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Chapter 4 Chapter 4 Atomic Structure Atomic Structure Anything in black letters = write it in your notes (‘knowts’)

Chapter 4 Atomic Structure

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Chapter 4 Atomic Structure. Anything in black letters = write it in your notes (‘knowts’). 4.1 – Defining the Atom. Atom -. smallest particle of an element that still has the properties of the element. comes from the Greek word atomos which means uncuttable or indivisible. - PowerPoint PPT Presentation

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Page 1: Chapter 4 Atomic Structure

Chapter 4Chapter 4

Atomic StructureAtomic Structure

Anything in black letters = write it in your notes (‘knowts’)

Page 2: Chapter 4 Atomic Structure

4.1 – Defining the Atom4.1 – Defining the Atom

Atom - smallest particle of an element that still has the properties of the element

comes from the Greek word atomos which means uncuttable or indivisible

Page 3: Chapter 4 Atomic Structure

Democritus (460 B.C. – 370 B.C.) one of the first to propose the idea of the atom; based on pure speculation

Page 4: Chapter 4 Atomic Structure

John Dalton (~1800) proposed 1st atomic theory

Page 5: Chapter 4 Atomic Structure

Daltons Atomic Theory (~1800) p. 1031. All elements are composed of tiny indivisible particles called atoms.

Atoms of element A

Atoms of element B

2. Atoms of the same element are identical. The atoms of any one element are different from those of any other element.

Mixture of atoms of elements A and B

3. Atoms of different elements can physically mix together or can chemically combine in simple whole-number ratios to form compounds.

Compound made by atoms of elements A

and B

4. Chemical reactions occur when atoms are separated from each other, joined, or rearranged in different combinations. Atoms of one element are never changed into atoms of another element as a result of a chemical reaction.

Page 6: Chapter 4 Atomic Structure

What we know now of Dalton’s Atomic Theory

1. All elements are composed of tiny indivisible particles called atoms.

2. Atoms of the same element are identical. The atoms of any one element are different from those of any other element.

3. Atoms of different elements can physically mix together or can chemically combine in simple whole-number ratios to form compounds.

4. Chemical reactions occur when atoms are separated from each other, joined, or rearranged in different combinations. Atoms of one element are never changed into atoms of another element as a result of a chemical reaction.

Atoms are not indivisible – they are made of subatomic particles

Every atom has at least one isotope; one atom’s isotope is NOT identical to another isotope of the same atom.

This is known as the Law of Definite Proportions – very important.

Atoms of one element can change into an atom of another element as a result of a nuclear reaction.

Page 7: Chapter 4 Atomic Structure

4.2 – Structure of the Nuclear Atom4.2 – Structure of the Nuclear Atom

Subatomic Particles

Electron – negatively charged particle in all atoms, discovered in 1897 by J.J. Thomson

Page 8: Chapter 4 Atomic Structure

Thomson performed experiments that involved passing electric current through gases at low pressure.

The result was a glowing beam, or cathode ray, that traveled from the cathode to the anode.

Thomson found that a cathode ray is deflected by electrically charged metal plates.

Thompson knew that opposite charges attract and like charges repel, so he hypothesized that a cathode ray is a stream of tiny negatively charged particles moving at high speed; now called electrons.

To test his hypothesis, Thompson set up an experiment to measure the ratio of an electron’s charge to its mass.

Also, the charge-to-mass ratio of electrons did not depend on the kind of gas in the cathode-ray tube or the type of metal used for the electrodes.

Page 9: Chapter 4 Atomic Structure

A cathode ray can also be deflected by a magnet.

Page 10: Chapter 4 Atomic Structure

The Atomic Nucleus

How are atoms structured?

DemocritusDalton

Thomson’s Plum Pudding Model

Page 11: Chapter 4 Atomic Structure

In 1911, Ernest Rutherford and others performed the Gold Foil Experiment to test the plum pudding model

Ernest Rutherford

Page 12: Chapter 4 Atomic Structure

The Gold Foil Experiment

The Gold Foil Experiment

Page 13: Chapter 4 Atomic Structure

The results…

It was expected that alpha particles would pass through the plum pudding model of the gold atom undisturbed.

It was observed that a small portion of the alpha particles were deflected, indicating a small, concentrated positive charge (the nucleus!)

Expected

Actual

Page 14: Chapter 4 Atomic Structure

“It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you. On consideration, I realized that this scattering backward must be the result of a single collision, and when I made calculations I saw that it was impossible to get anything of that order of magnitude unless you took a system in which the greater part of the mass of the atom was concentrated in a minute nucleus. It was then that I had the idea of an atom with a minute massive center, carrying a charge.”

— Ernest Rutherford

Page 15: Chapter 4 Atomic Structure

Nucleus – tiny positively charge core of an atom

Rutherford’s Nuclear Model of the Atom

• If an atom were the size of a football stadium, the nucleus would be about the size of a marble

Is this the current model of the atom?

NO…

Page 16: Chapter 4 Atomic Structure

Proton – positively charged particle in the nucleus of all atoms.

Neutron – particle with no charge in the nucleus of all atoms except 1H

Properties of Subatomic Particles

Particle SymbolRelative charge

Relative mass (mass of proton = 1)

Actual mass (g)

Electron e– 1– 1/1840 9.11 10–28

Proton p+ 1+ 1 1.67 10–24

Neutron n0 0 1 1.67 10–24

Page 17: Chapter 4 Atomic Structure

ASSIGN:

Read 4.1 & 4.2

Lesson Check 4.1 & 4.2; #1-15 (page 104 & 109)

Page 18: Chapter 4 Atomic Structure

Chapter 4 Quick QuizChapter 4 Quick Quiz1. Identify the idea or discovery these people are credited with.

Thompson,Dalton, Democritus,Rutherford

2. Place the above ideas or discoveries in chronological order.

3. Describe the setup of the gold foil experiment. Also describe the expected and actual results of this experiment. What conclusion was made about the atom from the gold-foil experiment?

4. Name the three subatomic particles. Also give their symbol and charge. What particles are present in the nucleus of the atom?

5. What is an atom?

Page 19: Chapter 4 Atomic Structure

4.3 – Distinguishing Among Atoms4.3 – Distinguishing Among Atoms

Atomic Number (Z) -

The number of protons in an atom; identifies the element.

Atoms have no net charge: # p+ = # e-

Page 20: Chapter 4 Atomic Structure

Mass Number (A) -

The number of protons (p+) and neutrons (n0) in an atom.

The mass number is NOT the atomic mass.

Element Atomic Number (Z)

Protons (p+)

Electrons (e-)

Neutrons (n0)

H

O

Ca

1 1 1

8 8 8

20 20 20

???

???

???

The number of n0 depends on the mass number of the isotope

Page 21: Chapter 4 Atomic Structure

Isotopes -

Atoms of the same element that have a different number of neutrons.

Page 22: Chapter 4 Atomic Structure

Chemical Symbols for Isotopes

A is the superscript

Ne2010 Ne21

10 Ne2210

Z is the subscript

Page 23: Chapter 4 Atomic Structure

Determining the Composition of an Atom

How many protons, electrons, and neutrons are in each atom?

p+

e-

n0

a. Be b. Ne c. Na94

2010

2311

Page 24: Chapter 4 Atomic Structure

Ne2010 Ne21

10 Ne2210

Naturally Occurring Isotopes of Neon

Percent Abundance in Nature

90.48% 0.27% 9.25%

Page 25: Chapter 4 Atomic Structure

The masses of atoms are rarely expressed in grams.

The C-12 isotope has been given a mass of exactly 12 atomic mass units (amu)

The masses of all other elements are based on the mass of the C-12 isotope.

Page 26: Chapter 4 Atomic Structure

Atomic Mass –

126C 13

6C 146C

12.000 amu

98.93 %

13.003 amu

1.07 %

14.003 amu

0.0000000001 %

Weighted average of all the naturally occurring isotopes of the element.

Atomic Mass of Carbon = 12.011 amu

011.12)0107.0 x 003.13( )9893.0 x 12(

Page 27: Chapter 4 Atomic Structure

12.000 amu

98.93 %

13.003 amu

1.07 %

14.003 amu

0.0000000001 %

Atomic Mass of Carbon = 12.011 amu

No atom of carbon actually weighs 12.011 amu. But a typical carbon atom averages 12.011 amu.

Atomic masses are weighted averages.

Page 28: Chapter 4 Atomic Structure

There are 2 stable isotopes of silver

Silver-107; 106.905097 amu; 51.84%

Silver-109; 108.904752 amu; 48.16%

Calculate the atomic weight of silver.

Atomic Weight of Silver = 107.868 amu

Page 29: Chapter 4 Atomic Structure

Weighted Averages are NOT just for Atomic Masses

Your Chemistry grade is calculated as a weighted average.

50% Quizzes/Tests, 15% Homework, 15% Lab Reports, 10% Quarter Project, 10% Respect & Participation

Calculate the un-weighted average grade

Calculate the weighted average grade

60/90 50/50 70/75 45/50 60/60

Page 30: Chapter 4 Atomic Structure

Mass Spectrometer – separates isotopes by mass differences.

Page 31: Chapter 4 Atomic Structure

Mass Spectrum for Cadmium

Page 32: Chapter 4 Atomic Structure

Mass Spectrum for Zinc; Atomic Weight = 65.395

Page 33: Chapter 4 Atomic Structure

Despite differences in the number of neutrons, isotopes of an element are chemically similar.

Neutrons do not determine chemical reactivity; the electrons do.

Page 34: Chapter 4 Atomic Structure

ASSIGN:

Read 4.3 & answer #18-34 within 4.3

p. 114-119

Page 35: Chapter 4 Atomic Structure

Terms & Things to KnowDemocritus, Dalton, Thomson, Rutherford

Atom

Atomic Number (Z)

Mass Number (A)

Proton, Neutron, Electron

Nucleus

Isotope

Atomic Mass (a.m.u.)

Weighted Average

Natural Abundance

Page 36: Chapter 4 Atomic Structure

How to determine the number of p+, n0, e-

How to write isotope symbols

How to calculate weighted averages

Explain Gold Foil Experiment (setup, expected and actual results, conclusion)

Different models of the atom (Democritus, Dalton, Thomson, Rutherford)

Page 37: Chapter 4 Atomic Structure

ASSIGN:

Ch. 4 #35, 44, 47-57, 61, 64-71, 75

p. 122 -

Page 38: Chapter 4 Atomic Structure
Page 39: Chapter 4 Atomic Structure

Example…Calculate

The average mass of zinc

The weighted average mass of zinc

Iso NA (%) Mass64Zn 48.6 63.92965Zn syn 64.92966Zn 27.9 65.92667Zn 4.1 66.92768Zn 18.8 67.92570Zn 0.6 69.92572Zn syn 71.927