4. All matter is made up of atoms.
Atoms of an element are
identical.
Each element has different
atoms.
Atoms can engage in a chemical
reactions.
Atoms can neither be created
nor be destroyed.
Atoms are indivisible.
Atomic Theory
John Dalton
(1776-1884)
5. atom has a positively charged
central part (nucleus)
Electrons are distributed
around nucleus
Mass of an atom is
concentrated at nucleus.
Compared with total volume
of an atom, the volume of
nucleus is meager
Rutherford’s Atomic
Model
Ernest Rutherford
(1871-1937)
8. Bohr's Model of the Atom
electrons orbit the nucleus like planets
orbit the sun
9. Bohr's Model of the Atom
electrons fills the orbits closest to the
nucleus
e.g. fluorine:
#P = 9
#e-
= 9
#N = 10
9P
10N
10. each orbit can hold a specific maximum
number of electrons
Shell maximum no: of
electrons
1 - K
2 - L
3 - M
4 - N
Bohr's Model of the Atom
2
8
18
32
12. What is the structure of an atom?
• Nucleus - center of the atom
Home of Protons and Neutrons
Has a positive charge
• Proton
Has a relative mass of 1
Has a positive (+) charge
Determines the atomic number
Found inside the nucleus
13. What is the structure of an atom?
• Neutron
Has no (0) charge
Has a relative mass of 1
Found inside the nucleus
14. What is the structure of an atom?
• Electron
Has a negative (-) charge
Found outside the nucleus
• Rutherford atom model - electrons are
around the nucleus
• Bohr model – electrons are in specific
energy levels called shells
15. How are p, n, e related?
• No: protons = No: electrons
• No: protons = atomic number
• No: protons + No:neutrons = mass
number
• No: neutrons=mass no: - atomic no:
16. ATOMIC STRUCTUREATOMIC STRUCTURE
the number of protons in an atom
the number of protons and
neutrons in an atom
HeHe
22
44Atomic mass
Atomic number
number of electrons = number of protons
