UNIT 11: MATTER
-
There are different kinds of matter around us.
-
Some matters are pure whereas others are impure.
-
The
substances which have mass and occupy some space are known as matter.
-
Matter has three states Solid, Liquid and Gas.
-
Matters are classified into Elements and Compounds.
Elements
-
The substances which neither can be broken into two or more simpler substances nor can be made from two or more
substances.
-
For example: hydrogen, oxygen, gold, silver,
iron etc.
-
Till now 118 elements have been discovered.
-
Among them 92 are natural and 26 are artificial.
-
Some elements are metals, some are non metals,
some elements are gas, some are liquid and some are solids.
Compounds
-
The substances which are formed after chemical
reaction between two or more elements in a fixed ratio are known as compounds.
-
There are unlimited numbers of compounds.
-
Carbon dioxide: CO2, Water: H2O,
Sodium Chloride: NaCl etc. are some examples of compounds.
-
Compounds can be broken down into two or more
than two substances.
Molecules
-
Molecules are smallest particles of elements or
compounds.
-
These show the all properties of that element or
compound.
Atoms
-
Atoms are the smallest particles of an element.
-
These atoms take part in chemical reaction.
Elements or Compounds
|
Atom
|
Molecule
|
Hydrogen
|
H
|
H2
|
Oxygen
|
O
|
O2
|
Magnesium
|
Mg
|
Mg
|
Water
|
-
|
H2O
|
Nitrogen
|
N
|
N2
|
Common Salt
|
-
|
NaCl
|
Washing Soda
|
-
|
Na2CO3
|
Diatomic Molecules
-
The molecules which contain two atoms are known
as diatomic molecules.
-
H2, N2, O2, F2,
Cl2, Br2, I2 are diatomic molecules.
Structure of an
Atom
An
atom is made up of electron, proton and neutron which are known as sub atomic
particles.
-
Electrons (e-) are negatively
charged, Protons (p+) are positively charged and Neutrons (n0)
are charge less particles.
-
These electron, proton and neutron are called as
sub atomic particles.
-
Protons and neutrons are present in the nucleus.
-
Electrons move around the nucleus in a circular
path.
-
The centre of atom is called nucleus, in which
proton and neutron are present.
-
The path
where an electron moves around the nucleus is called track or shell or orbit.
-
An atom
is generally neutral because it contains equal number of electrons and protons.
Atomic Mass Unit
(amu)
-
The mass of sub-atomic particles are very small.
-
It is very difficult to express them even in mg.
-
So, they are expressed in atomic mass unit
(amu).
-
The mass of one proton = 1 amu.
-
1 gram of hydrogen = 6 x 1023 atoms
of hydrogen.
=6 x1023amu
-
Therefore, 1gram = 6 x 1023 protons.
-
The mass of one proton is nearly equal to the
mass of one neutron but the mass of an electron is nearly 1/1837 parts
of the mass of one proton.
-
Therefore, the mass of 1837 electrons is equal to the mass of one
proton.
-
⸫
1 p+ = 1n0 = 1837 e- = 1 amu.
Electric Charge
-
Proton and electron have electric charge :
positive (+ve) and negative (-ve) charge respectively.
-
It is measured in coulomb.
-
In short it is written as:
-
1 coulomb
= 6.25 x 1018 electrons.
Sub
Atomic Particles
|
Symbol
|
Mass
|
Charge
|
Location
|
Proton
|
p+
|
1
amu
|
+ve
|
Nucleus
|
Electron
|
e-
|
1/1837 amu
|
-ve
|
Shell
|
Neutron
|
n0
|
1
amu
|
neutral
|
nucleus
|
Atomic Number
-
The number of protons present in the nucleus of
an atom is known as atomic number.
-
Atomic number = no. of protons = no. of
electrons.
Atomic Mass
(weight)
-
The atomic mass of an atom is defined as the total
sum of neuron and protons.
-
Atomic mass = number of neutrons (n0)
+ number of protons (p+).
Electronic
Configuration
-
As we know that electrons revolve around the
nucleus in shells or orbits.
-
So, the
distribution of electrons in shells is known as electronic configuration.
-
The distribution of electrons in shells can be
described with 2n2 rule.
-
Where, n = no. of shells.
-
For, K shell:
n=1,
-
For, L Shell: n=2,
-
For, M shell: n=3,
-
For, N shell: n=4.
Shells
|
K
|
L
|
M
|
N
|
Shell
no. (n)
|
1
|
2
|
3
|
4
|
Maximum
No. of electrons in shell as per (2n2)
rule
|
2
|
8
|
18
|
32
|
Atomic
Number
|
Name of
Element
|
Symbol
|
p+
|
e+
|
n0
|
Atomic Mass
(n0 +p+) in amu
|
Electronic configuration
On the basis of Shell
|
Valency
|
|||
K
|
L
|
M
|
N
|
||||||||
1
|
Hydrogen
|
H
|
1
|
1
|
0
|
1
|
1
|
-
|
-
|
-
|
1
|
2
|
Helium
|
He
|
2
|
2
|
2
|
4
|
2
|
-
|
-
|
-
|
0
|
3
|
Lithium
|
Li
|
3
|
3
|
4
|
7
|
2
|
1
|
-
|
-
|
1
|
4
|
Beryllium
|
Be
|
4
|
4
|
5
|
9
|
2
|
2
|
-
|
-
|
2
|
5
|
Boron
|
B
|
5
|
5
|
6
|
11
|
2
|
3
|
-
|
-
|
3
|
6
|
Carbon
|
C
|
6
|
6
|
6
|
12
|
2
|
4
|
-
|
-
|
4
|
7
|
Nitrogen
|
N
|
7
|
7
|
7
|
14
|
2
|
5
|
-
|
-
|
3
|
8
|
Oxygen
|
O
|
8
|
8
|
8
|
16
|
2
|
6
|
-
|
-
|
2
|
9
|
Fluorine
|
F
|
9
|
9
|
10
|
19
|
2
|
7
|
-
|
-
|
1
|
10
|
Neon
|
Ne
|
10
|
10
|
10
|
20
|
2
|
8
|
-
|
-
|
0
|
11
|
Sodium
|
Na
|
11
|
11
|
12
|
23
|
2
|
8
|
1
|
-
|
1
|
12
|
Magnesium
|
Mg
|
12
|
12
|
12
|
24
|
2
|
8
|
2
|
-
|
2
|
13
|
Aluminum
|
Al
|
13
|
13
|
14
|
27
|
2
|
8
|
3
|
-
|
3
|
14
|
Silicon
|
Si
|
14
|
14
|
14
|
28
|
2
|
8
|
4
|
-
|
4
|
15
|
Phosphorus
|
P
|
15
|
15
|
16
|
31
|
2
|
8
|
5
|
-
|
3
|
16
|
Sulfur
|
S
|
16
|
16
|
16
|
32
|
2
|
8
|
6
|
-
|
2
|
17
|
Chlorine
|
Cl
|
17
|
17
|
18
|
35
|
2
|
8
|
7
|
-
|
1
|
18
|
Argon
|
Ar
|
18
|
18
|
22
|
40
|
2
|
8
|
8
|
-
|
0
|
19
|
Potassium
|
K
|
19
|
19
|
20
|
39
|
2
|
8
|
8
|
1
|
1
|
20
|
Calcium
|
Ca
|
20
|
20
|
20
|
40
|
2
|
8
|
8
|
2
|
2
|
Atomic Structure
of elements as per electronic configuration
Valence Shell
& Valence Electrons
-
The outer most shell of an atom is known as
valence shell.
-
Other shells are known as inner shell or core
shell.
-
The electrons present in the valence shell are
known as valence electrons.
-
The valence electrons determine the valency or
combining capacity of an atom.
S.N.
|
Element
|
Core Shell
|
Valence Shell
|
Valence Electrons
|
Valency
|
1
|
Hydrogen
|
K
|
K
|
1
|
+1
|
2
|
Helium
|
K
|
K
|
2
|
0
|
3
|
Argon
|
K&L
|
M
|
8
|
0
|
4
|
Magnesium
|
K & L
|
M
|
2
|
+2
|
5
|
Chlorine
|
K & L
|
M
|
7
|
-1
|
Valency
-
The
combining capacity of an atom is known as valency.
-
According
to the valency of element its chemical reactivity is also different.
-
Metals have +ve valency, because they donate
electrons.
-
Non metals receive electrons, so they have –ve
valency.
-
Valency of some elements is more than one.
-
During the process of chemical reaction, only
the electrons of outer shell take part.
-
If the electrons present in the shell other than
valence shell also take part in reaction, it possesses more than one valency
also.
- Some metals which show more than one valency are known as transitional metals.
Name of element
|
Symbol of element
|
Valency
|
Iron
|
Fe
|
2 and 3
|
Copper
|
Cu
|
1 and 2
|
Silver
|
Ag
|
1 and 2
|
Gold
|
Au
|
1 and 3
|
Lead
|
Pb
|
2 and 4
|
Mercury
|
Hg
|
1 and 2
|
Noble or Inert Gas
-
The elements which have ‘0’ valency are known as
noble gas.
-
They are in gaseous state.
-
They do not take part in chemical reaction, so
they are called noble or inert gas.
-
Their outermost shell is complete, so they
neither lose nor accept any electrons.
-
Helium, Neon, Argon, Argon, Krypton, Xenon and
Radon are noble or inert gases.
Octet
-
While making chemical bond, an atom makes 8
electrons in its valence shell by exchanging or sharing electrons.
-
In this way, the state when there is 8 electrons
in the valence shell is called octet.
-
The rule of making octet in valence shell and obtaining
stable state in chemical form is called octet rule.
-
In K Shell octet rule is not applicable.
Duplet
-
As in K shell, only two electrons can make the
shell complete.
-
The rule of making its outer shell with 2
electrons are called duplet rule.
-
The state
when there are 2 electrons in the valence only in K Shell is called duplet.
-
When atoms reach duplet and octet state it
becomes inactive.
-
The reason of not reacting of the inert or noble
gases with other atoms is their octet or duplet state which has already been
completed.
-
As the
valence shell is complete their electron cannot be transferred or shared.
-
Therefore, they are called noble gases.
Element
|
No.
of electrons
|
Electronic
Configuration
|
Valency
indicator no. of electrons
|
Valency
|
Remarks
|
He
|
2
|
2
|
2
|
0
|
Duplet
|
Ne
|
10
|
2,8
|
8
|
0
|
Octet
|
Ar
|
18
|
2,8,8
|
8
|
0
|
Octet
|
Ion
-
We know that the number of positively charged
proton and the number of negatively charged electrons are equal.
-
Due to this, an atom is neutral.
-
When an atom gives electron to other or takes from
other, it becomes charged.
-
This kind of charged atom is called ion,
example: Na+, Mg++, Ca++, Al+++, O--,
N---, Cl- , etc.
-
When atoms give electrons present in it to other
it becomes positively charged whereas when atom takes electron from other it becomes
negatively charged.
-
So, an
atom or group of atoms which bears positive or negative electrical charges is
known as ion.
-
Positively charged ions are called cations and
negatively charged ions are called anions.
Radicals
-
The atom or group of atoms which carry +vely or
–vely charge and act as single unit during chemical reaction are known as
radicals.
Electropositive
or Basic Radicals
|
Electro
negative or acidic radicals
|
|||||
Radical Name
|
Symbol
|
Valency
|
Radical Name
|
Symbol
|
Valency
|
|
Hydrogen
|
H+
|
+1
|
Nitride
|
N-
- -
|
-3
|
|
Sodium
|
Na+
|
+1
|
Oxide
|
O-
-
|
-2
|
|
Potassium
|
K+
|
+1
|
Chloride
|
Cl-
|
-1
|
|
Ammonium
|
NH+4
|
+1
|
Hydroxide
|
OH-
|
-1
|
|
Magnesium
|
Mg+
+
|
+2
|
Bicarbonate
|
HCO3-
|
-1
|
|
Calcium
|
Ca+
+
|
+2
|
Nitrite
|
NO2-
|
-1
|
|
Zinc
|
Zn+
+
|
+2
|
Nitrate
|
NO3-
|
-1
|
|
Aluminum
|
Al+
+ +
|
+3
|
Sulfate
|
SO4-
-
|
-2
|
|
Carbonate
|
CO3-
-
|
-2
|
||||
Molecular Formula
-
We’ve already studied that elements are
represented by symbols.
-
Similarly molecules of an element or compounds
are also be represented by symbols.
-
The group
of symbols of atoms which are used to represent a molecule of a compound or
elements are known as molecular formula.
-
CH4 is molecular formula of methane
which is made by group of symbols of 3 hydrogen atom and one carbon atom.
Methods of writing
molecular formula
-
From valency
and criss-cross method, we can write
molecular formula of any compound.
-
Following steps will describe how write a
molecular formula of any compound.
o
First of all write the name of molecule: Ammonia
o
Write the symbol of element or radical from
which element or radical, that molecule is made:
o
H N
o
Above the symbols, write the valency of
respective element or radical.
o
1 3
o
H N
o
Exchange
the valency between element or radical and indicate it with arrow.
o
After exchanging the valency between element or radical,
write the symbol and valency together.
o
NH3
o
Write the
valency down at the right side of symbol.
o
If radical is made from more than one element
keep the group of radical’s symbol in bracket and write valency down at the
right side outside the bracket : Mg(HCO3)2.
o
If valency of any element or radical is 1, as it
is not be written remove.
o
If both the valencies can be divided by any
number, remove the divisible and write the molecular formula keeping the
remainder: CO2.
Information that can be obtained from molecular formula
-
The name and symbol of element present in
molecules.
-
Number of atoms present in molecules.
-
Valency of element or radical.
Molecular Weight
-
The sum of weights of the atoms present in a
molecule is called the molecular weight.
-
Hence, it is calculated by adding the atomic
weight of the atoms present in a molecule.
-
For example, since there are two hydrogen atoms
in hydrogen molecule, its molecular weight is two amu.
-
Molecular weight of water (H2O)
-
= 2 x H +1x O
-
= 2 x 1
+1 x 16
-
= 2+16 = 18 amu
Periodic Table
-
Altogether 118 elements have been discovered
till now which are either natural or manmade.
-
The study of these elements separately is
difficult.
-
Therefore scientists thought simpler and easier
way of studying elements.
-
In doing so, they arranged the elements in group
having similar properties.
-
The elements are arranged on the table according
to similarities or dissimilarities of their physical and chemical properties.
-
The table
which shows the grouping of the elements on the basis of their properties is
called periodic table.
Medeleev’s
Periodic Table
-
In this periodic table elements were arranged in
the increasing order of their atomic
mass.
-
Two elements also were kept in the same place.
-
There were some vacant spaces.
-
This periodic table contained some drawbacks.
-
Scientists again worked on this table to
overcome drawbacks and originated modern periodic table
Modern Periodic
Table
-
In the modern periodic table, elements are
arranged in the increasing order of their atomic number.
Chemical Reaction
-
The process by which substances undergo change
to produce new substances with new properties is called chemical reaction.
-
The substances which take part in chemical
reaction are called reactants.
-
The substances which are obtained from a
chemical reaction are called products.
-
Chemical reactions are represented with the help
of chemical equations.
Chemical Equations
-
Representation of Chemical reaction is known as
chemical equation.
-
Reactants are written on left side.
-
Products are written on right side.
-
Both reactants and products are linked with the
help of an arrow
-
- Conditions like heat, pressure, catalyst etc. are kept in arrow.
-
Chemical equations are of two types:
o
Word Equation
o
Formula Equation
Word Equation
-
If name of reactants and products are written in
words, then the equation is known as word equation.
-
Formula Equation
-
If reactants and products are written with the
help of molecular formula, then the equation is known as formula equation.
Formula equation needs to be balanced on both
side.
Balanced Equation
-
The equation in which atoms of both reactants
and products are equal then the equation is known as balanced chemical
equation.
-
Balance is done by hit & trial method.
-
-
Above equation is an example of balanced
chemical equation.
-
If balance is not done, then the equation is called unbalanced equation or skeleton
equation.
