Aim: How do scientists tell the exact age of a rock? Important Vocabulary: Radioactive dating, Absolute dating and Carbon dating all refer to a method of finding the exact age of a rock.

How are the three atoms of Hydrogen I. Isotopes : the unstable form of an element; found in rocks and organisms *different number of neutrons STABLE UNSTABLE - PROTON - NEUTRON UNSTABLE How are the three atoms of Hydrogen different?

Describe what is happening in the diagram II. Radioactive Decay : - process where an Isotope breaks down losing energy and particles. - transforms the Isotope into a new stable element. Describe what is happening in the diagram (Isotope)

III. Parts of Radioactive Decay a) Unstable Radioactive Isotopes, are called Parents. b) Stable Decayed elements, are called Daughters. Looking at the graph, what happens to the number of parents and daughters over time? How many parents do we start with at time zero? Daughters?

c) Half – Life (Rate of Decay) - time required for 50% of the unstable Parent Isotopes to decay (change) into stable daughter elements. - This time is constant and not affected by outside factors. - Knowing the rate of decay and the ratio of Parent Isotopes to Daughter elements, we can figure out how old the object is. cover of your ESRT

Which color dot represents the Parent elements? Which represents the Daughters?

- 50% or HALF of the parents are lost after each half-life How many parents do we loose each time? - 50% or HALF of the parents are lost after each half-life

IV. Common Isotopes Carbon14 Used to date most recent organic material. (anything once living) Shortest half-life. How long is the half-life for Carbon14? How does this compare to the other Isotopes?

Examples: Use your ESRT How many years will it take for two half-lives to pass of C14? What % of C14 will remain at this point? Which isotope has the longest half life? What is it? MAKE A CHART! 11,400 yrs 25% C14 will remain Rubidium-87 (87Rb)

THE CHART THAT MAKES HALF-LIFE EASIER % Parent Remaining *Number of years 1/1 (100%) 1 1/2 (50%) 2 1/4 (25%) 3 1/8 (12.5%) 4 1/16 (6.25%)

Closure: After analyzing a rock sample, it was found to have 25% (1/4) C14 and 75% (3/4) N14. a) How many half-lives has the sample undergone? Two half-lives. b) How old is this sample? 11,400 years old.

The sample has gone through 3 half-lives 2) A student brought a fossil to a laboratory and by analyzing the radioactive decay of C14 she found there to be (12.5%) 1/8th remaining in the fossil. a) How many half lives has this sample gone through? The sample has gone through 3 half-lives b) What percent of the rock sample has decayed into daughters? 87.5%

3) What is the half life of Strontium 90? 25 years

Take a worksheet from the back top bin

Basic Atomic Structure DO NOT COPY Electrons – orbit the nucleus. Protons – are in the atom’s nucleus.  Neutrons - are in the atom’s nucleus.

Do Now: Think about this… If you were standing 10 feet from the wall, and I asked you to walk half the distance to the wall, how close would you be? If I asked you to repeat this process, would you ever reach the wall?