Chapter 8 . Covalent Bonding VSEPR Theory Molecular Shape Polar or NonPolar Properties of Molecular Substances. Why Do Atoms Bond?. The stability of an atom, ion or compound is related to its energy lower energy states are more stable.
Polar or NonPolar
Properties of Molecular Substances
The most stable arrangement of atoms exists at the point of maximum net attraction, where the atoms bond covalently and form a molecule.
When more than one pair of electrons is shared, a multiple covalent bond is formed
Multiple bonds are made up of sigma bonds and pi bonds: formed when parallel orbitals share electrons.
Two pairs of electrons are shared
Contains one sigma and one pi bond.
Three pairs of electrons are shared
Has one sigma and two pi bonds.
An endothermic reaction is one where a greater amount of energy is required to break a bond in reactants than is released when the new bonds form in the products.
An exothermic reaction is one where more energy is released than is required to break the bonds in the initial reactants.
The first element is always named first using the entire element name
The second element is named using its root and adding the suffix -ide
Prefixes are used to indicate the number of atoms of each element that are present in the compound
Many compounds were discovered and given common names long before the present naming system was developed (water, ammonia, hydrazine, nitric oxide).
An acid that contains hydrogen and one other element Ex. HCl
ion ends –ide.
Name the acid with hydro-root of the anion-ic
HCl (hydrogen and chloride ) becomes hydrochloric.
HCl in a water solution is called hydrochloric acid.
A structural formula uses letter symbols and bonds to show relative positions of atoms.
Used to predict the structural formula
Show arrangement of the atoms and un-bonded electrons
Place any remaining electrons around the central atom to satisfy its octet. If the central atom cannot be satisfied, make a multiple bond using a lone pair from the terminal atoms.
Check your work
Drawing Lewis structures for polyatomic ions is very similar to drawing Lewis structures for covalent compounds EXCEPT in finding the number of electrons available for bonding
When a molecule or polyatomic ion has both a double bond and a single bond, it is possible to have more than one correct Lewis structure:
a condition that occurs when more than one valid Lewis structure can be written for a molecule or ion.
The structures are called resonance structures.
A molecule that undergoes resonance behaves as if it has only one structure.
Three Ways Molecules Might Violate the Octet Rule
How a molecule “looks”
The shape of a molecule determines whether or not two molecules can get close enough to react
We describe shape using the VSEPR model
This model is based on the fact that electrons pairs will stay as far away from each other as possible
Draw the Lewis Structure for a Molecule
Count the pairs of bonded electrons
Count the pairs of unbonded electrons
Match the information with the VSEPR chart to classify the shape of the molecule
Atoms will assume certain bond angles: the angle formed by any two terminal atoms and the central atom
Molecules are either polar or nonpolar depending on the bonds in the molecule.
We must look at the shape (geometry) of a molecule to determine polarity.
Symmetric molecules are nonpolar.
Asymmetric Molecules are Nonpolar
Bond type and shape of the molecule determine solubility
Polar substances and ionic substances will dissolve in polar solvents
Nonpolar substances will only dissolve in nonpolar substances