Chemaddicts: December 2015

Sunday 27 December 2015

Reaction of Group-2 Metals with Chlorine Gas :

Reaction of Group-2 Metals with Cl₂:

All Gr-2 metals except Be react with chlorine to give ionic chlorides whereas Be reacts with chlorine to give covalent chloride.

The equations for the reactions:

All metal chlorides above are white ionic solid.

Beryllium reacts with chlorine to form polymeric BeCl₂.

Here are some video tutorials about some other problems. Click the following link to visit:

Video Solutions for some other problems.

Saturday 26 December 2015

Reaction of Group 2 metals with oxygen:

Reaction of Group-2 metals with oxygen :

Hi fellows!! This is Chemaddicts again to the solution. Today, we will discuss about the reaction of Gr-2 metals with oxygen.

So, let’s get started!!

Before going to the discussion of the reaction of Gr-2 metals with oxygen, we need to clear the confusion between the concept of burning metal and metal ions .

Most of the students mix up the concept of burning metals and metal ions.

This is because most metals and metal ions in Gr-2 have same flame colour. There is a difference and we will see today:

Today, we will discuss the reaction of metals with oxygen gas:

All Gr-2 metals except Barium react with oxygen to give metal oxides whereas Barium reacts with oxygen to give Barium peroxide ( BaO₂ ).

Equations for the reactions:

Here Mg burns with bright white flames.

Here, in this case , we are burning Mg not Mg ion . This is the difference here. Mg²⁺ion have no flame colour. Don’t write the flame colour of Mg²⁺ion as Mg metal.

Other Group-2 metals below Mg give the same colour as the metal cations. So, don’t get confused.

Here Ca burns with brick red flames like Ca²⁺ ions.

Here Calcium metal will give the same colour as the Ca²⁺ ion.

Here Sr burns with crimson flames like Sr²⁺ ions.

Here Strontium metal will give the same colour as the Sr²⁺ ion.

(Here Ba burns with apple green flames like Ba²⁺ ions. )

Here Barium metal will give the same colour as the Ba²⁺ ion.

If you wanna have some other video tutorials, you will find them here:

Video tutorials.

What Are The Group-2 Elements ?

The Periodic Table ( Group – 2) :

Hi fellows!! Today we are going to analyse Group-2 Metals in this discussion.

At first, let us look at elements of Group-2.

Trend in ionisation energy down the Gr-2 :-

Down the Group-2 :-

Size/ Radius of cations increases.

Nucleus become more shielded.

Nuclear charge increases but it is not the dominating factor here.

Therefore ionisation energy decreases.

If you want to watch video tutorials, please click the following link :

Video tutorials.

Thanks for watching !!! Bye !! Bye !!! See you in next post!!!

Thursday 24 December 2015

The ionic and covalent character of an ionic compound:

Hi fellows , this is Chemaddicts to the solution!!!!

Today we are going to discuss about the Covalent and ionic character.

So let’s get started !!

We will come to know about the following concepts :

1) Covalent character

2) Ionic character

3) The relationship between ionic and covalent character.

1) Covalent character :

What is a covalent character ?

A covalent character is the covalency in ionic compounds which is due to the

High Polarising power of Cations and High Polarisability of anions.

Diagram :

Then gradually,

Finally the oxide ion is being distorted by Magnesium ion...

High Polarising power of Cations :

It is the ability of a cation to distort the electron cloud of the anion in an ionic compound.
Higher polarising power of cations means that ionic compound gains more covalent character.

Polarising power of cation depends on :

1) Size of Cations .

2) Charge of Cations . ( Not the Nuclear charge )

Diagram :

Here charge of the ions are involved here , not the nuclear charge.

1) Size of Cations :

Decreasing size of cations results in greater polarising power. From here, we can deduce that :

Here charge of cations are same (constant).

Therefore, small cations can distort the electron cloud of anions more effectively.

2) Charge of Cations:

Increasing Charge on Cations ( Not the nuclear charge ) results in increasing the Polarising power of Cations.
Greater Charge on Cations means it can have more attraction with the electron cloud of anions.

A new relationship can be obtained between Polarising power and the following factors :

1) Size of Cations

2) Charge of Cations

Now we are combining the equations that we have derived before,

Where,

ratio is also known as the charge density.

Charge Density:

It is simply a ratio of charge and size.

Polarising power cations down the Group:

Polarising power of cations decreases down the group.

Let’s see how,

Down the Group 1 ionic compounds ,

LiCl * Charge on the cations remain same.

NaCl * Size of Cations increases .

KCl * Charge density of cations decreases.

RbCl * So, the anions are distorted less.

CsCl * Covalent Character decreases

* Ionic Character increases

Down the Group 2 ionic compounds ,

BeO * Charge on the cations remain same.

MgO * Size of Cations increases .

CaO * Charge density of cations decreases.

SrO * So, the anions are distorted less.

BaO * Covalent Character decreases

* Ionic Character increases

High Polarisability of anions :

High polarisibility of anions is

the ease of distortion of the electron cloud of an anion

the ease with which Anions responds to the polarising power of the cations.

Diagram:

Cations are able to distort the electron cloud of anions because there is a weaker attraction between outer electron shells and nucleus of anions.

Polarisibility of anions depends on size :

Polarisibility of anions increases with increasing size.

Down the Group7 ionic compounds ,

LiF * Charge on the Anions remain same.

LiCl * Size of Anions increases .

LiBr * Polarisibility of Anions increases.

LiI * So, the anions are distorted more .

* Covalent Character increases

* Ionic Character decreases

Ionic character :

Ionic character is the opposite of covalent character.

Cations with greater size will have higher ionic character.

Anions with smaller size will have higher ionic character.

This is because of cations cannot distort the electron cloud.

When electron distortion becomes weaker or impossible, then that compound would have high ionic character and low covalent character.

Down the Group 1 ionic compounds ,

LiCl * Charge on the cations remain same.

NaCl * Size of Cations increases .

KCl * Charge density of cations decreases.

RbCl * So, the anions are less distorted.

CsCl * Covalent Character decreases

* Ionic Character increases

Down the Group 2 ionic compounds ,

BeO * Charge on the cations remain same.

MgO * Size of Cations increases .

CaO * Charge density of cations decreases.

SrO * So, the anions are less distorted .

BaO * Covalent Character decreases

* Ionic Character increases

Down the Group7 ionic compounds ,

LiF * Charge on the Anions remain same.

LiCl * Size of Anions increases .

LiBr * Polarisibility of Anions increases.

LiI * So, the anions are distorted more .

* Covalent Character increases

* Ionic Character decreases .

Well, this is the end of today's post ! Follow me on this blog for getting updated with my posts like this. And you may get a video solution to a problem on this topic by the clicking the following link :

Problem Relating the Ionic and Covalent Character of an Ionic Compound...

See you in the next post!! Bye Bye!!!