Chapter 2 Section 2 Notes The Nucleus

[Pages:2]Chapter 2 Section 2 Notes

The Nucleus

I.

Identifying Numbers

A. Atomic Number

1. The number of protons in the nucleus of an atom

2. This number never changes without changing the identity of the atom

3. Isotopes are atoms of the same element that have different numbers of neutrons

B. Mass Number--the number of Protons plus Neutrons

C. Strong Nuclear Force holds the nuclear particles together--even all of the positively

charged Protons that would normally repel each other

II.

Radioactive Decay

A. Many atomic nuclei are stable when they have about the same number of Protons and

Neutrons

B. Some nuclei, especially in the heavier elements, have too many or too few neutrons for

stability

1. Repulsion builds up and the nucleus must release a particle to become stable

2. Energy is given off along with the nuclear particle--called RADIOACTIVE DECAY

3. A different element results--the process is called TRANSMUTATION (the changing of

one element into another through radioactive decay)

C. Alpha Particles

1. Consists of 2 protons and 2 neutrons

2. Used in smoke detectors; Americium goes through radioactive decay losing an

alpha particle and energy to become Neptunium (aka transmutation)

D. Beta Particles

1. A high-energy electron that comes from the nucleus of an atom

2. A neutron has become unstable and split into a proton and electron; the electron is

released with a large amount of energy

3. The mass of the element stays almost the same because the electron has so little

mass

E. Rate of Decay

1. Radioactive decay is random

2. Half-life is the amount of time it takes for half of an element to decay

3. The radioactive decay of unstable atoms goes on at a steady pace unaffected by

conditions

4. Half-lifes are different for each isotope

F. Carbon Dating

1. Carbon 14 has a half-life of 5,730 years

2. The levels of carbon 14 atoms remain constant in a living organism because they are

being constantly exchanged with the environment

3. When an organism dies, it no longer exchanges carbon 14 with the environment

a. Carbon 14 undergoes radioactive decay b. Scientists can determine the age of an organism by comparing the amount of

carbon 14 left in it to the amount it would have had while still alive G. Uranium 238 Dating

1. Uranium 238 decays to Lead 206 with a half-life of 4.5 billion years 2. By comparing the amount of uranium to lead, scientists can determine the age of

rocks 3. There is some controversy

a. Some rocks could have had lead in them to begin with b. Some of the isotopes could have migrated out of the rock over the years H. Radioactive Disposal 1. Waste products from processes that involve radioactive decay can cause problems because they can leave radioactive isotopes that can continue to release harmful radiation 2. Special sites are built to contain the radiation such as in Carlsbad New Mexico III. Synthetic Elements A. Scientists create new elements by smashing atomic particles into a target element B. New elements are called synthetic because they are made by humans and don't exist in nature C. Elements #93-112, 114, 116, and 118 have been made this way IV. Uses of Radioactive Isotopes A. Medical uses--tracer elements are introduced into a living system and followed by a device that detects radiation while it decays B. Iodine 131 is used to diagnose problems with the tyroid C. Technetium 99 (half-life of 6 hours) is used to find tumors or fractures D. Phosphorus 32 is used to determine how a plant uses phosphorous to grow and reproduce

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