John Dalton was an English chemist known for developing modern atomic theory in 1808, proposing that matter consists of indivisible atoms that cannot be created or destroyed. Atoms are made up of electrons, protons, and neutrons, with the atomic number representing the number of protons and electrons in an atom. Dalton's theory marked a significant advancement in the understanding of chemistry, supported by earlier philosophical ideas from Democritus and subsequent experimental evidence.

1. Atomic Structure

2. Dalton’sAtomic
Theory

3. Who is Dalton?
John Dalton FRS (6 September 1766 – 27
July 1844) was an English Chemist,
Meteorologist and Physicist.
He is best known for his pioneering work
in the development of modern atomic
theory, and his research into colour
blindness (sometimes referred to as
Daltonism, in his honour).

4. Dalton’s Atomic Theory
 About 400 BC the Greek Philosopher Democritus proposed that all matter is
composed of tiny, indivisible particles that he called ATOMS.
 Although Democritus’ idea was not acceptable by his contemporaries, notably
Plato and Aristotle, his suggestion persisted through the centuries.
 Experimental evidence from early scientific investigations provided support for
the concept of atom.
 However, it was not until 1808 that the English Scientist and school teacher,
John Dalton, proposed an atomic theory that marked the beginning of the
modern era of chemistry.

5. The principal hypothesis of Dalton’s
atomic theory are:
1. Matter consists of tiny particles called ATOMS.
2. Atoms cannot be destroyed nor created during a chemical
process.
3. Atoms combine in simple whole number ratios to form
compounds.

6. Subatomic Particles
An ATOM is the smallest particle of an element that maintains its chemical
identity through all chemical and physical changes.
Atoms are therefore all matter, consist principally of three fundamental
particles:
ELECTRONS, PROTONS and NEUTRONS
These are the basic building blocks of all atoms. The symbol, mass, charge and
discoverer of each particle are shown in Table below.

7. Table 1: Fundamental Particles of the Atom
Particle Symbol Mass, amu Mass, g Charge Discoverer
Electron e 0.00055 9.109 x 10 -28 1- J.J. Thomson
Proton p 1.0073 1.673 x 10 -24 1+ Eugene
Goldstein
Neutron n 1.0087 1.675 x 10 -24 0 James Chadwick
The masses of protons and neutrons, in both the atomic mass
units and grams are nearly equal, but the mass of an electron is
much smaller.
Neutrons carry no charge.
The charge on a proton (+) is equal in magnitude but opposite in
sign, to the charge on an electron (-).

8. Periodic Table Key

9. Atomic Symbol
 An atom is identified by two numbers, the atomic number and the
mass number.
1. The ATOMIC NUMBER (Z) is the number of protons in the nucleus
of the atom. The number of protons is always equal to the
number of electrons.
For example:
The atomic number of sodium (Na) is 11; this means that each
sodium atom has:
11 protons and 11 electrons
Atomic Number

10. Example of Protons and Neutrons
Atomic Number = 20
No. of Protons = 20
Number of Electrons = 20
Atomic Number = 18
No. of Protons = 18
Number of Electrons = 18
Atomic Number = 13
No. of Protons = 13
Number of Electrons = 13

11. Atomic Symbol
2. The MASS NUMBER (A) refers to the total number of
protons and neutrons (collectively called nucleons). It is the
weight of the atom in atomic mass unit or amu.
The number of neutrons can be calculated, therefore, by
subtracting the mass number to atomic number:
Number of neutrons = A – Z
Z
A E
Where:
E = the symbol of element
A = mas number or atomic mass unit (amu)
Z = atomic number

12. Number of Neutrons
Number of Neutrons = atomic mass unit - atomic number
N = 65 - 30 = 35 N = 108 - 47 = 61 N = 207 - 82 = 125

13. Seatwork
Time