Atoms and Atomic Structure

Law of Conservation of MassLavoisier (1743-1794)

In a chemical reaction, matter is neither created nor destroyed.

P. 57

Click on picture for movie

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

123.6 g 79.6 g ? g

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

123.6 g 79.6 g 44.0 g

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

123.6 g 79.6 g 44.0 g

123.6 g 79.6 g + 44.0 g=

Law of Definite ProportionsProost (1754-1826)

Different samples of any pure compound contain the same elements in the same proportions by mass.

P. 58

Mass Ratio of Cu:O:C in copper carbonate

Cu:O:C = 53:40:10 = 5.3 : 4: 1Regardless of where the copper carbonate is found

Mass Ratio of Cu:O:C in copper carbonate

Cu:O:C = 53:40:10 = 5.3 : 4: 1If a sample of copper carbonate contains 20 g of carbon how many g of Cu will it contain?

Mass Ratio of Cu:O:C in copper carbonate

Cu:O:C = 53:40:10 = 5.3 : 4: 1If a sample of copper carbonate contains 20 g of carbon how many g of Cu will it contain?

Cu / C = 5.3g / 1g = x / 20g

Mass Ratio of Cu:O:C in copper carbonate

Cu:O:C = 53:40:10 = 5.3 : 4: 1If a sample of copper carbonate contains 20 g of carbon how many g of Cu will it contain?

(5.3g / 1g)20g = x

Mass Ratio of Cu:O:C in copper carbonate

Cu:O:C = 53:40:10 = 5.3 : 4: 1If a sample of copper carbonate contains 20 g of carbon how many g of Cu will it contain?

106 g = x

Law of Multiple Proportions (John Dalton)

The masses of one element that can combine chemically with a fixed mass of another element are in a ratio of small whole numbers.

2C + O2 2CO Carbon monoxide

C + O2 CO2 Carbon dioxide

P. 59

24 g 32 g

12 g 32 g

2:1

The idea of “whole numbers” suggests the presence of

“individual” particle

ATOMS !

Dalton’s 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 atoms4. atoms combine in certain whole-number ratios 5. In a chemical reaction, atoms are merely

rearranged to form new compounds; they are not created, destroyed, or changed into atoms of any other elements.

P. 56-57

OK! Matter is made of ATOMS

But what are ATOMS?

What are ATOMS themselves made of?

Cathode–Ray Tube

P. 61

J.J. Thompson (1856-1940)

Cathode Rays - JJ Thompson

P. 62

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 lightest element, hydrogen, is 1.7 x 10-24 g

• An electron is approx 1/2000th the mass of a H atom!

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?

Thompson’s Plum Pudding Model of the Atom

electronDiffuse positivecharge

Ernest Rutherford (1871-1937)

Nucleus of the AtomRutherford (1871-1937)

P. 64Click on picture for movie

Nucleus of the Atom Continued

P. 64

Nucleus of the Atom Continued (Rutherford)

At the center of the atom is a very dense nucleus that accounts 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

Nucleus of the AtomChadwick (1891-1974)

When atoms of beryllium were bombarded with alpha particles, new uncharged particles with mass identical to protons were emitted.

These uncharged particles were called neutrons.

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

P. 64-65

Characteristics of the Three Basic Subatomic Particles

P. 65

Arrangement of Subatomic Particles in the Atom

P. 66

Atoms are mainly EMPTY SPACE !

And so are ALL OF US !

Our first direct look at the atomic world

Get me out of here!

View of Atoms from STM

Scanning Tunneling Microscopy

Isotopes Atoms of an element that have the same number of protons

but different numbers of neutrons are called isotopes.

AX X = symbol of element

Z A = mass number

Z = atomic number The isotopes of sulfur are written:32

S33

S34

S36

S16 16 16 16

Isotopes Continued

Which of the following represent isotopes of the same element? Which element?

234 X

234 X 235

X238

X

92 93 92 92

Answer:

234 U

234 Np

235 U

238 U

92 93 92 92

234 Np is not an isotope of Uranium.

93

Isotopes of Carbon

12 C

13 C 14

C 6 6 6

12 C

13 C 14

C 6 6 6

12 - 6 = 6neutrons

13 - 6 = 7neutrons

14 - 6 = 8neutrons

Radioactive

Isotopes of Carbon

Carbon-14 Dating

• Used to date archeological artifacts up to 60000 years old

• measures amount of radioactive 14C left in a sample

• Amount of 14C decreases with time

• will be discussed in detail in Ch 5

Isotopic Fingerprinting

• The ratio of stable isotopes (e.g. 13C/12C) in a substance will vary slightly depending on the origin of the substance

• for example, petroleum samples from different parts of the world will have different 13C/12C ratios

• How could such information be useful?

Time for some nuclear chemistry…let’s begin Ch 5

Periodic TableMendeleev (1834-1907)

Atoms arranged by ascending atomic number Horizontal rows called periods Vertical columns called groups Elements within a group have similar chemical

properties

The Periodic Table

Properties of Alkali Metals and Halogens

Metals

Metals have distinctive properties Good conductors of heat and electricity Shiny appearance Ductile and malleable Are light purple in periodic table that is on the

inside cover of the book

Nonmetals

Do not conduct heat or electricity Not ductile or malleable Many exist as gases Are green in periodic table that is on the inside

cover of the book

Semimetals

Have properties that lie between those of metals and nonmetals

Are gold yellow in the periodic table that is on the inside cover of the book

REFERENCE

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