Chapter 3
“Atomic Structure”
Definition of an Atom
Origin of word atom: Greek word “atomos” which
means uncuttable, or indivisible, something that
cannot be divided further.
Dictionary definition
The smallest component of an element having
the chemical properties of the element,
consisting of a nucleus containing combinations
of neutrons and protons and one or more
electrons bound to the nucleus by electrical
attraction; the number of protons determines the
identity of the element.
Parts of the Atom
Parts of the Atom
Part
Symbol
Charge
Mass
Number
Mass in
amu
Proton
p+
+1
1
~ 1 amu
Neutron
no
0
1
~ 1 amu
Electron
e-
-1
0
~ 0 amu
An electron weighs 1/1836 of a proton
What Does an Atom Look Like?
- Let’s look at the Helium atom
Helium Atom
How small is an atom?
0.22 nanometers
0.00000000022 meters
What Makes Atoms Different
From Each Other?
The number of PROTONS!!!
The atomic number (Z) equals the number of proton’s
in an element’s atom.
Since elements on the periodic table are neutral (no
charge),
we can assume the # of electrons = # of protons.
The mass number equals the total number of protons and
neutrons in the nucleus of an atom.
How Many Neutrons?
The mass number equals the total number of protons and
neutrons in the nucleus of an atom.
If we know the mass number then we can figure out how
many neutrons are present by the following equation:
mass # - atomic # = # of neutrons
Q: How do we figure out what the mass number is???
A: Round the atomic mass on the periodic table to the
nearest whole number
Nuclides
The particles that make up the nucleus of an atom are
called nuclides. The nuclide shows the mass number along
with the atomic number (# of protons) of an atom.
# protons
# neutrons
# electrons
2
2
2
# protons
# neutrons
# electrons
22
26
22
# protons
# neutrons
# electrons
3
4
3
What the Quark?
Turns out protons and neutrons are
made from smaller parts!! Uggh!
Quarks
Same Element Different Atom
All atoms of a particular element are not exactly alike.
Some elements have atoms with different masses (isotopes)
Cool Down
What are two things you learned today?
What do you still not understand?
Homework due Wednesday
Worksheets 4.1 and 4.2