Question: What is Radioactivity?
Answer: Unstable atomic nuclei will spontaneously decompose to form nuclei with a higher stability. The decomposition process is called radioactivity.
Radioactivity = the release of high-energy particles and rays of energy from a substance as a result of changes in the nuclei of its atom
 Radioactivity refers to the particles that explode from the nucleus as a result of nuclear instability. Because the nucleus experiences the intense conflict between the two strongest forces in nature (electromagnetic force) it’s not surprising that this occurs.
Think about it:
+ + The protons are packed tightly together in the nucleus, yet their charges repel
  them from each other…
Question: What is Radiation?
Answer: The energy and particles that are released during the decomposition process are called radiation
Natural background radiation = the stream of high-energy, fast-moving particles or waves that is found in our environment
 Background radiation has the potential to interact with an atom and turn it into an ion
Radiation = high-energy rays and particles emitted by radioactive sources
 This includes radio waves, microwaves, infrared rays, visible light rays, and ultraviolet rays
 Light is one form of radiation that you can see
Hmm… the word “radiation” comes from the word radiate, which means to spread out in all directions from a central point
Atomic Theory Review:
Atoms are made up of 3 subatomic particles: protons, neutrons, and electrons
The nucleus is the middle of the atom – this is made up of the protons and the neutrons
The electrons whirl around the nucleus in energy levels
Protons have a +1 charge, neutrons have no charge, and electrons have a -1 charge
The atomic number tells us the number of protons and electrons in a neutral atom
The atomic mass tells us how many protons and neutrons are in the atom
The number of protons in an element never changes (if it does, it’s then a different element… worry about this later). The number of electrons in an element can change, depending on if gaining or losing electrons will make the atom more stable.

Isotopes and Mass Number
Which elements are radioactive? Why are there different types of radiation emitted by radioactive nuclei?
Lighter elements tend to have about as many neutrons as protons; heavy elements need more neutrons than protons in order to stick together. Atoms with a few too many neutrons, or not quite enough can sometimes exist for a while, but they’re unstable. o (Since the neutrons have no charge, they act as buffers between the positive protons that are repelled from each other because of their charges)
Unstable atoms are radioactive: their nuclei change or decay by spitting out radiation in the form of particles or electromagnetic waves
Isotopes are different atoms of a particular element that have the same number of protons but different numbers of neutrons.
 Basically, atoms of the same element will have the same number of protons, but can have different numbers of neutrons; the different possible versions of each element are called isotopes.
Example: Hydrogen has no neutrons at all. There’s also hydrogen isotope called deuterium, with one neutron, and another isotope called tritium, with two neutrons:
Key to remember: All isotopes of an element have the same atomic number (number of protons) but since they have different numbers of neutrons, their atomic mass differs from one isotope to the next.
Mass number = atomic number + number of neutrons
Reminder from chapter 4: The atomic number tells you how many protons are in an atom of an element. To find the number of neutrons in an isotope, subtract the atomic number from the mass number
Number of neutrons = Mass number – atomic number
The different isotopes of an element still have the same element symbol. For example, all isotopes of potassium have the symbol K.

Representing Isotopes
Isotopes are written using Standard Atomic Notation:
Mass number is written as a superscript (above) on the left of the symbol
The atomic number is written as a subscript (below) on the left of the symbol
K
isotope: potassium; mass number: 39; atomic number: 19 Example: 3919
 This means that there are 19 protons and 20 neutrons
Another name for the standard atomic symbol is the nuclear symbol
Key Points to remember:
The nucleus is composed of protons and neutrons, and is held together by a strong attraction BUT only certain combinations of neutrons/protons seem to be stable
Any isotope of any element that does not lie in the stability curve with a stable proton/neutron ratio is likely to be radioactive
Radioactivity results from the random and spontaneous breakdown of the unstable nucleus of an atom. Radioactivity is the decomposition process of the nuclei to a more stable condition
Radiation is the energy and particles that are released from the nucleus during the decomposition process are called radiation
All atoms are isotopes. Isotopes are simply referring to that particular proton/neutron combination. The elements listed on the PT are the most common isotope form (the most stable form)
Isotopes are written with standard atomic notation: the symbol stays the same for each isotope, and the atomic number stays the same, but the atomic mass changes
The atomic mass is written as a superscript (above) and the atomic number is written as a subscript (below). Both are written to the left of the symbol.