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The basic unit of all matter
Small in size
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Proton
Neutron
Electron
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Proton and Neutron – NUCLEUS of the atom
(center)
Electrons – found rapidly moving in energy
levels (energy clouds)
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Proton = Positive (+)
Neutron = Neutral (0)
Electron = Negative (e-)
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Proton
Neutron
Remember – the electrons are SOOOO LIGHT
that they are not part of the mass (atomic
weight)
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There is an equal number of protons and
electrons
If there are more protons – then the atom
would have an overall POSITIVE charge
If there are more electrons – then the atom
would have an overall NEGATIVE charge
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Use the terms
◦ Symbol
◦ Atomic Weight (Mass)
◦ Atomic Number
A
Atomic Number
Symbol
Atomic Weight
(mass)
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Hydrogen
Oxygen
Nitrogen
Carbon
There is also phosphorus and sulfur, but I
only want you to focus on the four listed
above.
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The symbol for Krypton is

The mass number for Calcium is
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The atomic number for Beryllium is
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The symbol for Krypton is
Kr
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The mass number for Calcium is
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The atomic number for Beryllium is 4
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The number of molecules present
LARGE NUMBER written before the element
symbol
Ex: 4CO2
There are 4 molecules of carbon dioxide
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The number of atoms present
SMALL NUMBER written within the chemical
formula
Ex: 4CO2
There are 8 atoms of oxygen
Remember to distribute (4 x 2=8)
 5C2H4
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How many molecules are present?
How many atoms of Carbon are present?

How many atoms of Hydrogen are present?
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How many TOTAL atoms are present?
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 5C2H4
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How many molecules are present? 5
How many atoms of Carbon are present?
10 (5x2 – remember to distribute)
How many atoms of Hydrogen are present?
20 (5x4 – remember to distribute)
How many TOTAL atoms are present?
30 (distribute and then add up)
(5x2) = 10
(5x4) = 20
10 + 20 = 30
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A. Electrons
B. Protons
C. Neutrons
D. Valence Electrons
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A. Electrons
B. Protons
C. Neutrons
D. Valence Electrons
Choice D is the most accurate answer here
A.
B.
C.
Gained
Lost
Shared
A.
B.
C.
Gained
Lost
Shared
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In the outermost energy level of an atom
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8 electrons!
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8 – OCTET rule
◦ The outermost energy level will be complete when it
contains 8 electrons.
◦ Atoms will gain/lose/share electrons to reach this
stability!
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****EXCEPTION****
◦ Hydrogen and Helium follow the DUET RULE (can
only have 2 electrons in the outermost shell to be
stable and unreactive)
A.
B.
C.
D.
Carbon
Neon
Helium
Magnesium
A.
B.
C.
D.
Carbon – 4 opportunities to bond (vacancies)
Neon
Helium
Magnesium – 6 opportunities to bond
(vancancies)
Neon is stable because it is a noble gas – already
has 8 electrons
Helium is stable because it is also a noble gas –
but follows duet rule so it has 2 electrons
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Single Bond
Double Bond
Triple Bond
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Single Bond
◦ Atoms share 2 electrons (1 pair)
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Double Bond
◦ Atoms share 4 electrons (2 pairs)
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Triple Bond
◦ Atoms share 6 electrons (3 pairs)
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Types of Elements
Number of atoms
Location of atoms
Example –
 1 Oxygen
 2 Hydrogen
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COVALENT BONDS
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SHARING OF ATOMS!!
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Phosphorus
Hydrogen
Nitrogen
Oxygen
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Phosphorus
Hydrogen
Nitrogen
Oxygen
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WATER
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Changes or transforms one set of chemicals
into another
CHANGES to the BONDS – breaking and
reforming bonds
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Reactants

Products
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Reactants
◦ ENTER into a chemical reaction (before the arrow)

Products
◦ PRODUCED by a chemical reaction (after the arrow)
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Reactants
Products
Coefficients
Subscripts

C - Reactants
D - Products
A - Coefficients
B – Subscripts
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Reactants REACTto produce PRODUCTS
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Matter cannot be created nor destroyed
Arrangement of atoms is what is changed
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Reactants must equal products
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Na + Cl2  NaCl
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ANSWER - NO
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2Na + Cl2  2NaCl