Lessons 13 & 15

Subatomic Heavyweights

Isotopes

Isotopes - atoms of the same element that have the same number of protons and electrons but different numbers of neutrons

Isotopes associate with the atomic number and the mass number of an element

• The difference in neutrons but not protons in an atom of an element means that the element doesn't change into another element and the atomic number stays the same while the atomic mass number changes
• Isotopes are referred to by their atomic mass number
• The average atomic mass number of an element on the periodic table is the weighted average of all the naturally occurring isotopes

- the isotope with the mass closest to the average atomic mass is the most common isotope
How do you write an isotope?

Hyphenotation: symbol - mass #

Nuclear notation: mass # with the symbol to the right . atomic #

Practice Problems

4) How many protons, neutrons, and electrons are in each?

a. Fluorine-23: 9,14,9     b. 59                          c. Molybdenum-96: 42,54,42 
                                      27 Co: 27,32,27 

5) An isotope of iron, Fe, has 26 protons and 32 neutrons.

1. What is the approximate mass of this isotope? - 58 amu
2. How would you write the symbol for this isotope? Fe-58

Nuclear Quest

Nuclear Reactions

Nuclear Reaction - a process that involves changes to the nucleus of an atom

Radioactive Decay - a spontaneous process by which an atom emits radiation or a particle from its nucleus to become more stable

• Changes in the nucleus of an atom can change the identity of an element

Alpha Decay

Alpha Decay - emits an alpha particle, atomic # decreases by 2 and mass # decreases by 4

Alpha particle - a particle composed of two protons and two neutrons, or the nucleus of a helium atom

Beta Decay

Beta Decay - neutron changes into proton and electron and atomic number increases by one

Beta particles - an electron emitted from the nucleus of an atom during beta decay

Since during beta decay an electron from the original element leaves, that means the atomic mass goes down by one. However, that neutron then changes into a proton and electron. Therefore, the atomic mass goes back up by one because of the proton and the new proton also cause the atomic number to go up by one making it a whole new element.

Gamma ray - a form of high-energy electromagnetic radiation emitted during nuclear reactions

Practice problems
4) Explain why the mass of an atom changes when an alpha particle is emitted. When an atom emits an alpha particle it is getting rid of 2 protons and 2 neutrons and since protons and neutrons make up an atom's mass, the resulting atom has a mass of 4 less.

6) An alpha particle is not a neutral atom. It has a charge of +2. Why is this? An alpha particle is basically a helium nucleus thus doesn't have electrons meaning the 2 protons make the particle positively charged.

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