State the number of atoms present in NH 3(Ammonia) and K2SO4(Potassium Sulphate)
Answers
Answer:FORMULAS: A chemical formula shows the elemental composition of a substance: the
chemical symbols show what elements are present and the numerical subscripts show how
many atoms of each element there are in a formula unit. Examples:
NaCl: one sodium atom, one chlorine atom in a formula unit
CaCl2: one calcium atom, two chlorine atoms in a formula unit
Mg3N2: three magnesium atoms, two nitrogen atoms in a formula unit
The presence of a metal in a chemical formula indicates an ionic compound, which is composed
of positive ions (cations) and negative ions (anions). A formula with only nonmetals indicates a
molecular compound (unless it is an ammonium, NH4
+
, compound). Only ionic compounds are
considered in this Tutorial.
There are tables of common ions in your lecture text, p 56 (cations) and p 57 (anions). A
combined table of these same ions can be found on the inside back cover of the lecture text. A
similar list is on the next page; all formulas needed in this and subsequent Tutorial problems can
be written with ions from this list.
Writing formulas for ionic compounds is very straightforward: TOTAL POSITIVE CHARGES
MUST BE THE SAME AS TOTAL NEGATIVE CHARGES. The formula must be neutral. The
positive ion is written first in the formula and the name of the compound is the two ion names.
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