chapter 6 Flashcards
why do molecules have a 3D shape?
because pairs of electrons repel to be as far apart as possible
what is the name of the shape of a molecule that has two regions?
linear
what is the bond angle in a molecule that has two regions (linear)?
180 degrees
what is the name of the shape of a molecule that has three regions?
trigonal planar
what is the bond angle in a molecule that has three regions (trigonal planar)?
120 degrees
what is the name of the shape of a molecule that has four regions?
tetrahedral
what is the bond angle in a molecule that has four regions (tetrahedral)?
109.5 degrees
what is the name of the shape of a molecule that has five regions?
trigonal bipyramidal
what is the bond angle in a molecule that has five regions (trigonal bipyramidal)?
120 and 90 degrees
what is the name of the shape of a molecule that has six regions?
octahedral
what is the bond angle in a molecule that has six regions (octahedral)?
90 degrees
what happens to the shape of a molecule if it has lone pairs?
lone pairs repel more because they are slightly closer to the central atom so changes the shape
what is the name of the shape of the molecule that has three regions and a lone pair?
pyramidal
what is the bond angle of a molecule with three regions and a lone pair?
107 degrees
what is the name of the shape of the molecule that has two regions and two lone pairs?
non-linear
what is the bond angle of a molecule with two regions and two lone pairs?
104.5 degrees
why do lone pairs reduce the bond angle?
lone pairs push bonded pairs slightly closer together (so take away 2.5 degrees for each lone pair)
what is electronegativity?
measure of the ability of an atom in a molecule to attract a pair of electrons
what are the most electronegative elements?
F
O
Cl
what does the higher the electronegativity value mean?
the more strongly the bonded electrons are attracted to that atom
what happens to the electronegativity as the number of protons increases?
the pulling on bond electrons increases due to increased nuclear charge
how can distance also effect electronegativity?
the greater the distance from the nucleus the lower the pull on shared electrons despite having a higher nuclear charge
what does it mean if a molecule is non-polar?
bonded atoms are the same or have the same/similar electronegativity value
what is a non-polar bond?
bonded electron pair is shared equally between the bonded atoms
what does it mean if a molecule is polar?
bonded electron pair is shared unequally between bonded atoms
what does the delta sign mean?
partial charge
what is a dipole?
separation of opposite charges in a molecule
how can something contain polar bonds but not be a polar molecule overall?
polar bonds/dipoles cancel out
when do polar bonds/dipoles cancel out to make a non-polar molecule?
if there is a line of symmetry
why does water (polar molecule) dissolve things?
polar molecules can form strong enough attractions to permit dissolving
what is an example of why a molecule is polar?
if there are lone pairs then the bond angle is not symmetrical so the molecule is polar
what are intermolecular forces?
weak interactions between molecules
what are london forces?
instantaneous dipoles attracted to each other
the weakest type of intermolecular force and exist between all molecules
how are instantaneous dipoles formed?
electrons in an atom move constantly
temporary uneven distribution of electrons forms an instantaneous dipole
how do instantaneous dipoles form and become attracted to each other?
instantaneous dipole induces a dipole in its neighbour
these dipoles are attracted together due to opposite charges
what are permanent dipole-dipole intercations?
formed when molecules which are polar interact
opposite dipoles attract to each other
(full time strong forces)
what are hydrogen bonds?
specific type of permanent dipole-dipole interaction
what do hydrogen bonds need to form?
electronegative atom with a lone pair of electrons (O, N, F)
hydrogen atom attached to that electronegative atom (H-O, H-N, H-F)
why is ice less dense than water?
hydrogen bonds hold water molecules apart in an open lattice structure
water molecules are further apart in ice than in water
why do molecules with hydrogen bonds have high melting/boiling points?
strongest type of weak bond
more energy is needed to break the bonds
