Class notes
Chem 1120 Molecular Compounds Notes
- Course
- Chem 1120
- Institution
- East Carolina University
This is a comprehensive and detailed note Chapter 4; molecular compounds for Chem 1120. *Essential Study Material!!
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Molecular CompoundsWhy do compounds form?
○ The driving force for formation of any compound is to attain a noble gas
electronic configuration for each element in the formula of a compound
○ As m observed with noble gasses, there is a stability associated with eight
valence electrons
○ Octet rule - atoms exchange or share electrons during a chemical process
in a manner such as to attain an electronic configuration with eight
valence electrons
There are two bonding models among the elements, including;
○ Ionic bonding - generally occurs between a metal and a nonmetal atom by
complete transfer of electrons
○ Covalent bonding - generally occurs between two nonmetals through
sharing electrons
Ionic compounds - formed by a complete transfer of electrons typically from the
metal to the nonmetal as in the formation of sodium chloride
Properties of molecular compounds
○ Can be solids, liquids or gasses (usually slow melting solids or low boiling
liquid)
○ Soluble in nonpolar solvents and less soluble in polar solvents
○ Aqueous solutions do not conduct electricity
Covalent bonding - occurs between two nonmetals when they share electrons in
a manner such that both atoms attain an octet of electrons or a noble gas
electron configuration
Covalent bond types
○ Two atoms can share more than a single pair of electrons
○ If two atoms share four electrons as in the example of ethylene below,
then the bond is referred to as a double bond
○ If two atoms share six electrons as in N_2, then the bond is referred to as
a triple bond
● Lewis dot symbols
, ○ Steps for determining the lewis structure for a polyatomic molecule that
obey the octet rule
■ Decide which atom is the central atom, usually the atom closest to
the metals on the periodic table is the central atom and usually it is
an atom in the formula which is listed once
■ Perform a total electron count by adding the number of each type of
atom in the formula multiplied by the group number in which they
are found
■ Connect the central atom to peripheral atoms, each bond counts as
two electrons, subtract these bonding electrons from the total
number possible, place the remaining electrons around the
peripheral atoms such that they attain an octet or eight electrons
■ Excess electrons are placed around the central atom, if there is not
enough electrons to be placed around the central atom to provide
an octet, move electrons from a peripheral atom in to the central
atom to form a multiple bond
○ You may have noticed that OF_2 has a lewis structure that is very similar
to SCI_2
■ They are similar because fluorine and chlorine are found in the
same group and oxygen and sulfur are found in the same group on
the periodic table
○ Lewis structures for polyatomic ions
■ When determining the total number of available valence electrons
available in polyatomic ions, the change of an ion must be taken
into account
■ If the polyatomic ion is an anion, electrons must be added to the
total electron count and if the polyatomic ion is cationic, then the
electrons must be subtracted from the total count
● Shapes of molecules
○ Steps for determining the shape of a molecule
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