CHAPTER 4:
Chemical Bonding
Chemical bonding:
is the union of two or more atoms involving the redistribution of electrons either by transfer or sharing between themselves
ionic bonding:
Bonding which involves the transfer of electrons between atoms
covalent bonding:
Bonding which involves the sharing of electrons
metallic bonding:
Metal atoms bonded to other metal atoms
~Metal to nonmetal
~Ionic bond results from (+) to (−) attraction
~between two nonmetals
Properties:
Crystalline structure
Ions are strongly bonded(electrostatic force)
Able to conduct electricity
High melting points
Structure is rigid
Properties:
Atoms tend to gain, lose or share electrons until they have achieved an outer shell that contains an OCTET(8) of electrons
Low melting points
Unable to conduct electricity
two atoms are bonded together when both hold onto the same electrons
A dative/coordinate bond:
a covalent bond in which both shared/bonding electrons originate from one of the joined atoms
Polar bonds:
formed when one of the elements attracts the shared electrons more strongly than the second element
EXCEPTIONS TO THE OCTET RULE:
~Molecules in which an atom has less than an octet
~Molecules in which an atom has more than an octet
~Molecules with an odd numbers of electrons.
INTERMOLECULAR FORCES
The van der Waals forces:
weak forces of attraction between neutral molecules or particles
Dipole-dipole forces:
permanent attractive forces between polar molecules
Dipole-induced dipole forces
(London dispersion force):
temporary dipole moment may be induced due to the fluctuation of electron distribution within a molecule
The hydrogen bond:
a permanent attraction which occur between molecules that contain hydrogen atom covalently bonded to small highly electronegative atoms
Hydrogen bonds increase the boiling points of compounds
The boiling point INCREASE as the mw INCREASE the sizes of molecules increase the van der Waals forces increase
The hydrogen bond is responsible for the ‘open’ crystal structure of ice
Parameter Related to Chemical Bonding
Bond energy:
a measure of bond strength between two bonded atoms
Bond length:
Distant between two nuclei of bonded atoms in a molecule
(The shortest of the bond the higher of bond energy)
Bond angle:
Is the internal angle of intersection between two lines drawn through the nucleus of a central atom from the nuclei of two atoms bonded to it.
Lattice energy
Factors Determine Bond Energy & Length:
Covalent compound:
~Number of sharing electrons between two bonded atoms
~Size of two bonded atoms present
~The electronegativity between the atoms
~Number of atoms bonded to a central atom
~Number of non-bonding electron present at central atom
Non-Covalent Compound:
~The size of two bonded atoms
~The product of the charge of two bonded atoms
~Number of atoms bonded to a central atom
RESONANCE:
~Resonance stabilizes the molecule
~Maximum stabilization comes when resonance forms contribute equally to the hybrid
consists of atoms held together by their valence electrons that are moving freely throughout the structure(electron sea)
in 3-dimensions
THE BAND THEORY:
an expansion of the Molecular Orbital theory applied to a large number of atoms
~atomic orbitals on two atoms would combine to form bonding and antibonding orbitals
INSULATOR:
Large band gap between bands
SEMICONDUCTOR:
A small band gap
CONDUCTER:
has no bad gap between the bands
The conduction band:
the band that are "high in energy" and are generally half filled or empty
The valence band:
the band that are "low in energy" and are generally full in semiconductor