structure of an atom

1. DEVELOPMENT OF THE ATOMIC
THEORY
WSU CHY15M0 - electronic properties of
an atom

2. PURPOSE OF ATOMIC MODELS
The models of the atom do not
provide a complete understanding
of the atom.
The models help us to make useful
predictions about how matter will
behave.
WSU CHY15M0 - electronic properties of an atom

3. Dalton
Thomson
Rutherford
Bohr
Schrodinger
WSU CHY15M0 - electronic properties of an
atom

4. JOHN DALTON (1766-1844),
❑Proposed the first atomic theory in
1808.
WSU CHY15M0 - electronic properties of an atom

5. JOHN DALTON (1766-1844),
❑The atom is a solid sphere – billiard
ball model.
⮚All matter consists of tiny particles called
atoms, which cannot be broken up.
⮚All the atoms of a particular element are the
same. Atoms of different elements are
different.
WSU CHY15M0 - electronic properties of an atom

6. JOHN DALTON (1766-1844),
❑The atom is a solid sphere – billiard
ball model.
⮚When atoms combine, they form compounds.
⮚Atoms cannot be created or destroyed in a
chemical reaction
WSU CHY15M0 - electronic properties of an atom

7. Thomson
WSU CHY15M0 - electronic properties of
an atom

8. Thomson
WSU CHY15M0 - electronic properties of
an atom

9. JOSEPH J THOMSON
❑JJ Thomson discovered electrons in 1897.
❑The atom is a positive sphere where the
electrons were randomly spread out inside
the atom.
❑This model was known as the “plum-
pudding” model.
WSU CHY15M0 - electronic properties of an atom

10. Rutherford
WSU CHY15M0 - electronic properties of
an atom

11. Ruther-
ford
WSU CHY15M0 - electronic properties of
an atom

12. ERNEST RUTHERFORD
❖In 1911 Ernest Rutherford used the discovery
of an alpha particle to do further experiments
on the atom.
❖The alpha(α) particle has the same mass as a
helium atom but as a positive charge.
❖Rutherford directed a beam of alpha particles
at a thin gold foil so that he could explore the
inside of the atom.
❖The alpha particle scattering experiment.
WSU CHY15M0 - electronic properties of an atom

13. ERNEST RUTHERFORD p38
❖Almost all the mass of the atom is found in a
very small positively charged nucleus in the
centre of the atom. He later found the positive
charge comes from protons.
❖The space around the nucleus is empty for the
negatively charged electrons to be found there.
❖Rutherford’s nuclear atomic model.
❖One drawback: Opposite charges must
attract each other and electrons should lose
energy and spiral inward.
WSU CHY15M0 - electronic properties of an atom

14. Bohr
WSU CHY15M0 - electronic properties of
an atom

15. NIELS BOHR
❖Electrons move in orbits(or energy levels)
around the nucleus.
❖Electrons with the same energy move
around in the same orbit.
❖Electrons in orbits that are further away
from the nucleus have a higher energy than
the orbits closer to the nucleus.
WSU CHY15M0 - electronic properties of an atom

16. MODERN ATOMIC MODEL
❖The quantum mechanical model or electron
cloud model
❖An atom consists of a nucleus and electrons
spinning around the nucleus.
❖The electrons move in a cloud around the
nucleus.
❖We cannot tell exactly where the electrons are
at any given time.
❖We do know that electrons exist more
frequently in certain regions around the nucleus
than others. WSU CHY15M0 - electronic properties of an atom

17. MODERN ATOMIC MODEL
p39
WSU CHY15M0 - electronic properties of an atom

18. WSU CHY15M0 - electronic properties of
an atom