Chapter 19.2 Chemical Formulas

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Transcript Chapter 19.2 Chemical Formulas

Chapter 19.2
Chemical Formulas
•Oxidation Numbers
•Writing Chemical Formulas
•Ionic Compounds
•Writing Chemical Formulas
•Naming Ionic & Covalent Compounds
•Empirical and molecular Formulas
Oxidation Numbers
An oxidation number indicates how many
electrons will be lost, gained or shared
when bonding occurs
ALL COMPOUNDS have an electrical
charge of ZERO

When the oxidation numbers are added up for
all of the atoms in a compound, the answer
equals zero
Oxidation Numbers &
the Periodic Table
You can use the periodic table to predict
the oxidation numbers for some of the
groups.
The transition metals are an exception,
they have variable oxidation numbers
Periodic Table
Writing Chemical Formulas for Ionic
compounds
1) Write the symbol for the positive .
monatomic ion. (Groups 1, 2, & 13)
2) Write the symbol for the negative
monatomic ion. (Groups 15, 16, & 17)
3) Add superscripts so that the sum of the
oxidation numbers equals zero
Writing a Chemical Formula
CrissCross Applesauce is all you need to
know
Ionic Compounds
Polyatomic Ions
Most Ionic compounds are made up of
more than 2 types of atoms called
Polyatomic Ions. (see table on p. 337)
Treat them just as you would when
working with monatomic ions, except you
need to put the polyatomic ion in brackets
and place the oxidation number as a
superscript on the outside of the bracket.
Naming monatomic Ionic
Compounds
1) Write the root name of the second
element
2) Add “ide” to the root name
3) Write the name of the first element in the
compound
Ex: Na + Cl = NaCl, Naming this chemical
formula would be , Sodium plus Chlorine
equals Sodium chloride.
Naming Compounds with
Polyatomic Ions
1) Write the name of the positive ion first
2) Write the name of the negative ion second
You can use the periodic table or an ion chart to
get the names- There is one on p. 337 of your
text book.
Treat them just as you would the monatomic ions.
Empirical Formula
The simplest whole number ratio by which
the elements combine.
Ex: Hydrogen peroxide, each molecule
contains 2 hydrogen and two oxygen
atoms, but the empirical formula is HO
Molecular Formula
A molecular formula contains the actual
number of atoms for each element in one
molecule of the compound
Ex: Hydrogen peroxide, each molecule
contains 2 hydrogen and two oxygen
atoms, and the molecular formula is H2O2