Atomic structure

ATOMIC STRUCTURE

DEVELOPMENT OF ATOMIC MODEL Plum Pudding Model -discovery of electron 1897- put forward the “plum pudding” model of the atom. The atom is like a sphere with small electrons embedded in a positively charged mass J.J Thompson (1856-1940) An atom is like a miniature billiard ball 1808- suggested that matter is made of tiny particles which are indivisible and indestructible John Dalton (1766-1844) Atomic Model Atomic Structure Scientist

- - - - - Rutherford’s Solar System Model
1911- shows that:
atom is spherical & has a centre or nucleus with a dense positive charge
Protons are the positively charged particles in the nucleus
A system of electrons rotates around the nucleus much like the planets orbiting around the sun
Ernest Rutherford (1871-1937) Atomic Model Atomic Structure Scientist

1932- discovered that:
A particle in the nucleus which has no electric charge and called it neutron
All nuclei (except hydrogen) contain neutrons as well as protons
James Chadwick (1891-1974) Bohr’s electrons orbiting in shells
1913- showed that:
Electrons orbit in specific energy levels called shells
Each shell is capable of holding a certain number of electrons.
Niels Bohr (1885-1962) Atomic Model Atomic Structure Scientist

Atomic structure of an atom
Atoms are made of three different types of subatomic particles called protons, neutrons and electrons
Protons and neutrons are found in the nucleus and they are known as nucleons
Nucleus is positively charged because the protons are positively charged and the neutrons are electrically neutral
Electrons rotate around the nucleus in a certain orbit called shells, just like planets rotate around the sun
SUBATOMIC PARTICLES proton neutron shell electron { nucleon + +

THE PROPERTIES OF SUBATOMIC PARTICLES
An atom is neutral when it has the same number of protons and electrons
_1__ 1840 1 1 Relative mass -1 0 +1 Relative electric charge e ¯ n p Symbol Electron Neutron Proton Subatomic particles

PROTON NUMBER
The number of protons in an atom of an element
Proton number = number of protons

NUCLEON NUMBER
The sum of protons and neutrons in an atom element
Nucleon number = number of protons + number of neutrons

NUMBER OF NEUTRONS
the difference between the nucleon number and the proton number
A neutral atom has the same number of protons and the number of electrons
Different elements have different numbers of protons
Number of neutrons = nucleon number – proton number

The number of protons, electrons and neutrons in a particular atom are given in the Periodic Table by the nucleon number and proton number
A : proton number
Z :nucleon number
X: symbol of an element
The number of protons, electrons and neutrons can be determined from the nucleon number and proton number
A X Z

Example: (a) Sulphur
the symbol of the element above shows that it is sulphur
Nucleon number = 32
Proton number = 16
Number of neutron =
So, sulphur atom has 16 protons, 16 electrons and 16 neutrons
32 S 16 32-16 = 16

Example: (b) Aluminium
The symbol of the element above shows that it is aluminium
Nucleon number = 27
Proton number = 13
Number of neutron =
Aluminium atom has 13 protons, 13 electrons and 14 neutrons
27 Al 13 27 – 13= 14

Example: (c) Sodium
Number of protons =
Number of neutrons
So, number of electrons =
23 Na 11 11 = 23 - 11 = 12 11

Exercises
What is matter?
What are atoms, molecules and ions?
How does the state of matter change with the change in temperature?
How does the kinetic theory of matter explain the inter-conversion of the state of matter?
How was the atomic model developed?
What are the main subatomic particles of an atom?
What is proton number?
What is nucleon number?

Atomic structure

by Ministry of Education Malaysia on May 23, 2010

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