3. atomic theories

8/21/2019 3. Atomic Theories

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INSIDE THE

ATOM

Mr. Don King EvangelistaChiang Kai ShekCollege

Development of different

EMPEDOCLES

Matter is made of four

elements in natureAIR,

FIRE, EARTH, and

WATER.

DEMOCRITUS

Matter is made ofATOMOS.

ATOMOS are the smallest

uncuttable unit of matter.

ATOMOS of differentsubstances vary in size and

shape.

JOHN DALTON

Element is composed of small,indivisible, and indestructible

particles called ATOMS.

Daltons Atomic Theory

1.Atoms of the same element are

alike in mass and size.

Atoms of different elements are

unlike in mass and size.


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2. Atoms of two or more elements

combine to form compound insimple numerical ratios. During

combinations, no atom is created

nor destroyed.


3. Atoms may combine with

different element in varied ratios toform many compounds.


Law of Conservation of Mass

In a chemical reaction, matter

is neither created nor

destroyed, or, more accurately,

there is no detectable change

in mass during an ordinary

chemical reaction.

Law of Definite Proportions

Joseph Proust (1754-1826)

States that different samples of

any pure compound contain

the same elements in the

same proportions by mass.

Law of Multiple Proportions

States that the mass of oneelement that can combine with

a fixed mass of another

element are in a ratio of small

whole numbers.

Joseph Thomson

Electron

Plum Pudding Model

Atom is a positively

charged material in which

detachable electrons are

embedded.
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J.J. Thomson, measured mass/charge of e-

2.2

Thomsons Experiment

Voltage source

+-

Metal Disks

Passing an electric current makes a

beam appear to move from the negativeto the positive end

Thomsons Experiment

Voltage source

+-Voltage source

Thomsons Experiment

By adding an electric field

+

-

Voltage source

Thomsons Experiment

By adding an electric field he found that

the moving pieces were negative

+

-

By adding an electric field

Thomsons Experiment

Used many different metals and gases

Beam was always the same

By the amount it bent he could find the

ratio of charge to mass

Was the same with every material

Same type of piece in every kind of

atom
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Joseph Thomsons Model of

Atom Ernest Rutherford

Ernest Rutherford

OBSERVATION:Most

alpha particles penetrated

through the foil with no or

slight deflection.

EXPLANATION:Atom is

mostly an empty space

where electrons are moving.

OBSERVATION:Some alpha

particles deflected at large angles

or bounce back in the direction

where they had come from.

EXPLANATION: The mass of an

atom is concentrated in anextremely small and positively

charged center called nucleus.
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Niels Bohr

Electrons revolve around thenucleus in planetary rings

called energy levels.

Electron can move only in a

limited number of fixed orbits.

As long as they stay in such

orbit, they dont emit energy.

If an electron jump from one

to another energy level,they gain or lose energy in

fixed amount called quanta.

Erwin Schroedinger Erwin Schroedinger

Electrons do not move in circularorbits.

Electrons move in orbital that arefound in an energy level.

Heisenbergs Principle of Uncertainty

It is impossible to identify theexact position and speed of a very

small particle with certainty.

Particle Charge Mass (g) Mass (amu) Location

Electron

(e-) -19.11 x 10-28

0.0054 0 Electron

cloud

Proton

(p+) +1 1.673 x 10-241.0073 1

Nucleus

Neutron

(no) 01.675 x 10-24

1.0087 1 Nucleus

ATOMIC NUMBER (Z)

the number ofprotons found in

the nucleus of an

atom


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MASS NUMBER (A)

The sum of protons andneutron inside the

nucleus of an atom

Complete the table.ATOM Atomic

Number

(Z)

MassNumber

(A)

No. ofElectrons

No. ofProtons

No. ofNeutrons

13 14

35 80

Cu 64 29

N 7 7

53 127

Symbols

Find each of these:

a) number of protons

b) number of

neutrons

c) number of

electrons

d)Atomic number

e) Mass Number

Br80

35

35

45

35

35

80

Symbols

If an element has an atomic

number of 34 and a massnumber of 78, what is the:


b) number of neutrons

c) number of electrons

d) complete symbol

34

44

34

Se78

34

Symbols

If an element has 91

protons and 140 neutrons

what is the

a)Atomic number

b) Mass number

c) number of electrons

d) complete symbol

91

231

91

Pa231

91


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Symbols

If an element has 78

electrons and 117 neutrons

what is the

a)Atomic number

b) Mass number

c) number of protons

d) complete symbol

78

195

78

Pt195

78

Symbols

Find each of these:


b) number of

neutrons

c) number of

electrons

Cd112

48

48

65

48

IONS

Electrically charged

atoms

CATIONS

-positively charged ions

-obtained when protonsare greater than electronbecause the atom donatessome of its electrons


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ANIONS

-negatively charged ions

-obtained when protons are

less than electrons because

the atom accepts additional

electrons from other elements

Complete the table.ION Atomic

Number

(Z)

MassNumber

(A)

No. ofElectrons

No. ofProtons

No. ofNeutrons

3517Cl

-

168O

2-

3919K

+

6530Zn

2+

2713Al3+


Number(Z)

Mass

Number(A)

No. of

Electrons

No. of

Protons

No. of

Neutrons

3517Cl

- 17 35 18 17 18

168O

2- 8 16 10 8 8

3919K

+ 19 39 18 19 20

6530Zn

2+ 30 65 28 30 35

2713Al

3+ 13 27 10 13 14


Number(Z)

Mass

Number(A)

No. of

Electrons

No. of

Protons

No. of

Neutrons

3115P

3-

7934Se

2-

8537Rb

+

13756Ba

2+

7031Ga

3+


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Number

(Z)

MassNumber

(A)

No. ofElectrons

No. ofProtons

No. ofNeutrons

3115P

3- 15 31 18 15 16

7934Se

2- 34 79 36 34 45

8537Rb

+ 37 85 36 37 48

13756Ba

2+ 56 137 54 56 81

7031Ga

3+ 31 70 28 31 39

red-proton gray- neutron

ISOTOPES

Atoms of an element having

the same Atomic number (Z)

but different Mass number

(A), hence the same number

of protons but differentnumber of neutrons.

Isotopes

Dalton was wrong about allelements of the same typebeing identical

Atoms of the same element canhave different numbers ofneutrons.

Thus, different mass numbers.

Naming Isotopes

We can also put the mass

number afterthe name of the

element:

carbon-12

carbon-14

uranium-235

Isotopes are atoms of the same

element having different masses, due

to varying numbers of neutrons.

Isotope Protons Electrons Neutrons Nucleus

Hydrogen1

(protium) 1 1 0

Hydrogen-2

(deuterium) 1 1 1

Hydrogen-3

(tritium)

1 1 2


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1

IsotopesElements

occur in

nature as

mixturesofisotopes.

Isotopes are

atoms of the

same element

that differ in

the numb er of

neutrons.

Atomic Mass

How heavy is an atom of oxygen?

It depends, because there are

different kinds of oxygen atoms.

We are more concerned with theaverage atomic mass.

This is based on the abundance(percentage) of each variety of thatelement in nature.

We dont use grams for this massbecause the numbers would be too small.

Measuring Atomic Mass

Atomic Mass Unit (amu)

- It is defined as one-twelfth themass of a carbon-12 atom.

Carbon-12 chosen because of its isotope purity.

Each isotope has its own atomic

mass, thus we determine theaverage from percent abundance.

To calculate the average:

Multiply the atomic mass ofeach isotope by itsabundance (expressed as adecimal), then add theresults.

Average Atomic Mass = (Isotope 1s

Mass X Isotope 1 s Abundance) +(Isotope 2s Mass X Isotope 2 sAbundance) ++ (Isotope ns Mass(Isotope ns Abundance)

Atomic Masses

Isotope Symbol Composition ofthe nucleus % in nature

Carbon-12 12C 6 protons

6 neutrons

98.89%


7 neutrons

1.11%


8 neutrons


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Question

Solution

Answer

Knowns

andUnknown

SAMPLE PROBLEM

Calculate the average atomic mass

of bromine. One isotope of brominehas an atomic mass of 78.92amu

and a relative abundance of 50.69%.

The other major isotope of bromine

has an atomic mass of 80.92amu

and a relative abundance of 49.31%.

Exercise: Calculate the Atomic Mass

Answer:

Average Atomic Mass = (78.92 amu X 0.5069) +

(80.92 amu X 0.4931)

Average Atomic Mass = 79.91 amu

Exercise: Lets solve this!

There are 2 isotopes of gallium that occur naturally;69Ga and 71Ga. The 69Ga atoms have a mass of

68.925581 amu and the 71Ga atoms have a mass

of 70.924707 amu. What is the percent natural

abundance for each isotope?

Exercise: Lets solve this!

Antimony has two naturally occurring isotopes. Themass of antimony-121 is 120.904 amu and

the mass of antimony-123 is 122.904 amu. Using

the average mass of 121.760 amu, find

the abundance of each isotope.

1. Copper, a metal known since ancient times, is used in

electrical cables, and pennies, among other things. Theatomic masses of its two stable isotopes, 63Cu (69.09

percent) and 65Cu (30.91 percent), are 62.93 amu and

64.9278 amu, respectively. Calculate the average atomic

mass of copper. The relative abundances are given in

parentheses.

Follow-up Problems

2. Iridium is composed essentially of two isotopes: 191Ir and193Ir. The average mass of an iridium atom is 192.217 amu.

Determine the percent natural abundance of each of these

isotopes in a naturally occurring sample. (The mass of an191Ir atom is 190.961 amu, and the mass of an 193Ir atom is

192.963 amu.)

3. atomic theories

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