[PDF] Accelerated Chemistry Study Guide Atomic Structure Chapter 3

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Accelerated Chemistry Study Guide

Atomic Structure, Chapter 3

Terms and definitions

atom law of constant composition atomic theory of matter cathode ray tube electron radioactivity nucleus proton neutron atomic mass unit atomic number ion isotope mass number atomic mass nuclear reaction strong nuclear force radioactive decay nuclear equation alpha radiation beta radiation gamma radiation

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Specific topics to know

Development of Atomic Theory

Composition of the atom

balancing nuclear equations: both atomic number and mass number must be conserved Important People in the Development of Atomic Theory

Democritus

Antoine Lavoisier

Joseph Louis Proust

John Dalton

Michael Faraday

Benjamin Franklin

J.J. Thomson

Robert Millikan

Henri Becquerel

Marie and Pierre Curie

Ernest Rutherford

Henry Moseley Page 2 of 46

The World of Chemistry

1. What are the three basic components (particles) that make up an atom? 2.

What are the two regions of any atom?

3. How does the size of the nucleus compare to the size of an atom? 4. What is the Scanning and Tunneling electron Microscope (STM) used for? 5. What holds the electrons and the nucleus together? 6. Unlike charges _______________; like charges _________________. . 7. What are the charges on the electron ________, the proton ________, and the neutron ________? 8.

Why is the overall charge of the atom neutral?

9.

What did Rutherford's gold foil experiment show?

10. When two atoms meet, what parts of the atoms interact? 11. What are some ways that signals from the atom can be used? Page 3 of 46

Chapter 3 Notes: Accelerated Chemistry

Early models of the atom:

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Atomic structure, isotopes and isotope notation.

Subatomic Particle Location Charge Relative

mass

Atomic number

UNIQUEONLY

Ions

Mass number

Isotopes

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The amu (atomic mass unit) is approximately the mass of either a proton or a neutron. More precisely, the amu is defined so that a carbon-12 atom has a mass of exactly 12 amu.

1 amu = 1.66 X 10

-24 g This equality appears a bit bizarre at first until you consider that the size of an amu works out perfectly with something you'll learn more about later called the 'mole' A mole of carbon-12 atoms (a mole of C-12 means a sample containing 6.022 X 10 23
of these atoms) has a mass of exactly 12 grams. So this happens:

1 carbon-12 atom = 12.0000000.... amu

1 mole of carbon-12 atoms = 12.0000000..... grams

The masses of the elements on the periodic table are called the or the of the elements. They are NOT the same thing as the mass number of an isotope (defined above). The atomic mass of an element is determined by taking a "weighted average" of all the masses of all the naturally occurring isotopes along with their percent abundances:

Isotope Mass Number Mass Natural

Abundance

Carbon

12

C 12 12.000... (exactly 12) 98.99%

13

C 13 13.003 1.11%

Atomic mass = (Isotope Mass)(Natural Abundance as a decimal) + (Isotope

Mass)(Natural Abundance)....

= 12.0000(0.9899) + (13.003)(0.0111) = 12.01

Try the data for silicon on page 110.

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Nuclear Equations

Alpha decay - decay of a radioactive nucleus in which an alpha particle is produced 24

He or

2 4 example 84210
Po 24
He + 82206
Pb

Beta decay - decay of a radioactive nucleus in which an beta particle (an electron) is produced and a neutron is

converted into a proton e 0 1 or 0 1 example Bi 210
83
84210

Po + e

0 1

Specific topics to know

nuclear stability types of radioactive decay balancing nuclear equations: both atomic number and mass number must be conserved

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1

Cathode Ray Tube (CRT)

Thomson's Plum Pudding ModelPage 9 of 46

2

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3

Rutherford's Gold Foil Experiment

ExpectedActualPage 11 of 46

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Model 1

0.6 L of hydrogen gas + 0.6 L chlorine gas yields 1.2 L muriatic acid gas

0.6 L of hydrogen gas + 1.2 L chlorine gas yields 1.2 L muriatic acid gas + 0.6 L chlorine gas

1.2 L of hydrogen gas + 1.2 L chlorine gas yields 2.4 L muriatic acid gas

1.2 L of hydrogen gas + 0.6 L chlorine gas yields 1.2 L muriatic acid gas + 0.6 L hydrogen gas Page 15 of 46

Dalton's 5 Part Atomic Theory (1803)

Dalton's Model of the Atom

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Model with a m removed connecte

He found

tube fro magnet a the posit the nega

He foun

d charged mass.

Critica

3. W e 4. W e l 2

Thomson us

metal plate o d the air fro ed the tube d that "rays om the catho

Thomson e

and found t tive end of ative end of

Thomson u

s d this ratio hydrogen a al Thinkin

What techno

xperiments

What part of

xperiments sed a hollow on either en om the tube to an elect s" travelled ode to the a xposed the hat the ray a magnet, a a magnet. sed an elect to be almos atom. So.. e g Questio ological adva f the atom to support w glass tube d. Thomson e, and tricity sourc across the anode. ray to a bent towa r and away fro tric field to st 2000 tim either the ra ons ancement w did Thomso your claim. e n ce. rd om o measure th mes larger th ay particles was required on discover? he mass to han the mas s had a HUG d for Thoms ? Give spec charge rati ss to charge

GE charge, o

son to condu ific evidenc o of the ray e ratio for a or a very sm uct his ce from his y. a mall Page 17 of 46

Thomson's Model of the Aton:

Rutherford's Experiment (1911)

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Critical Thinking Questions

6.What technological advancement was required for Rutherford to conduct his

experiment?

7.What part of the atom did Rutherford discover? Give specific evidence from his experiment to support your claim.

Rutherford's Model of the Atom

: Rutherford held on to Thomson's idea that atoms were made up of positive and negative parts. He modified Thomson's model to specify that the positive part of the atom was contained in a small, dense nucleus, and the electrons orbited the nucleus like planets orbit the sun.

8.What part of Rutherford's model do we still agree with today? What part of the

model has been discarded?

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Model 5

Bohr observed that when a sample of hydrogen gas was exposed to electric current it released energy as light. When this light was viewed with a spectroscope, specific wavelengths of light were seen. Different wavelengths of light correspond to different levels of energy. Bohr used this same method to test other elements and found that each emitted its own distinct color of light, each made up of its own wavelength combinations. Bohr realized that this phenomenon was not possible with Rutherford's model of the atom, since electrons travelling in an elliptical orbit would produce a continuous rainbow of colors instead of the distinct lines seen. high energy low energy Page 20 of 46

Bohr's Model of the Atom

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C 12 6 C 13 6 C 14 6

Information

Note the following symbols: (they are not to scale) = proton (positive charge) = electron (negative charge) = neutron (no charge)

The following three diagrams are hydrogen atoms:

The following three diagrams are carbon atoms:

(6 protons, 6 neutrons) (6 protons, 7 neutrons) (6 protons, 8 neutrons)

Notice the type of notation used for atoms:

X = chemical symbol of the element

Z = "atomic number"

A = "mass number"

, , and are notations that represent of carbon. , and are notations that represent of hydrogen. The part of the atom where the protons and neutrons are is called the . X A Z C 12 6 C 13 6 C 14 6 H 1 1 H 2 1 H 1 1 H 2 1 H 3 1 H 3

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Critical Thinking Questions

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: Atoms, Ions, Masses of Subatomic Particles The atomic mass unit (amu) is a special unit for measuring the mass of very small particles such as atoms. The relationship between amu and grams is the following: 1.00 amu = 1.66 x 10 -24 g Note the following diagrams comparing atoms and ions.

9 protons

10 neutrons

9 protons 10 neutrons

mass = 18.9980 amu mass = 18.9985 amu

12 protons

12 neutrons

12 protons 12 neutrons

mass = 23.9978 amu mass = 23.9968 amu 10. What is structurally different between an atom and an ion? Note: This is the ONLY structural difference between an atom and an ion. 11. In atomic mass units (amu), what is the mass of an electron? F 19

91- 19

9 F Mg 24

122 24

12 Mg

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12.Is most of the mass of an atom located in the nucleus or outside the nucleus? How do you

know? 13. If protons and neutrons have the same mass, what is the approximate mass of a proton and neutron in atomic mass units (amu)?

14. The mass of is about 14 amu. Does this agree with what you determined in questions

11 and 13?

15. The charge (in the upper right hand corner of the element symbol) is -1 for a fluorine ion.

Why isn't it +1 or some other number?

16. What is the charge on every atom? Why is this the charge?

17. How do you determine the charge on an ion?

18. An oxygen ion has a -2 charge. (Use your periodic table if necessary) a)How many protons does the oxygen ion have? b)How many electrons does the oxygen ion have? C 14

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Skill Practice 8

ion

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