Download The Structure of the Atom

The Structure of the Atom
The Building Block of Matter
Atoms are the smallest particles of an
element that retains the chemical
properties of that element

Parts:


Nucleus – small region in
the center of the atom.
(+ charged protons, =
charged neutrons)
Electron Cloud – large
region, compared to
nucleus, where electrons
are found.
Size of nucleus vs. electron cloud
If an atom was the size of a sports stadium, the
nucleus would be the size of a marble!
Subatomic Particles:


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Protons : + charge, relative mass = 1.007 atomic mass
units (amu); round to 1
Neutrons: = charge, relative mass = 1.009 atomic mass
units (amu); round to 1
Electrons: - charge, relative mass = 0.0005 atomic mass
units (amu); round to 0 (not factored in when figuring
total mass of an atom)
Structure of Subatomic Particles

Subatomic particles composed of fast moving
points of energy called quarks
Quark Calculations
(for protons and neutrons)
Each proton is 2 up quarks and 1 down quark
2(2/3) – 1(1/3) = 4/3 – 1/3 = 3/3 or +1
Each neutron is 2 down quarks and 1 up quark
2(-1/3) + 2/3 = 0
Each electron is composed of 2 down quarks
3(-1/3) = -1
Isotopes
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Atoms with the same number of protons &
electrons but a different number of neutrons.
They are the same element, but have
different masses.
All isotopes are used to calculate atomic
mass (reason why weight is a decimal).
Most elements consist of a mixture of
isotopes.
Atomic Number


Number of protons in the nucleus (also the
number of electrons)
Typically the number on top of the symbol on
the Periodic Table.
13
Al
26.981
Atomic Number
Mass Number
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Number of protons + number of neutrons in
an atom.
When solving for number of neutrons: round
mass number properly, subtract atomic
number from mass number.
Element Symbols
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Hyphen Notation:
Element symbol – Mass # (rounded)
Example: Helium  He-4
Nuclear Symbol:
Superscript Mass Number, Subscript
Atomic Number, Symbol
Example:
4
2
He