what is a polar bond
an unequal sharing of electrons (one atom is more electronegative than the other)
what is a non-polar bond
when the atoms involved in the bond are identical
what is electronegativity
the tendency of an atom to attract the electrons in a bond towards itself
how does electronegativity differ with periods and groups
increase across a period
decreases down a group
what has zero electronegativity
inert gases
what is the most electronegative element
fluorine (Fe)
why do polar bonds occur
the most electronegative atom of a bond has the greater attraction for the shared electrons and has a slightly negative charge (holds the shared electrons closer)
the less electronegative atom has a slight positive charge
as a result a charge separation occurs across the bond (dipole)
what happens when there is a large difference in electronegativity between two bonded atoms
it causes electrons to be completely transferred to the more electronegative atom (from the other atom)
resulting in the formation of a negative ion from the most electronegative atom gaining an electron
this is known as an ionic bond
what bond is it if the two atoms have the same electronegativity
non-polar covalent bond
what bond is it when there is an electronegativity different
polar covalent bond
what bond is it when the electronegativity difference is large
the bonding takes on more of an ionic character
how does electronegativity difference increase
description of non-polar covalent bonding
atoms have the same tendency to attract bonding electrons
electrons are shared equally
description of polar covalent bonding
atoms have small differences in their tendency to attract bonding electrons
electrons shared unequally between atoms
description of ionic bonding
atoms have large differences in their tendency to attract bonding electrons
one atom donates its valence electrons to the other
ions are formed resulting in an ionic bond
when does a non-polar covalent bond occur
when identical non-metal atoms bond or when bonded atoms have nearly the same electronegativity values
when does a polar covalent bond occur
usually between two different non-metal atoms
when does an ionic bond occur
usually between the atoms of metals and non-metals
how does polarity interlink with the shape of the molecule
what will polar molecules have
one end of the molecule slightly positive and the other slightly negative - resulting in an uneven distribution of electron density
what does the polarity of a molecule depend on
the molecule containing polar bonds
the way the polar bonds are arranged
what happens in diatomic molecules if the bond joining the two atoms is polar
then the molecule as a whole will be polar
for molecules containing more than two atoms and has polar bonds what is the polarity of the molecule determined by
the shape (the arrangement of the polar bonds)
when can a polarity cancel and cause the molecule to be non-polar
when equivalent polar bonds are evenly arranged around a central atom
how can polar molecules be identified
polar bonds in the molecule arranged unevenly around the central atom so that the bond dipoles do not cancel
more than one type of atom bonded to the central atom
how to test for polarity in liquids
when placed near an electrically charged object, the polar molecules align and are attracted to the charged object
causes the liquid polar substance to deflect towards a charged object
non-polar liquids flow without deflection past charged objects
(water and rod test)
why are water molecules polar
they have polar bonds (O-H) arranged in a V shape around the oxygen atom
the large electronegativity difference between hydrogen and oxygen atoms produces strong attractive forces between the molecules
substances that contain polar molecules
hydrogen chloride HCl
phosphorus trichloride PCl3
ammonia NH3
water H2O
dichloromethane CH2Cl
substances that contain non-polar molecules
carbon dioxide CO2
oxygen O2
hydrogen H2
nitrogen N2
methane CH4
polar shapes and why
bent and v-shaped
trigonal planar
asymmetrical shapes, dipoles don’t cancel → polar molecules
non-polar shapes and why
tetrahedral
linear
symmetrical shapes, dipoles can cancel if equal and opposite → non-polar molecules
what makes a polar molecule
different electronegativity values between Z and X
not arranged symmetrically around the central atom due to shape
effect of dipoles is not cancelled
what makes a non-polar molecule
bonds are arranged symmetrically around the central atom in a certain shape
the effect of any dipoles formed by the different electronegativity of the X-Z bond is cancelled
what is the solubility rule of “like dissolves in like”
polar molecules can dissolve in polar liquid
non-polar molecules dissolve in other non-polar molecules but not in water