4 Writing and Naming
4 Writing and Naming
4 Writing and Naming
Crisscross Method – is a method of finding out the chemical formula of a metal and non-metal that
combine to form an ionic bond
(RULES)
1.) Identify the charge of the element. Drop down the charge of each element (cross multiply to
become subscript)
Ex. H+1 + O-2= H2O1
2.) When the valence number is 1, Subscript 1 is not written Ex.H2O
3.) When the oxidation numbers of both elements are numerically equal but greater than 1, the
subscript is not also written.
Ex. Mg+2+ O-2= Mg2O2 (MgO)
4.) All radicals take more than one (the subscript is 2 or more) must be enclosed parenthesis ().
Ex. Zn+2 + NO3-1= Zn (NO3)2
5.) All subscript must be reduced to lowest terms (except for molecular or covalent compound)
Ex. C+4 + O-2 = C2O4 (CO2)
Empirical Formula - The empirical formula or the simplest formula of a compound gives the smallest
whole number ratio of atom that make up the compound.
This can be determined from the percentage composition of the compound or form the experimental
determined mass relationship of the elements that make up compounds.
Molecular Formula –it is formula giving the number of atoms of each of the elements present in one
molecule of a specific compound.
Ex. 1.) A compound is found to contain 27.3g of carbon,4.55g of hydrogen and 36.4g of oxygen. The
molecular weight is found to be 90g/mol. Calculate its molecular formula.
C = 1x 12 = 12
H = 2x 1 = 2
O = 1x 16 =16
EF mass = 30g/mole
90𝑔/𝑚𝑜𝑙
MF = x CH2O
30𝑔/𝑚𝑜𝑙
MF= 3 x CH2O
MF= C3H6O3
Naming Chemical Compounds
1.) Binary Compounds
- Consist of 2 elements (Metal with fixed valence number + non-metal)
[ Name of metal + stem name of non-metal + IDE]
KI (Potassium Iodide)
b. Classical Method – using the suffix – ous (lower oxidation no.) -ic (higher oxidation no.)
GREEK PREFIX
Al(NO3)3 – Aluminum
Nitrate MONO 1 HEXA 6
HCl- Hydrogen Chloride (Hydrochloric Acid) HF- Hydrogen Fluoride (Hydrofluoric Acid)
HBr- Hydrogen Bromide (Hydrobromic Acid) Hl- Hydrogen Iodide (Hydroiodic Acid
Ex.