CHM 101 GENERAL CHEMISTRY I (2 Units)
Lecture 2 Lecturers: Mr. Ogundele, O.D.
Mrs. Ajobiewe, O.D.
CHEMICAL SYMBOLS, FORMULAS AND EQUATIONS
Chemical symbols are the chemist abbreviated form of writing or representing the names of
elements. The principle applied when representing element was put forward by Berzkelius in 1814.
The principle entails the following.
1. The first principle uses the first letter, (written in capital letter) of the name of an element
as its symbol. Examples includes; Hydrogen (H), Boron (B), Carbon (C), Nitrogen (N),
Oxygen (O), Fluorine (F), Phosphorus (P).
2. When the first letter had already been adopted. The first letter and any other letter in the
name of the element is used as the symbol. Here, the first letter is written in capital letter
while the second letter is written in small letter. Examples includes; Helium (He), Lithium
(Li), Beryllium (Be), Neon (Ne), Magnesium (Mg), Aluminum (Al).
3. When these two methods have been adopted, the symbol of the elements is then derived
from the Latin names of the elements using method one and two above. Example includes;
Sodium (Natrium, Na), Potassium (kalium, K), Iron (Ferrum, Fe) and Copper (Caprum,
Cu).
As earlier stated, these abbreviations are written in capital letter when the symbol is only one
letter. In cases where it has two letters, only the first letter is written in capital letter, while the
other letter is written in small letter.
The symbols of an element represent
1. One atom of the element
2. A definite mass of the element often expressed in grams
Chemical Formula
A chemical formula is an expression involving chemical symbols and numerical. The symbols
represent the different types of elements present (i.e. composition) in the compound while the
numerical indicates the number of atoms in one molecule of a compound, when it is written as a
subscript after the symbol of the element. Example is H2 which show that it contains two atoms
of hydrogen; H2SO4 shows that the chemical formula contains two atoms of hydrogen, one atom
of sulphur and four atoms of oxygen. There are basically three types of chemical formulas namely
empirical, molecular and structural formulas.
, Empirical Formula
This is the simplest formula of a compound that shows the simplest whole number ratio of atoms
of different elements present in a compound. Hence the empirical formula of the compound
C2H4O2 is CH2O, where the integer multiplier is 2. Normally, the results of chemical analysis are
expressed as percentage by mass of each constituent element, so to know the identity of the
compound the empirical formula will be calculated from the percentage composition. Calculation
of the empirical formula of the compound entails first determining the relative number of moles
of atoms of each element present in the given mass of the compound. Thereafter, the number of
moles of each element is then divided by the smallest number of the mole present.
Molecular Formula
This is a formula of a compound that shows the exact (actual) number of atoms of different
element present in a compound. The molecular formula is given by
Molecular Formula = Empirical formula X integer multiplier
Molecular formula = n (Empirical formula)
Sometimes, empirical formula and molecular formula can be the same. This is when the molecular
formula cannot be reduced further. Examples includes NH3 (ammonia), CaCO3 (calcium
trioxocarbonate (IV), H2O (water) CO2 (carbon(IV)oxide) etc.
Structural Formula
The structural formula shows the way that atoms are joined together in a molecule. Knowledge
of the structural formula of compound is important in the study of chemistry because some
compounds may have the same molecular formula and empirical formula and the only thing that
will show that the compounds are different is their structural formula. As an illustration, Butanol
and ethyl ether have the same empirical and molecular formula as C4H10O. The only thing that
differentiates the two and gives both their respective unique set of properties is the structural
formula.
Predicting Formulas from Valencies
Recall that we earlier defined vacancy as the number of electrons an atom can lose, gain or share
to acquire an octet or duplet electronic configuration. The formulas of compounds can be
deduced from the valences of component elements or radicals using the following rules
Rule 1: Write the symbols of the component elements or radicals
Rule 2: Place the valences of each elements or radical below the respective element or radical
Rule 3: Interchange the valences and write them as subscript immediately after the respective
symbols of the atoms.
Rule 4: Write the formula of the compound by first writing the metals followed by the non- metal
Lecture 2 Lecturers: Mr. Ogundele, O.D.
Mrs. Ajobiewe, O.D.
CHEMICAL SYMBOLS, FORMULAS AND EQUATIONS
Chemical symbols are the chemist abbreviated form of writing or representing the names of
elements. The principle applied when representing element was put forward by Berzkelius in 1814.
The principle entails the following.
1. The first principle uses the first letter, (written in capital letter) of the name of an element
as its symbol. Examples includes; Hydrogen (H), Boron (B), Carbon (C), Nitrogen (N),
Oxygen (O), Fluorine (F), Phosphorus (P).
2. When the first letter had already been adopted. The first letter and any other letter in the
name of the element is used as the symbol. Here, the first letter is written in capital letter
while the second letter is written in small letter. Examples includes; Helium (He), Lithium
(Li), Beryllium (Be), Neon (Ne), Magnesium (Mg), Aluminum (Al).
3. When these two methods have been adopted, the symbol of the elements is then derived
from the Latin names of the elements using method one and two above. Example includes;
Sodium (Natrium, Na), Potassium (kalium, K), Iron (Ferrum, Fe) and Copper (Caprum,
Cu).
As earlier stated, these abbreviations are written in capital letter when the symbol is only one
letter. In cases where it has two letters, only the first letter is written in capital letter, while the
other letter is written in small letter.
The symbols of an element represent
1. One atom of the element
2. A definite mass of the element often expressed in grams
Chemical Formula
A chemical formula is an expression involving chemical symbols and numerical. The symbols
represent the different types of elements present (i.e. composition) in the compound while the
numerical indicates the number of atoms in one molecule of a compound, when it is written as a
subscript after the symbol of the element. Example is H2 which show that it contains two atoms
of hydrogen; H2SO4 shows that the chemical formula contains two atoms of hydrogen, one atom
of sulphur and four atoms of oxygen. There are basically three types of chemical formulas namely
empirical, molecular and structural formulas.
, Empirical Formula
This is the simplest formula of a compound that shows the simplest whole number ratio of atoms
of different elements present in a compound. Hence the empirical formula of the compound
C2H4O2 is CH2O, where the integer multiplier is 2. Normally, the results of chemical analysis are
expressed as percentage by mass of each constituent element, so to know the identity of the
compound the empirical formula will be calculated from the percentage composition. Calculation
of the empirical formula of the compound entails first determining the relative number of moles
of atoms of each element present in the given mass of the compound. Thereafter, the number of
moles of each element is then divided by the smallest number of the mole present.
Molecular Formula
This is a formula of a compound that shows the exact (actual) number of atoms of different
element present in a compound. The molecular formula is given by
Molecular Formula = Empirical formula X integer multiplier
Molecular formula = n (Empirical formula)
Sometimes, empirical formula and molecular formula can be the same. This is when the molecular
formula cannot be reduced further. Examples includes NH3 (ammonia), CaCO3 (calcium
trioxocarbonate (IV), H2O (water) CO2 (carbon(IV)oxide) etc.
Structural Formula
The structural formula shows the way that atoms are joined together in a molecule. Knowledge
of the structural formula of compound is important in the study of chemistry because some
compounds may have the same molecular formula and empirical formula and the only thing that
will show that the compounds are different is their structural formula. As an illustration, Butanol
and ethyl ether have the same empirical and molecular formula as C4H10O. The only thing that
differentiates the two and gives both their respective unique set of properties is the structural
formula.
Predicting Formulas from Valencies
Recall that we earlier defined vacancy as the number of electrons an atom can lose, gain or share
to acquire an octet or duplet electronic configuration. The formulas of compounds can be
deduced from the valences of component elements or radicals using the following rules
Rule 1: Write the symbols of the component elements or radicals
Rule 2: Place the valences of each elements or radical below the respective element or radical
Rule 3: Interchange the valences and write them as subscript immediately after the respective
symbols of the atoms.
Rule 4: Write the formula of the compound by first writing the metals followed by the non- metal
