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Structure of
the Atom
Structure of the Atom
• Subatomic particles are
smaller than the atom
• 3 main subatomic particles:
proton, neutron, & electron
Nucleus
• “the core”
• Contains 99.9% of
the mass of the
atom
• Contains protons
and neutrons
• Has a positive
charge
Protons
• Positively
charged
particle
• They are
identical in
every element
• Mass is 1
atomic mass
unit (amu)
Neutrons
• Have no charge
• All neutrons are
identical in
every element
• Mass 1 amu
Atomic number
• # of protons in the nucleus determines
the atomic # of the element
Isotopes
• Atoms of the same element will have the
same number of protons, but can have
different numbers of neutrons
Hydrogen Isotopes
Mass Number and
Atomic Mass
• The mass number:
sum of the protons
and neutrons
• Used to distinguish
one isotope from
another
• Atomic mass:
average mass of all
the isotopes of an
element
The Electrons
• Electrons whirl around the nucleus
• Mass: 1/2000th of a proton or neutron
• Have a negative charge equal,
opposite of the proton
• Spin around in energy levels billions of
times a second!
• move so fast that the space they spin
is sometimes is referred to as an
electron cloud
Each energy level
can hold a
certain number
of electrons
-the 1st 2 electrons
-the 2nd 8 electrons
-the 3rd 18 electrons
The further away
from the nucleus an
electron is, the more
energy it possesses
The number of electrons
an atom has determines
its chemical properties
The size of an atom… very
small
• A 70 kg body would have
approximately 7x1027
atoms or
7,000,000,000,000,000,000
,000,000,000 (27 zeros)
• everything that you can
touch has billions of atoms
inside it!
Quarks
• Protons and neutrons: made of
smaller particles called quarks
• 2 groups of quarks
• One: “color” with 3 different types
• The other: “flavor” with 6 different
types
• 3 quarks combined to form
protons and neutrons
The Electromagnetic
Force
•
•
•
•
Can either attract or repel forces
Positive to negative is a force of attraction
Positive to positive is a force of repulsion
Keeps the electrons spinning around the
nucleus
The Strong Force
• Glues the protons together to form
the nucleus
• Cancels out the proton to proton
positive charge repelling
• The greatest of the four forces, but
has a small range
The Weak Force
• key to the power of the sun
• Responsible for radioactive
decay
Gravity
• weakest force
• Force of attraction between objects
• Its role in the atom is not fully
understood