•ttp://www.youtube.com/watch?v=NNcQX033V_M&NR=1&feature=fvwp • http://www.youtube.com/watch?v=zLFRIiflSgU&feature=related

Nuclear Chemistry

LecturePLUS Timberlake 2

Review - Atomic Symbols

Show the mass number and atomic number

Give the symbol of the element

mass number

23 Na

atomic number 11

Sodium-23

Protons + Neutrons

Protons

LecturePLUS Timberlake 3

Review - Isotopes

Atoms with the same number of protons,

but different numbers of neutrons.

Atoms of the same element (same atomic

number) with different mass numbers

Isotopes of chlorine

35Cl

37Cl

17 17

chlorine - 35 chlorine - 37

Radiation• Radioactive Decay - When nuclei

are unstable (due to an unfavorable ratio of neutrons to protons) they throw off particles and energy to become more stable.

What is the significance of the

number of neutrons?

• In atoms with a low atomic number, stable isotopes have N (# of neutrons) = Z (# of protons) .

• As atomic number increases, it takes more neutrons (N) to be stable.

• All atoms with an atomic number > 82 (lead) are radioactive.

Nuclear Decay reactions

There are Three Main Types of Radioactive Decay

1.Alpha ( ) Decay2.Beta ( ) Decay3.Gamma ( ) DecayNuclear Reaction: Any reaction in which the particles that make up the nucleus (protons and neutrons) are rearranged to form a different element or isotope.

Nuclear Decay reactions

Alpha Decay: When an element is broken down in alpha decay it emits 2 neutrons and 2 protons. Alpha decay is the most common in elements with an atomic number greater than 83.

symbol: (alpha particle) = or

alpha particle is the same as a Helium nucleus

Write the alpha decay of U-235.ThHeU 231

9042

23592

He42 4

2

Nuclear Decay ReactionsNuclear Decay Reactions

Example: Example: Alpha emissionAlpha emission

•Note that mass number (A) goes down by 4 and atomic number (Z) goes down by 2.

•Nuclear particles (protons and neutrons) are rearranged but conserved (not created or destroyed)

He

Properties of an Alpha Particle

• Relatively large• Positively charged (2+).• It has very low penetration and can

be shielded by a thin piece of paper.

Nuclear Decay Reactions

Beta Decay : • When an element is broken down in

beta decay a neutron converts to a proton and an electron is emitted.

• Beta emission increases the atomic number by one, but the mass stays thesame. Symbol: (beta particle) = or

• Beta decay is most common in elements with a high neutron to proton ratio.

• Write the beta decay of sulfur-35CleS 3517

01

3516

e01 01

Properties of a Beta Particle

• Relatively small with very low mass• Negatively charged (1-).• A beta particle is much more

penetrating. It can be shielded by a layer of lead.

Gamma Decay: • In gamma emission, there is no change in

the atomic number or the mass number. • Gamma rays are NOT particles, but a

high-energy photon of light.• A high-energy gamma ray is given off

when the parent isotope falls into a lower energy state. Symbol: or

• They often accompany nuclear decay of other type.

• Example:

Nuclear Decay Reactions

00

00

23490

42

23892 2 ThHeU

Penetrating AbilityPenetrating Ability

Effects of RadiationEffects of Radiation

• Rem or Rad is the biological effect of radiation

• It is related to the strength of the radiation as well as the damage it causes

Geiger Counter• Used to detect radioactive substances• Click the pictures

Nuclear FissionNuclear Fission

•Nuclear fission can be induced by bombarding atoms with neutrons.

•Induced fission decays are also accompanied by the release of neutrons and LOTS of energy

•The nuclei of the atoms then split into 2 parts.

Each time a fission occurs, large amounts of energy are released

Under certain conditionsa chain reaction is startedthat creates a HUGE amount of energy to be released very quickly!

• They have found a way to tap the energy in nuclear reactions in a controlled way.

http://www.msnbc.msn.com/id/42029294/ns/technology_and_science-science/t/how-nuclear-plant-works/

Link to Animation

Nuclear Fusion

Energy

Fusion – perfect, but difficultsmall nuclei combine to create larger atoms

2H + 3

H 4He + 1

n +

1 1 2 0

Occurs in the sun and other stars

Energy and Mass • When a nuclear reaction occurs, there is a

mass loss.• This mass is called the “mass defect” and

is the result of mass being converted to energy.

• The energy can be calculated from the mass by Einstein’s famous equation:

E = mC2

E is energy in joules, m is mass defect in KgC is speed of light 3.0 x 108 m/s

Energy and Mass • What is the total energy in one mole of

Carbon atoms?• One mole of Carbon atoms has a mass

of 12.01 grams

E = mC2

E = .01201 kg x (3.0 x 108 m/s)2 = 1.08 x 1015 Joules

• Roughly the annual output of the Grand Coulee Dam in eastern Washington!