Atomic and Molecular Structure 1.a. – Students
know how to relate the position of an element in
the periodic table to its atomic number and
atomic mass.
• Everything in nature is made of matter.
• Atoms are the building blocks of all matter.
• The atom is the smallest part of an element but still
has all the chemical properties of that element.
• Atom in Greek means “uncuttable”.
• An Atom is very small.
• It consists of a nucleus,
which contains the protons
and neutrons, and electrons
which orbit in electron
shells around the nucleus.
• The nucleus is very small
compared to the size of the
entire atom.
• Most of the atom is empty space!
• Even though an Atom’s nucleus is so small….it
contains most of its MASS!
• Because all the mass comes from the protons
and neutrons!
• An Atom is made up of 3 Subatomic Particles.
1. Proton – positive charge
2. Neutron – no charge
3. Electron- negative charge
• Protons and neutrons about the same size
and are located in the nucleus.
• Electrons are very small and move around
the atom in electron shells.
• All elements are made up of their own unique
atom.
• Element - a material which cannot be broken
down or changed into another substance
using chemical means.
• Each element has its own unique number of
protons.
• So…..the number of protons in an atom gives us
the identity of the element!
Hydrogen
1 Proton
Helium
2 Protons
Lithium
3 Protons
Beryllium
4 Protons
• Periodic Table – A tabular arrangement of the
elements according to their atomic numbers
so that elements with similar properties are in
the same column.
• The Periodic Table was invented in 1869 by
Dmitri Mendeleev.
Periodic Table:
• Arranged by atomic number
• Has 18 vertical columns or families
• Has 7 horizontal rows or periods
• Elements in columns have similar properties
• Elements in rows are NOT ALIKE!
1
18
2
1314 1516 17
3 4 5 6 7 8 9 101112
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1
2
3
4
5
6
7
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• Approximately 92 naturally occurring
elements
• The rest are made in labs or short-lived
• Lightest Element = Hydrogen (#1)
• Heaviest Element = ununoctium (#118)
Atomic Number = number of protons
• In a neutral atom (no charge), the number of
protons (+) always equals the number of
electrons (-)!
Atomic Mass = number of protons + neutrons
• To find out how many neutrons an atom has
just subtract the atomic mass from the
atomic number!
The Atom
Question:
You have 2 identical containers. One is filled with
hydrogen gas and the other is filled with oxygen
gas. The containers are not labeled. How could
you tell which one is filled with oxygen? (They
have the same number of gas molecules in each
container.)
Hint: How are hydrogen and oxygen atoms
different?
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The Atom
Answer:
Both containers have the same number of gas
molecules, but they differ in the type of atom they
contain. Hydrogen has only 1 proton in its
nucleus. Oxygen has 8 protons and 8 neutrons.
Oxygen is 16 times heavier than hydrogen. The
heavier container is oxygen and the lighter is
hydrogen.
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