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Atoms, Elements, and the
Periodic Table
Ch. 17 & 19
Ch. 17 Section 1
Structure of the Atom
Warm Up
• Diagram an atom. Include protons,
neutrons, quarks, and the electron cloud.
Atoms
• An element is matter
with a fixed
composition – it is
made of the same
atoms
• An atom is the
smallest piece of
matter that still retains
the properties of its
element.
Atoms
• The main particles that compose an atom are:
– Protons: positively charged
– Neutrons: neutrally charged
– Electrons: negatively charged
• Protons and neutrons are
found in the center of the atom
- the nucleus
• Electrons are found orbiting in
the electron cloud surrounding
the nucleus
Atoms
• Protons and neutrons
are made up of
smaller particles
called quarks
• Two up-quarks and a
down-quark produce
a proton, while two
down-quarks and an
up-quark produce a
neutron
Atoms
• The electron cloud
model of an atom is
used today
• The electron cloud is
the area around an
atom’s nucleus where
electrons are found
• The electron cloud is 100,000 times larger
than the diameter of the nucleus, but
electrons are much smaller than both protons
and neutrons
Subatomic Particle Masses &
Charges
Particle
Mass (g)
Mass
Charge
(atomic
mass unit amu)
Proton
1.67 x 10-24
1
+1
Neutron
1.67 x 10-24
1
0
Electron
9.11 x 10-28
<<1
-1
Atoms
• The mass of an
atom comes from
particles in its
nucleus
• The electron is so
small, it is
considered
negligible when
finding the mass of
an atom
Atoms
• The unit of measurement used for atomic
particles is the atomic mass unit (amu)
Masses of Atoms
• An atom’s atomic
number is equal to
the number of protons
in an atom
• An atom’s mass
number is the sum of
the protons and
neutrons in an atom
11
Sodium
Na
22.98976928
Atomic Mass
• The mass of a proton or a neutron is
approximately 1 amu
• A chlorine atom containing 17 protons and 18
neutrons has a mass of 35 amu
Masses of Atoms
• Copper (Cu) has an
atomic number of 29
and a mass number
of 64
• 29 amu of its mass
comes from its 29
protons
• The remaining 35
amu comes from its
35 neutrons
29
Cu
Copper
63.5
Masses of Atoms
• Atoms of the same
element can have
different numbers of
neutrons
• These are isotopes
• Isotopes are identified
by the name of the
element followed by
its mass number
Masses of Atoms
• Carbon-12 has 6 protons
and 6 neutrons
• Carbon-14 has 6 protons
and 8 neutrons
• The average atomic mass of an element
is the weighted average mass of the
element’s isotopes
Atomic Structure
• Energy levels are the level at which electrons orbit
the nucleus
• They are numbered from the inside to the outside
• The first level can contain a maximum of 2
electrons, the second 8 electrons, the third 18, and
the fourth 32
The Bohr
Model
• The Bohr Model of an atom shows all its
electrons in their specific energy levels.
• Energy level maximums are: 2, 8, 18, 32
• Numbers can repeat and go back down,
but cannot skip
• The outer energy level has a maximum of
8 electrons
The Bohr Model
• Argon has 18 electrons. 2 are in the first
energy level, 8 in the second, and the
remaining 8 are in the third.