Ionic And Molecular Compounds - Chemistry Lab
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4Ionic and Molecular Compounds
Name: _____________________________
Chemistry 2
Date: ______________________
Purpose:
The purpose of this activity is to differentiate between ionic and molecular
compounds.
Introduction
While we often speak of two distinct types of chemical bonding, ionic and covalent
bonding, the nature of chemical bonding is actually more of a continuum based on the
electronegativity difference between the two elements involved in the bond. The
electronegativity of an element describes how strongly an atom of that element attracts electrons
from another atom. Each element has an electronegativity value using a scale that goes from
zero to 4.0, with 4.0 being the most electronegative. Recall that metals tend to have low
electronegativity values and nonmetals tend to have high electronegativity values. When there is
little or no difference in electronegativity (0.4 or less) between two elements, the atoms share
electrons equally and we describe the bond as being nonpolar covalent. When there is an
intermediate difference in electronegativity ( generally between 0.4 and 2.0) the electrons are
shared unequally, meaning that the electrons are held closer to the more electronegative element,
and the bond is described as being polar covalent. When there is a large electronegativity
difference (generally 2.0 or higher) one atom is so much more electronegative that it completely
pulls the electrons away from the other atom and the bond is described as being ionic.
Electronegativity difference: 0.0-----------------------0.4---------------------------- 2.0-----------4.0
Type of bond:
Nonpolar Covalent-----------Polar Covalent----------------Ionic-----------
As the electronegativity difference between the atoms becomes smaller, the chemical
bond has more covalent character. As the electronegativity difference between the atoms
becomes greater, the chemical bond has more ionic character.
When a compound has chemical bonds that are mostly ionic in nature, the structure that is
formed is a crystal lattice. In a crystal lattice there is a repeating pattern of positive and negative
ions that make a three dimensional shape. In this activity, you will construct a model of a simple
crystal lattice. An example of an ionic compound that forms a crystal lattice is sodium chloride,
NaCl.
When a compound has chemical bonds that are mostly covalent in nature, the structure
that is formed is a molecule. An example of a covalently bonded compound that forms a
molecule is water, H
O. In the preceding module, you studied several shapes of molecules such
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as tetrahedral, trigonal planar, linear, bent, and trigonal pyramid.
Pre-activity
1. What is electronegativity? __________________________________________________
________________________________________________________________________
2. Do metals tend to have high or low electronegativity values? _______________________
________________________________________________________________________
Do nonmetals tend to have high or low electronegativity values? ___________________
_______________________________________________________________________
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