Chapter 3 Notes

Atomic Theory

Atomic Theory Essential Questions

1. What are the characteristics of each of the three elementary subatomic particles?

2. How are different isotopes of elements written?

3. How are the atomic number and mass number of element abbreviated (A

ZX)?

Dalton’s Atomic Theory Note: write yellow parts in notes & include the orange, underlined part as a modification to the theory

All matter is made up of atoms. Defined by Democritus to mean “small,

indestrucible, building blocks of matter”, but the nuclear fission (bomb) changed this definition of atom.

Atoms combine in simple, whole number ratios to create compounds.

Dalton’s Atomic Theory Note: write yellow parts in notes & include the orange, underlined part as a modification to the theory

Atoms of the same element are identical modified when isotopes were discovered to

specify that identical meant number of protons

Atoms of different elements are different. modified to specify that different elements

have different numbers of protons

1.All matter is composed of extremely small particles called atoms

2. Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, & other properties

ELEMENT 3

ELEMENT 3

ELEMENT 1

ELEMENT 1

ELEMENT4

ELEMENT4

Atomic TheoryAtomic Theory

ELEMENT2

ELEMENT2

3. Atoms cannot be subdivided, created, or destroyed

4. atoms of different elements combine in simple whole # ratios to form chem compounds

5. in chemical rxns, atoms are combined, separated, or rearranged

++ ++

Atomic TheoryAtomic Theory

Particles of an Atom

Particle Symbol Charge Mass Location

Proton p+ +1 1 amu Nucleus

Electron e- -1 ~ 0 amu Outside nucleus

Neutron n0 0 1 amu Nucleus

An Atom Becomes an Ion

Charges of the electron and proton are used to calculate the atom’s net charge. If an atom has a charge other than zero it is called an ION. Net charge = # protons - # electrons Mg has 12 protons and 12electrons as an

atom. When it becomes an ion (like Neon) it has only 10 electrons.

12 p+ - 10 e- = +2 net charge

Net Charge Example

Phosphorus (P) has 15 protons and 18 electrons as an ion. What is its net charge?

15 p+ - 18 e- = -3 net charge

II. Isotopes

Defined as atoms with the same atomic number (or number of protons), but with different atomic

mass due to change in number of neutrons.Hydrogen isotopes (look at the patterns!) 1. Protium (Hydrogen-1) 1 p, 1 e, 0 n; Mass = 1 amu 2. Deuterium (Hydrogen -2) 1 p, 1e, 1 n; Mass = 2 amu 3. Tritium (Hydrogen - 3) 1 p, 1e, 2 n; Mass = 3 amu

Note: Isotopes commonly named with element name followed by isotope’s mass number

Carbon Isotopes

Try this example now

Carbon isotopes 1. Carbon - 12 2. Carbon - 14

How many p, e and n does each carbon isotope have?

Carbon’s p, e and n totals

Answer 1. Carbon - 12 has atomic number 6 so it has 6

protons and 6 electrons. Its mass is 12, so 12 - the 6 protons = 6 neutrons 6 p, 6 e, and 6 n

2. Carbon - 14 - only the neutron number changes for this isotope. 6 p and 6 e and (14-6) = 8 n.

Nucleons - particles that make up the nucleus

A. Protons number of protons = atomic number = # of electrons (if neutral atom) atomic number (and therefore # p) identifies an

element atomic number = Z atomic numbers 1- ____ identified so farB. Neutrons = atomic mass - number of protons mass of neutron = mass of proton = 1/12 mass of C

atom

Atomic Mass and Mass Number

A. mass number = sum of protons and neutrons in nucleus

= whole number=A

B. atomic mass = average of the masses of isotopes = decimal number on the periodic table

Atomic Mass and Mass Number

C. AZX - isotope abbreviation or “element name-isotope

mass number”

X = symbol of elementA = mass numberZ = atomic numberA - Z = number of neutrons

Note: isotopes have a different “A” number

AZX examples

5927Co (Mass # written directly above atomic

#)

Atomic # 27 Mass # 59 Protons 27 Electrons 27 Neutrons = 59-27

= 32

AZX examples

235 92U

Atomic # =92 Mass # =235 Protons =92 Electrons =92 Neutrons = 235-92

= 143

Nucleus - Gold Foil Experiment

• Nucleus discovered by Lord Ernest Rutherford

• Gold Foil Experiment a.k.a. Alpha Scattering Experiment

• Alpha particle - positively charged helium atom released when radioactive elements decay

• Particles entered a closed, circular, luminescent screen and hit gold foil, which was suspended in the center of the circle

Gold Foil Conclusions

Since nearly all the alpha particles passed through the foil, the atom is mostly empty space.

Since some particles were deflected backwards, the atom contains a nucleus.

A nucleus is a small, dense, positively-charged center of an atom.

Planetary Model of the Atom

(a.k.a. Rutherford-Bohr Atom)proposed by Lord Rutherford and Niels

Bohrcontains a nucleushas energy levels - definite orbits in which

an electron can travelLooks like sun with planets in circular

orbits around it

ATOMS OF THE 1ST TEN ATOMS

NAME SYMBOLATOMIC

#MASS

# p+ e- n0

Hydrogen H 1 1 1 1 0Helium He 2 4 2 2 2Lithium Li 3 7 3 3 4

Beryllium Be 4 9 4 4 5Boron B 5 11 5 5 6

Carbon C 6 12 6 6 6Nitrogen N 7 14 7 7 7Oxygen O 8 16 8 8 8Fluorine F 9 19 9 9 10

Neon Ne 10 20 10 10 10

Chapter 19 - Radioactivity

Essential Questions:1. How are nuclear decay reactions

written and balanced?2. How is half-life used to find the amount

of a radioactive isotope that remains over time?

3. How do nuclear power plants make electricity?

Chapter 19 - Radioactivity

I. Radioactivity - the phenomenon of rays being produced spontaneously from unstable atomic nuclei

A. Three forms of natural radiation (Rutherford)1. Alpha particle [ a] = helium nucleus (4He+2)2. Beta particle [ b-] = an electron (-1e)3. Gamma Rays [ g ] = a high energy x-ray(0 g )

B. Radioactive Decay - spontaneous emission of charged particles (radiation) resulting in the transformation of radioactive nuclei

C. Types of Nuclear Reactions

1. alpha particle emission (a) 42

He

2. K electron capture (EC) 0-1e

3. positron emission (b+) 0+1e

4. beta emission (b-) 0-1e

5. neutron emission (n) 10n

E. A Geiger Counter - instrument for detecting radioactive decayStudy examples and do self-check exercises - p. 610-612

Nuclear Decay Equations

241Am 4He 1.Determine the atomic number for the isotope

given… Here Americium has a 95 subscript since 95 is the atomic number of Am

2. A helium atom being produced means that an alpha particle has been emitted. Its atomic number is 2.

241 95

Am 4 2

He

Decay Example #1 cont’d

3. To predict the products of the decay reaction we need to determine what superscript number (mass #) is needed to make the equation true.241

95 Am 4

2 He + 237 since 241 – 4 = 237

4. To predict the isotope that is produced we need to determine the subscript number (atomic #) using the same method. 241

95 Am 4

2 He + 237

93 since 95 – 2 = 93

Decay Example #1 Answer

5. Finally determine the element’s symbol using the atomic number of the isotope and the periodic table. Here we look up #91 to find Protactinium (Pa) and fill in the symbol to complete the isotopic abbreviation and the decay equation.

241 95

Am 4 2

He + 237 93Np

Decay Example #2

Silver-110 undergoes beta emission. Write a balance decay equation for this isotope.

110 47Ag 0-1e + ?

Decay Example #2 Answer

11047Ag 0

-1e + 11048Cd

Since 110 - 0 = 110And 47 - (-1) = 48

Since 48 is cadmium’s atomic number Cd

Decay Example #3

Cobalt – 58 undergoes positron emission. Complete its decay equation.

58 Co 0+1e

Decay Example #3 Answer

5828Co 0

+1e + 5827Fe

58 - 0 = 58 superscript

28 – 1 = 27 subscript27 is iron’s atomic number

Fe

Half-Life

1. HALF_LIFE -(t1/2) length of time it takes for half of the atoms in a given radioactive sample to decayA. Table of Half-lives found on full color/2-sided periodic tableB. Actinium-227 has a half-life = 22 y. If you start with 500 grams, how long will it take for less than one gram to remain?

Time 0 22 44 66 88 110 132 154 176 198

Amount 500 250 125 62.5 31.25 15.62 7.81 3.90 1.95 0.98

Answer= 198 years or 9 half-lives

Radioactive decay curve for 500g of actinium-227

TIME ( )

( )

III. Nuclear Transmutation or Nuclear Transformation - an atom with a different atomic number is produced as a result of a nuclear reactionA. Natural decay reactions emit only alpha particles, beta particles, and gamma rays.

example: (see p. 610 decay of U-238 to Pb-206)

B. Artificial Transmutation combines an element with a radioactive particle, another element or neutron

1. earliest artificial transmutation by Rutherford in 1919

14 N + 4 He 17 O + 1 H

2. Synthetic elements are made from smaller elements and are produced by transmutations

a. Occur in particle acceleratorb. Elements with at. # > 100 are formed this way.c. 254 Es + 4 He 256 Md + 2 n 1

Use of Radioactive Nuclides

A. Radiotracers - a radioactive isotope of an element being studied that is used to follow a reaction or process. See Table 19.4 p. 619

1. I-131 – used to study thyroid gland2. Tl -201 - … damage to heart muscle3. Ba - - … digestive system

B. Dating objects that were once living1. Carbon - 14 has a half life of 5730 years2. accurate for dating once living organisms

70,000 + years old

Radioactive isotopes in common things

C . Smoke Detectors contain Americium - 241D. Fluorescent lamps contain Promethium – 147.

Nuclear Fission

V. Fission - the splitting of a nucleus into 2 approximately equal partsA. releases a large amount of energy and some neutronsB. occurs when a very heavy nucleus is split.C. bombarding an element with neutrons_ makes it unstable emitted neutrons cause a chain reaction.

A Critical Mass is a certain mass of fissionable material needed in order to cause a fission event. If subcritical the neutrons escape and chain reaction stops

Manhattan Project

F. Manhattan Project - World War II project to build fission bombs that were dropped on Hiroshima and Nagasaki. Bombs contained 2 subcritical masses that were combined suddenly to create the explosion.

G. See p. 620 Figures 19.4 and 19.5

VI. Nuclear Reactors- control nuclear fission

A. reactors produce heat for electric power or propulsion units for ships & submarines

B. heated water produces steam, which turns turbinesC. Uranium-238 and Plutonium-239 are used as fuel

for nuclear reactorsD. Moderators (like water and graphite) slow down

neutronsE. Control rods regulate rate of reaction by absorbing

neutronsF. Breeder Reactors create fissionable Pu-239 from

non-fissionable U-238; make fuel for other nuclear reactors.

VII. Fusion – combining 2 atomic nuclei into 1

A. produce much more energy than fission reactions

B. doesn’t produce radioactive wastes

C. occurs in the sunD. combines isotopes of hydrogen to

make heliumE. uses water as a source of hydrogenF. fusion reactors will be created in your

lifetime.