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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 energy

C.12.A describe the characteristics of alpha, beta, and gamma radiation

C.12.B describe radioactive decay process in terms of balanced nuclear equations

C.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

Ato

mic R

ad

ii Incre

ase

s

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 Reactions

Occur when bonds are broken Occur when nuclei emit particles and/or rays

Atoms 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

C6

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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.

4

2He

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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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Review

Type of Radioactive Decay

Particle Emitted

Change in Mass

#

Change in

Atomic #

Alpha α He

-4 -2

Beta β e 0 +1Gamma γ 0 0

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0-1

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 % Remaining

0 100%

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 10

1 29 5

2 58 2.5

3 87 1.25

4 116 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