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Isotope Notes
1. Essential Questions
a. EQ #12: What are isotopes?
b. EQ #13: How can you calculate the number of protons, neutrons, and electrons
for an isotope of an element?
2. Isotopes and Mass
a. ISOTOPES are atoms of the ______________________ that have the same
number of protons but different numbers of ___________________
i. They have different masses.
b. Different elements can have several different isotopes that exist in nature.
c. The ATOMIC MASS of an element is the weighted average of the
______________________ of these isotopes.
i. Since it is an average, it is usually not a whole number.
3. Mass Numbers
a. The MASS NUMBER of an atom is the sum of the ____________________ and
_________________________ in that atom and is a whole number.
i. It CANNOT be found on the periodic table and is NOT the same as the
atomic mass.
ii. It CANNOT be found by rounding off the atomic mass.
4. Isotope Representations
Mass number
12
Symbol of Element
Atomic number
Symbol of the element
6
Mass number
5. Stability
a. Some isotopes are stable and some are unstable.
b. In order for a nucleus to be _____________________, there must be enough
neutrons present between the protons to block the repulsive forces between the
protons.
c. If an isotope of an element is _________________________, it is radioactive and
will undergo nuclear decay.
6. Nuclear Decay
a. NUCLEAR DECAY is a nuclear reaction (not chemical) in which energy or particles
are ____________________ (given off) from the nucleus.
i. Result is a more stable nucleus.
b. ______________________ is the particles and/or energy that are emitted during
nuclear decay.
i. It can include:
1.
2.
3.
c. Nuclear decay occurs naturally in many elements that are common on earth.
d. There is always some radiation present in every environment.
7. Calculating Particle Numbers
a. The ATOMIC NUMBER of an element is equal to the number of protons.
i. It is always the same for a given element and is always a whole number.
ii. It can be found on the periodic table.
b. The MASS NUMBER must be given in order for you to determine the number of
neutrons.
i. It is NOT on the periodic table.
c. In a neutral atom, the number of electrons is equal to the number of protons.
i. Therefore, the atomic number also tells how many electrons are present.
d. Practice Problem
i. This is Carbon-14, an isotope of carbon.
ii. # of protons =
14
iii. # of neutrons =
______
iv. # of electrons =
6