Elements combine to form compounds

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Chapter 6.1

• Elements combine to form compounds

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Definition of Compound

• A substance made up of atoms of two or more
  different elements.

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The Elements of a periodic table

• Can form millions of compounds
• Atoms of different elements are held together by
  chemical bonds.

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Chemical Bonds

• Can hold atoms together in large networks or
  small groups
• Help determine the properties of a compound.

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The properties of a compound depend on

• which atoms the compound contains
• how the atoms are arranged

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The properties of a compound are often very
different from the properties of the elements
that make them.

• Calcium is a soft, silvery, metallic solid.
• Chlorine is a greenish-yellow gas that is
  extremely reactive and poisonous to humans.
• Together they make Calcium Chloride which is a
  non-porous, white solid used to melt ice on
  streets

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Atoms Combine in Predictable Numbers

• A given compound always contains atoms of
  elements in a specific ratio.

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Definition of Chemical Formula

• An expression that shows the number and type of
  atoms joined in a compound.

H20
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Definition of Subscript

• A number written to the right of a chemical
  symbol and slightly below it in a chemical
  formula.
• The subscript of 1 is never used.
• Ex) CO2

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Use the Chemical Formula chart on Page 172

• How many more hydrogen atoms does propane have
  than methane?
• Why is the ratio of atoms in a chemical formula
  so important?

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Use the Chemical Formula chart on Page 172

• How many more hydrogen atoms does propane have
  than methane? 4
• Why is the ratio of atoms in a chemical formula
  so important? Different ratios of elements
  indicate different compounds

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The properties of compounds can be different even
if they are made up of the same elements
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6.1 Review Questions, pg. 173

• Answer each question in complete sentences.

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Answers to 6.1 Review

1. In many cases, they are different
2. There are 45 total atoms in the formula 12
   carbon, 22 hydrogen, and 11 oxygen.
3. Atoms can combine in many different ratios.
4. All atoms are in a 11 ratio.
5. Compare how they react with other substances.
6. The ratios of the compounds are different.

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Ch. 6.2

• Chemical bonds hold compounds together

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Chemical bonds between atoms involve electrons

• When do chemical bonds form?
• When valence electrons (electrons in the
  outermost shell) in the electron cloud around two
  atoms interact

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1. Chemical bonds between atoms involve electrons

• Atoms can transfer electrons (ionic bonds)
• Atoms can share electrons (covalent bonds)
• Chemical bonds give all materials their structure.

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2. Atoms can transfer electrons.

• When is a positive ion formed? A positive ion is
  formed when an atom loses electrons.
• When is a negative ion formed? A negative ion is
  formed when an atom gains electrons

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An elements location on the periodic table can
give a clue as to the type of ions that atoms of
that element will form

• What type of ions do metals form? ions (Group
  1 loses 1 e-(electron),Group 2 loses 2 e-)
• What type of ions do nonmetals form?
• - ions (Gr. 16 gains 2 e-, Gr. 17 gains 1 e-)
• What group on the table does not normally form
  ions? Why?
• Noble Gases (group 18) because their outer
  energy level are full.

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Ionic Bonds

• How are ionic bonds held together? by the force
  of attraction between positive and negative ions
  (transfer electrons)
• Ionic compounds form between all nearby ions of
  opposite chare. These interactions make ionic
  compounds very stable and their crystals very
  strong.
• Octet Rule Rule of 8 ? 8e- in outer shell
  stable atom

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Ionic Bonds

• Ionic bonds form between a metal ( ion) and a
  nonmetal(-ion).

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Ionic Bonds

• Steps for naming a chemical compound
• Take the name of the positive metal element
• Take the name of the negative nonmetal element
• Combine the two names.

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3. Atoms can share electrons.

• Nonmetal atoms usually form bonds by sharing
  electrons.

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Covalent Bonds

• How are covalent bonds held together? By sharing
  electron pairs
• How can you help yourself remember how covalent
  bonds are held together? Co partner

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What does each line in the model stand for?

• A shared pair of electrons

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What is a molecule?

• A molecule is a group of atoms held together by
  covalent bonds.

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4. Chemical bonds give all materials their
structures.

• What is responsible for many of the properties of
  the substances? The structure of their crystals
  and molecules that make it up

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Ionic Compounds

• Have a regular crystal structure
• Because of these rigid structures, when enough
  force is applied to the crystal it shatters
  rather than bends.

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Covalent Compounds

• How are covalent compounds different from ionic
  compounds? Covalent bonds exist as individual
  molecules
• How does molecular structure affect the
  properties of compounds? Ex. We detect scents
  because molecules fit into receptors in our nose
  drugs can work because molecules fit into
  specific receptors in the body.

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Polar Covalent Bond

• The unequal sharing of electrons between two
  atoms that gives rise to negative and positive
  regions of electric charge.

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Ch. 6.2 Review Questions pg.182

1. What part of an atom is involved in bonding?
2. How are ionic bonds and covalent bonds different?
3. What kind of bond would you expect strontium and
   iodine to form? Why? Name the compound

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Ch. 6.2 Review Questions pg.182

• What part of an atom is involved in bonding?
  Electrons in the cloud (valence e-)
• How are ionic bonds and covalent bonds different?
  Ionic bonds transfer and are held together by
  electrical attraction, covalent bonds share
  electrons
• What kind of bond would you expect strontium and
  iodine to form? Why? Name the compound
• Ionic bond metal nonmetal
• Strontium is in Gr. 2 and forms a ion Iodine
  is in Gr. 17 and forms a ion. They have
  opposite charges and attract. Name Strontium
  Iodide