Chapter #8 Ionic Compounds: Names and Formulas 8.1
Chapter #8 Ionic Compounds: Names and Formulas 8.1 Writing Chemical Formulas Compounds are pure substances made of more than one kind of atom joined together. The atoms are held together with chemical bonds. Compounds come in two basic types: covalent
and ionic. Covalent compounds share electrons to form molecules. Example: water Ionic Compounds Ionic solids exist as a solid in the form of an ionic lattice. The positive ions attract all of the negative ions, and vice versa.
In ionic compounds, atoms gain or lose electrons to form ions. Example: NaCl Polyatomic Ions Covalent and ionic bonds can occur together A molecule can gain or lose electrons to become charged, forming a polyatomic ion. Polyatomic ions form compounds like other ions.
Example: Ammonium ion (NH4+) There are many types of polyatomic ions, but they occur in a few basic 8.2 Ion Charge 8.3 Naming Ionic Compounds Naming Monovalent Compounds
Each different compound has its own name which tells what elements are in the compound Monovalent elements have only one ion charge 1. 2. e.g. lithium (1+), calcium (2+), aluminum (3+)
When naming, there are 2 steps to follow: Write the name of the metallic element first Write the name of the non-metallic Some tricky endings: hydrogen hydride oxygen oxide phosphorus phosphide nitrogen nitride Examples: 1. Magnesium + oxygen _Magnesium Oxide_ 2. Chlorine + calcium __Calcium Chloride__ 3. ZnO ___Zinc Oxide_____ 4. Al2S3 ___Aluminum Sulphide_____
Writing Monovalent Formulas 1. 2. To write the chemical formula of a compound, do the following: Write the metal and non-metal elements in their ion form (metal always goes first) Rewrite the elements without ion charges, and then crisscross the numbers (omit + and - signs)
the numbers are written as subscripts If there is a common factor, reduce the subscripts the number 1 is never written Examples Naming Multivalent Compounds Also referred to as transition metals, these only occur after atomic number 20 and have more than one ion charge
e.g. lead (2+, 4+), iron (3+, 2+), gold (3+, 1+) When naming these compounds, you must use Roman Numerals to indicate which ion charge has been used I=1 1. 2. II = 2 III = 3
IV = 4 V=5 VI = 6 There are 2 steps to follow: Write the name of the metallic element first, the non-metallic element second and change its ending to -ide Work backward from the non-metal ion charge to determine the metal ion charge and write the roman numeral in brackets after the metal Examples 3.
AuCl ______Gold (I) Chloride________ 4. Fe2O3 _____Iron (III) Oxide________ Writing Multivalent Formulas 1. To write the chemical formula, do the following: Write the metal and non-metal elements in their ion form
the Roman numeral tells you which ion charge to use for the metal Rewrite the elements without ion charges, and then crisscross the numbers 2. If there is a common factor, reduce the subscripts Examples
Naming Polyatomic Compounds Group of atoms with a common name and ion charge. e.g. hydroxide (OH)1-, sulphate (SO4)2- It is simple to identify compounds containing polyatomic ions because the formula has 3 or more different elements There are 2 steps to follow: 1.
2. Positive polyatomic ions are written first, like metals Negative polyatomic ions are written second and the name of the ion is not changed Examples 3. Calcium + nitrate _____Calcium Nitrate_________ 4. Hydrogen + dichromate ____Hydrogen Dichromate______ 5.
K2SO4 _____Potassium Sulphate________ 6. KMnO4 ____Potassium Permanganate______ Writing Polyatomic Formulas To write the chemical formula, do the following: 1. Write the metal and non-metal elements in their ion form (polyatomic is always written in brackets) 2. Rewrite the elements without ion charges, and then crisscross the numbers (keep the brackets)
If there is a common factor, reduce the subscripts if you have only one of a polyatomic group, omit the brackets Examples
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