Chapter 3 - Structure & Properties of Ionic & Covalent Bonds
Chemical Bond: Force of attraction between any two atoms
This attraction overcomes the repulsion of the two positively charged nuclei
Valence electrons are the ones responsible for chemical bonds
Lewis Symbols
Lewis symbol (Lewis structure) - a way to represent atoms using the element symbol and
valence electrons as dots
As only valence electrons participate in bonding, this makes it much easier to work with the
octet rule
The number of dots used corresponds directly to the number of valence electrons located in
the outermost shell of the atoms of the element
The four sides around the atomic symbol can each have two dots for a maximum of eight
(octet)
1
,Using Lewis Symbol
Place one dot on each side until there are four dots around the symbol
Now add a second dot to each side in turn
The number of valence electrons limits the number of dots placed
Each unpaired dot (unpaired electron of the valence shell) is available to form a chemical
bond
Principal types of chemical bonds
Ionic Bonds: A transfer of one or more electrons from one atom to another (Forms
attractions due to the opposite charges of the atoms)
Covalent Bonds: Attractive force due to the sharing of electrons between atoms
2
,Some bonds have characteristics of both types and not easily identified as one or the
other
3
, Lewis Structures & Polarity
A molecule is polar if its centers of positive and negative charges do not coincide
Polar molecules when placed in an electric field will align themselves in the field, non-polar
molecules will not
Molecules that are polar behave as a dipole (having two “poles” or ends), one end is
positively charged the other is negatively charged
Use the following symbol to denote the polarity of each bond
Determining Polarity
Molecules that have no lone pair on the central atom, and all terminal atoms are the same are
non-polar
Molecules with one lone pair on the central atom are polar
Molecules with more than one lone pair on the central atom are usually polar
Si - Cl: polar
4
Chemical Bond: Force of attraction between any two atoms
This attraction overcomes the repulsion of the two positively charged nuclei
Valence electrons are the ones responsible for chemical bonds
Lewis Symbols
Lewis symbol (Lewis structure) - a way to represent atoms using the element symbol and
valence electrons as dots
As only valence electrons participate in bonding, this makes it much easier to work with the
octet rule
The number of dots used corresponds directly to the number of valence electrons located in
the outermost shell of the atoms of the element
The four sides around the atomic symbol can each have two dots for a maximum of eight
(octet)
1
,Using Lewis Symbol
Place one dot on each side until there are four dots around the symbol
Now add a second dot to each side in turn
The number of valence electrons limits the number of dots placed
Each unpaired dot (unpaired electron of the valence shell) is available to form a chemical
bond
Principal types of chemical bonds
Ionic Bonds: A transfer of one or more electrons from one atom to another (Forms
attractions due to the opposite charges of the atoms)
Covalent Bonds: Attractive force due to the sharing of electrons between atoms
2
,Some bonds have characteristics of both types and not easily identified as one or the
other
3
, Lewis Structures & Polarity
A molecule is polar if its centers of positive and negative charges do not coincide
Polar molecules when placed in an electric field will align themselves in the field, non-polar
molecules will not
Molecules that are polar behave as a dipole (having two “poles” or ends), one end is
positively charged the other is negatively charged
Use the following symbol to denote the polarity of each bond
Determining Polarity
Molecules that have no lone pair on the central atom, and all terminal atoms are the same are
non-polar
Molecules with one lone pair on the central atom are polar
Molecules with more than one lone pair on the central atom are usually polar
Si - Cl: polar
4
