Atoms, Molecules and Ions

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Atoms, Molecules and Ions

• Prof. G. Matthews

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The Atomic Theory Of Matter

• Democritus
• Matter is composed of a finite number of
  incredibly small but discrete units called atoms.
• The texture, mass and color of a material were a
  function of the texture, mass, and color of its
  atoms.

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The Atomic Theory Of Matter

• Element as any material made of only one
  component.
• Compound as any material composed of two or more
  elements.

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The Atomic Theory Of Matter

• Law of conservation of mass
• There is no detectable change in the total mass
  of materials when they react chemically to form
  new materials.

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The Atomic Theory Of Matter

• Proust developed the Law of multiple proportions
• Elements combine in definite mass ratios to form
  compounds.

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The Atomic Theory Of Matter

• John Dalton reintroduced Democritus idea
• Each element consists of indivisible, minute
  particles called atoms.
• Atoms can neither be created nor destroyed in
  chemical reactions.
• All atoms of a given element are identical. Atoms
  chemically combine in definite whole-number
  ratios to form compounds.
• All atoms of different elements have different
  masses.

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The Atomic Theory Of Matter

• Joseph Gay-Lussac
• When gases react they react in the ratio of small
  whole numbers.
• 1811- Amadeo Avogadro said hydrogen and oxygen
  were diatomic.

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The Discovery of Atomic Structure

• Scientists applied a voltage across other gases
  in sealed glass tubes.
• Originated at the negative terminal (cathode)
  called cathode ray.
• Cathode ray was negatively charged.

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The Discovery of Atomic Structure

• J.J. Thompson measured the deflection angles of
  the cathode ray tube using a magnetic field.
• Deflection of particle depended on their mass and
  electric charge.
• Greater mass, greater resistance to change in
  motion and the smaller the deflection.
• Angle of deflection charge/mass.
• Didnt know charge on particle or mass.

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The Discovery of Atomic Structure

• Milliken Oil Drop
• Calculated droplets mass.
• Charge on any droplet was always a multiple of
  1.60 x 10-19 Coulomb.
• Electrons determine many of the materials
  properties.

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The Discovery of Atomic Structure

• It was assumed that if atoms contained negative
  particles then they must also contain positive
  particles.
• In 1910, Ernest Rutherford conducted the gold
  foil experiment.

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The Discovery of Atomic Structure

• Deflection pattern showed they must be bouncing
  off a positive, dense center.
• Called this the atomic nucleus.

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The Modern View of Atomic Structure

• Positive charge came from the proton.
• 1.6 x 10-19 Coulomb
• The extra mass in the atom is because of the
  neutron
• Same mass as proton but no electrical charge.

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The Modern View of Atomic Structure
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The Discovery of Atomic Structure

• Alpha Rays
• Helium nucleus 4 2 He.
• Beta rays
• Identical to a cathode ray i.e. electron 0 -1 e
• Gamma rays
• Extremely energetic form of non visible light.

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The Modern View of Atomic Structure

• In atomic notation, the mass number, the atomic
  number, and the chemical symbol are shown.
• Mass number total number of protons and neutron
  in an atom.
• Atomic number the number of protons in its
  nucleus.

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The Modern View of Atomic Structure

• Ions Particle with an unequal number of protons
  and electrons.
• Isotope Atoms with the same number of protons
  but different numbers of neutrons.
• Atomic weight Weighted average of the masses of
  the isotopes.

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Atomic Weights

• Cannizzaro
• The relative masses of can be obtained by
  weighing equal volumes of gases that are at the
  same temperature and pressure.

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Atomic Weights

• Today we can measure atomic masses using a mass
  spectrometer.
• By definition, the mass of 12C is exactly 12 amu.
• The atomic weight is also known as an average
  atomic mass (atomic weight).

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The Periodic Table

• 1869 - Mendeleev created the periodic table
• Period elements that appeared in one interval of
  repeating properties.
• Group elements of similar properties.
• Predict elements not yet discovered.

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The Periodic Table

• Metals shiny substances, opaque, good
  conductors of heat and electricity, malleable,
  ductile i.e. Cu.
• Nonmetals do not conduct electricity or heat,
  not malleable or ductile, brittle.
• Metalloids Elements that have properties of
  both metals and nonmetals. Weak conductors of
  electricity.

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Molecules and Molecular Compounds

• Molecule Assembly of two or more atoms tightly
  bound together.
• 7 diatomics H2, O2, N2, F2, Cl2, Br2, I2.
• Molecular Compounds Compounds that are composed
  of molecules.
• Most molecular substances contain only nonmetals.

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Molecules and Molecular Compounds

• Molecular formula Contains the actual number of
  atoms present in the molecule
• H2O2 2 hydrogen atoms and 2 oxygen atoms.
• Empirical formula Gives the relative numbers of
  atoms in the molecule
• HO 1 hydrogen atom 1 oxygen atom.

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Ions and Ionic Compounds

• Metal atoms tend to lose electrons to form
  cations.
• Nonmetal atoms tend to gain electrons to form
  anions.
• Polyatomic ion atoms joined together as a
  molecule, but they have a net positive or
  negative charge.

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Ions and Ionic Compounds

• Representing ions
• Use a superscript to the right of the element
  symbol to indicate the charge on the ion.
• Ions are isoelectronic to the nearest noble gas.

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Ions and Ionic Compounds

• Ionic compound Compound that contains both
  negatively and positively charged ions..
• Ionic compounds are made from a metal and a
  nonmetal.

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Ions and Ionic Compounds

• Ionic compounds have different physical and
  chemical properties than its constituent ions.
• Compound must be electrically neutral.

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Naming Inorganic Compounds

• 1. A. Positive Ions Cations
• Cations formed from metal atoms have the same
  name as the metal.
• B. Transition metal Multiple charges.
• Stock System name of the metal, roman numeral
  indicating charge, plus ion.
• Latin system Use the Latin name plus the suffix
  ous (lower charge) or ic (higher charge).

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Naming Inorganic Compounds

• C. Cations formed from nonmetal ions have names
  that end in ium.
• 2. Negative Ions
• A. Monoatomic anions have names formed by
  replacing the end of the element with ide.

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Naming Inorganic Compounds

• Polyatomic anions containing oxygen have names
  ending in ate or -ite.
• Called the oxyanions. The ending ate is used for
  the most common oxyanion of an element.
• Suffix ate (more oxygen) or ite (less oxygen)
• Some have the suffix ide i.e. hydroxide ion, OH-.

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Naming Inorganic Compounds

• If the oxyanion contains four members than a
  prefix is used
• Per indicates one more oxygen atom than the
  oxyanion ending in ate.
• Hypo indicates less oxygen atom than the
  oxyanion ending in ite.
• ClO3- chlorate ion ClO4- perchlorate ion
• ClO2- chlorite ion ClO- hypochlorite ion

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Naming Inorganic Compounds

• C. Anions derived by adding H to an oxyanion are
  named by adding as a prefix the word hydrogen or
  dihydrogen as appropriate
• CO32- carbonate ion HCO3- hydrogen carbonate
  ion
• Older system uses bi for adding a hydrogen
• HCO3- bicarbonate ion
• 3. Ionic Compounds
• Name of the compound consists of the cation name
  plus the anion name.

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Naming Inorganic Compounds

• Names and Formulas of Acids
• 1. Acids based on anions whose name end in ide
  have the hydro prefix and an ic ending
• Anion Cl- chloride Acid HCl hydrochloric
  acid.
• Anion S2- sulfide Acid H2S hydrosulfuric
  acid.

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Naming Inorganic Compounds

• 2. Acids based on anions whose names end in ate
  or ite
• Anion ate Acid ic
• Anion- ite Acid ous
• ClO3- chlorate HClO3 chloric acid
• ClO2- chlorite HClO2 chlorous acid

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Naming Inorganic Compounds

• Names and Formulas of Binary Molecular Compounds
• 1. The name of the element farthest to the left
  in the periodic table is written first (except
  oxygen.)
• N2O4 dinitrogen tetroxide
• Cl2O dichlorine monoxide

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Naming Inorganic Compounds

• 2. If both elements are in the same group, the
  lower one is named first.
• SO2 Sulfur dioxide
• 3. The name of the second element is given an
  ide ending.
• CO2 Carbon dioxide

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2.8 Naming Inorganic Compounds

• 4. Greek prefixes are used to indicate the number
  of atoms of each element.
• P4S10 tetraphosphorous decasulfide.

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Naming Inorganic Compounds

• Determining Charge
• Main group cation and anion i.e. AlCl3. Note how
  the charge is neutral, balance charge using
  anion.
• Transition metal determine the charge on the
  metal by using the charge on the anion (fixed),
  then the cation (variable). i.e. Fe2O3.

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Simple Organic Compounds

• Hydrocarbon only contain carbon and hydrogen.
• Alkane Each carbon is bonded to four other
  atoms. After five or more carbon atoms use
  prefixes penta, hexa.
• Methane, Ethane, Propane.

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Simple Organic Compounds

• Derivatives of Alkanes
• Functional group Specific group of atoms i.e.
  Alcohol OH.
• Nomenclature Add the suffix ol.
• Methanol, ethanol, butanol.