Covalent Bonding
A non-metal atom bonds with another non-metal atom.
Because non-metals have high electronegativities, they
must share their valence electrons with each other.
If they have the same electronegativity value, then they will
share their electrons equally.
If one atom is more electronegative than the other then
they will share their electrons unequally.
Covalent bonding is the strongest type of bonding because atoms share electrons.
Covalent bonding usually involves nonmetals and nonmetals.
A molecule is a group of atoms joined with covalent bonds that act as a single unit.
When 2 bonding nonmetal atoms have the
same electronegativity
their valence electrons are
shared equally. This bond
is called "non-polar"
because neither pole is
more negative than the
other.
When 2 non-metal
atoms have different
electrongativities, valence
electrons are shared
unequally. This bond is
called "polar" because
one pole is more
negative than the other.
Multiple Bonding
A double bond occurs when 2 atoms share 2 pairs of electrons.
A triple bond forms when 2 atoms share 3 pairs of electrons.
Molecular Compounds
A molecular compound is composed of molecules with covalent bonding.
Molecular compounds generally have lower melting and boiling points than ionic
compounds.
Molecular compounds do not conduct electricity when dissolved in water.
They commonly exist as gases, liquids or soft solids at room temperature.
Molecules exist as separate particles and the IMFA's (intermolecular forces of
attraction) varies.
In general, they have low melting and boiling points.
They are usually poor conductors of heat and electricity.
Polar molecules are water soluble.
Water is a polar molecule: "Like Dissolves Like".
Non-polar molecules are insoluble in water. For example oil is non-polar.
Chemical formulas
Compounds are represented by chemical formulas that show the ratio of the elements
that compose them.
The subscript is the number of atoms of each element in the
compound. Number 1 is understood if no number is shown.
Polar bonds
A covalent bond in which electrons are shared unequally is
called a polar bond, formed because atoms of some elements
pull more strongly than others on shared electrons
Polar molecules are attracted to each other, as nonpolar
molecules are attracted to nonpolar molecules.
Metallic Bonding
Bond forms between metal atoms only.
The valence electrons are mobile and move through the entire metallic crystal.
The inner core of a metal atom is known as the kernel.
It includes the nucleus and the inner electrons, making it carry an overall positive
charge.
Electrons are loosely held to metal atoms, creating metal cations and allowing valence
electrons to wander among the metal cations in metal crystals.
These wandering electrons allow metals to be conductive and to easily form alloys,
compounds of metals.
Metallic bonding also makes metals malleable, ductile and lustrous.
They are insoluble in water.
Like other crystalline solids, they have high melting and boiling points. (it is why we cook
our food in metal pots and pans)
When atoms are bonded we can use what we know to draw a bonded Lewis dot
diagram:
Still use valence electrons, but now we can pair up lone pairs of electrons in the
compound:
OH
H2O
CH4