10.1 the nucleus of an atom intensives
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CHAPTER 10
10.1 UNDERSTAND THE NUCLEUS OF AN
ATOM
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1. Describe the composition of thenucleus of an atoms in terms of
protons and neutrons.
2. Define proton numbers and nucleonnumber.
3. Explain the terms nuclide.
4. Use the nuclide notationX
A
Z
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5. Define the term isotope.
6. Describe the experiment to prove theatomic model
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NUCLEUS OF AN ATOM
Matter is made up of very small
particles called atoms
Each atom has a very small and very dense
core called nucleus. Most of the mass of atomis contained in the nucleus
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Nucleus
proton
neutron
electronNucleus
Structure of an Atom
The positively charged
mass within an atom,composed of neutrons and
protons, and possessingmost of the mass butoccupying only a smallfraction of the volume of theatom.//
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The electrons move in orbits around the nucleus.
There are a lot of empty space within atom A nucleus consists of a number of proton and
neutron.
Protons and neutrons also known as nuclide.
A proton has a positive charge.
A neutron is a neutral particle of about the same
mass as the proton.
An atom is neutral because it contains an equal
number of negatively charged electrons. So the net
charge is zero.
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Define proton number, Z Proton number, Z, is defined as the number
of protons in a nucleus.
The number of protons = the number of
electrons
An element is identified by its proton number
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Define nucleon number (A)
Nucleon number, A is defined as the total
number of protons and neutrons in anucleus. It is also known as mass number.
Nucleon number,
A = number of proton Z + number of neutrons
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What is nuclide?
A nuclide is an atom of a particular structure.Each element has nucleus with a specific
number ofprotons.
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Nuclide Notation
AX A = nucleon number
Z Z = proton number
X = chemical symbol of theelement
Example
Proton number of carbon = ___, Number of proton = _____ Number of electron = ___ Number of neutron = ______
C12
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DefineIsotope
Isotopes of an element contain the samenumber of protons and the same number ofelectrons. So isotopes have the samechemical properties chemical reactionsinvolve the electrons in an atom.
However they have different physicalproperties because their mass is different.
Some isotopes exist naturally. Isotopes canalso be made artificially.
Isotopes are atoms with the
same proton number butdifferent nucleon number.
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Geiger and Marsden planned and carried out an
experiment proposed by Sir Ernest Rutherford and found
evidence for Rutherford Model.
They fired a stream of alpha particles at a very thin gold
foil and counted how many alpha particles were scattered
at a number of different angles.
History of Rutherford
Atomic Model
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Geiger and Marsdenexperiment
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The result and the conclusion of the
experiment is simplified in the table below:
Result Conclusion
Most of the alphaparticles passedstraight through thefoil in their originaldirection.
Most of the space takenup by an atom must becompletely empty. Avery small nucleus isplaced at the centre of
the atom.
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Result Conclusion
A few alphasparticles were
deflected throughvery small angles
The nucleus arepositively charged. The
alpha particles alsopositively charged arerepelled by the nucleusbecause repulsion force
is produced between thelike electric charges.
The result and the conclusion of the
experiment is simplified in the table below:
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Result Conclusion
A very small
number of alphaparticles werebounced backby the gold foil.
The alpha particles collides
head on with the nucleus
The result and the conclusion of the
experiment is simplified in the table below:
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