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history and development of atoms.
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Atomic Structure
Matter is anything that takes up space
and has mass
All matter is made of atoms
the building blocks of matter, sort of how bricks are the building blocks of houses.
Smallest particles of matter
• An atom has three parts:
• Proton = positive
• Neutron = no charge
• Electron = negative
• The proton & neutron are found in the center of the atom, a place called the nucleus.
• The electrons orbit the nucleus.
HISTORY OF THE ATOM
460 BC Democritus develops the idea of atoms
he pounded up materials in his
pestle and mortar until he had
reduced them to smaller and
smaller particles which he
called ATOMA (greek for
indivisible)
Democritus’ Atom
Indivisible particle
HISTORY OF THE ATOM
1808 John Dalton
suggested that all matter was
made up of tiny spheres that
were able to bounce around
with perfect elasticity and
called themATOMS
Postulated the Atomic Theory
Dalton’s Atom
HISTORY OF THE ATOM
Thompson develops the idea that an atom was made up of
electrons scattered unevenly within an elastic sphere
surrounded by a soup of positive charge to balance the
electron's charge
1904
like plums surrounded by pudding.
PLUM PUDDING
MODEL
Electrons embedded in positive mass
HISTORY OF THE ATOM
1910 Ernest Rutherford
He suggested that the
positive charge was all in a
central nucleus. With this
holding the electrons in place
by electrical attraction
Positive nucleus
HISTORY OF THE ATOM
1913 Niels Bohr
studied under Rutherford at the
Victoria University in Manchester
Bohr refined Rutherford's idea by
adding that the electrons were in
orbits. Rather like planets orbiting
the sun. With each orbit only able
to contain a set number of
electrons.
Bohr’s Atom
electrons in orbits
nucleus
Bohr’s Atom
Electron
Nucleus
Fixed electron orbit
Electron Cloud model
Electron Cloud model
Electron Cloud model
DE BROGLIE’S ATOM
DE BROGLIE’S ATOM
Isotopes Atoms that have the same number of
protons but different numbers of neutrons
Example:
the number of protons in an atom
the number of protons and neutrons in an atom
He2
4Atomic mass
Atomic number
number of electrons = number of protons
Mass defect is the difference between the mass of nucleons
(protons and neutrons) and the mass of the nucleus
HELIUM ATOM
+N
N
+-
-
proton
electron
neutron
Shell
What do these particles consist of?
Particle Electrical Charge
Mass (amu)
Proton +1 1.0072766 or 1
Neutron 0 1.0086654 or 1
Electron -1 0.000549
Particle
proton
neutron
electron
Charge
+ ve charge
-ve charge
No charge
1
1
0.000549
Mass
Total Mass of Nucleus = 1.00794
Total Mass of Nucleus= 4.00260
Total Mass of Nucleus= 12.011
Ground State – lowest energy level of an electronExcited State – the electron goes into a higher energy level
An electron emits energy as it returns to its ground state
When an electron absorbs
energy in the form of light or
heat, it goes into a higher
energy level. The electron is
said to be in the excited state.
When an excited electron
returns to its ground state, it
emits the energy it previously
absorbed .
SPECTRUM
If light is passed
through a
prism, an array
of colors called
SPECTRUM is
formed.
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