Chemical Foundations: Elements, Atoms, and Ions

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Chemical Foundations Elements, Atoms, and Ions

• Chapters 45
• Pages 85-155

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Early History of Chemistry-

• Greeks (around 500-400 BC)
• divided matter into four elements earth, air,
  fire, and water.
• Aristotle- __________________? matter can be
  divided and subdivided into smaller and smaller
  parts indefinitely- each part, no matter how
  small would retain the original properties of
  matter.
• Democritus
  ?believed all matter is made up of tiny partices,
  or ATOMOS (indivisible), which could not be
  broken down into smaller particles

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History- 500 BC?1600s

• Alchemy-
• Alchemists discovered many elements in their
  attempts to convert metals to gold. Many
  elements names have Latin origins

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History- 1600s

• Robert Boyle (1627-1691)-
• Science should be grounded in experiments
• Termed ELEMENTS- a substance was an element
  unless it could be broken down into two or more
  simpler substances

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History- 1800s

• Most natural materials are mixtures of pure
  substances.
• Pure substances are either elements or
  combinations of elements called compounds.
• Law of Constant Composition / Law of Definite
  Proportions (Proust- 1797)- a given compound
  always has the same proportion of elements by
  mass. Carbon tetrachloride- always 1 atom carbon
  per 4 atoms of chlorine
• Law of Conservation of Mass (Lavoisier- 1783)-
  Atoms cannot be created or destroyed in a
  chemical reaction. They are simple rearranged to
  form new compounds..

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Daltons Atomic Theory

• 1766-1844- English School Teacher
• Elements are made up of
• All atoms of a given element
• The atoms of a given element are
• Atoms of one element can combine with atoms of
  other elements to form compounds. A given
  compound always has the same relative numbers and
  types of atoms. (Law of constant composition).
• Atoms are indivisible in chemical processes.
  That is, atoms are not created or destroyed in
  chemical reactions. A chemical reaction simply
  changes the way the atoms are grouped together.
  (Law of conservation of matter).
• Impact Dalton used his model to predict the
  outcome of chemical reactions

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Early Experiments to Characterize the Atom-
1800-1900s

• William Crooks- Cathode Rays- negatively charged
  particles (1880s).
• JJ Thomson (1897) Cathode Ray Tube- Credited with
  discovering the electron.

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Thomsons Experiment

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Vacuum tube
Metal Disks
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Thomsons Experiment

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Thomsons Experiment

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Thomsons Experiment

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Thomsons Experiment

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• Passing an electric current makes a beam appear
  to move from the negative to the positive end

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Thomsons Experiment

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• Passing an electric current makes a beam appear
  to move from the negative to the positive end

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Thomsons Experiment

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• Passing an electric current makes a beam appear
  to move from the negative to the positive end

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Thomsons Experiment

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• Passing an electric current makes a beam appear
  to move from the negative to the positive end

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Thomsons Experiment

• By adding an electric field

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Thomsons Experiment

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• By adding an electric field

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Thomsons Experiment

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• By adding an electric field

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Thomsons Experiment

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• By adding an electric field

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Thomsons Experiment

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• By adding an electric field

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Thomsons Experiment

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• By adding an electric field

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Thomsons Experiment

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• By adding an electric field he found that the
  moving pieces were negative

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Thomsons Model
Spherical cloud of positive charge

• Found the
• Couldnt find positive (for a while)
• Said the atom was like
• A bunch of positive stuff, with the electrons
  able to be removed
• established the ratio of mass to electric charge
  for cathode ray
• m/e -5.6857x10-9 g/coulomb.

Electrons
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Millikans Oil-Drop Experiment Mass of Electron
1909 Robert Millikan determined the electronic
charge through a series of oil-drop experiments.
The currently accepted value of the charge of the
e is 1.6022x10-19C. Substituting into
Thomsons mass to charge ratio then gives the
mass of electron as 1/1836( 9.1094x10-28g).
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1911 Rutherfords Gold Foil Experiment
Florescent Screen
Lead block
Uranium
Gold Foil
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Rutherford Expected

• The alpha particles to pass through without
  changing direction very much
• WHY?
• The positive charges were spread out evenly.
  Alone they were not enough to stop the alpha
  particles

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What he expected
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Because
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Rutherford thought the mass was evenly
distributed in the atom
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Rutherford thought the mass was evenly
distributed in the atom?a particles should pass
through the low density model.
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What he got

• The majority of ?-particles penetrated the foil
  undeflected.
• Some ? particles experienced slightly
  deflections.
• A few (about one in every 20,000) suffered rather
  serious deflections as they penetrated the foil.
• A similar number did not pass through the foil at
  all, but bounced back in the direction from which
  they had come.

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Rutherfords Gold Foil Experiment (1911)
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How he explained it

• Atom is mostly
• Alpha particles are deflected by it if they get
  close enough

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Rutherfords Gold Foil Experiment (1911)

• The Results of Rutherfords Gold Foil Experiment
  led scientists to believe that the atom must have
  a densely packed positive center (NUCLEUS) around
  which tiny electrons moved in a space that was
  otherwise empty.
• 1919- Rutherford concludes that the atoms
  nucleus must have particles positively charged
  called protons and that the number of protons in
  an atom equal the number of electrons.

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History- 1900sThe Nuclear Atom

• Rutherfords colleague- James Chadwick determined
  that the mass of the atom did not equal the mass
  of electrons protons. Therefore, there must be
  another particle without a charge (NEUTRON) found
  in the nucleus.

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Size of an atom

• Atoms are small 10-10 meters
• Hydrogen atom, 32 pm radius
• Nucleus tiny compared to atom
• IF the atom was the size of a stadium, the
  nucleus would be the size of a marble.
• Radius of the nucleus near 10-15m.
• Density near 1014 g/cm

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Conclusion

• Matter is composed, on a tiny scale, of particles
  called atoms. Atoms are in turn made up of
  minuscule nuclei surrounded by a cloud of
  particles called electrons. Nuclei are composed
  of particles called protons and neutrons, which
  are themselves made up of even smaller particles
  called quarks. Quarks are believed to be
  fundamental, meaning that they cannot be broken
  up into smaller particles.

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History 1920s

• Following Rutherfords planetary model of the
  atom, it was realized that the attraction between
  the electrons and the protons should make the
  atom unstable
• Neils Bohr (1922) proposed a model in which the
  electrons would stably occupy fixed orbits, as
  long as these orbits had special quantized
  locations

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History- 1920s The Bohr Model of the Atom

• Neils Bohr expands Rutherfords model of the atom
  allowing the electrons to travel in successively
  larger distinct orbits around the nucleus. The
  outer orbits hold more electrons than the inner
  orbits and the outer orbits determine the atoms
  chemical properties.

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White Light is Composed of Light of Various
Wavelengths
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Electromagnetic Spectrum
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History The Bohr Model

• In the Bohr model, the electron can change
  orbits, accompanied by the absorption or emission
  of a photon of a specific color of light.

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History- The Bohr Model

• Bohrs Model was used to explain why the
  negatively charged electrons did not fall into
  the positively charged nucleus of the atom.
• The electrons were only able to occupy distinct
  energy levels or orbits.

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History- The Bohr Model

• If an atom absorb a specific amount of energy
  (_________), the outer shell electrons
  (___________) could be excited into higher energy
  states. This ___________ is unstable, so the
  electron releases a photon of energy (__________)
  as light. Light of specific wavelength
  correspond to the energy emitted by the electron
  dropping back to the ___________.

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History- The Bohr Model
http//www.mhhe.com/physsci/chemistry/essentialche
mistry/flash/linesp16.swf
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Introduction to the Modern Concept of Atomic
Structure

• From a very simplistic perspective- the atom is
  composed of a tiny nucleus (10-13 cm in diameter)
  and electrons that move about the nucleus at a
  distance of about 10-8 cm from it.
• If the nucleus was a golf ball, the electrons
  would be about 2 Km away.
• The nucleus contains protons and neutrons.
• The mass of the protons is about equal to the
  mass of neutrons.
• Neutrons have zero charge, electrons 1, protons
  1.
• The number of protons the number of electrons
  in a neutral atom.

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• X
• A
• Z

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The Hydrogen Atom

• One electron orbiting a nucleus
• 1 proton Z atomic number
• 0 neutrons N
• Total mass A ZN 1
• Singly ionized Hydrogen is missing one electron
  1H

1H
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The Helium Atom

• Two electrons orbiting a nucleus
• 2 protons Z atomic number
• 2 neutrons N
• Total mass A ZN 4
• Singly ionized Helium is missing one electron
  4He
• Doubly ionized Helium is missing both electrons
  a particle 4He

4He
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Isotopes

• Daltons theory is modified as a result of
  Chadwicks studies of the nucleus and the
  discovery of the neutron.
• All atoms of the same element contain the same
  number of protons and electrons, but atoms of a
  given element may have different numbers of
  neutrons.
• Isotopes-

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Isotopes of Hydrogen
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Isotopes of Carbon
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Introduction to the Periodic Table
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Periodic Table

• Arranged according to increasing atomic
• number (number of protons)
• Horizontal Rows
• Vertical Columns
• This arrangement is based on chemical
  similarities that exist in the vertical columns
  (groups). These groups are referred to as
• This system of arrangement was 1st proposed by
  Dmitri Mendeleev in 1869. His first table
  consisted of 62 known elements. He was able to
  predict the presence of several elements that had
  not yet been discovered based on his table.

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Periodic Table

• The name periodic table refers to the fact that
  as we increase the atomic numbers, every so often
  an element occurs with properties similar to
  those of an earlier (lower atomic number) element.

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Chemical Families of the Periodic Table

• Metals
• Nonmetals
• Metalloids
• The Alkali Metals
• The Alkaline Earth Metals
• Transition Metals
• The Oxygen Family
• Halogens
• Nobel Gases

http//www.papernapkin.com/
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The Chemists Shorthand Formulas

• Chemical Formula-
• Elements symbols are used to simplify the
  formulas. Subscripts are used to indicate the
  number of each type of element.

Glucose- C6H11O6
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Ions

• Ions
• Neutral atoms become ions through the addition or
  removal of electrons. Atoms form ions to gain
  stability in their valence electron levels.

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Ions

• Cations
• Metals want to lose electrons to gain a stable
  octet
• Anions
• Nonmetals want to gain electrons to gain a stable
  octet

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Ions

• The resulting charge on the ion is determined
  based on the number of electrons gained or lost.
• Sodium atom ?
• Fluorine atom 1 electron ?

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Ion Charges and the Periodic Table

• The position of an element in the periodic table
  can help determine the resulting charge on its
  ion.

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Electrostatics

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Compounds That Contain Ions

• Substances that want to lose electrons (metals)
  will react with substances that want to gain
  electrons (nonmetals) to forms ions. The
  resulting ions are attracted to each other
  through electrostatic forces.
• 2Na Cl2 ? 2Na 2Cl- ? 2NaCl
• 2 Sodium atoms transfers an electron each to 2
  chlorine atoms. The resulting ions (sodium and
  chloride) are attracted to each other through
  electrostatic forces.

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Ionic Bond Electrostatic Force
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Properties of Ionically Bonded Substances

• 1. Composed of
• 2.
• 3. _____________________ in liquid or aqueous
  state.

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Ionic Compounds

• ____________________________
• ____________________________
• ____________________________

NaCl
Na
Cl-
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Always check the substances location in the
Periodic Table!
Mg2
Cl-
Cl-
Li
Li
N3-
Li
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Nomenclature Naming Compounds

• Binary Compounds- compounds that contain two
  elements
• 1. Compounds that contain a metal and a nonmetal
  ? ____________________
• 2. Compounds that contain two nonmetals ?
  __________________________

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Binary Ionic Compounds

• 1. The cation is always named first and the anion
  second.
• 2. A simple cation (obtained from a single atom)
  takes its name from the name of the element. For
  example, Na is called sodium in the names of
  compounds containing this ion.
• 3. A simple anion (obtained from a single atom)
  is named by taking the first part of the element
  name (the root) and adding ide. Thus the Cl- ion
  is called chloride.

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Examples- Binary Ionic Compounds

• NaCl ?
• KI ?
• CaS ?
• CsBr?
• MgO ?

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Binary Ionic Compounds Containing Transition
Metals

• Many metals can form more than one type of
  cation.
• Lead (Pb) can form Pb2 or Pb4
• Gold (Au) can form Au or Au3
• Iron (Fe) can form Fe2 or Fe3
• Chemists use Roman numerals to specify the charge
  on the cation.
• Fe2 Fe3

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Examples Binary Ionic Compounds with Transition
Metals

• CuCl ?
• HgO ?
• Fe2O3 ?
• MnO2 ?
• PbCl4 ?

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Naming Compounds That Contain Polyatomic Ions

• Polyatomic ions charged entities composed of
  several atoms bonded together.
• In order to name these compounds, you must
  memorize the names of the polyatomic ions. Using
  Table F in your reference tables will help you to
  do this.

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Examples

• Na2SO4 ?
• KH2PO4 ?
• Fe(NO3)3 ?
• Na2SO3 ?
• Mn(OH)2 ?

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Naming Binary Compounds That Contain Only
Nonmetals

• 1. The first element in the formula is named
  first, and the full element name is used.
• 2. The second element is named as through it were
  an anion.
• 3. Prefixes are used to denote the numbers of
  atoms present. (see next slide)
• 4. The prefix mono- is never used for naming the
  first element. CO is carbon monoxide NOT
  monocarbon monoxide.

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Prefixes Used to Indicate Numbers in Chemical
Names
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Examples

• BF3 ?
• NO ?
• N2O5 ?
• CCl4 ?
• NO2 ?
• IF3 ?

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Naming Acids

• Acids-
• 1. If the anion does not contain oxygen, the acid
  is named with the prefix hydro- and the suffix-
  ic attached to the root name for the element.
• HCl (aq) ?
• H2S (aq) ?

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Naming Acids Cont.

• 2. When the anion contains oxygen, the acid name
  is formed from the root name of the central
  element of the anions or the anion name, with a
  suffix of -ic, or ous. When the anion name ends
  in ate, the suffix ic is used. When the anion
  name is -ite, the suffix ous is used.
• H2SO4 ? hydrogen sulfate ?
• H2SO3 ? hydrogen sulfite ?

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Writing Formulas from Names

• Empirical Formulas- uses element symbols to
  indicate the atoms or ions in a compound, with
  subscripts to indicate their smallest whole
  number ratio.
• Calcium fluoride ?
• Potassium hydroxide ?
• Cobalt (III) nitrate ?