Video Transcript
The salt, sodium chloride, can be
formed from the reaction between an acid and an alkali. What is the chemical formula of
sodium chloride?
A chemical formula is an expression
of chemical symbols and numerical subscripts that represents the composition of a
molecule or one unit of a compound. An example of a chemical formula is
H2O. Capital H is the chemical symbol of
hydrogen, and capital O is the chemical symbol of oxygen. The subscript two after hydrogen
means that there are two atoms of hydrogen in one molecule of H2O. When no value is written, only one
atom of that element is present in the molecule or unit.
To answer this question, we need to
determine the chemical formula of a compound from its name. In order to write a chemical
formula from a name, we need to know two key pieces of information. We need to identify what elements
the compound contains and also what type of compound it is, covalent or ionic. We can determine what elements the
compound contains by looking at the name and the periodic table.
Sodium is a metallic element found
in the first column of the periodic table. The name chloride doesn’t appear on
the periodic table exactly as written. This is because when compounds are
named, the end of the second element name is changed to I-D-E. So the name chloride represents the
element chlorine, a nonmetal found in column 17 of the periodic table. We can see that sodium chloride is
a compound formed when a metal and a nonmetal combine. In addition, when we look at the
name, no prefixes appear in front of sodium or chloride. This all points to sodium chloride
being an ionic compound.
Now we’re ready to write the
chemical formula of sodium chloride, an ionic compound. First, we’ll write the chemical
symbol and valence for each element in the compound. We can determine the valence of
many elements by looking at the periodic table. Sodium in column one has a valence
of one. Chlorine in column 17 also has a
valence of one. Next, we crisscross the valence
values writing each valence value as a subscript to the right of the opposite
chemical symbol. This gives us Na1Cl1. But ones in a chemical formula
don’t have to be written. So, the chemical formula of sodium
chloride is NaCl.
