Atoms and Atomic Structure. Law of Conservation of Mass Lavoisier (1743-1794) In a chemical...
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Transcript of Atoms and Atomic Structure. Law of Conservation of Mass Lavoisier (1743-1794) In a chemical...
Law of Conservation of MassLavoisier (1743-1794)
In a chemical reaction, matter is neither created nor destroyed.
P. 57
Click on picture for movie
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
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
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?
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
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
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?
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
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