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6a - Molecular Compounds

Science Focus 9 pg 136 -138

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Properties of Ionic & Molecular Compounds

Ionic

  • Composed of a metal and non-metallic elements
  • Forms ions in solution.
  • Conducts electricity
  • Solid at room temperature.
  • High melting and boiling point
  • brittle

Molecular

  • Composed of only non-metallic elements
  • Does not form ions in solution.
  • Usually does not conduct electricity.
  • Solid, liquid, or gas at room temperature.
  • Low melting and boiling point

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Reading Chemical Formulas

  • If there is more than one atom of an element, a subscript follows the element’s symbol.

Ex: Glucose, C6H12O6(s)

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Ex: ammonium hydroxide, NH4,OH(aq)

    • If there is no subscript then there is only 1 atom of that element.

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  • CHALLENGE Ex: magnesium nitrate, Mg(NO3)2(l)

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Identifying Molecular Compounds

If ALL elements in the compound are non-metals.

Ex: which of the following are molecular?

CH3OH Na2CrO4

AgCl Cl2O

H2S O2

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How are Molecular Compounds formed?

Share valence electrons to make a full octet

Ex: HF

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Prefixes

  • Prefixes (added to the beginning of a word) are used to identify the number of each atom in a molecular compound

# of Atoms

Prefix

1

mono

2

di

3

tri

4

tetra

5

penta

6

hexa

7

hepta

8

octa

9

nona

10

deca

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Binary Compounds

Binary compounds are made of only TWO elements.

Ex: Which of the following could be considered binary compounds?

CH3OH Na2CrO4

AgCl Cl2O

H2S O2

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Naming Binary Molecular Compounds

  • Write the entire name of the first element
  • Change the ending on the name of the second element to “–ide”
  • Use a prefix to indicate the number of each type of atom in the formula
  • Exception: when the first element has only one atom, the prefix mono is not used.

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Example

Name the following:

  • CS2
  • O6F2
  • NI3
  • C4H10

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Writing Formulas for Molecular Compounds

  • Write the element symbols in the same order as they appear in the name.
  • Use subscripts to indicate the numbers of each type of atom.
  • Do not include a subscript 1, it is implied

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Example

Write the formula for the following

  • Triphosphorus heptoxide
  • Carbon tetraiodide
  • Bromine pentafluoride
  • Disulfur dihydride

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Practice

Complete the learning guide for topic 6a - Molecular compounds