The Atom
Year 9 Science 2012
Have you ever wondered?
Short Pre-Test: What do you know
already?
1. Draw what you think an atom looks like.
2. Explain the term ion
3. Describe roughly how many different
types of atoms there are
4. Define the difference between fission
and fusion
5. Explain some of the risks of nuclear
radiation
Goals:
Vocab:
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Atom
Atomic model
Atomic number
Atomic symbol
Compound
Crystal lattice
electron
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Electron configuration
Electron shell
Element
Isotopes
Mass number
Molecule
Neutral
Neutron
Nucleus
Periodic table
Proton
Atoms:
• Everything is made of atoms
• No one has ever seen an atom!
What we know about atom
• The are 119 known different atoms
• An only 95 of these are found on Earth
Atoms in elements and compounds
• When elements stick together, they form
clusters called COMPOUNDS or large grid-like
structures called LATTICES
Elements:
• If a substance has
only one type of
atom, it is called
an ELEMENT
Compounds:
• If a substance is made up of molecules or a
crystal lattice with different types of atoms,
then it is known as a compound
Lattices:
Inside Atoms:
• We now know that the atom is
made from sub-atomic particles –
protons, neutrons and electrons
Atomic Nuclei:
• The number of protons an atom has is called
its ATOMIC NUMBER
• The number of protons + neutrons is called
the atoms MASS NUMBER
• This is written:
• So, He is:
– Helium
• Number of protons =
2 protons
• Number of neutrons =
4 – 2 = 2 neutrons
• Number of electrons in a neutral He atom:
2 electrons
Activity Book:
• 1.1 Atomic symbols Page 1
Isotopes:
• Atoms of the same elements can have
different numbers of neutrons
• Eg most Helium atoms have two protons and
two neutrons, denotes by He-4
• BUT: He-3 atoms also exist:
– These still have 2 protons (He) but only one
neutron
Activity Book:
• 1.2 Isotopes Page 2-3
Focus on Electrons:
Electrons and the nucleus:
• If the number of electrons in an atom is
EXACTLY equal to the number of protons, the
atom is then NEUTRAL
• This is because the electrons have a negative
charge and the protons have a positive charge
Electrons:
• Although each electron is 1800 times smaller
than a proton, together the electrons form
'clouds' around the nucleus.
• The clouds can be 100 or even 1000 times wider
than the nucleus.
• This means that if the nucleus was the size of a
golf ball, the electrons would form clouds the size
of a football stadium.
• It also means that most of an atom is empty
space.
How do we now that the atom is
mostly empty space?
Practical Activity: Experimenting like
Rutherford
Ernst Rutherford:
• The New Zealand scientist Ernest Rutherford
discovered that the nucleus only takes up a
small fraction of the space inside an atom.
• In his famous experiment, Rutherford fired a
beam of helium nuclei (alpha particles) at a
thin sheet of gold foil.
• To his surprise, most of the nuclei passed
straight through the foil and only a small
fraction were deflected back.
• Up until that point, most scientists had
believed that atoms were completely solid.
• Rutherford realised that atoms are mostly
empty space. However, they had a small,
positively charged nucleus surrounded by a
cloud of electrons.
Electron Shells:
• The electrons in an atom are attracted to the
nucleus by the positive charge of the protons.
• However, the electrons never fall into the
nucleus.
• This is because the electrons are trapped
inside electron shells which surrounds the
nucleus which surround the nucleus like the
layers of an onion
• Once the 1st electron shell is full, electrons
start to fill the 2nd electron shell, which can
hold up to 8 electrons.
• The 3rd electron shell holds up to 18
electrons.
• The 4th electron shell can hold 32 electrons.
Video: Periodic Table Hockey
championship
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Electron Shells:
• Many of the electron shells in an atom are
empty.
• The biggest known element at present has
118 electrons in 6 shells.
• The 1st electron shell is the innermost shell. It
is the smallest electron shell and can only
contain 2 electrons.
Electronic Configuration:
• The number of electrons in each shell of an
atom is known as its electron configuration
• For example, carbon has 6 protons and
therefore 6 electrons. The first 2 electrons fill
the 1st electron shell, and the remaining 4
electrons go into the 2nd electron shell.
• Therefore the electron configuration for
carbon is 2,4
Activity Book:
• 1.4 Electronic Configuration of Ions: Page 6-7
The Atomic Model:
Activity Book:
• 1.3 Model Scientists Page 4-5
Revision Questions:
1. How many protons, neutrons and electrons are in a
potassium atom? ( 2919K )
2. Describe the structure of a potassium atom
3. Potassium forms a metal lattice. What does this
mean?
4. Talcum powder is a compound made from powdered
magnesium oxide. What is a compound?
5. The compound magnesium oxide does not contain
molecules. What are molecules?
6. Will the properties of magnesium oxide be an average
of the properties of magnesium and oxygen?