Sec 4 Mid-Year Review

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Sec 4 Mid-Year Review
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History of the atom

• Evolution of the very small

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In the beginning

• Democritus

• Aristotle

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Clash of two philosophers

• Democritus
• Discontinuous Hypothesis
• All matter was made of tiny particles called
  atoms
• These particles could not be divided

• Aristotle
• Continuous Hypothesis
• All matter was made of 4 elements (earth, wind,
  water and fire)
• You could continue to divide matter as much as
  you want

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Modern Chemistry Lavoisier
Nothing is destroyed and nothing is created
The Law of Conservation of Mass
(1743-1794)
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The law of Conservation of mass
The total weight of the reactants before a
reaction, must be equal to the total amount of
products after a reaction
(1743-1794)
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Lavoisiers questions

• 1. How many grams of salt will be created if I
  mix 20g of sodium with 35g of chlorine?
• 2. If I wanted to create 18g of water, how many g
  of oxygen do I need to combine with 2g of
  Hydrogen?

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• Dalton

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Dalton

1. Matter is made of indivisible particles
2. These particles can combine together in
   predefined proportions
3. The atoms of a same element are the same
4. The atoms of one type of element differs from
   another
5. During chemical reactions no atom is destroyed

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Thomson and the Cathode Ray Tube
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• Observation 1
• the propeller moved
• Observation 2
• All cathode ray tubes do the same
• Observation3
• The cathode ray is attracted to the negative
  pole of a magnet

• Particles (smaller than atoms) are being emitted
  and are pushing the propellers
• The particle is common to all atoms
• The particles forming the stream are negative

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Rutherford
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• As most alpha particle traveled through the gold
  sheet, atoms are mostly made of empty space.
• Those deviated, encountered similar positive
  charges and were repelled
• Those that bounced back

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• Bohr Established the energy levels around the
  nucleus
• Chadwick Discovered the neutrons (neutral glue
  that keeps the protons together in the atom)

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History questions

• Place the following scientist/philosophers in
  chronological order
• Chadwick, Dalton, Rutherford, Bohr, Democritus
• Give two characteristics for each of their
  models.

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Exercise Break

• Place on the given timeline, the scientist and
  the name of the atomic model in chronological
  order.

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The periodic table
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Review of the Atom
Proton () Neutron (o) Electron (-) Orbit
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Connections

• The information held in the picture is also
  written in the periodic table.

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Be
Beryllium
9.01
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How it works

• Each column of the table are called
  groups/families.
• Each member of a group has the same number of
  valence electrons

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Group 1A Alkali

• 1st column except hydrogen
• They are soft and highly reactive
• Must be stored in oil due to their high
  reactivity and are never found in their elemental
  state in nature but always as a compound

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Group 2A Alkaline Earth Metals

• Highly malleable and reactive, they burn easily
  in presence of heat
• Never found in their elemental state but can be
  exposed to air (often stored in oil)
• They often form the compound of rocks

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Group 7A Halogens

• Salt creator
• Second to last column
• Non-metals that react easily to form compounds
  including salts

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Group 8A Noble Gases

• Final column
• Very stable
• Can be found in their elemental state

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How does it work?

• Each row is called a period numbered 1 to 7
• Not all periods have the same length

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Important Definitions

• A Period corresponds to the rows of the periodic
  table.
• All elements of the same period have the same
  number of orbits/shells

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Other divisions

• The staircase indicates the separation of the
  metals (under the stair case) from the non-metals
  (above the stair case).
• The metalloids are located on either side.

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Other divisionsMetals

• Generally good conductors of electricity and heat
• Ductile and malleable
• Usually shiny
• All are solid at room temperature (except Hg)
• Many react with acids

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Other divisionsNon-Metals

• Poor conductors of electricity and heat
• Many are gases at room temperature
• The solid non-metals can easily be reduced to
  powder

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Other DivisionsMetalloids

• Properties depend on conditions
• Seven elements that share properties with the
  metals and non-metals.
• Semi conductors (are good conductors in certain
  conditions, bad in others

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Representing the invisible
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General Rules

• Electrons seek to fill the shells nearest the
  nucleus before occupying a further shell
• The 1st shell contains a maximum of 2 electrons
• The 2nd shell contains a maximum of 8 electrons
• The third shell 8

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Lewis Notation

• Notation in which only the valence electrons
  (electrons on the last shelf) are represented

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Rutherford-Bohr

• Important rules
• the period indicates the number of shells
• the group indicates the number of valence
  electrons
• the atomic number indicates the total number of
  protons and electrons in the atom

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Chemical Changes
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Chemical Reactions

• a) Definition
• A reaction that alters the nature and
  characteristic properties of matter.
• The atoms are rearranged.
• New molecules are formed

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Chemical Reactions

• b) Observable characteristics
• A chemical reaction occurs when
• A gas is released
• Heat is absorbed (endothermic) or released
  (exothermic)
• Light is emitted
• The color changes
• A precipitate forms

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Chemical Reactions

• c) Types of chemical reactions
• i) Basic reactions
• Synthesis
• Two or more reactants become one product
• Decomposition
• One reactant is decomposed into two or more
  products
• Oxidation
• A reaction where one of the reactants is oxygen
  (O2)
• Precipitation
• A reaction where two liquid reactants form a
  solid product

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Chemical Reactions

• ii) Other chemical reactions
• Acid-Base Neutralization
• Reactants Acid Base
• Products Water Salt
• Combustion
• Type of oxidation that releases a large amount of
  energy
• Combustion requires
• Oxidation agent
• Ignition temperature
• Fuel

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Chemical Reactions

• Cellular respiration
• Takes O2 glucose to form CO2 water energy
• Photosynthesis
• Takes CO2 water energy to form O2 glucose

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• When practicing the stop, drop and roll
  technique, what part of the combustion (fire)
  triangle are we attempting to control?
• Name 5 differences between photosynthesis and
  cellular respiration.
• What kind of chemical reaction occurs when a
  substance increases in mass by heating it?
• Give three signs of a chemical change

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• Balance the following equations
• (NH4)2Cr2O7 ? N2 H2O Cr2O3
• 4Fe 3O2 ? 2 Fe2O3
• Before After
• Fe 1 x4 4
• O 2x3 3 x 2
• N2 H2 ? NH3

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Molecules and Solutions
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Important Definitions

• Molecule
• A group of two or more chemically bonded atoms
• Ion
• - an atom that has become electrically
  charged by loosing or gaining one or more
  electrons
• An ion is negatively charged when it has more
  electrons (-) than protons ()
• An ion is positively charged when it has less
  electrons than protons

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Solutions

• A) Characteristics of solutions
• 1. Concentration
• 2. Electrical Conductivity
• 3. pH
• pH of 7 neutral
• pH above 7 base
• pH below 7 acid

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Properties of solutions

• 1. Concentration
• Definition
• The amount of solute placed in a given solvent
• Once the concentration of a solution reaches the
  solubility point we have a saturated solution
• Can be measured in (g/100ml)
• Can be measured in g/L (g/1000 ml)
• Can be measured in ppm (g/1 000 000 ml)