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?

Aim: How can the decay of an organism tell us its age?

Basic Atomic Structure

Electrons – Orbit the nucleus (negative electrical charges).

Atomic number is the number of protons in the atom’s nucleus.

Mass number is the number of protons plus neutrons in an atom’s nucleus.

DO NOTCOPY

I. Isotopes - the unstable form of an element.- The atoms have the same number of protons and different number of neutrons.

EXAMPLE Stable Element, Carbon-12:-6 Protons -6 Neutrons

Unstable Element (Isotope), Carbon-14:-6 Protons -8 Neutrons

DO NOTCOPY

II. Radioactivity refers to energy and particles emitted from unstable isotopes.

This is known as radioactive decay

(Isotope)

III. Absolute Age : (Radioactive dating)- Using precise numbers to tell when an organism lived or an event occurred.- This can be done by using radioactive isotopes.

cover of your ESRT.

IV. Radioactive Decay

• Continues at a regular rate (not affected by outside factors).

• The first isotope is called the parent nuclei. (unstable)

• When it decays, it turns into the daughter nuclei. (stable isotope)

A. Half – Life:- time required for half of the atoms in a sample of radioactive element to decay.

**The parent nuclei (Red) changes to the daughter nuclei (Blue)

V. Dating with Carbon-14

- Used to date most recent organic material. (organisms and plants)

- Shortest half-life.- Found in people

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?

11,400 yrs

25% C14 will remain

Rubidium-87 (87Rb)

Example 1: Use your ESRT

If you can see in a rock sample there is 1/4 C14 and 3/4 N14, the sample must have gone through how many half-lives?

Two half-lives.

How old is this sample?

11,400 yrs old.

EXAMPLEA student found a fossil and by looking

at the radioactive decay of C14 she found there to be 1/16th of C14

remaining in the fossil. How many half lives has this sample gone through?

The sample has gone through 4 half-lives

22,8001/164

17,1001/83

11,4001/42

5,7001/21

01/10

Number of years

% Parent Remaining

Half-Life

• Closure:

Obtain the worksheet form the back, we are going to work on it together.