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Composition of Matter
Atom
• From a Greek word
meaning “uncuttable”
• the basic unit of matter
• it has a positively charged
dense nucleus and a
negatively charged electron
cloud
Nucleus
• contains a positively charged body
(proton) and a body with no charge
(neutron)
Electron Cloud
• negatively charged bodies are
found circling the nucleus in the
electron cloud
Element
• a pure substance made up of one
type of atom
• the number of protons in the atom’s
nucleus determine the element
• 90 occur naturally and the rest
(currently 31) are synthesized in
the lab
Periodic Table
• arranged by Mendeleev
• an arrangement of the elements by
increasing atomic number
• elements in the same column (called
groups or families) share properties
Notice group number
Atomic Number
• the number of protons in the
atom’s nucleus
• It identifies the element
• Therefore every element has a
different atomic number
Neutral Atom (no charge)
• In a neutral atom….
the # protons (+) = the # of electrons (-)
Atomic Mass or Mass Number
• the atomic mass equals the number
of the protons plus the number of
neutrons in the atom’s nucleus
Atomic Mass or Mass Number
• the units are amu (atomic mass
units)
• 1 amu = 1.66 X 10 -24g
• Proton = 1 amu
• Neutron = 1 amu
• Electron = 0.0005amu
Can I determine the number of
neutrons in an atom by using
the periodic table?
Isotope
• atoms of the same element that have a
different number of neutrons
• Some isotopes are not stable – these
are radioactive
# neutrons = A-Z
Importance of Isotopes
• They use in agriculture, biology, geology,
health, nutrition, chemistry, drug testing,
physics as well as diagnostic techniques in
medicine.
https://www.youtube.com/watch?v=phZeE7Att_s
How do atoms combine to
form molecules and
compounds?
• A molecule is formed when two or more
atoms join together chemically.
•Combinations of two or more different
elements are called compounds.
•All compounds are molecules but not all
molecules are compounds. (ex. H2O vs. O2)
•Molecules can also join together to form
larger molecules.
•Many, many repeating small molecules
joined together form a polymer.
http://pslc.ws/macrog/kidsmac/basics.htm
Valance Electrons
• Electrons that are
involved in bonding.
• For main group
elements, they are
in the outer most
shell
“Octet Rule”
• Atoms will lose, gain, or share electrons
until they have a full shell.
• The first shell only holds 2 electrons (full),
but the shells after hold 8 (full)
Creating Compounds:
Bonding
• Electrons can be transferred or shared.
IONIC
Bonding
Electrons
are
transferred
H2 O
COVALENT bonding
Electrons are shared