Organization of The Periodic
Table
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Nucleus
• Center of the atom.
• Makes majority of the atom’s mass.
• Made of Protons and Neutrons.
Nucleus
Protons
• Part of the nucleus
• Have positive (+) charge
Neutrons
• Part of the nucleus
• Have neutral charge
Electrons
• Orbit around the nucleus
• Have negative (-) charge
Atomic Number
• Definition: the number of protons in the
nucleus
• Tells us the identity of the element.
Every element is defined by the number of protons in its nucleus
Questions
• 1) What particles make up an atom?
• 2) What are the charges on these
particles?
• 3) What particles make up the nucleus?
Questions
• 1) What is Oxygen’s atomic number?
• 2) How many protons does Oxygen have?
• 3) If I have 4 protons what element am I?
• 4) If I have 4 neutrons what element am I?
Reading the Periodic Table
Mass
Atomic Mass
• Definition: the ~ mass of one atom of an
element
• Tells us how much one atom weighs in
atomic mass units.
Mass
Subatomic Particles
(Protons, Neutrons, and Electrons)
The number of protons in an atom is
called the atomic number.
If you know the atomic number of an
atom, you know how many protons – and
how many electrons – the atom contains.
# of protons = # of electrons (e-)
The mass number is the sum of protons
and neutrons in the atom.
Assessment
• Which element has the greatest atomic
mass?
• Lithium
• Sodium
• Potassium
• Rubidium
Question
• How many electrons does an oxygen
have?
• How many electrons are in its outer shell?
• Which group is oxygen most likely to react
with?