Atoms: The Building Blocks of Matter

1
Chapter 3
Chapter 3 ATOMS The Building Blocks of
Matter

• Atoms The Building Blocks of Matter

2
3-1 Early Atomic Theory
Do Not need in notes

• Atoms are so small they cannot be observed
  directly. Scientists could use only experimental
  data to help describe the atom.
• Around 400 B.C., Democritus (a Greek philosopher)
  suggested that the world was made of two things -
  empty space and tiny particles called atoms.
• During the 1800's, a French Chemist (Antoine
  Lavoisier) discovered that chemical "changes"
  occurring in a closed system - the mass after a
  chemical change equaled the mass before the
  chemical change.
• He proposed that, in ordinary chemical reactions,
  matter can be changed in many ways, but it cannot
  be created or destroyed (Law of Conservation of
  Mass).
• Work by another French Chemist, Joseph Proust,
  had observed that specific substances always
  contain elements in the same ratio by mass (Law
  of Definite Proportions.)

3
Foundations of Atomic Theory

• Law of Definite Proportions The elements
  composing a compound are always found in the same
  ratio by mass.
• Law of Multiple Proportions The masses of one
  element that combine with a fixed amount of
  another element to form more than one compound
  are in the ratio of small whole numbers. Example
  CO, CO2

4
For example Oxygen can combine with Carbon to
form Carbon Monoxide, CO, or form Carbon Dioxide,
CO2.
Compound Mass of C in Sample Mass of O in Sample Ratio of O masses combined with constant mass
Carbon Monoxide, CO 12 g 16 g 11
Carbon Dioxide, CO2 12g 32 g 21

• Dalton was the founder of Atomic Theory.

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Daltons Atomic Theory

• All matter is composed of extremely small
  particles called atoms.
• Atoms of a given element are identical in size,
  mass and other properties atoms of different
  elements differ in size, mass, and other
  properties.
• Atoms cannot be subdivided, created, or
  destroyed.
• Atoms of different elements combine in simple
  whole-number ratios to form chemical compounds.
• In chemical reactions, atoms are combined,
  separated, or rearranged.

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Modern Atomic Theory

• Element have a characteristic average mass which
  is unique to that element.
• Atoms cannot be subdivided, created, or destroyed
  in ordinary chemical reactions. However, these
  changes CAN occur in nuclear reactions!
• All matter is composed of atoms
• Atoms of any one element differ in properties
  from atoms of another element

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Section 3-2

• Atom- the smallest particle of an element that
  retains the chemical properties of that element.
• Nucleus- is the positively charges, dense central
  portion of the atom that contains nearly all of
  its mass but takes up only an insignificant
  fraction of its volume.

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Subatomic Particles
Electrons e- Negatively charged particles found around the nucleus in shells, energy level or electron clouds
Protons p Positively charged particles. Found in the nucleus
Neutrons N No charge. Found in the nucleus.
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The Atomic Scale

• Most of the mass of the atom is in the nucleus
  (protons and neutrons)
• Electrons are found outside of the nucleus (the
  electron cloud). e- have very tiny mass.
• Most of the volume of the atom is empty space

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Drawing atoms

• In the nucleus
• Symbol
• of p
• of N
• Outside the nucleus in the energy shells/level
• electrons

11
Famous Scientist
Scientist Experiment Name What it proved
JJ Thomson Cathode Ray Electrons have a negative chare
Robert Millikan Oil Drop Mass of an electron
Ernest Rutherford Metal Foil or gold foil Nucleus contains positive charge
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Discovery of the Electron
Do NOT need in Notes

• In 1897, J.J. Thomson used a cathode ray tube to
  deduce the presence of a negatively charged
  particle.
• Cathode ray tubes pass electricity through a gas
  that is contained at a very low pressure.

13

• Thomson was awarded the Nobel Prize in 1906 for
  his "discovery" of the first sub-atomic particle
  the electron. This discovery strongly implied
  that Dalton was wrong and that the atom was not
  the smallest particle of matter. It looked as if
  the atom could be broken down into even smaller
  pieces, and to Thomson these smaller pieces were
  his negatively charged electrons.

Do NOT need in NOTES
14
Conclusions from the Study of the Electron
Do NOT need in NOTES

• Cathode rays have identical properties
  regardless of the element used to produce them.
  All elements must contain identically charged
  electrons.
• Atoms are neutral, so there must be positive
  particles in the atom to balance the negative
  charge of the electrons
• Electrons have so little mass that atoms must
  contain other particles that account for most of
  the mass

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Thomsons Atomic Model
Do NOT need in NOTES

• Thomson believed that the electrons were like
  plums embedded in a positively charged pudding,
  thus it was called the plum pudding model.

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Rutherfords Gold Foil Experiment
Do NOT need in NOTES

• Alpha particles are helium nuclei
• Particles were fired at a thin sheet of gold
  foil
• Particle hits on the detecting screen (film) are
  recorded

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Rutherfords Findings
DO NOT Need in Notes

• Most of the particles passed right through
• A few particles were deflected
• VERY FEW were greatly deflected
• Conclusions
• The nucleus is small
• The nucleus is dense
• The nucleus is positively charged

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Section 3-3

• Atomic number (Z) of an element is the number of
  protons in the nucleus of each atom of that
  element.
• The number of protons the number of electrons

• 6
• C
• Carbon
• 12.011

19

• Mass Number
• Mass number is the number of protons and neutrons
  in the nucleus of an isotope.
• Mass p n
• SOooo the number of Neutrons
• n Mass - p

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Isotopes

• Isotopes are atoms of the same element that have
  different masses. (number of neutrons)

Mass Atomic Symbol
21
Nuclear Symbols

• 235
• 92

Mass number (p n)
Mass number (p n)
Element symbol
Atomic number ( of p)
U
235 92
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Hyphen Notation

• Sodium-23
• (23 is the mass )
• Sooo 23- 11 (atomic ) 12 for the of
  neutrons.
• 11 is the of protons and electrons.

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Isotopes of H
Isotopes p e- n
Hydrogen1 (protium) 1 1 0
Hydrogen-2 (deuterium) 1 1 1
Hydrogen-3 (tritium) 1 1 2
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The Mole

• 1 dozen 12
• 1 gross 144
• 1 ream 500
• 1 mole 6.022 x 1023
• There are exactly 12 grams of carbon-12 in one
  mole of carbon-12.

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CalculationsConverting moles to grams

• Given of mole X ? g (look at periodic table)
  g of
• 1 mole
• How many grams of lithium are in 3.50 moles of
  lithium?
• 3.50 mole X 6.941 g 24.29 g Li
• 1 mol

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CalculationsConverting grams to moles

• Given of g X 1 mol mol of
• g (look at periodic table)
• How many moles of lithium are in 18.2 grams of
  lithium?
• 18.2 g X 1 mol Li 2.622 mol Li
• 6.941 g

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Avogadros Number

• Is the number of particles in exactly one mole of
  a pure substance.
• 6.022 x 1023 is called Avogadros Number in
  honor of the Italian chemist Amadeo Avogadro
  (1776-1855).

I didnt discover it. Its just named after me!
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CalculationsConverting Moles to Particles

• Given of mol x 6.022 x 1023 part atoms
• 1 mol
• How many atoms/particles/molecules of lithium are
  in 3.50 moles of lithium?
• 3.50 mole X 6.022 x 1023 2.11 x 1024 atoms
  of Li
• 1 mol

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CalculationsConverting Particles to Moles

• Given of particles x 1 mole mol
• 6.022 x 1023
• How many moles of lithium are there in 1.2044 x
  1024 particles of Li?
• 1.2044 x 1024 part x 1 mole 2.0 mol
  Li
• 6.022 x 1023 part

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CalculationsConverting grams to particles

• Given of grams x 1 mol x 6.022 x 1023
  particles
• ? g 1 mol
  
• How many atoms/particles/molecules of lithium are
  in 18.2 g of lithium?
• 18.2 g x 1 mol x 6.022 x 1023 1.58 x 1024
  particle Li
• 6.941g 1 mol

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CalculationsConverting particles to grams

• Given of particles x 1 mol x ? g
  g
• 6.022 x 1023 1
  mol
• How many grams are there in 8.02 x 1025 particles
  of lithium?

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Work Cited

• JJ Thomson. Photo. July 28, 2006.
  http//www.sciencemuseum.org.uk/online/electron/se
  ction2/recording.asp
• Cathode Ray Image and JJ Thomson Model. Image.
  July 28, 2006. http//www.brooklyn.cuny.edu/bc/ahp
  /LAD/C3/C3_Electrons.html
• Gold Foil Experiment. Image. July 28, 2006.
  http//www.avon-chemistry.com/atom_lecture.html
• Rutherford. Photo. July 28,2006.
  http//www.anthroposophie.net/bibliothek/nawi/phys
  ik/rutherford/bib_rutherford.htm
• Mole. Photo. Aug 8, 2006. http//www.mwt.net/bi
  onorse/chemistry.htm

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• Hydrogen Isotopes. Picture. August 4, 2006.
  www.sr.bham.ac.uk/xmm/atom.html
• Amedeo Avogadro. avagadroc.jpg August 4, 2006.
  poohbah.cem.msu.edu/Portraits/PortraitsH...
• Uranium symbol. Picture. August 4, 2006.
  www.webelements.com/webelements/scholar/...
• Holt, Rinehart and Winston. Modern Chemistry.
  Harcourt Brace Company. 1999.
• Atom Comic Cover. Photo. Aug. 12, 2006.
  http//home.cfl.rr.com/fradford/Atom/Atom20.jpg