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Understand atomic structure in physics
ATOM: Is the smallest particle of an element that can take part
in a chemical reaction.
Atoms as the smallest particles have
ability to exist on its own. Dalton was the first person to use the word ATOM.
DALTON ATOMIC THEORY
- All matter are made up of tiny particles called ATOM.
- Atoms can neither be created nor destroyed.
- Atoms of a given element are identical. They have the
same atomic mass and similar chemical properties.
- Atoms of one elements can combine with atoms of other
elements to form molecules.
- Atoms of given element are different from those of
other elements.
MODIFICATION OF DALTON ATOMIC THEORY
1. Atoms are made up of smaller particles called electrons, protons and neutrons.
2. Atom can be created or destroyed or split up by nuclear reaction/ nuclear fission.
3. Some element have atom of more than one type. They are called Isotopes.
4. Atoms of different elements combine together to form complex compound.
1. Atoms are made up of smaller particles called electrons, protons and neutrons.
2. Atom can be created or destroyed or split up by nuclear reaction/ nuclear fission.
3. Some element have atom of more than one type. They are called Isotopes.
4. Atoms of different elements combine together to form complex compound.
SUB ATOMIC PARTICLES
- Atom are made up of 3 particles these are;
- PROTON
- ELECTRON
- NEUTRON
- All atoms of an element have both 3 particles except
hydrogen which has no Neutron.
A: THE ELECTRON
- This is a negatively charged particle (-ve)
- It's mass is about;
- It's symbol is 'e'
- It rotates around the nucleus in a particular patten
called shell or energy level
B: THE PROTON
- This is a positively charged particles (+ve)
- It has mass approximately the same as that of hydrogen
atom ie atomic mass
- It is symbol is (p) or +11P
- It is found in the nucleus of an atom
C: THE NEUTRON
- This is a neutral particle or is a
particle which has .no charge
- The mass is the same as that of protons ie atomic mass
unit
- It symbol is (n)
- It is found in the nucleus of an atom
- summary
- ATOMIC STRUCTURE
Although an atom contain charge
particles (protons) and electron is natural because the number of protons (+Ve)
are equal to the number of electron (-Ve)
THE ARRANGEMENT OF
ELECTRONS IN ATOM
ELECTRONIC CONFIGURATIONS
Electronic configuration: Is the distribution of electrons in various
shell of an atom.
The maximum number of electrons held within each energy level. It can be determined by the formula 2n2
Where n is the position of energy level from the nucleus
The maximum number of electrons held within each energy level. It can be determined by the formula 2n2
Where n is the position of energy level from the nucleus
- The first shell from the nucleus of an atom
have ability of carrying only 2 electron. ⇒(2×12 ) = 2 electrons
- The second shell from the nucleus of an
atom has ability of carrying only 8 electrons. ⇒( 2×22) = 8 electrons
- The third shell from the nucleus of an atom
have ability of carrying only 8 electronic. ⇒ (2×32) =18 electrons
- The forth shell from the nucleus carry a
maximum of 18 electrons. ⇒ (2×42) = 32 electrons
NOTE;
But the third energy level is stable with 8 electrons
Example of electron diagrams of an
atom;
1. Hydrogen, 1=1
2. Aluminium, 13=2:8:3
1. Hydrogen, 1=1
2. Aluminium, 13=2:8:3
3.
Chlorine, 17 =2:8:7
4. Oxygen, 8= 2:6
ELECTRONS CONFIGURATIONS OF FIRST
ELEMENT
Element
|
Symbol
|
Number of neutron
|
Atomic number/Proton
and Electron
|
Atomic
Mass
|
Electronic configuration
(KLMN)
|
Number of shell
|
Hydrogen
|
H
|
0
|
1
|
1
|
1
|
1
|
Helium
|
He
|
2
|
2
|
4
|
2
|
1
|
Lithium
|
Li
|
4
|
3
|
7
|
2:1
|
2
|
Beryllium
|
Be
|
5
|
4
|
9
|
2:2
|
2
|
Boron
|
B
|
6
|
5
|
11
|
2:3
|
2
|
Carbon
|
C
|
6
|
6
|
12
|
2:4
|
2
|
Nitrogen
|
N
|
7
|
7
|
14
|
2:5
|
2
|
Oxygen
|
O
|
8
|
8
|
16
|
2:6
|
2
|
Florine
|
F
|
10
|
9
|
19
|
2:7
|
2
|
Neon
|
Ne
|
10
|
10
|
20
|
2:8
|
2
|
Sodium
|
Na
|
12
|
11
|
23
|
2:8:1
|
3
|
Magnesium
|
Mg
|
12
|
12
|
24
|
2:8:2
|
3
|
Aluminum
|
Al
|
14
|
13
|
27
|
2:8:3
|
3
|
Silicon
|
Si
|
14
|
14
|
28
|
2:8:4
|
3
|
Phosphorus
|
P
|
16
|
15
|
31
|
2:8:5
|
3
|
Sulphur
|
S
|
16
|
16
|
32
|
2:8:6
|
3
|
Chlorine
|
Cl
|
18
|
17
|
35
|
2:8:7
|
3
|
Argon
|
Ar
|
18
|
18
|
36
|
2:8:8
|
3
|
Potassium
|
K
|
19
|
19
|
38
|
2:8:8:1
|
4
|
Calcium
|
Ca
|
20
|
20
|
40
|
2:8:8:2
|
4
|
NOTE
- In the above the element are arranged according
to the increase in atomic number
- The number of proton = number of electron = Atomic
number
- The mass number (A) is the sum of
proton (P) and neutron (N): (A = P+N)
ATOMIC NUMBER, MASS NUMBER AND
ISOTOPES
ATOMIC NUMBER (Z)
Is the number of proton in the nucleus of an atom which is equal to the number of electron in the shell.
ATOMIC NUMBER (Z)
Is the number of proton in the nucleus of an atom which is equal to the number of electron in the shell.
- It's official symbol is (Z).
- Atomic number is written on left hand side below the
symbol of an element.
- Therefore atomic number of the following element are
written as 6C , 8O , 17Cl , 20Ca
- Also atomic number = number of proton = number of
electron
2. MASS NUMBER / ATOMIC MASS (A)
- It is written on left hand side above the symbol of an
element.
E.g;
.E.g. Carbon atomic mass is 12 written as 12C
chlorine atomic mass is written as 35Cl
- The official symbol for mass number is A.
- Combination of mass and atomic number are;
Therefore Atomic mass = Proton
(atomic number)
Example; Atom R has mass number of 40 and an atomic number of 20. What is it’s neutron number , and what is the number of electrons in an atom R ?
Solution ; mass number = 40
atomic number = 20
(a) Neutron number = mass number − atomic number
= 40 − 20
∴ Neutron number = 20
(b) Number of electrons = number of protons = atomic number = 20
Example; Atom R has mass number of 40 and an atomic number of 20. What is it’s neutron number , and what is the number of electrons in an atom R ?
Solution ; mass number = 40
atomic number = 20
(a) Neutron number = mass number − atomic number
= 40 − 20
∴ Neutron number = 20
(b) Number of electrons = number of protons = atomic number = 20
ISOTOPES
These are atoms of the same element which have the same atomic number but they differ in mass number.
These are atoms of the same element which have the same atomic number but they differ in mass number.
- Isotopes have the same proton electron and atomic
number.
- They have same chemical properties but have slight
different physical properties.
- Isotopes has different mass number because they have
different number of neutrons.
- Example of element which have the isotopes;
NOTE:
- in the above four examples, the numbers above
the element in the isotopes are the mass numbers.
- The numbers below the element are atomic numbers.
- From the definition of the isotopes, it is true that
mass number are different and atomic number are the same.
RELATIVE ATOMIC MASS (RAM)
- The relative atomic mass of an element is the mass of
an atom of carbon twelve(12) Isotopes .
- If an element has several Isotopes its relative atomic
mass will be the mass of Isotopes on calculation. The average mass of the
proportion (abundance) of each Isotope in the sample of element must be
known.
- This is calculated by working out the
relative abundance of each isotope
CALCULATING RELATIVE ATOMIC NUMBER
Relative atomic mass (RAM) =( Relative abundance × Atomic mass ) + ( Relative abundance × Atomic mass )
100
Relative atomic mass (RAM) =( Relative abundance × Atomic mass ) + ( Relative abundance × Atomic mass )
100
Example:
1. A sample of chlorine gas contains 75% and 25% of the Isotopes with it’s relative abundance of 35 and 25 respectively. What is the relative atomic mass (R.A.M) of chlorine?
RAM =( Relative
abundance × Atomic mass ) + ( Relative abundance × Atomic mass)
100
100
To get the answer multiply the mass
number of each Isotopes with the abundance.
Solution
R.A.M of chlorine
= 35.5
- The relative atomic mass of chlorine is 35. 5. The word
symbol of relative atomic mass is (RAM).
2. A sample of chlorine is a mixture of two Isotopes in the ratio of 3:1. What is the relative atomic mass of chlorine atom?
Solution
R.A.M of
chlorine = 35.5
3. A sample of Oxygen is mixture of 3 Isotopes in the ratio of 3:2:1. What is relative atomic mass (R.A.M).
Solution
R.A.M of
Oxygen = 16.6
REVIEW QUESTION
1. Define the following
(i) Atomic
(ii) Electronic configuration
(iii) Atomic number
(iv) Mass number
(V) Isotope
3. Copy and complete the following table of atomic / electron structure of same element
(a).
1. Define the following
(i) Atomic
(ii) Electronic configuration
(iii) Atomic number
(iv) Mass number
(V) Isotope
3. Copy and complete the following table of atomic / electron structure of same element
(a).