Science 9: Unit B

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Science 9 Unit B Matter and Chemical Change

• Topic 4 Classifying Elements

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What is an element?

• An element is a pure substance that cannot be
  broken down into anything simpler.
• Everything in the universe is made up of
  elements. Elements in their simplest form exist
  as atoms.

3
Elements and Compounds

• As stated in the Law of Definite Proportions,
  compounds are made up of a fixed proportion of
  elements. Eg. A molecule of water is made up of
  two hydrogen atoms to one oxygen atom.
• Elements can only be destroyed or changed in
  nuclear reactions. Compounds can be changed in
  chemical reactions.

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How are elements organized?

• There are over 100 known elements. Elements are
  organized according to their chemical properties
  and structure in the periodic table. For example
  metals are grouped with metals, non-metals with
  other non-metals and metalloids (have properties
  of both) are placed between them.
• Each element has its own element symbol. Eg.
  Oxygen O. Some elements have been known since
  the beginning of time such as copper. Their
  symbols reflect their old Latin name (CuCuprum).

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What kinds of elements are there?

• There are three basic groups of elements
• Metals (on the left side of the periodic table)
  almost always solid at room temperature, denser
  than other elements, good conductors of heat and
  electricity, shiny and malleable. Usually give
  up/donate electrons in a chemical reaction.

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Non-Metal Elements

• Non-Metals (on the right side of the periodic
  table) mostly gases at room temperature, less
  dense than metals, poor conductors of heat and
  electricity, tend to be dull. Almost always take
  in extra electrons in a chemical reaction.

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Metalloids

• Metalloids (2/3 of the way to the right of the
  periodic table near the staircase) Solid at
  room temperature. Properties are between those of
  metals and non-metals. (ie. they are
  SEMI-conductors of heat and electricity).

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Families are elements which have similar chemical
properties

• In addition to these three general groups, there
  are a number of elements whose properties are so
  similar that they are grouped together in
  families. A family is represented as a column in
  a periodic table. There are four element families
  you need to know for Science 9.
• The reason why they share similar properties is
  based on their VALENCE ELECTRONS.

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Orbitals and Valence Electrons

• All elements need to have their orbitals filled
  up with the right number of electrons to be
  stable. This is why some elements are much more
  reactive than others, and the Noble Gases who
  already have their orbitals filled up do not
  react at all.
• Valence electrons are those electrons which exist
  in the outermost (valence) orbital.

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The Noble Gases

• Column 18 in the periodic table (far right).
• Elements include Helium (He), Neon (Ne), Krypton
  (Kr).
• Chemical properties These elements have all of
  their orbital level filled. They are unreactive
  and only exist as single atoms in nature (ie.
  they do not form compounds).

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Halogen Gases

• Column 17 in the periodic table (right).
• Elements include Fluorine (F), Chlorine (Cl),
  Bromine (Br), Iodine (I).
• Chemical properties These elements need one more
  electron to fill all of their orbital levels and
  are therefore very reactive with metals and
  hydrogen forming compounds.

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Alkali Metals

• Column 1 in the periodic table (far left).
• Elements include Lithium (Li), Sodium (Na),
  Potassium (K),
• Chemical properties These metals need to get rid
  of just one electron to have all of their orbital
  levels filled with the proper of electrons.
  They therefore are very reactive with non-metals.

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Alkali Earth Metals

• Column 2 in the periodic table (left).
• Elements include Beryllium (Be), Magnesium (Mg),
  Calcium (Ca),
• Chemical properties These metals need to get rid
  of two electrons to have their orbital levels
  full. Because they are further away from their
  goal, they are less reactive than Alkali Metals
  or Halogens.