Science 10 Unit 2 CHEMISTRY: ATOMIC THEORY EXPLAINS RADIOACTIVITY

7.1 Atomic Theory and Radioactive Decay Natural background radiation exists all around us. Radioactivity is the release of high energy particles or waves that we call radiation When atoms lose high energy particles and waves, new atoms can be formed. Radiation can be good or bad: X-rays, radiation therapy and electricity generation are beneficial. High energy particles and waves can do damage to DNA in our cells.

The Electromagnetic Spectrum

Early Discoveries of Radiation Roentgen named X rays with an “X” 100 years ago because they were previously unknown. Becquerel realized uranium emitted seemingly invisible energy as well. Marie Curie and her husband Pierre named this energy radioactivity. Early discoveries of radiation relied on photographic equipment. Later, more sophisticated devices such as the Geiger-Müller counter

Isotopes Are atoms of the same element, with a different number of neutrons. changing the # of neutrons changes the mass number Remember: mass # = # protons + # neutrons isotopes still have the same number of protons and the same element symbol Atomic mass = average of the mass numbers for all isotopes of an element (that’s why there are decimals)

Quick Example Calculation Isotopes Eg. Potassium Quick Example Calculation K39 K40 (39 x 9 + 40)/10 = 39.1

Representing Isotopes Isotopes are written two ways with the mass number at the end Ex. Potassium – 39 With its chemical symbol Mass number Atomic number 19 19 19 20 21 22 19 19 19

Radioactive Decay Can result in new atoms forming. Radioactivity results from having an unstable nucleus. Radioactive decay = when nuclei break apart + release energy from the nucleus. Radioactive decay continues until a stable element forms. An element may have isotopes that are radioactive called radioisotopes (the unstable ones) Ex. carbon-12, carbon-13 and carbon-14 (only C-14 is radioactive)

Uranium goes through many decay steps before it becomes stable Radioactive Decay Uranium goes through many decay steps before it becomes stable

Radioactive Decay Rutherford identified three types of radiation using an electric field. Positive alpha particles were attracted to the negative plate. Negative beta particles were attracted to the positive plate. Neutral gamma particles did not move towards any plate.

Radioactive Decay: Alpha Radiation positively charged weighs the most (big and slow) – a sheet of paper will stop an alpha particle are the same as a helium nucleus Example: the alpha decay of Radium - 226

Radioactive Decay: Beta Radiation A Beta particle, , is a high energy electron. negatively charged, and weigh less than alpha particles (move faster) Beta particles are represented by 2 symbols electrons are very tiny, so beta particles are assigned a mass of 0. *The real reason it’s -1: Proton from nucleus is splitting into Neutron/Electron

Radioactive Decay: Gamma Radiation has no charge and no mass. is the highest energy form of electromagnetic radiation. It takes thick blocks of lead or concrete to stop gamma rays. Gamma decay results from energy being released from a high-energy nucleus. Think of it like a rearrange/rubiks cube or cracking of knuckles Shows unstable nucleus for gamma decay

Nuclear Equations: Are written like chemical equations, but represent changes in the nucleus of atoms. Chemical equations represent changes in the position of atoms, not changes to the atoms themselves. Remember: The sum of the mass numbers on each side of the equation should equal. The sum of the charges on each side of the equation should equal. *Top has to equal top, bottom has to equal bottom *Be careful if there are multiple neutrons! Lets Try some together