Molecules
Molecule is combination of two or more atoms , these may be of
the same element as oxygen molecule O2
or different elements as in the hydrogen chloride (HCL) . Amore
complicated molecule is that of glucose C6H12O6
Stability of the atom
When the atom become stable when contain the highest
energy level has eight electron so must bond with other atom
to become more stable
Symbols and formula
explain the structure of molecule
NaCL indicated the compound (sodium chloride ) consist of
sodium and chlorine
Na (sodium) + (Cl)chlorine)
Symbols and formula
Formula molecular explain the structure of molecule
For example C6H8O6
Contain six atom +eight atom of hydrogen+ six
atom of oxygen
HNO3
K2Cr2O7
O2
H2O
( 1H+ 1N+3(O)
( 2K+ 2Cr+7(O)
(2O)
nitric acid
potassium dicromate
Oxygen
(O+ 2H)
Water
Formation of ions
Stability of the atom
When the atom become stable when contain the highest energy
level has eight electron so must bond with other atom to become
more stable
 Na atom has 11 protons and 11 electrons.
 It has only 1 valence electron.
If it loses it
 Therefore, Na becomes more stable by
losing an e-
Na
.
→Na

+
Howard Howson, Eastside HS, Paterson NJ.
11+
But with 11 protons and 10
electrons, Na will have a charge
of 1+.
The resulting cation is written as
Na+
Howard Howson, Eastside HS, Paterson NJ.
+
11+
This loss of e- can be expressed in an
equation: Na  Na+ + eMagnesium atoms will lose 2 e- to obtain a
full outer shell. The equation is:
Mg  Mg2+ + 2eAluminum forms a 3+ cation by losing 3 e-.
The equation is:
Al  Al3+ + 3e-
Howard Howson, Eastside HS, Paterson NJ.
11+
 When a neutral atom loses an electron,
the resulting positively charged ion is
called a cation.
 We know from our definition of metals
that they will lose electrons, and thus
usually form cations.
Howard Howson, Eastside HS, Paterson NJ.
11+
Cl now has 17 protons and 18
electrons, producing a charge of
1–.
The resulting anion is written
as Cl–
Howard Howson, Eastside HS, Paterson NJ.
–
17+
 This gain of e- can be
expressed in an equation:
Cl + e-  Cl-
17+
 Oxygen atoms will gain 2 e- to
obtain a full outer shell.
The equation is: O + 2e-  O2 Anions are named by dropping the ending and adding –ide
to the end of the element name
Example, Cl- is chloride ion, O2- is oxide ion.
Howard Howson, Eastside HS, Paterson NJ.
Size of ions become small
Size of ions become large
Type of chemical bond
Ionic bond
Covalent bond
Ionic Bond
• Between atoms of metals and nonmetals with
very different electronegativity
• Bond formed by transfer of electrons.
• Examples; NaCl , CaCl2
1). Ionic bond – electron from Na is transferred to Cl,
this causes a charge imbalance in each atom. The Na
becomes (Na+) and the Cl becomes (Cl-), charged
particles or ions.
Naming of ionic compound
What the name of the compound CaBr2
Name of positive ion followed by stem of negative ion
+ide
Calcium positive charge
Br bromine negative charge
First write calcium
Second write stem of negative charge Brom +ide
Calcium bromide
COVALENT BOND
bond formed by the sharing of electrons
for example
CL2 - NH3-CO2 -N2
type of covalent bond
Signal covalent bond
CL – CL
CL2
double covalent bond
0=C=O
CO2
triple covalent bond
N
N
N2