Science 10
Mr. Jean
November 28th, 2011
The plan:
• Video clip of the day
• Classification of matter
• Atom & Subatomic particles
Interesting Quotation:
“Expect people to be better than they are; it
helps them become better. But don’t be
disappointed when they are not; it helps
them to keep trying.”
M. Browne
The Atom
• The atom is the basic unit of matter,
everything is made up of atoms.
• Atoms are very small, and cannot even be
seen by a regular microscope.
• Atoms have no charge (neutral) and are
made up of several sub-atomic particles.
Sub – atomic particles:
Charge
ELECTRON
Negative
(-)
Location
Relative
Mass
Orbiting
outside
nucleus
Light
PROTON
Positive
(+)
Nucleus
Heavy
NEUTRON
Neutral
Nucleus
Heavy
Diagram of the atom:
What makes atoms different?
• The number of protons, neutrons and
electrons an atom has determines what
kind of atom it is.
– Example: The oxygen atom has 8 electrons
and protons therefore we know it is an oxygen
atom.
What makes atoms different?
• You can determine the number of
electrons and protons an atom has by
looking at its atomic number found on
the periodic table.
Atomic Number
• The atomic number of an element is found
on the periodic table. They are arranged
in increasing order going from left to right.
• So Hydrogen has an atomic number of 1,
Helium is 2 and so on.
Atomic Number
• The atomic number tells us how many
protons an atom has. This also tells us
how many electrons an atom has,
because the number of protons and
electrons are balanced.
• So an atom has the same number of
protons as electrons.
To calculate the number of protons and
electrons an atom has we must look at the
atomic number.
Examples:
1. Si
14 electrons, 14 protons
2. Rb
37 electrons, 37 protons
3. Ag
47 electrons, 47 protons
4. N
7 electrons, 7 protons
Isotopes
• All atoms of the same type would have the
same number of protons and electrons,
but they don’t have to have the same
number of neutrons.
• Isotope = atoms of the same type, but
having different numbers of neutrons,
changing the atomic mass.
Atomic Mass
• The atomic mass on the periodic table a
weighted average of the isotopes
Atomic mass = #protons + # neutrons
# Neutrons = atomic mass - # protons
Example:
1. Na has a mass # of 22.98. How many e-,
p+ and neutrons does Na have?
e-, p+ = 11
22.98 – 11 = 11.98  12 neutrons
Quote of the day:
“ A man (woman) would do nothing if he
waited until he could do it so well that no
one could find fault.”
J.H.C. Newman
Electron Shells
• Electrons are found orbiting in shells
outside the nucleus
• Bohr Diagrams are a way to represent
where the electrons in an atom are located
• 1st shell holds 2 electron
• 2nd shell holds 8 electrons
• 3rd shell holds 8 electrons
• 4th shell holds 18 electrons
Drawing Bohr Diagrams
1. Put the symbol of the element in the
centre
2. Start placing electrons in the innermost
shells and work outwards
3. Place electrons at N, S, E and W
4. GO back and double if necessary
(electrons are usually found in pairs)
Example: Carbon
•Carbon has an atomic number of 6
• Therefore C has 6 electrons
• 2 electrons in 1st shell
• 4 electrons in 2nd shell
Valence Electrons
• The outer most electron shell in any atom is
called the valence shell
• The electrons in the valence shell are called
Valence Electrons
• By looking at the number of valence electrons an
element has we can predict its reactivity.
• THE OCTET RULE: Atoms will try to lose, gain
or share electrons to obtain a filled outer level
(to form a stable octet).
• Stable octet = 8 electrons
You can tell the number of valence electron
that an elements has by looking at the group
number
Group 1 has 1 valence electron
Group 2 has 2
Group 13 has 3
Group 14 has 4
Group 15 has 5
Group 16 has 6
Group 17 has 7
Group 18 has 8
Electron Dot Diagrams
•
•
An easier way to represent the number
of valence electrons an atom has is to
use electron dot diagrams.
Electron dot diagrams show only the
valence electrons
Predicting Chemical reactivity:
• By looking at the number of valence
electrons an element has we can predict
its reactivity.
• Atoms will try to lose, gain or share
electrons to obtain a filled outer level, or to
form a stable octet (8 electrons)
Quote of the day:
“To be upset over what you don’t have is to
waste what you do have.”
K.S. Keyes
Ions
• When atoms gain or lose electrons they
form something called IONS. Energy is
released when this happens.
• Ions are electrically charged atoms.
(positive or negative)
Cations (+)
• CATIONS: are positively charged
ions. Cations are formed when an
atom loses electrons.
• Metals and Hydrogen form cations
• Ex: Na lose 1 electron
 Na1+
Anions (-)
• ANIONS: are negatively charged
ions. Anions are formed when atoms
gain electrons.
• Most non-metals form anions.
• Ex: Cl gains one electron
 Cl1-
Charges of Ions
Group 1  loses 1 electron = +1
Group 2  loses 2 electrons = +2
Group 13  loses 3 electrons = +3
Group 15  gains 3 electrons = -3
Group 16  gains 2 electrons = -2
Group 17  gains 1 electron = -1
Group18  has a full outer shell
= very stable 