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Atoms and Atomic Structure. Law of Conservation of Mass Lavoisier (1743-1794). In a chemical reaction, matter is neither created nor destroyed. P. 57. Click on picture for movie. CuCO 3 (s)  CuO(s) + CO 2 (g). 123.6 g. 79.6 g. ? g. CuCO 3 (s)  CuO(s) + CO 2 (g). 123.6 g. 79.6 g.

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law of conservation of mass lavoisier 1743 1794
Law of Conservation of MassLavoisier (1743-1794)

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

P. 57

Click on picture for movie

slide4

CuCO3(s)  CuO(s) + CO2(g)

123.6 g

79.6 g

44.0 g

slide5

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 proportions proost 1754 1826
Law of Definite ProportionsProost (1754-1826)

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

P. 58

slide7

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

slide8

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?

slide9

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

slide10

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

slide11

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
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

24 g

32 g

2:1

12 g

32 g

P. 59

dalton s atomic theory
Dalton’s Atomic Theory

John Dalton (1766-1844) proposed an atomic theory

  • 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

mass of an electron
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!
slide20
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
Thompson’s Plum Pudding Model of the Atom

electron

Diffuse positive

charge

nucleus of the atom rutherford 1871 1937
Nucleus of the AtomRutherford (1871-1937)

P. 64

Click on picture for movie

nucleus of the atom continued rutherford
Nucleus of the Atom Continued (Rutherford)
  • At the center of the atom is a very densenucleus 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
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
Isotopes
  • Atoms of an element that have the same number of protons but different numbers of neutrons are called isotopes.

AXX = symbol of element

ZA = mass number

Z = atomic number

  • The isotopes of sulfur are written:

32 S33S34 S36 S

16 16 16 16

isotopes continued
Isotopes Continued

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

234X234 X235X238 X

92939292

answer
Answer:

234 U234 Np235 U238U

92939292

234 Np is not an isotope of Uranium.

93

isotopes of carbon
Isotopes of Carbon

12C13 C14C

666

slide42

Isotopes of Carbon

12C13 C14C

666

12 - 6 = 6

neutrons

13 - 6 = 7

neutrons

14 - 6 = 8

neutrons

Radioactive

carbon 14 dating
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
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 table mendeleev 1834 1907
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

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