Bonding (3.1.3) Flashcards
what does ionic bonding involve (giant ionic structure)?
many strong electrostatic forces of attraction going in all directions between oppositely charged ions in a lattice
(state ions if given compound)
what does metallic bonding involve (giant metallic structure)?
strong electrostatic forces of attraction between positive ions and delocalised electrons arranged in a lattice
what does the bonding in simple molecular structures involve?
strong covalent bonds between atoms in the molecule, but weak intermolecular forces of attraction between molecules
what does a single covalent bond contain?
a shared pair of electrons
what do multiple bonds contain?
multiple pairs of electrons
what does a coordinate (dative covalent) bond contain?
a shared pair of electrons with both electrons supplied by one atom
what is a lone pair of electrons?
when forming covalent bonds, a pair of electrons which aren’t involved in forming a bond
what is a vacant orbital?
when forming covalent bonds, an orbital in the outer energy level of an atom which doesn’t contain any electrons
draw the dot and cross diagram for AlCl3 and label the lone pairs of electrons/vacant orbital?
lone pairs on Cl atoms
vacant orbital on Al atom
how is a covalent bond represented?
using a line
how is a coordinate bond represented?
using an arrow
draw a diagram to show what happens when NH3 and BCl3 react, and write the equation?
NH3 + BCl3 –> H3NBCl3
draw a diagram to show what happens when Cl^- and AlCl3 react, and write the equation?
Cl^- + AlCl3 –> AlCl4^-
what is electronegativity?
the ability of an atom to attract the pair of electrons (electron density) in a covalent bond towards itself
what is the trend in electronegativity going across a period?
electronegativity values increase because the nuclear charge on the atoms increases but shielding is similar, so atoms attract the electrons more strongly
what is the trend in electronegativity going down a group?
electronegativity values decrease because atoms have more energy levels and therefore more shielding, so atoms attract the electrons less strongly
how is a polar covalent bond produced?
when electron distribution in a covalent bond between elements with different electronegativities is unsymmetrical
which covalent bond is more polar and why - H-Cl and H-F?
H-F, because the bigger the difference in electronegativity between the atoms, the more the covalent bond is polar
how can you show that a bond is polar?
using partial charges
how do partial charges in a polar covalent bond work?
the atom with lower electronegativity has a positive partial charge (delta +) and the element with higher electronegativity has a negative partial charge (delta -)
what can bonding pairs and lone pairs of electrons be described as?
charge clouds which repel each other
what do pairs of electrons in the outer shells of atoms do?
they arrange themselves as far apart as possible to minimise repulsion
what are the strengths of the repulsion between different types of bond?
strongest - lone pair-lone pair repulsion
lone pair-bond pair repulsion
weakest - bond pair-bond pair repulsion
when drawing 3D shapes of molecules, what does a solid line mean?
atoms lie on the plane
when drawing 3D shapes of molecules, what does a solid wedge mean?
the atom is coming out of the plane of the page
when drawing 3D shapes of molecules, what does a dotted wedge mean?
the atom is projecting behind the plane of the page
what is the effect of lone pairs of electrons on bond angles?
the lone pairs repel the bonding pairs more strongly, so the bond angle decreases as atoms are pushed further away (the more lone pairs, the stronger the repulsion)
shape name and bond angles - 2 bps and no lps?
linear, 180 degrees
shape name and bond angles - 3 bps and np lps?
trigonal planar, 120 degrees
shape name and bond angles - 2 bps, 1 lp?
bent, 118 degrees
shape name and bond angles - 4 bps, no lps?
tetrahedral, 109.5 degrees
shape name and bond angles - 3 bps, 1 lp?
trigonal pyramidal, 107 degrees
shape name and bond angles - 2 bps, 2 lps?
bent, 104.5 degrees
shape name and bond angles - 5 bps, no lps
trigonal bipyramidal, 120 and 90 degrees
shape name and bond angles - 4 bps, 1 lp?
seesaw, 90, 120 and 180 degrees
shape name and bond angles - 3 bps, 2 lps?
t-shaped, 90 degrees
shape name and bond angles - 2 bps, 3 lps?
linear, 180 degrees
shape name and bond angles - 6 bps, no lps?
octahedral, 90 degrees
shape name and bond angles - 5 bps, 1 lp?
square pyramidal, 90 degrees
shape name and bond angles - 4 bps, 2 lps?
square planar, 90 degrees
how can you identify a polar molecule?
it will have an unequal distribution of bonding pairs around the central atom of the molecule, and the molecule will have a permanent dipole-dipole moment
how can you identify a non-polar molecule?
it will have an equal distribution of bonding pairs around the central atom of the molecule, and the molecule doesn’t have a permanent dipole-dipole moment
what do you also need to consider when determining if a molecule is polar or non-polar?
look at what atoms are present and consider their electronegativities and therefore where the partial charges are
what does VSEPR stand for?
valence shell electron pair repulsion
what is a valence electron?
a electron in the outer shell of an atom
how would you use VSEPR to determine the shape of a molecule eg. H2O?
- number of valence electrons for each element present: H=1, O=6
- total number of valence electrons in molecule = 1+1+6=8
- number of valence electrons needed by each atom bonding to central atom - each H needs 2 VE so 2+2=4
- number of valence electrons left over = 4
- therefore number of lone pairs = 2
- 2 bonds and 2 lps means the shape is V-shaped
what are the three types of intermolecular forces and where are they found?
van der Waals - between all atoms and molecules
permanent dipole-dipole forces - between certain types of molecules
hydrogen bonding - between certain types of molecules
how do van der Waals/induced dipole-dipole forces form?
- the random, rapid movement of electrons causes one side of a molecule to have a partially negative charge (unequal distribution of electrons across molecule which is polar)
- the partially negative side of one molecule repels the electrons in a neighbouring molecule making it polar (inducing a dipole)
- the partially negative side of the first molecules attracts the partially positive side of the neighbouring molecule
- this process repeats with the 2nd molecule inducing a dipole in the 3rd molecule and van der Waals forces forming between them
- molecules have enough energy that the van der Waals forces between them quickly break leaving the molecules free to move again and form more van der Waals forces
why do boiling points increase as you go down the halogens in the periodic table?
the atoms have more electrons, meaning the electron cloud surrounding each molecule gets larger
therefore, the van der Waals forces formed between molecules become stronger and require more energy to overcome
what is a permanent dipole-dipole interaction?
an intermolecular force which forms between the permanent dipoles of two molecules
what must the molecules involved in permanent dipole-dipole forces be?
polar, so they have a permanent dipole
how do permanent dipole-dipole interactions form?
the partially negative side of one molecule attracts the partially positive side of another molecule
where there is a permanent dipole-dipole interaction or hydrogen bond, what is also always present?
van der Waals forces
what are hydrogen bonds?
an attraction between a partially positive H atom on one molecule and a lone pair of electrons on an atom of another molecule
how does the strength of hydrogen bonds compare to the other intermolecular forces?
they are the strongest type of intermolecular force
when does hydrogen bonding occur and why?
between molecules which have a H atom covalently bonded to a N, O or F atom - there is a large difference in electronegativity between the atoms creating a polar bond
how does hydrogen bonding cause anomalous boiling points of compounds?
when looking at the boiling points of hydrides of elements in groups 5,6 and 7, the general trend is that they increase down the group
however, the hydride of the first element is much higher than the hydride of the second element because the first elements are N, O or F, meaning the hydride has hydrogen bonds which are very strong and require lots of energy to overcome
why is ice less dense than liquid water?
when water is a liquid, the molecules move randomly and hydrogen bonds are constantly formed and broken between them
when water freezes, the molecules arrange themselves into an ordered structure with a network of hydrogen bonds between molecules - this means the water molecules in ice are further apart than in liquid water
how can you use bonding to predict solubility?
if you know that intermolecular forces exist between molecules, you can predict if one substance will be soluble in another ie. ammonia molecules form hydrogen bonds with water molecules, so ammonia is soluble in water
