A. ATOMS
1. All matter is made of
atoms
2. Atomic Parts
 Protons-positive (+); some mass;
in nucleus
 Neutrons-no charge (0); some
mass; in nucleus
 Electrons-negative (-); no real
mass but do take up most of
the space around an atom
Atomic Structure
3. Describing Atoms
a. Atomic Number = number of
protons
-In a neutral atom (0 charge), the
# of protons = the # of electrons
b. Atomic Mass=number of neutrons
+ Protons
4. Changing Parts
a. The number of protons for an atom
never changes.
BUT-the number of neutrons can
change
b. Isotopes are atoms of the same
element with a different number of
neutrons.
Examples of Isotopes
c. Ions
• An atom that gains or loses an electron is called
an ion
– If the atom loses electrons, it becomes
positively charged
– If an atom gains electrons it becomes
negatively charged
WHY?
-Remember p+ = e- so if we change those
numbers, the charge moves in the direction
of the larger number of particles.
-More on this later when we talk about
bonding
ION Example
B. Atomic Theory
1. Early Theory
a. Aristotle-all matter flows
continuously and is composed of 4
elements
-fire, air, earth and water
b. Democritus-Disagreed with
Aristotle and said that matter
was made of small units called
“atomos” that were indivisible
Aristotle was more popular than
Democritus so this theory was ignored
for over 2000 years!c
2. Modern Theory
a. Dalton (England, 1800’s) atoms.
1. All elements are composed of atoms and
they are indestructible-like a solid sphere.
They cannot be created or destroyed-LAW
OF CONSERVATION OF MATTER
2. Atoms of the same element are exactly
alike.
3. Atoms of different elements are different.
4. Compounds are formed by the joining of
atoms of two or more elements.
b. Thomson (1897-England)Discovered negatively charged
electrons
c. Rutherford(1897-England)-In
1908, discovered the nucleus.
c. Bohr (1913)-Denmark –
said electrons were in
orbits or energy levels
around the nucleus.
•Energy Levels
The energy that an
electron has is based on
its location around the
nucleus. (Electrons that
are closer to the
nucleus have less energy
than those that are
farther away from the
nucleus)
Energy Levels (cont’d)
•
•
•
•
•
Level
Level
Level
Level
Level
1-2 electrons
2=8 electrons
3-8 electrons
4-18 electrons
5-32 electrons
Each level must be full before
another can be started.
EXAMPLE
• Nickel has an atomic number of 28
1.
2.
3.
4.
Level 1 hold 2-------------28-2=26 to place
Level 2 can hold 8--------26-8=18 to place
Level 3 can hold 8--------18-8=10 to place
Level 4 can hold 18 BUT only 10 are left so it will
only have 10 in it
• We have to show Neutrons (n) and Protons (p+) too.
• Protons and electrons are usually equal so we know
there 28 protons.
– Neutrons are found by subtracting the Atomic number from
the atomic mass.
Atomic mass
59
-
Atomic # 28 =31 neutrons
EXAMPLE
It would look like this..
28 p
31n
d. Electron Cloud Model
• Electrons travel in regions called “electron
clouds”
• You cannot predict exactly where an
electron will be found
• Electrons move in