Wednesday 30 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:
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 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.
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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.
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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,
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
or
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 :
See you in the next post!! Bye Bye!!!
Sunday 20 December 2015
Friday 18 December 2015
Monday 7 December 2015
Thursday 3 December 2015
Wednesday 2 December 2015
Tuesday 1 December 2015
Monday 30 November 2015
Sunday 29 November 2015
Saturday 28 November 2015
Friday 27 November 2015
Thursday 26 November 2015
Sunday 22 November 2015
How do mass spectrometry works?
How do mass
spectrometry works?
A mass spectrometer can split atoms and molecules
based on the mass. It can also give us a series of data about the compounds and
elements present in the sample. With that series of data about the atoms or
molecules, that would be represent on a graph in a computer from which we can
identify the elements and compounds present in the sample.
The mass spectrometry is an ideal device for
measuring relative mass of an element/
compound in a given sample since it can
measure very accurately.
In order to move through the mass spectrometer,
sample must be
a) first vaporised,
b) secondly ionised.
The air is first pumped out of the mass
spectrometer to avoid ionisation of air.
Diagram:
Vaporisation
:
The sample which is needed to analyze
must be in gaseous state in order to move
easily through the mass spectroscopy. There is a high vacuum area in the
1st section of the instrument where the given sample is vaporised.
The air particles are first pumped out
of the vacuum chamber from the mass spectroscopy in order to prevent air
particles get ionised . This is because we want only the sample to be ionised.
If there is any air molecules present, then that will also get ionised. So, it
would be pretty difficult for us to analyse the actual ions present in the
sample.
Then,
the desired sample is injected into the mass spectroscopy and is first
vaporized. Here, the given sample is vaporised at a given temperature , if the
sample is not in the gaseous state.
Ionisation
:
Then in the next section , the vaporised
sample is bombarded with high energy electrons. These high energy electrons
knock one or more electrons in the valence making ions , molecular ions. It
doesn’t make any significant differences in mass since the mass of electrons
are negligible. Now the cations are formed which can move to the electric
field.
X (g) + e - → X+ + 2e-
Two types of ions and free radicals are formed in the ionisation:
1) Molecular ions 2) Fragmented ions
Diagram:
** Note : Later we will study the fragmentation pattern of molecular ions .
Acceleration
:
Then the cat ions passes through the
electric field to get accelerated. The positive ions pass through the slits and
comes out like stream of beams. The cat
ions get accelerated but negative ions don’t get accelerated in the electric
field.
Velocity
selector :
Then the positive ions pass through the
velocity selector where a fixed velocity is set for all the ions . The velocity
selector makes sure that all the positive ions are travelling at constant speed
.
This means that affect of the magnetic
field in the next section would be due to the differing mass and charge / mass/
charge ratio (m/z) but not for the speed since the speed is constant.
Uniform
Magnetic field :
Then the ions passes through the uniform
magnetic field where deflection of ions occurs. Deflection depends on both mass
and charge. The ions with large mass
and small charge would deflect least . On the other hand, the ions
with small mass and large charge would deflect most .
The strength of magnetic field is
gradually increased, only ions with
specific mass/charge ratio can pass through the passage at a selected settings
of the magnetic field. Others would strike the wall by deflecting high or low
and failed to move through the pathway to the detector.
Detector
:
Then the detector detects the no. of positive
ions pass through and transform them as a tiny currents and transmit as
electric signal to the computer.
Display:
Then the Mass spectrum is obtained as a
result. The computer would produce a graph of abundance against mass/ charge
ratio (m/z) where you would have relative peaks and different m/z ratio values.
The relative height shows relative
abundance cations . The m/z ratio gives us the information about relative mass
of the particles present in the compound. Most of the charge of the ion is +1.
So mass of the ions = m/z ratio of the ions.
***Note: We will later study the mass
spectroscopy graph in later chapter.
Saturday 21 November 2015
What is Mass spectrometry ?
Mass spectrometry:
The mass
spectrometer happens to be an important device to measure the relative mass
associated with atom, a molecule or a particular ion accurately.
Typically the
mass spectrometer separates atoms and molecules as reported by their mass and
also shows the relative variety of the different atoms and molecules present.
Then the data is
generated from ion detector of mass spectrometer which can be use to make a
graph in the computer where we can identify different elements or compounds present
in the sample.
Typically the masses of atoms, molecules
and fragments of molecules are generally measured using a mass spectrometer.
Atoms are very
tiny. It is almost impossible to measure the mass of an atom in the traditional
way. A mass spectrometry separates the
atoms and molecules
Definition of Isotopes :
Isotopes are the
atoms of the same element with same atomic no. but differing mass no.
The isotopes are the atoms of the same elements
which have:
same atomic
numbers
same no. of
protons
same no. of
electrons
similar chemical
properties
same symbol
but
differing mass numbers
differing number of neutrons
differing
physical properties.
We will find the
following things by using mass
spectrometer:-
a) Relative atomic mass :
It is the average mass of an atom of an element compared
to 1/12 th of the mass of 1 atom of Carbon-12
isotope.
b) Relative isotopic mass :
It is the mass of 1 atom of an isotope of an
element compared to 1/12 th of the mass of 1 atom of Carbon –
12 isotope.
c) Relative molecular mass :
It is the mass of 1 molecule of a substance compared
to 1/12th of the mass of 1
atom of Carbon – 12 isotope.
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