Chem Chapter 8 - Nuclear Chemistry

nuclear reactions

a reaction that changes the numbers of particles (protons, neutrons)in the nucleus of an atom

nuclear reaction differences

1. nuclear reactions do not need to be balanced in normal sense

2. nuclear reactions involve more energy than chemical reactions

3. nuclear reactions are not generally affected by temperature or by catalysts

nuclear symbols show

1. mass # of atom

2. atomic # of atom

mass #

number of protons and neutrons (written at the top of the element)

atomic #

number of protons (written at the bottom of the element)

nuclear symbol

identifies the element, and shows the atomic # and mass # of a particular atom of that element

stable nuclei

a stable nucleus; the nuclei of most naturally occurring isotopes remain unchanged indefinitely

radioactive

an atom whose nucleus is unstable 9able to break down spontaneously with the production of ionizing radiation)

radioisotope

a radioactive form of a particular element

nuclear equation

shows the symbols of all the reactants and products in the reaction

*can convert one element into another

nuclear reactions form a variety of products

original nucleus gives off a small particle such as an electron or a helium nucleus (particles ejected @ high speeds = high energy)

1. beta particles

2. alpha particles

3. positron

nuclear radiation

high energy product; ionizing radiation that is produced during a nuclear reaction, including alpha, beta, and radiation

beta particles

when electrons are produced in a nuclear reaction (an electron that is emitted during a nuclear reaction)

alpha particles

combination of 2 protons and 2 neutrons; a particle produced in certain nuclear reactions, consisting of 2 protons and 2 neutrons

combo is a helium - 4 nucleus ⁴He₂ 

positron

does not occur in atoms; it has the same mass as an electron but a +1 charge

types of radiation

1. proton (hydrogen-1 nucleus)

2. neutron

3. beta particle (electron)

4. alpha particle (helium-4 particle)

5. positron

proton (hydrogen-1 nucleus)

mass # = 1

atomic # / charge = +1

symbol = ₁¹P or ₁¹H

neutron

mass # = 1

atomic # / charge = 0

symbol = ₀¹N

beta particle (electron)

mass # = 0

atomic # / charge = -1

symbol = _-1⁰ e or B

alpha particle (helium-4 nucleus)

mass # = 4

atomic # / charge = +2

symbol = ₂⁴ H or a

positron

mass # = 0

atomic # / charge = +2

symbol = ₊₁⁰e or B+

subatomic particlces

when we write an equation for a nuclear reaction, must include symbols for any subatomic particle formed

• atomic # of an atom = charge on nucleus

• for subatomic particles we use charge instead of atomic #

2 principles that govern all nuclear reactions

atomic #’s and mass #’s must be balanced in a nuclear equation

1. the sums of the mass numbers of the products and reactants must be equal

2. the sums of the atomic numbers of the products and reactants must be equal

alpha decay

a nuclear reaction in which an atom emits a helium nucleus (alpha particle)

• loses 2 protons and 2 neutrons

beta decay

for lighter radioisotopes; a nuclear reaction in which an atom emits a beta particle (electron), which is formed when a neutron breaks down into a proton and an electron

• a nucleus emits an electron

• proton remains in nucleus while electron is ejected

electrons

produced in beta decay are called beta particles = these move faster than alpha particles

balanced nuclear equation for beta decay

• always increases the # of protons while leaving mass unchanged

• because electron is -1 the atomic # of product is greater than atomic # of reactant

positron emission

a nuclear reaction in which an atom emits a positron, formed when a proton breaks down into a neutron and a positron

nuclear reaction energy

produces far more energy than any chemical reaction

the energy of a nuclear reaction can appear in 2 forms

1. kinetic energy

2. electromagnetic radiation

kinetic energy

of the small particle (alpha or beta) that is released

electromagneticc radiation

energy that is not contained by matter, such as visible light, radiowaves, and xrays

photons

a particle of electromagnetic radiation; all forms of electromagnetic radiation come in these tiny packets of energy

• energies expressed in kilocalories / mole

gamma radiation

when a nuclear reaction produces electromagnetic radiation it does so in the form of gamma radiation (produced during nuclear reactions) 

gamma radiation nuclear symbol

γ

difference between a reaction that produces a particle and one that produces only gamma radiation

1. when a nuclear reaction produces alpha, beta, or positrons the product is a different element

2. gamma emissions produces a more stable nucleus of the same element

nuclear reactions produce

ionizing radiation

ionizing radiation

any form of radiation that can knock an electron out of an atom or molecule; ie gamma radiation, alpha and beta particles

radicals

molecules or ions that have an odd # of electrons

geiger counter

machine for measuring beta or gamma radiation

• ionizing radiation passes through a tube filled with argon

• when a particle of ionizing radiation enters the tube, it ionizes an argon atom

scintillation counter

a machine that detects and measures radioactivity using fluorescent material to detect ionizing radiation

equivalent radiation dose

the amount of tissue damage that is produced by an exposure to ionizing radiation (the measure of it)

• unit = rem or millirems (mrem)

equivalent dose depends on 2 factors

1. amount of energy absorbed as the radiation passes through our bodies

• 1 rem = 0.01J (0.0024cal)

2. type of radiation

radiation weighting factor

(WR) the relative effect of each type of radiation compared to x-rays

x-rays

radiation weighting factor = 1

gamma radiation

radiation weighting factor = 1

beta particles (electrons)

radiation weighting factor = 1

positrons

radiation weighting factor = 1

protons

radiation weighting factor = 2-5 (depends on energy)

neutrons

radiation weighting factor = 5-10 (depends on energy)

alpha particles

radiation weighting factor = 20

relating radiation dose to equivalent dose

multiply equivalent dose for x-rays by the WR

activity

the # of decay products (beta, alpha particles, gamma photons) that a radioactive sample produces per second

• same as the # of atoms that break down / disintegrate in one second

traditional activity unit

curie (Ci) = 37 billion disintegrates per second

• mostly uses millicuries (mCi) or microcuries

dimensional analysis

1 curie = 1000mCi or 1,000,000 microcurie

1 equivalent dose

1 Sievert (SV)

1 curie =

1000mCi or 1,000,000 microcurie

activity =

becquerel (Bq)

1 curie =

3.7 × 10¹⁰ Bq (37,000,000,000)

1 rem =

0.01Sv

1mCi =

37MBq

1 rad =

0.01J

• rods x WR = rems

background radiation

ionizing radiation that is produced by naturally occurring materials

common types of ionizing radiation have different penetrating abilities

the hazard of an external source of radiation depends on how effectively the ionizing radiation passes through obstructions between radiation source and the body

alpha particles / emitters

only dangerous if ingested or inhaled

gamma emitters

dangerous even if they are some distance away

beta particles / emitters

complex, takes more to shield

effects of radiation depend on distance and time

decrease exposure by increasing distance and decreasing time spent in vicinity

• if triple your distance you decrease your exposure by 3²

exponential decay

nuclear reactions undergo this, a process in which the number of particles decreases by a factor of two in a constant amount of time

half life

all radioisotopes have this, time required for half of a sample of a radioactive element to decay / break down

fission reaction

a large nucleus splits into 2 similarly sized pieces

chain reaction

a process in which a fission reaction produces neutrons that causes other atoms to undergo fission @ an ever increasing rate

nuclear reactors

used to produce electrical power

fusion reaction

the combining of 2 nuclei into one large nucleus

• produces energy if product is an element no heavier than iron

• produces more energy than fission but less radioactive by products

• only happens during high temps