2. 1. The Atom
A. Smallest whole part of matter.
B. Contains 3 sub-particles:
1. Proton
2. Neutron
3. Electron
3. 2. The Proton
C. If the number of
protons in an element
ever changes, the
element has changed!
A. Each element is
determined by its
number of protons.
B. # OF PROTONS=
ATOMIC #
1. The periodic table is
arranged by increasing
atomic number.
4. 2. The PROTON D. Discovered in 1909.
E. Located in the Nucleus.
F. Positive charge.
G. Held together by the
Strong Nuclear Force.
1. Like repels like, so the force
needed to hold protons
tightly packed is incredible.
2. A nuclear explosion breaks
that bond and releases a
massive amount of energy.
5.
6. The NEUTRON
A. The number of neutrons is determined by:
Atomic mass (rounded) – atomic number= Neutrons
A. Number of neutrons can change!
1. Isotope: atoms of an element that have different
numbers of neutrons.
C. Atomic Mass Number
is the average of the
masses of the
isotopes for an
element.
7. 3. The NEUTRON
D. Discovered in 1931.
E. Located in the nucleus.
F. No charge.
G. Held together by the
strong nuclear force.
8. 4. The ELECTRONA. Negative charge.
B. Almost no mass.
C. In an element’s NATURAL state, the # of protons &
electrons are equal, neutralizing the atom’s
charge.
THEREFORE,
ATOMIC NUMBER
IS ALSO EQUAL TO THE
NUMBER
OF ELECTRONS
9. 4. The ELECTRON
D. Discovered in 1897.
E. Located in Electron Cloud,
OUTSIDE the nucleus.
F. Electron orbits:
1. 1st
orbit: 2 electrons
2. 2nd
, 3rd
, 4th
orbits: 8 electrons
10. 5. Valence
Electrons
A. Electrons located in the outermost
level of the cloud.
B. These electrons move from atom to
atom during chemical reactions to
form bonds.
1. Each atom is trying to fill its outermost
level and will take in or lose electrons
accordingly.
2. Atoms closer to the maximum number
react more violently, since it’s very easy
to gain or lose only 1 or 2 electrons.
3. Atoms at the maximum are stable & will
not react (noble gases).
C. When the electrons move, IONS are
formed.
1. Ions are elements with a charge.
2. Sodium loses an electron, becoming +1.
3. Chlorine gains an electron, becoming -1.
