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The Structure of the Atom. Chap. 4. I. History. I. History. A. Early Greeks. Explain matter with 4 ‘elements’. I. History. A. Early Greeks. 1. Air 2. Earth 3. Fire 4. Water. Explain matter with 4 ‘elements’. I. History. A. Early Greeks B. Democritus.

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I. History

A. Early Greeks

Explain matter with 4 ‘elements’


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I. History

A. Early Greeks

1. Air

2. Earth

3. Fire

4. Water

Explain matter with 4 ‘elements’


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I. History

A. Early Greeks

B. Democritus

Greek philosopher who first introduced concept of ‘atomos’


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I. History

A. Early Greeks

B. Democritus

C. Alchemists

Devoted to making precious metals from base metals


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I. History

A. Early Greeks

B. Democritus

C. Alchemists

D. Dalton

Formulated the ‘Atomic Theory of Matter’


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Atomic Theory of Matter

1. All matter is made of . . .


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Atomic Theory of Matter

1. All matter is made of . . .

2. Atoms cannot be . . .


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Atomic Theory of Matter

1. All matter is made of . . .

2. Atoms cannot be . . .

3. Atoms of a given element . . .


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Atomic Theory of Matter

1. All matter is made of . . .

2. Atoms cannot be . . .

3. Atoms of a given element . . .

4. Atoms of 2 different elements . .


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Atomic Theory of Matter

1. All matter is made of . . .

2. Atoms cannot be . . .

3. Atoms of a given element . . .

4. Atoms of different elements . . .

5. In a chemical reaction atoms are


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I. History

  • A. Early Greeks

  • B. Democritus

  • C. Alchemists

  • Dalton

  • Definition of Atom


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Atom

The smallest particle of an element that retains properties of that element.


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II. Discoveries of atoms

  • J.J. Thomson – 1890s

Used a cathode ray tube (CRT) to measure the charge:mass ratio of an electron


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II. Discoveries of atoms

  • J.J. Thomson – 1890s

  • chg:mass =

  • 1.76 x 1011 C/kg


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II. Discoveries of atoms

  • J.J. Thomson – 1890s

  • chg:mass =

  • 1.76 x 1011 C/kg

  • Discovery led to plum-pudding model


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II. Discoveries of atoms

  • J.J. Thomson – 1890s

  • Robert Millikan - 1909

Measured the charge of an electron in his ‘oil drop’ exper.


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II. Discoveries of atoms

  • J.J. Thomson – 1890s

  • Robert Millikan - 1909

  • Charge = 1.6 x 10-19


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II. Discoveries of atoms

  • J.J. Thomson – 1890s

  • Robert Millikan - 1909

  • Rutherford - 1911

Discovered nucleus in gold-foil experiment


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II. Discoveries of atoms

  • J.J. Thomson – 1890s

  • Robert Millikan - 1909

  • Rutherford - 1911

  • Fired alpha particles at thin metal sheet.


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II. Discoveries of atoms

  • J.J. Thomson – 1890s

  • Robert Millikan - 1909

  • Rutherford - 1911

  • Fired alpha particles at thin metal sheet.

  • Expected them to go straight through, but some deflected.


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II. Discoveries of atoms

  • J.J. Thomson – 1890s

  • Robert Millikan - 1909

  • Rutherford - 1911

  • Fired alpha particles at thin metal sheet.

  • Expected them to go straight through, but some deflected.

  • This led to nuclear model.



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II. Discoveries of atoms

  • The atom

  • The electron was discovered first


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II. Discoveries of atoms

  • The atom

  • The electron was discovered first

  • The proton was described by Rutherford


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II. Discoveries of atoms

  • The atom

  • The electron was discovered first

  • The proton was described by Rutherford

  • The neutron was described by Chadwick


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III. Representing Atoms

What makes a carbon atom different from a nitrogen atom?


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III. Representing Atoms

  • The atomic number


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III. Representing Atoms

  • The atomic number

  • The number of protons


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III. Representing Atoms

  • The atomic number

  • The number of protons

  • Written on the periodic table.


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III. Representing Atoms

  • The atomic number

  • The number of protons

  • Written on the periodic table.

  • This will equal the number of electrons, too.


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III. Representing Atoms

  • The atomic number

  • The mass number


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III. Representing Atoms

  • The atomic number

  • The mass number

  • The number of protons + neutrons


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III. Representing Atoms

  • The atomic number

  • The mass number

  • The number of protons + neutrons

  • Always a whole number


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III. Representing Atoms

  • The atomic number

  • The mass number

  • Isotopes


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III. Representing Atoms

  • The atomic number

  • The mass number

  • Isotopes

  • Atoms with the same number of protons, different number of neutrons


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III. Representing Atoms

  • The atomic number

  • The mass number

  • Isotopes

  • Atoms with the same number of protons, different number of neutrons

  • Isotopes have same properties, but different masses


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III. Representing Atoms

  • The atomic number

  • The mass number

  • Isotopes

  • Notation



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Nuclide Symbol Notation

Element symbol

Cl

37

17


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Nuclide Symbol Notation

Cl

37

17

Atomic number


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Nuclide Symbol Notation

Mass number

Cl

37

17


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Self Check – Ex. 1

Write the nuclide symbols for elements with these particles:

Nuclide #1

22 protons

24 neutrons

Nuclide #2

22 protons

26 neutrons


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Self Check – Ex. 2

How many protons, neutrons, and electrons are in this element?

95

Mo

42


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Self Check – Ex. 3

How many protons, neutrons, and electrons are in this element?

40

K



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IV. Mass of atoms

  • Measured in amu


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IV. Mass of atoms

  • Measured in amu

  • Protons and neutrons both weigh about 1 amu (neutrons are a bit more)


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IV. Mass of atoms

  • Measured in amu

  • Protons and neutrons both weigh about 1 amu (neutrons are a bit more)

  • The amu is defined as 1/12 the mass of carbon-12



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V. Atomic Mass

  • A weighted average of all the isotopes for a given element


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An analogy

The older pennies have a mass of 3.0 g while the newer pennies have mass of 2.5 g. What is the average mass of these pennies?


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An analogy

The older pennies have a mass of 3.0 g while the newer pennies have mass of 2.5 g. What is the average mass of these pennies?

5

older

5

newer


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An analogy

What is the average mass of this sample? There are 4 older pennies (3.0 g) while there are 10 newer pennies have mass of 2.5 g.

10

newer

4 older


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An analogy

The older pennies have a mass of 3.0 g while the newer pennies have mass of 2.5 g. What is the average mass of these pennies?

older

newer


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V. Atomic Mass

  • A weighted average of all the isotopes for a given element

  • Formula


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Atomic Mass

% Isotope #1 x Mass of isotope #1

+

% Isotope #2 x Mass of isotope #2

+

% Isotope #3 x Mass of isotope #3

+

all other isotopes

=

Atomic mass


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Self Check – Ex. 4

Use the following to find the atomic mass for chlorine.

Chlorine-35

75.53 %

34.969 amu

Chlorine-37

24.47 %

36.966 amu



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VI. Radioactive Decay

  • Some atoms spontaneously emit radiation


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VI. Radioactive Decay

  • Some atoms spontaneously emit radiation

  • Atoms change their identities in the process


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VI. Radioactive Decay

  • Some atoms spontaneously emit radiation

  • Atoms change their identities in the process

  • Atoms undergo radioactive decay because their nuclei are unstable



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VII. Types of Radiation

  • Alpha radiation


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VII. Types of Radiation

  • Alpha radiation

  • Make unstable heavy nuclei lighter


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VII. Types of Radiation

  • Alpha radiation

  • Make unstable heavy nuclei lighter

  • This radiation is attracted to negative electric fields


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VII. Types of Radiation

  • Alpha radiation

  • Make unstable heavy nuclei lighter

  • This radiation is attracted to negative electric fields

  • Comprised of alpha particles


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Alpha Particles

2 protons & 2 neutrons

Made of:

Charge:

Mass:

Symbol:


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Alpha Particles

2 protons & 2 neutrons

Made of:

Charge:

2 +

Mass:

Symbol:


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Alpha Particles

2 protons & 2 neutrons

Made of:

Charge:

2 +

Mass:

4 amu

Symbol:


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Alpha Particles

2 protons & 2 neutrons

Made of:

Charge:

2 +

Mass:

4 amu

4

4

Symbol:

He

or

α

2

2


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VII. Types of Radiation

  • Beta radiation


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VII. Types of Radiation

  • Beta radiation

  • Increases the proton to neutron ratio


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VII. Types of Radiation

  • Beta radiation

  • Increases the proton to neutron ratio

  • Radiation is attracted to positive electric field


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VII. Types of Radiation

  • Beta radiation

  • Increases the proton to neutron ratio

  • Radiation is attracted to positive electric field

  • Comprised of beta particles


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Beta Particles

An electron from the nucleus

Made of:

Charge:

Mass:

Symbol:


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Beta Particles

An electron from the nucleus

Made of:

Charge:

1 -

Mass:

Symbol:


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Beta Particles

An electron from the nucleus

Made of:

Charge:

1 -

Mass:

1/1840 amu

Symbol:


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Beta Particles

An electron from the nucleus

Made of:

Charge:

1 -

Mass:

1/1840 amu

0

0

Symbol:

e-

or

β

-1

-1


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VII. Types of Radiation

  • Gamma radiation


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VII. Types of Radiation

  • Gamma radiation

  • These accompany alpha and beta radiation


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VII. Types of Radiation

  • Gamma radiation

  • These accompany alpha and beta radiation

  • Not deflected by electric field


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VII. Types of Radiation

  • Gamma radiation

  • These accompany alpha and beta radiation

  • Not deflected by electric field

  • Gamma rays are high energy radiation


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Gamma Particles

Energy (not matter)

Made of:

Charge:

none

Mass:

none

Symbol:

γ

0

0



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VIII. Penetrating Ability

  • Alpha radiation penetrates the .


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VIII. Penetrating Ability

  • Alpha radiation penetrates the least.

  • Gamma radiation penetrates the .


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VIII. Penetrating Ability

  • Alpha radiation penetrates the least.

  • Gamma radiation penetrates the most.



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IX. Writing Equations

  • Atomic numbers and mass numbers are conserved


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IX. Writing Equations

  • Atomic numbers and mass numbers are conserved

  • Examples


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Self Check – Ex. 5

Complete the following nuclear equation.

40

40

K Ca + ?

19

20


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Self Check – Ex. 6

Complete the following nuclear equation.

239

4

Pu ? + α

94

2


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