The Atom, The History, and The Periodic Table (Chemical Naming and Formula Writing)

1
The Atom, The History, and The Periodic
Table(Chemical Naming and Formula Writing)

• Unit 3
• Part I
• Chemistry

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Theories Involving Matter and Atoms

• Democritus
• Greek
• 400 B.C. Greeks all matter is
• composed of 4 fundamental
• substances
• Earth, air (wind), water fire
• Democritus matter is composed
• of small, indivisible parts, (Greek
• atomos)
• No experiments to test no definitive conclusion
• First scientist to discover the idea of an atom

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Alchemy (next 2000 years)

• Mixture of science and mysticism.
• Lab procedures were developed, but alchemists did
  not perform controlled experiments like true
  scientists.

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Theories cont.

• Aristotle
• Greek
• Rejected the idea of atoms
• Expanded on idea of 4
• elements
• Reasoning from logic observation
• Also in line with religion

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Theories cont.

• Lavoisier
• French chemist
• Father of Modern Chemistry
• Experimented and measured the masses of
  reactants and products of various reactions
• Law of Conservation of Matter

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Theories cont.

• Proust
• French chemist
• Showed that a given compound always contains the
  same proportion of elements by mass
• Law of Definite Proportions

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Theories cont.

• John Dalton (1803)
• English schoolteacher
• Thought about atoms as particles that might
  compose elements
• Billiard Ball Model
• atom is a uniform, solid sphere
• Elements combine in the ratio of small whole
  numbers
• Law of Multiple Proportions

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John Dalton
Daltons Four Postulates
1. Elements are composed of small indivisible
particles called atoms. 2. Atoms of the same
element are identical. Atoms of different
elements are different. 3. Atoms of different
elements combine together in simple proportions
to create a compound. 4. In a chemical reaction,
atoms are rearranged, but not changed.
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Henri Becquerel (1896)

• Discovered radioactivity
• spontaneous emission of radiation from the
  nucleus
• Three types
• alpha (?) - positive
• beta (?) - negative
• gamma (?) - neutral

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J. J. Thomson (1903)

• Cathode Ray Tube Experiments
• beam of negative particles
• Discovered Electrons
• negative particles within the atom
• Plum-pudding Model

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J. J. Thomson (1903)

• Plum-pudding Model
• positive sphere (pudding) with negative
  electrons (plums) dispersed throughout

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Ernest Rutherford (1911)

• Gold Foil Experiment
• Discovered the nucleus
• dense, positive charge in the center of the atom
• Nuclear Model

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Ernest Rutherford (1911)

• Nuclear Model
• dense, positive nucleus surrounded by negative
  electrons

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Niels Bohr (1913)

• Bright-Line Spectrum
• tried to explain presence of specific colors in
  hydrogens spectrum
• Energy Levels
• electrons can only exist in specific energy
  states
• Planetary Model

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Niels Bohr (1913)
Bright-line spectrum

• Planetary Model
• electrons move in circular orbits within specific
  energy levels

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Erwin Schrödinger (1926)

• Quantum mechanics
• electrons can only exist in specified energy
  states
• Electron cloud model
• orbital region around the nucleus where e- are
  likely to be found

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Erwin Schrödinger (1926)

• Electron Cloud Model (orbital)
• dots represent probability of finding an e- not
  actual electrons

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James Chadwick (1932)

• Discovered neutrons
• neutral particles in the nucleus of an atom
• Joliot-Curie Experiments
• based his theory on their experimental evidence

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James Chadwick (1932)

• Neutron Model
• revision of Rutherfords Nuclear Model

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Atoms

• Best current representation of the atom is a
  charged-cloud
• Smallest particle of an element that retains its
  properties
• Electrically neutral Protons electrons
•  Parts of an atom
• Nucleus (contains both protons and neutrons)
• Electron Cloud (contains electrons)

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Parts of an Atom

• Nucleus
• Small, dense center of positive charge.
• Protons
• Positively charged particles within the nucleus
• Neutrons
• Particles within the nucleus with no charge
• About the same mass as protons

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Parts of an Atom cont.

• Electron Cloud
• Empty Space
• Holds electrons, which are densely packed
• Negatively charged particles found outside the
  nucleus
• Much smaller than protons and neutrons
• Proton/neutron mass 1.67 x 10-24 g
• Electron mass 9.11 x 10-28 g
• More about electron behavior later

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Picture of an atom
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Atoms and Elements

• What is the difference between an element and an
  atom?
• An atom is a single example of an element.
• An element is the collective term for many atoms
  of a single substance.

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Periodic Table of Elements Structure

• Listed in order of inc. atomic
• Columns Families or GROUPS
• Have similar chemical properties
• Referred to by the number and letter (A or B)
  over the column
• Many have special names
• Rows PERIODS

• Contains info on physical properties
• (i.e. mp, bp, density, physical states, etc)

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Element Characteristic

• Each square usually contains
• Element name
• Element symbol
• Atomic number
• The number of protons
• Symbolized at Z
• Atomic mass or mass number
• Atomic mass decimal mole weight
• to the average mass numbers of all isotopes
• Mass number rounded mole weight
• Mass number The sum of the number of the protons
  and the number of neutrons
• State of matter (usually)

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Short Handing Element Characteristics

• Symbolizing
• AzX
• A mass (NO DECIMALS!)
• Z atomic ( of protons electrons)
• X symbol of the element

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Isotopes

• Isotopes
• Atoms with the same number of protons but a
  different number of neutrons
• Atoms of the same element have the same atomic
  number but different mass numbers

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Isotopes cont.
Potassium-39 Potassium-40 Potassium-41
Protons 19 19 19
Neutrons 20 21 22
Electrons 19 19 19
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Isotopes cont.
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Isotopes cont.
The diagram shows three oxygen isotopes. Each
nucleus has eight protons (gray) and eight, nine,
or ten neutrons (green).
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Oxidation Numbers

• Indicate the charge on the ion
• Found on the periodic table
• Common oxidation numbers are given in additional
  table
• Note
• Group 8 elements do not form ions No ox
• Transition metals have multiple ox s

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Valence Electrons

• Electrons in the outer most shell
• The electrons on an atom that can be gained or
  lost in a chemical reaction
• More on this to come with Electron
  Configurations.

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Alkali Metals

• Group IA (except H)
• Li, Na, K, Rb, Cs, Fr
• Soft, gray metals
• Very reactive
• Especially with water
• React with water to form bases
• Alkali basic

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Alkali Metals cont.

• Why are they so reactive?
• One electron in their outer shell
• Only 1 electron away from a full outer shell
• Want to lose that electron easily react
• So reactive dont occur as free elements

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Interesting Tidbits

• Li used as depression medication
• Cs used in atomic clocks
• Fr predicted by Mendeleev in 1870s discovered
  in 1939
• Less than 1 oz. of Fr exists at any given time

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Alkali Earth Metals

• Group IIA
• Be, Mg, Ca, Sr, Ba, Ra
• Shiny, silvery-white metals
• Harder and denser than Group IA
• Distributed in rock formations
• Reactive but not as reactive as Group IA
• 2 outer electrons
• Want to lose 2 to have a complete outer shell
• 2 oxidation number

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Interesting Tidbits

• Used in pyrotechnics and fireworks
• Mg white Sr red Ba green

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Calcium

• Widely distributed as limestone
• Important biologically for bones and teeth

• Compounds of Calcium
• - CaCO3 limestone
• - CaO lime or quicklime
• - Ca(OH)2 limewater treat antacid

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Nobel Gases

• Group VIIIA
• He, Ne, Ar, Kr, Xe, Rn
• Aka Inert Gases b/c they are unreactive
• Aka Rare Gases b/c they are very rare on
  Earth
• Colorless, tasteless, odorless

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Nobel Gases cont.

• Why are they unreactive?
• Their outer shells are full
• Recall the outer shell electrons are the ones
  involved in bonding
• When the outer shells are full, these electrons
  cant bond and, therefore, react with other
  elements
• Used in
• Lighting
• Fill light bulbs, neon lights, black lights,
  flashlight bulbs, strobe lights, headlights, etc.

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Halogens

• Group VIIA
• F, Cl, Br, I, At
• Non-metals
• - Exist in all 3 states at room temperature
• Solid I, At
• Liquid Br
• Gas F, Cl
• Very reactive
• Most often, bond with metals
• Diatomic (F2, Cl2, etc.)

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Halogens cont.

• Why are the halogens diatomic?
• 1 electron away from a full outer shell
• Too reactive/unstable by itself
• Bonds with another atom so both have 8
• Dot diagrams
• What is the mole weight of chlorine gas?
• Which is more reactive, F2 or Cl2?
• F2

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Transition Metals

• Middle section of the periodic table
• Exhibit metallic properties
• Ductile
• Malleable
• Good conductors of heat and electricity
• Silvery luster (except Cu and Au)

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Ions

• Atoms that have a positive or negative charge
• To become an ion, an atom gains or loses
  electrons
• Cation positively charged ion
• Lose electron(s)
• Metals form positive ions
• Anion negatively charged ion
• Gain electron(s)

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Polyatomic Ions

• Def tightly bound groups of atoms that behave as
  a unit and carry a charge
• Ion composed of more than one atom
• List of common polyatomic ions
• Ex
• SO4-2
• NO3-1 Must memorize these
• CO3-2 polyatomic ions!
• PO4-3
• OH-1
• C2H3O2-1
• NH41