another in a fixed proportion.

Water, sugar, salt, carbon dioxide, methane etc are the examples of compounds.

Objectives:Diagonal Relationship of Lithium with Magnesium.

Anomalous Behaviour of Lithium.

The s-Block Elements

Diagonal Relationship of Beryllium with Aluminium.

Anomalous Behaviour of Beryllium.

ElementElements and Compounds Extraction of SulphurNon-metals

Compounds



Mineral Coal and Mineral Oil PetroleumThe s-Block Elements Dual Nature of Matter and Radiation

Diagonal Relationship of Li with Mg

Due to small size of lithium, it differs from other alkali metals but resembles with Mg as its size is closer to Mg. Its resemblance with Mg is known as diagonal relationship. Generally the periodic properties show either increasing or decreasing trend along the group and vice versa along the period which brought the diagonally situated elements to closer values.

Shapes of s, p and d-orbitalsDiagonal Relationship and Irregularity


Compounds



Mineral Coal and Mineral Oil PetroleumStructure of Atom Dual Nature of Matter and Radiation

Both Li and Mg are harder and have higher melting points.

Shapes of s, p and d-orbitalsThe s-Block Elements Diagonal Relationship and Irregularity


Due to covalent nature, chlorides of both Li and Mg are deliquescent and soluble in alcohol and pyridine.

Fluorides, phosphates of Li and Mg are sparingly soluble in water.

Carbonates of Li and Mg decompose on heating and liberate CO2.

Hydroxides and nitrates of both Li and Mg decompose on heating to give oxide. Hydroxides of both Li and Mg are weak alkali.

Both Li and Mg combine directly with N2 to give nitrides Li3N and Mg3N2.

Li2CO3 → Li2O + CO2 ; Mg CO3 → MgO + CO2


Compounds




Bicarbonates of Li and Mg are more soluble in water.



Both Li and Mg combine with carbon on heating.

2Li + 2C → Li2C2 ; Mg + 2C → MgC2

Li and Mg Form only monoxide on heating in oxygen.

4Li + O2 → 2 Li2O ; 2Mg + O2 → 2 MgO

Li2SO4 like MgSO4 does not form alums.


Compounds




Anomalous Behaviour of Lithium

The small size of the lithium atom and the ion make them behave differently from other elements of the same group.

Shapes of s, p and d-orbitals

Lithium is the hardest of all the alkali metals.

The s-Block Elements Diagonal Relationship and Irregularity

The melting and boiling points of lithium are much higher than those of other elements of group 1.

Lithium is less reactive as compared to other metals and it does not get tarnished readily in air.

Lithium is deliquescent and crystallizes as a hydrate, LiCl.2H2O whereas other alkali metal chlorides do not form hydrates.

Lithium bicarbonate is not obtained in the solid form while all other elements of this group form solid bicarbonate.


Compounds



Mineral Coal and Mineral Oil PetroleumStructure of Atom Dual Nature of Matter and RadiationShapes of s, p and d-orbitals

It forms only monoxide, Li2O with oxygen while sodium forms peroxide, Na2O2 and other elements form superoxide, MO2.

The s-Block Elements Diagonal Relationship and Irregularity

Anomalous Behaviour of Lithium

The salts of lithium have lower ionic character than salts of other alkali metals. This is because of high polarizing power of Li+ ion.


Compounds




The ionic radius of Be2+ is estimated to be 31 pm : the charge/ radius ratio is nearly the same as that of the Al3+ ion. Hence beryllium resembles aluminium in some ways.


Diagonal Relationship of Be with Al

Like aluminum, beryllium is not readily attacked by acids because of the presence of an oxide film on the surface of the metal.

Beryllium hydroxide dissolves in excess of alkali to give a beryllate ion, just as aluminium hydroxide gives aluminate ion.

The chlorides of both beryllium and aluminium have Cl- bridged chloride structure in vapour phase. Both the chlorides are soluble in organic solvents and are strong Lewis acids. They are used as Friedel Craft catalysts.


Compounds



Mineral Coal and Mineral Oil PetroleumStructure of Atom Dual Nature of Matter and RadiationShapes of s, p and d-orbitalsThe s-Block Elements Diagonal Relationship and Irregularity

Diagonal Relationship of Be with Al

Beryllium and aluminium ions have strong tendency to form complexes.

Carbides of both the metal reacts with water liberating methane gas.

The oxides of both Be and Al i.e. BeO and Al2O3 are high melting insoluble solids.

Be2C + 4H2O → 2Be (OH)2 + CH4 , AI4C3 + 12H2O → 4Al (OH)3 + 3CH4


Compounds




The properties of beryllium the first member of the alkaline earth metal, differ from the rest of the member. Its is mainly because of its small size, high polarizing power and absence of vacant d – orbitals in its valence shell.


Anomalous Behaviour of Beryllium

The melting and boiling points of Be are higher than those other members of Group II.

Beryllium forms covalent compounds whereas other members form ionic compounds.

Beryllium carbide reacts with water to give methane whereas carbides of other alkaline earth metals gives acetylene gas.

Beryllium does not exhibit coordination number more than four as it has four orbitals in the valence shell. The other members of this group has coordination number 6.

element elements and compounds diagonal relationship and irregularity structure of atom compounds a...

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