Fall 2011 – Week 6 (Atomic Structure & Nuclear) Chemistry catalysts Fall 2011 – Week 6 (Atomic Structure & Nuclear)

Catalyst (5 min) Helium – 4 Neon - 21 9/17/12 Atomic Models EQ: How can I model the parts of an atom? Calculate the numbers of protons, neutrons, and electrons in these three isotopes. Helium – 4 Neon - 21 Draw Bohr models of these three isotopes.

1. How many protons, neutrons, and electrons does Neon have? Review Question 1 1. How many protons, neutrons, and electrons does Neon have?

Draw a Bohr model of an oxygen atom? Question 2 Draw a Bohr model of an oxygen atom?

Who discovered electrons? Question 3 Who discovered electrons?

Question 4 How many protons, neutrons, and electrons does Oxygen-15 have?

Catalyst (5 min) 9/14/11 Nuclear Decay EQ: How does the nucleus of an atom change during decay? What do you think when you hear the word nuclear? Is it a positive word or a negative word? Write 4-6 detailed sentences describing your reaction.

When it all just falls apart… Nuclear Decay When it all just falls apart…

Nuclear decay occurs when the nucleus of an atom is unstable. What is Nuclear Decay? Nuclear decay occurs when the nucleus of an atom is unstable. Particles and/or energy are emitted (given off) from the nucleus to help stabilize it.

Nuclear Foldable (Front)  alpha  beta  gamma

Nuclear Foldable (Inside) Composition: Charge: Mass: Penetration: Shielding: Symbols:

Alpha Particles () He  Made of 2 protons & 2 neutrons Charge = +2 Mass = 4 amu (Heavy and slow particles) Low penetrating power Can be blocked by a single sheet of paper Symbols used: He 

Alpha Decay Alpha decay occurs when a large nucleus ejects two protons and two neutrons (an alpha particle). The results are a mass change of 4 amu and a more stable nucleus.

Beta Particles ()  e Made of 1 electron Charge = -1 Mass = 1/1840 amu (Fast and light particles) Medium penetrating power Can be blocked by thin metal like aluminum foil or thin wood Symbols used:  e

Beta Decay Beta decay occurs when a neutron splits into a proton and an electron. This results in no change in mass, but the isotope does become a different element.

Gamma Rays ()  Made of waves, not particles Charge = 0 Mass = 0 High penetrating power Can be mostly blocked by using 10cm or more of solid lead, but never completely Symbol used: 

Gamma Ray Radiation Gamma radiation is produced by a nucleus in the “excited state.” When a nucleus has too much energy, it can release some of it as gamma radiation. The result of this is no change in mass, charge, or composition – just a more stable nucleus with less energy.

1 1 1 1 2 2 2 2 3 3 3 3

Determining Charge of Radiation

Shielding Radiation

Alpha () shielding Beta () shielding Gamma () shielding   

Warm Up You have three radioactive cookies: 9/15/11 Nuclear Decay EQ: What is the half-life of a radioactive isotope? You have three radioactive cookies: One emits  particles. One emits  particles. One emits  particles. You must eat one, hold one in your hand, & hold one in your pocket. Which cookie goes where? Explain.

Nuclear Cookies

4 + ___ = 12 8 10 = ___ + 4 12 + 9 = ___ + -1 6 22 Math Equations Can use the number and type of nucleons present to write a balanced equation for a nuclear decay reaction Procedure allows us to predict the identity of either the parent or daughter nucleus if the identity of only one is known Regardless of the mode of decay, the total number of nucleons is conserved in all nuclear reactions, as is the total positive charge • To describe nuclear decay reactions, the AX notation for nuclides has been extended to include radioactive emissions The following table lists the name and symbol for each type of emitted radiation The left superscript in the symbol for a particle gives the mass number, which is the total number of protons and neutrons For a proton or a neutron, A = 1 Because neither an electron nor a positron contains protons or neutrons, its mass number is 0 The left subscript gives the charge of the particle Protons carry a positive charge, so Z = +1 for a proton A neutron contains no protons and is electrically neutral, so Z = 0 For an electron, Z = –1, and for a positron, Z = +1 Because  rays are high-energy photons, both A and Z are 0 In some cases, two different symbols are used for particles that are identical but produced in different ways Symbol 0e, simplified to e– represents a free electron or an electron associated with an atom Symbol 0, simplified to – denotes an electron that originates from within the nucleus, which is a  particle 4He refers to the nucleus of a helium atom, and 4 is an identical particle ejected from a heavier nucleus There are six fundamentally different kinds of nuclear decay reactions, each of which releases a different kind of particle or energy (see table) 22

Chemistry Equations Math uses an = sign. Chemistry uses an . Example: H2 + O2  H2O reads “Hydrogen plus oxygen yields water.”

U  Th + He  - decay Add this equation to your foldable. Note that the left side and right side are equal for the top number and bottom numbers.

C  N + e  - decay Add this equation to your foldable. Note that the left side and right side are equal for the top number and bottom numbers.

Al  Al +   - decay Add this equation to your foldable. Note that the left side and right side are equal for the top number and bottom numbers.

Review Nuclear Equations Alpha decay of Uranium-235. Beta decay of Uranium-235. Gamma decay of Uranium-235. 235 U He 4 2 231 Th 92 90 235 U e -1 235 Np 92 93 235 U  235 U 92 92

Examples of Nuclear Equations Xe Po Es Ti

How to Play Nuclear Decay Decide who goes first. This person rolls both dice. Starting with Am-241, all players write an equation for , , or  decay that matches the roll on the die. Players earn points for correct answers The roller earns the # of points from the numbered die. Everyone else earns 1 point for any correct answer. No points for incorrect answers. Keep going until you run out of protons or neutrons. Highest score wins!

Example 3  Correct! 3 points  0 points  Incorrect! 1 point  Suppose I rolled these dice. I write this equation. Group member A writes: Group member B writes:  3 Correct! 3 points  0 points  Incorrect! 1 point  Correct!

How to Play Nuclear Decay Decide who goes first. This person rolls both dice. Starting with Am-241, all players write an equation for , , or  decay that matches the roll on the die. Players earn points for correct answers The roller earns the # of points from the numbered die. Everyone else earns 1 point for any correct answer. No points for incorrect answers. Keep going until you run out of protons or neutrons. Highest score wins!

Catalyst (5 min) Use your foldable for help! Write equations for: 9/16/11 Half Lives EQ: What is the half-life of a radioactive isotope? Write equations for: Alpha decay of Np-237 Beta decay of Np-237 Gamma decay of Np-237 Use your foldable for help!

What is a half-life? A half-life is the amount of time it takes for half of the amount of a substance to decay. For example: 241Pu has a half-life of 14 years. Suppose we start with 100 grams of 241Pu 14 years later, we have 50 grams 28 years later, we have 25 grams 42 years later, we have 12.5 grams… Band of Nuclear Stability & Half-Lives