Atoms:
Everything
is made of small particles called atoms.
The
smallest division of every matter is atom.
Atoms
are made up of sub-atomic particles called protons, neutrons and electrons.
Protons and neutrons are in the nucleus which is situated in the centre of an atom.
Electrons
are in different energy levels (shells) around the nucleus . Energy level
(shell) are the electron clouds around the nucleus. There are gaps between the
shells.
Diagram:
|
Sub-atomic
particles
|
Relative
mass
|
Relative
charge
|
|
Protons
|
1
|
+1
|
|
Neutrons
|
1
|
0
|
|
Electrons
|
1
1840
|
-1
|
Atomic number
and Mass number:
Atomic no. :
Atomic
no. of an element are the total no. of protons in a nucleus of an atom of that
element. Each elements in the periodic table have unique atomic no.
Atomic no. =
Total no. of protons
In
a neutral atom,
Total no. of
protons = Total no. of electrons
Mass no. :
Mass
no. of an element are the total no. of protons and neutrons in the
nucleus of an atom of that element.
Mass no. = Total
no. of protons + Total no. of neutrons.
Notation:
A
X
Z
where,
A=
Atomic no.
Z
= Mass no.
X=
Symbol of any Element
For example:
40
Ca
20
Here,
Mass
no. = 40
Atomic
no. = 20
Since
it is a neutral atom of an element,
No.
of protons =No. of electrons = 20
No.
Neutrons = Mass no. –atomic no.
= 40 -20
= 20
Shells
(Different Energy levels):
The
space outside the nucleus are called shells. Shells exist as different energy
levels for electrons in an atoms. It is just a cloud of electrons around the nucleus. There is a gap
between the shells.
Shells
can be divided further into sub-shells and orbitals.
Sub-shell:
Shells
are made up of sub-shells.
There
are four types of sub-shell.
They
are :
s-subshells,
p-subshells,
d-subshells,
and
f-subshells.
Orbitals:
It
is the region of space around the nucleus where there is a high probability of
finding an electron or a pair of electrons .
An
Orbital can hold up to a maximum no.
of 2 electrons in opposite spin.
There
are also four kinds of orbitals:
s-
orbitals,
p-
orbitals,
d-
orbitals,
and
f-
orbitals.
s-
orbitals have round spherical shapes.
p-
orbitals have dumbbell like shapes. The p- orbitals are like a pair of balloon
attached together.
We
only need to study about the shape
of “s” and “p” orbitals in AS Chemistry.
We don’t have “d” and “f” orbitals in our syllabus. The shape of “d” and “f”
orbitals are much more complicated.
Diagram:
“s”
sub-shells consists of one “s” orbital .
It is like the outer skin of orange fruit.
Diagram:
“p”
sub-shell consists of three “p” orbitals: Px , Py ,
Pz . They are all perpendicular to each other i.e. the three
dumbbells are set at 90° to each other in “p” subshell.
Diagram:
We
don’t have “d” and “f” sub-shell in our syllabus. They are much more
complicated.
|
Shell no.
|
Sub-shell
|
Number of
sub-shells in each shell
|
Maximum number
of electrons in the shell
|
|
1
|
1s
|
1st
shell has 1 sub-shell.
|
2
|
|
2
|
2s
2p
|
2nd
shell has 2 sub-shells.
|
8
|
|
3
|
3s
3p 3d
|
3rd
shell has 3 sub-shells.
|
18
|
|
4
|
4s
4p 4d 4f
|
4th
shell has 4 sub-shells.
|
32
|
|
Sub-shell
|
Number of
orbital(s)
|
Maximum
number of electrons in the sub-shell.
|
|
s
|
1
|
2
|
|
p
|
3
|
6
|
|
d
|
5
|
10
|
|
f
|
7
|
14
|
An
Orbital can hold up to a maximum no.
of 2 electrons in opposite spin.
Thanks for help me
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