Chapter Two: Atoms and Molecules

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Chapter Two Atoms and Molecules

• Suggested Problems 5, 9, 15, 17, 21, 29, 31, 45,
  51, 55, 59, 67, 68, 71

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Some Common Elements
Aluminum Al Silvery white metal
Barium Silvery white metal
Bromine Reddish brown liquid
Calcium Silvery white metal
Carbon Graphite Diamond Soft, black, conducting solid Hard colorless crystal
Chlorine Greenish poison gas
Chromium Silvery white metal
Cobalt Silvery white metal
Copper Reddish metal
Fluorine Yellowish poisonous gas
Gold Aurum, sun
Helium Colorless inert gas
Hydrogen Colorless flammable gas, water forming
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Some Common Elements
Iodine Bluish black solid
Iron From ferrum
Lead From plumbum (plumber)
Lithium Silvery highly reactive metal
Magnesium Silvery white metal
Manganese Gray white metal
Mercury Hg Silvery white liquid metal
Neon Colorless inert gas
Nickel Silvery white metal
Nitrogen Colorless gas 80 of air
Oxygen Colorless reactive gas 20 of air
Phosphorous Either red or white solid
Potassium Silvery white metal
Silicon Gray lustrous solid
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Some Common Elements
Silver From argentum
Sodium From natrium highly reactive metal
Sulfur Yellow solid
Tin Silvery white metal
Zinc Bluish white metal
You will need to become familiar with the names,
symbols and charges of these common elements.
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Important People in Early Chemistry

• Lavoisier
• Laid the experimental foundation of modern
  chemistry
• Father of Modern Chemistry
• John Dalton (1766- 1844)
• Provided the atomic theory

http//encarta.msn.com/find/Concise.asp?ti02DFD00
0
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Postulates of Daltons Atomic Theory

1. All matter is comprised of atoms. Atoms are
   indivisible and indestructible.
2. All atoms of a given element are identical. Atoms
   of different elements have different masses and
   chemical properties.
3. Compounds are formed by combination of atoms in
   small, whole-number ratios.
4. Chemical changes recombine atoms. Atoms are not
   destroyed during chemical changes.

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Daltons Atomic Theory

• All matter is comprised of atoms. Atoms are
  indivisible and indestructible.
• We now know this to not be true.
• Atoms are composed of protons nuetrons and
  electrons

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Structure of the Atom

• Atoms are made of
• Protons p, positively charged particles
• Nuetrons no, neutral particles
• Electrons e-, negatively charged particles

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Discovery of the electron

• In 1897 by British physicist J.J. Thompson

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Cathode Ray Tube
Anode ()
Charged Plate
Cathode (-)
Charged Plate
Thompson was able to calculate me/e
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Sir Ernest Rutherford 1871-1937

• Characterized alpha, beta and gamma radiation
• His lab discovered protons, neutrons and
  transmutation
• Discovered atomic nucleus

Transmutation The conversion of one element into
another by a process taking place in the nucleus
http//www2.slac.stanford.edu/vvc/nobel/rutherford
.html
http//www.xmission.com/dparker/twins.html
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The Nuclear Atom

• The existence of the the atomic nucleus was
  demonstrated by Ernest Rutherfords gold foil
  experiment

ZnS phosphor
Lead box containing radiuma source of alpha
particles
http//micro.magnet.fsu.edu/electromag/java/ruther
ford/
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Mostly Empty Space

• The mass of the atom (protons and neutrons)
  resides in the nucleus, surrounded by a cloud of
  electrons
• The nuclear radius is only about 0.001 of the
  atomic radius
• 1 part in 100,000
• If the nucleus were the size of a baseball (3),
  the atom would be 5 miles in diameter

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Atomic Number and Mass

• Atomic Number (Z) is equal to the number of
  protons in the nucleus of an atom
• Atomic Mass Number or Mass Number (A) is equal to
  the sum of the protons and neutrons in the
  nucleus of an atom
• The atomic weight is reported relative to atomic
  weight of 12C (carbon-12)
• The unit of atomic weight is the amu
• 1 amu 1/12 the weight of 12C atom

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Electron number

• In neutral atoms the number of electrons equals
  the number of protons
• The mass of an e- is so small that scientists
  disregard its contribution to the overall mass of
  the atom

17 Cl 35.454
Z
A
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Practice Problem

• Determine the identity/value of ?. Then determine
  the number of p, no and e- in each species.

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Mass Spectroscopy
Provides a spectra of intensity vs. m/z
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J.J. Thompson

• Performed MS on a sample of neon (Ne)
• Noticed a m/z of 22
• Should this occur? Or was this a contaminated
  sample
• Isotopes
• Isotopes have the same atomic number but
  different atomic weights
• Isotopes have the same number of protons, but
  different number of (_______)
• How does this compare with Daltons theory?

2H and 3H deuterium and tritium
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Atomic Weights (A) and the periodic table

• Atomic weights listed on the periodic table are
  weighted averages of the naturally occurring
  isotopes
• Example Chlorine (Cl)
• What is the atomic weight of Cl?

Isotopic Mass (amu) Fractional Abundance
34.97 0.7577
36.97 0.2423
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Dmitri Mendeleev 1834-1907
Russian who constructed periodic table of the
elements, emphasizing that chemical and physical
properties are repeated in a predictable way
Periodic Table a tabular arrangement of elements
in rows and columns, highlighting the regular
repition of properties of the elements
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Metals, Non-metals and Metalloids
Metals Non-Metals Metalloids (Semimetals)
Shiny, lustrous Variable Shiny, lustrous
Malleable, Ductile Brittle Variable
Electrical and Thermal Conductor Non-conductor (except graphite) Poor conductor
Located on the left side of the table Located on right side of table Located on stairstep in table
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Physical State of the Elements
1A 8A
H 2A 3A 4A 5A 6A 7A He
Li Be B C N O F Ne
Na Mg 3B 4B 5B 6B 7B -- 8B -- 1B 2B Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
Rb Sr cY Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
Fr Ra Ac Rf Db Sg Bh Hs Mt

S L G Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr
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Representative, Transition and Inner Transition
Elements
1A 2A 8A
H 3A 4A 5A 6A 7A He
Li Be B C N O F Ne
Na Mg 3B 4B 5B 6B 7B -- 8B -- 1B 2B Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
Rb Sr cY Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
Fr Ra Ac Rf Db Sg Bh Hs Mt

R T IT Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr
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Counting Atoms

• An atomic mass unit is far to small to measure
  with a balance
• 1 amu 1.66x10-24 g
• So (like creating the amu) an operational
  definition was developed the mole

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Moles

• A mole quantity of a given substance that
  contains as many molecules or formula units as
  exactly 12 grams of carbon-12
• A mole of any element has a mass equivalent to
  its atomic mass in grams
• A mole contains 6.022 x 1023 ions, molecules,
  atoms, particles, etc.
• Avogadros number is
• 6.022 x 1023 (things)/mole

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Example

• What is the mass in amu of a Ne atom?
• What is the mass of a mole of Ne? (Hint use the
  definition of amu and mole)

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Chemical Formulas

• When groups of atoms combine to give
  compounds/molecules, the numbers of each atom are
  reported in the chemical formula as subscripts
• Example water

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Formula Weight and Molar Mass

• The formula weight (sometimes called molecular
  weight or more correctly as molecular mass) is
  the sum of the atomic masses of each element in
  the compound/molecule units will be in amu
• Molar mass is the mass of one mole of molecules,
  formula units, etc of an element or compound
  units in g/mol

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Sample problems

• What is the formula weight of glucose, C6H12O6?
• What is the molar mass of Calcium Nitrate,
  Ca(NO3)2?

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What can we say based on a chemical formula?

• Take the formula for Sucrose
• C12H22O11
• One molecule contains how many atoms of each
  element?
• One mole of sucrose contains how many moles of
  each element?
• The formula weight of sucrose in amu is?
• The molecular weight of sucrose in g/mol is?

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Example

• What is the percent carbon by weight in methane
  (CH4) ?

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Stoichiometry The Big Overview
atoms
ions
particles
Conversion Factor Avogadros number
Conversion Factor Stoichimetric Coefficients or
Formula Subscripts
moles
moles
Conversion Factor Formula Weight
grams