unit 4: periodicity and nuclear chemistry

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C.5.C use the Periodic Table to identify and explain periodic trends, including atomic and ionic radii, electronegativity, and ionization energyC.12.A describe the characteristics of alpha, beta, and gamma radiationC.12.B describe radioactive decay process in terms of balanced nuclear equationsC.12.C compare fission and fusion reactions

Unit 4: Periodicity and Nuclear Chemistry

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Table of Contents

Periodicity 3-17

Nuclear Chemistry ITypes of Radiation and Nuclear formulas

18-29 Nuclear Chemistry II

Nuclear Fission and Fusion & Half-Life30-41

Periodicity Periodic Trends

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Periodic Law

The chemical and physical properties of the elements are periodic functions of their atomic numbers; properties of the elements occurred at repeated intervals called periods.

This defines the property of periodicity

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Periodic Trends properties that show patterns when

examined across the periods or vertically down the groups

while there are many periodic trends, we will focus on› atomic radii (the plural of radius)› ionization energy› Electronegativity› Ionic radii (the plural of radius)

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Atomic Radii One half the distance between the nuclei of identical

atoms that are bonded together. 

Distance between nuclei decreases across periods because the higher nuclear charge (positive) pulls the electrons closer to the nucleus

increases down groups because energy levels are being added outside the nucleus

Atomic Radii Increases

Atomic Radii Decreases

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Graphing Atomic radiiThe graph of Atomic Radius vs. Atomic Number shows the trend in atomic radius as one proceeds through the first 37 elements in the periodic table.

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Ionization Energy The energy required to remove

one electron from a neutral atom of an element.

increases across periods because it takes more energy to overcome the electrons attraction to the increasing nuclear charge

decreases down groups because it is easier to overcome the nuclear charge for the outermost electrons as the number of energy levels increases

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Graphing Ionization Energy These trends are visible in the graph of ionization energy versus

atomic number.

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Electronegativity a measure of the ability of an atom in a compound to attract

electrons from other atoms increases across periods as a result of the increasing nuclear charge

and ability of the nucleus to attract electrons from a neighboring atom

decreases down groups because the nuclear charge is less able to attract electrons from another atom as additional energy levels are added

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Graphing Electronegativity The graph of Electronegativity vs. Atomic Number shows the

trend in the electronegativity as one proceeds through the first 37 elements in the periodic table.

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Ionic Radii The radius of an atom forming ionic bond or an ion.

The radius of each atom in an ionic bond will be different than that in a covalent bond.

The reason for the variability in radius is due to the fact that the atoms in an ionic bond are of greatly different size. One of the atoms is a cation, which is smaller in size, and the other atom is an anion which is a lot larger in size.

decreases across the period until formation of the negative ions then there is a sudden increase followed by a steady decrease to the end

The sudden increase on formation of negative ions is due to the new (larger) outer shell

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Graphing ionic radii

NUCLEAR CHEMISTRYI. Types of radiation & Nuclear formulas

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Introduction to Nuclear Chemistry

Nuclear chemistry is the study of the structure of atomic nuclei and the nuclear change they undergo.

Characteristics: Isotopes of one

element are changed into isotopes of another element

Contents of the nucleus change

Large amounts of energy are released

Nuclear Chemistry Nuclear Reactions

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Chemical vs. Nuclear Reactions

Chemical Reactions Nuclear ReactionsOccur when bonds are broken Occur when nuclei emit

particles and/or raysAtoms remain unchanged, although they may be rearranged

Atoms often converted into atoms of another element

Involve only valence electrons May involve protons, neutrons, and electrons

Associated with small energy changes

Associated with large energy changes

Reaction rate influenced by temperature, particle size, concentration, etc.

Reaction rate is not influenced by temperature, particle size, concentration, etc.

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Chemical Symbols A chemical symbol looks like…

To find the number of , subtract the

from the

C614

mass #atomic #

mass #atomic #neutrons

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Types of Radiation Radioactive Decay – when unstable

nuclei lose energy by emitting radiation to attain more stable atomic configurations (spontaneous process) Alpha – radioactive decay of an atomic

nucleus that is accompanied by the emission of an alpha particle( ).

Beta – Radioactive decay in which an electron is emitted ( ).

Gamma – High energy photons that are emitted by radioactive nuclei.

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Alpha Decay Alpha decay – emission of an alpha

particle (α), denoted by the symbol , because an α has 2 protons and 2 neutrons, just like the He nucleus. Charge is +2 because of the 2 protons

Alpha decay causes the mass number to decrease by 4 and the atomic number to decrease by 2.

Atomic number determines the element. All nuclear equations are balanced.

42He

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Alpha Decay Example 1: Write the nuclear equation

for the radioactive decay of polonium – 210 by alpha emission.

Step 1: Write the element that you are starting with.210Po84

Mass #

Atomic #

Step 2: Draw the arrow.Step 3: Write the alpha particle.Step 4: Determine the other product (ensuring everything is balanced).

4He2 206Pb82

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Beta decay Beta decay – emission of a beta particle

(β), a fast moving electron, denoted by the symbol e- or . β has insignificant mass (0) and the charge is -1 because it’s an electron.

Beta decay causes no change in mass number and causes the atomic number to increase by 1.

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Beta Decay Example : Write the nuclear equation for

the radioactive decay of carbon – 14 by beta emission.

Step 1: Write the element that you are starting with.14 C6

Mass #

Atomic #

Step 2: Draw the arrow.Step 3: Write the beta particle.Step 4: Determine the other product (ensuring everything is balanced).

0e-1 14N7

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Gamma decay Gamma rays – high-energy electromagnetic

radiation, denoted by the symbol γ. γ has no mass (0) and no charge (0). Thus, it

causes no change in mass or atomic numbers. Gamma rays almost always accompany alpha

and beta radiation. However, since there is no effect on mass number

or atomic number, they are usually omitted from nuclear equations.

Example: ϒ +

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Penetration of Radiation Alpha and beta are particles emitted

from an atom.  Gamma radiation is short-wavelength electromagnetic waves (photons) emitted from atoms. The figures show the penetration of the

different types of radiation.

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ReviewType of

Radioactive Decay

Particle Emitted

Change in Mass

#

Change in

Atomic #

Alpha α He

-4 -2

Beta β e 0 +1Gamma γ 0 0

420

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NUCLEAR CHEMISTRYII. Nuclear Fission and Fusion & Half Life

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Nuclear Fission Fission - splitting of a nucleus. - Very heavy nucleus is split into two

approximately equal fragments. -Chain reaction releases several neutrons

which split more nuclei. - If controlled, energy is released slowly

(like in nuclear reactors). Reaction control depends on reducing the speed of the neutrons (increases the reaction rate) and absorbing extra neutrons (decreases the reaction rate).

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Nuclear Fission - Examples – atomic bomb, current

nuclear power plants → + + 2 x 102 kJ/mol

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Nuclear Fusion Fusion - combining of a nuclei

Two light nuclei combine to form a single heavier nucleus

- Does not occur under standard conditions (+ repels +)

- Advantages compared to fission Inexpensive, No radioactive waste

- Disadvantages requires large amount of energy to start,

difficult to control

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Nuclear Fusion Examples – energy output of stars, hydrogen

bomb, future nuclear power plants

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Half-Life Half Life is the time required for half of a

radioisotope’s nuclei to decay into its products.

For any radioisotope,# of ½ lives % Remaining0 100%1 50%2 25%3 12.5%4 6.25%5 3.125%6 1.5625%

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Half-Life For example, suppose you have 10.0

grams of strontium – 90, which has a half life of 29 years. How much will be remaining after x number of years?  

You can use a table:# of ½ lives Time (Years) Amount

Remaining (g)

0 0 101 29 52 58 2.53 87 1.254 116 0.625

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Half-Life Or an equation!

mt = m0 x (0.5)n

mass remaining

initial mass

# of half-lives

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Half-Life Example 1: If gallium – 68 has a half-life

of 68.3 minutes, how much of a 160.0 mg sample is left after 1 half life? ________ 2 half lives? __________ 3 half lives? __________

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Half-Life Example 1: If gallium – 68 has a half-life

of 68.3 minutes, how much of a 160.0 mg sample is left after 1 half life? ________ mt = 160.0 mg x (0.5)1 = 80.0 mg 2 half lives? __________ mt = 160.0 mg x (0.5)2 = 40.0 mg

3 half lives? __________mt = 160.0 mg x (0.5)3 = 20.0 mg

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Half Life Iodine-131 is a radioactive isotope with a

half-life of 8 days. How many grams of a 64 g sample of iodine-131 will remain at the end of 8 days? ________

How many grams of a 64 g sample of iodine-131 will remain at the end of 24 days? ________

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Half Life Iodine-131 is a radioactive isotope with a half-

life of 8 days. How many grams of a 64 g sample of iodine-131 will remain at the end of 8 days? ________

Mt = 64 g x (0.5)1 = 32 g How many grams of a 64 g sample of iodine-

131 will remain at the end of 32 days? ________ First how many ½ lives have gone by.

32/8 (the ½ of iodine-131) = 4 Then plug 4 into formula.

Mt = 64 g x (0.5)4 = 4 g