SL Chem - Unit #1: Isotopes and Radioisotopes

What determines an atoms weight?

It’s weight is composed of the atoms protons and neutrons

• Electrons don’t weigh enough to make a significant impact

Isotopes

Different atom of the same element with different masses due to the difference in the amount of neutrons they have

Similarites and differences between isotopes

Isotopes will have the same chemical properties as one another but different physical properties (Caused by their different masses)

Nuclear Symbol Notation

Isotopes are labeled using this notation:  ^A_ZX

• A: # of protons + Neutrons (mass)

• Z: Atomic number

Relative Atomic Mass

• AKA, Average atomic mass(AAM) or Atomic Weight or Relative Atomic Mass (A_r)

refer to the weighted average (in AMU) of all natural occurring isotopes of an element

• isotopes are found in different abundancies

Implication of isotopes…

Having isotopes means that the mass number(A) of an element is not the same as the elements relative atomic mass (Ar)

• Memorize: “The existence of isotopes explains the apparent contradiction between the mass number (A) and the relative atomic mass (A_r) of the elements.”

1 AMU is relative to…

1/12 of a C-12 atom

• Carbon-12 is the standard element that they measure/compare others to

Average Atomic Mass (AAM) Equation

Average atomic mass = [(mass #1)x(abundance #1)] + [(mass #2)x(abundance #2)]

Radioisotopes

Unstable forms of elements that undergo decay creating different elements and releasing radioactive particles

• Normally very heavy elements that are constantly trying to break down

Mass Spectrometer

Scientist use this instrument to help determine the abundancy of each isotope in a naturally occurring sample