Transcript Document

Atoms and Atomic
Structure
Law of Conservation of Mass
Lavoisier (1743-1794)
P. 57
In a chemical reaction, matter is neither created
nor destroyed.
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
123.6 g
79.6 g
44.0 g
= 79.6 g + 44.0 g
Law of Definite Proportions
Proost (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: 1
Regardless 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: 1
If 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: 1
If 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: 1
If 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: 1
If 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.
2:1
2C +
O2 
24 g
32 g
C +
O2 
12 g
32 g
2CO Carbon monoxide
CO2 Carbon dioxide
P. 59
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.
2.
3.
4.
5.
matter is composed, indivisible particles (atoms).
all atoms of a particular element are identical
different elements have different atoms
atoms combine in certain whole-number ratios
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
Diffuse positive
charge
electron
Ernest Rutherford
(1871-1937)
Nucleus of the Atom
Rutherford (1871-1937)
P. 64
Click 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 Atom
Chadwick (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
16
S
33
16
S
34
16
S
36
16
S
Isotopes Continued
Which of the following represent isotopes of the
same element? Which element?
234
92
X
234
93
X
235
92
X
238
92
X
Answer:
234
U
92
234
93
234
93
Np
235
U
92
is
not
an
isotope
of
Uranium.
Np
238
92
U
Isotopes of Carbon
12
6
C
13
6
C
14
6
C
Isotopes of Carbon
12
6
C
12 - 6 = 6
neutrons
13
6
C
13 - 6 = 7
neutrons
14
6
C
14 - 6 = 8
neutrons
Radioactive
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 Table
Mendeleev (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/C111
7_Ch3.ppt