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Atoms and Atomic

Structure

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Law of Conservation of MassLavoisier (1743-1794)

In a chemical reaction, matter is neither created

nor destroyed.

P. 57

Click on picture for movie

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CuCO3(s) CuO(s) + CO2(g)

123.6 g 79.6 g ? g

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CuCO3(s) CuO(s) + CO2(g)

123.6 g 79.6 g 44.0 g

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CuCO3(s) CuO(s) + CO2(g)

123.6 g 79.6 g 44.0 g

. . .=

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Law of Definite ProportionsProost (1754-1826)

Different samples of any pure compound containthe same elements in the same proportions by

P. 58

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Mass Ratio of Cu:O:C in copper carbonate

Cu:O:C = 53:40:10 = 5.3 : 4: 1

Regardless of where the copper carbonateis found

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Mass Ratio of Cu:O:C in copper carbonate

Cu:O:C = 53:40:10 = 5.3 : 4: 1

If a sample of copper carbonate contains20 g of carbon how many g of Cu will it

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Mass Ratio of Cu:O:C in copper carbonate

Cu:O:C = 53:40:10 = 5.3 : 4: 1

If a sample of copper carbonate contains20 g of carbon how many g of Cu will it

(5.3g / 1g)20g = x

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Mass Ratio of Cu:O:C in copper carbonate

Cu:O:C = 53:40:10 = 5.3 : 4: 1

If a sample of copper carbonate contains20 g of carbon how many g of Cu will it

106 g = x

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Law of Multiple Proportions(John Dalton)

The masses of one element that can combinechemically with a fixed mass of another

2C + O2 2CO Carbon monoxide

C + O2 CO2 Carbon dioxide

P. 59

24 g 32 g

12 g 32 g

2:1

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The idea of whole numbers

suggests the presence ofindividual particle

ATOMS !

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Daltons Atomic Theory

John Dalton (1766-1844) proposed an atomic theory

1. matter is composed, indivisible particles (atoms).2. all atoms of a particular element are identical3. different elements have different atoms

- .

5. In a chemical reaction, atoms are merelyrearranged to form new compounds; they are notcreated, destroyed, or changed into atoms of any

other elements.

P. 56-57

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OK! Matter is made of ATOMS

But what are ATOMS?

What are ATOMS themselves

made of?

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CathodeRay Tube

P. 61

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J.J. Thompson

(1856-1940)

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Cathode Rays - JJ Thompson

P. 62

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Mass of an electron Experiments performed by Thompson

together with those of Robert Millikan were

able to show that an electron has a mass of

9.1 x 10-28 g

The mass of one atom of the lightestelement, hydrogen, is 1.7 x 10-24 g

An electron is approx 1/2000th the mass of

a H atom!

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So the electron appears to be an

insignificant part of the atom -from a mass point of view!

How are electrons arranged

inside an atom?

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Thompsons Plum PuddingModel of the Atom

electronuse pos ve

charge

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Ernest Rutherford

(1871-1937)

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Nucleus of the AtomRutherford (1871-1937)

P. 64Click on picture for movie

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Nucleus of the Atom Continued

P. 64

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Nucleus of the Atom Continued(Rutherford)

At the center of the atom is a very dense nucleus thataccounts for almost all the mass of the atom and

contains all the positive charge.He named these positive particles protons.

Protons have a relative mass of 1 and a charge of +1.

P. 64

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Nucleus of the AtomChadwick (1891-1974)

When atoms of beryllium were bombardedwith alpha particles, new uncharged particles

.

These uncharged particles were calledneutrons.

Neutrons have a relative mass of 1 and acharge of zero.

P. 64-65

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Characteristics of the Three Basic

Subatomic Particles

P. 65

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Arrangement of SubatomicParticles in the Atom

P. 66

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SPACE !

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And so are ALL OF US !

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Our first direct look at the atomicworld

Get me out of here!

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View of Atoms from STM

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Scanning Tunneling Microscopy

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Isotopes

Atoms of an element that have the same number of

protons but different numbers of neutrons are calledisotopes.

Z A = mass number

Z = atomic number

The isotopes of sulfur are written:32

S33

S34

S36

S16 16 16 16

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Isotopes Continued

Which of the following represent isotopes of the

same element? Which element?

234

X234

X235

X238

X92 93 92 92

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Answer:

234 234 235 238

92 93 92 92

234

Npis not an isotope of Uranium.

93

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Isotopes of Carbon

12 13 14

6 6 6

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12 13 14

Isotopes of Carbon

6 6 6

12 - 6 = 6neutrons

13 - 6 = 7neutrons

14 - 6 = 8neutrons

Radioactive

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Carbon-14 Dating

Used to date archeological artifacts up to60000 years old

14

sample

Amount of 14C decreases with time

will be discussed in detail in Ch 5

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Isotopic Fingerprinting

The ratio of stable isotopes (e.g.13

C/12

C) ina substance will vary slightly depending on

the ori in of the substance

for example, petroleum samples fromdifferent parts of the world will have

different 13C/12C ratios

How could such information be useful?

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Time for some nuclear chemistry

lets begin Ch 5

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Periodic Table

Mendeleev (1834-1907)

Horizontal rows called periods

Vertical columns called groups

Elements within a group have similar chemicalproperties

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The Periodic Table

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Properties of Alkali Metals andHalogens

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Metals

Metals have distinctive properties

Good conductors of heat and electricityShiny appearance

Ductile and malleable

Are light purple in periodic table that is on the

inside cover of the book

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Nonmetals

Do not conduct heat or electricity

Not ductile or malleableMany exist as gases

Are green in periodic table that is on the inside

cover of the book

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Semimetals

Have properties that lie between those of

metals and nonmetalsAre gold yellow in the periodic table that is on

the inside cover of the book

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REFERENCE

www.langara.bc.ca/chemistry/A_Mosi/C1117_Ch3.ppt