3.1.3 - bonding Flashcards
how are ions formed?
when electrons are transferred from one atom to another
equations showing the formation of a cation
(sodium)
Na = Na+ + e-
equations showing the formation of an anion
(chlorine)
Cl + e- = Cl-
what do elements in the same group have in common?
they all have the same number of outer elctrons
what is the trend of charges of ions in the same group?
when elements in the same group form ions, they all have the same charge
what charge ions would group one elements form?
1+ ions
what charge ions would group seven elements form?
1- ions
what are compound ions?
ions made up of groups of atoms with an overall charge
examples of compound ions
ammonium, carbonate, hydroxide, nitrate, sulfate
ionic formula for an ammonium ion
(NH4)+
ionic formula for a carbonate ion
(CO3)2-
ionic formula for a hydroxide ion
OH-
ionic formula for a nitrate ion
(NO3)-
ionic formula for a sulfate ion
(SO4)2-
what is ionic bonding?
the net electrostatic attraction between oppositely charged ions
general ionic structure
-ions arranged in giant lattice
-cations/anions arranged alternately
-3D array
-lattice is very strong (many ionic bonds)
do ionic compounds conduct electricity?
ionic compounds conduct electricity when they are molten or dissolved but not when solid
explanation for ionic compounds conductivity
ions in a liquid are free to move and they can carry a charge. in a solid they’re fixed in position by the strong ionic bonds
ionic compounds melting point
ionic compounds have high melting points
explanation for ionic compounds melting point
giant ionic lattices are held together by strong electrostatic forces which takes lots of energy to overcome them
ionic compounds and solubility
ionic compounds tend to dissolve in water
explanation for ionic compounds solubility
water molecules are polar so the water molecules pull the ions away from the lattice and cause it to dissolve
ionic formula for a sulfite ion
(SO3)2-
when does ionic bonding occur?
if there is a big difference in electronegativities i.e. metals and non metals
when does covalent bonding occur?
electronegativities are identical/similar (and high) i.e. non metals
what is covalent bonding?
the sharing of pairs of electrons between non metal atoms to form molecules or giant structures so they both have a full outer shell
what is a covalent bond defined as?
a shared pair of electrons
single covalent bonds
contains 1 shared pair of electrons. the positive nuclei are attracted electrostatically to the shared electrons
double covalent bonds
2 shared pairs of electrons
triple covalent bonds
3 shared pairs of electrons
covalent molecular substances melting and boiling points
covalent molecular substances have low melting and boiling points
explanation for covalent molecular substances melting and boiling points
only intermolecular forces are broken during boiling and melting , these forces are weak so require little energy to break
do covalent molecular substances conduct electricity?
No as there are no mobile charged particles - electrons aren’t free to move
what holds covalently bonded atoms together?
electrostatic attraction between positive nuclei and the negative electron pairs shared between those nuclei
graphite structure
carbon atoms arranged in sheets of flat hexagons, covalently bonded with 3 bonds each. 4th outer electron of each carbon atom is delocalised. sheets of hexagons bonded together by weak Van der Waals forces
uses of graphite
- dry lubricant
- pencils
why is graphite soft?
weak bonds between the layers in graphite are easily broken, so the sheets can slide over each other
is graphite a conductor and why?
yes, delocalised electrons in graphite are free to move along the sheets so an electric current can flow
graphite - density
layers far apart compared to the length of the covalent bonds so graphite has a low density = used to make strong/lightweight sports equipment
graphite melting point
strong covalent bonds in the hexagon sheets so graphite has a high melting point
graphite solubility
insoluble in any solvent as the covalent bonds in the sheets are too difficult to break
diamond structure
made up of carbon atoms, each of which is covalently bonded to 4 other carbon atoms. tetrahedral shape
diamond melting point
has a high melting point as its strong covalent bonds require lots of energy to break
diamond - hard or soft?
due to its strong covalent bonds it is very hard , used in diamond-tipped drills and saws
diamond - thermal conductivity
vibrations travel easily through the stiff lattice so is a good THERMAL conductor
diamond - does it conduct electricity?
doesn’t conduct electricity = all outer electrons held in localised bonds/no delocalised electrons
diamond- solubility
diamond won’t dissolve in any solvent
define metallic bonding
net attraction between cations and delocalised electrons
metallic bonding structure
lattice of closely packed cations in a sea of delocalised electrons
metals - melting points
high melting points = strong metallic bonds between cations and delocalised electrons, lots of energy to break them
metals - melting point as you go down a group
melting point decreases as you go down a group
metals - melting point as you go down a group explanation
as there are the same number of delocalised electrons per atom but cations get heavier/larger so less strongly held in place by attraction of fixed number of delocalised electrons
metals - melting point across a period
across a period, melting point increases
metals - melting point across a period explanation
the number of delocalised electrons per atom increases and so does the charge on cations. therefore more strongly held in place by increasing force of attraction
metals - conductivity across a period
conductivity increases as you go along a period as the number of delocalised electrons increases
metals - malleability
layers of cations can slide over each other, still bonded by delocalised electrons so metals are malleable and ductile
metals - conductivity (thermal)
delocalised electrons can pass kinetic energy to each other so they are good thermal conductors
metals - electrical conductivity
good electrical conductors, delocalised electrons can move and carry a charge
metals - solubility
insoluble except in liquid metals, because of the strength of the metallic bonds
co-ordinate/dative covalent bond
covalent bond formed when both shared electrons are provided by only one atom e.g. pair comes from a lone pair on the donor atom. the atom sharing the lone pair must have an incomplete outer energy level
what does the shape of a molecule depend on
number of pairs of electrons in the outer shell of the central atom
what are shared electrons called
bonding pairs
what are unshared electrons called
lone pairs/non bonding pairs
what do bonding pairs and lone airs of electrons exist as?
bonding pairs and lone pairs of electrons exist as charge clouds
what is a charge cloud
an area where you have a big chance of finding an electron
where can electrons be found
electrons can be found quickly moving around nuclei in charge clouds
do charge clouds repel or attract each other
electrons are negatively charged so charge clouds repel each other until they are as far apart as possible
what does shape of a charge cloud affect?
shape of a charge cloud affects how much it repels other charge clouds
valance shell electron pair repulsion theory
lone pair charge clouds repel more than bonding pair charge clouds, so bond angles are often reduced as bonding pairs are pushed together by lone pair repulsion (valance shell electron pair repulsion theory)
which bond angle is the biggest
lone pair/lone pair angles
which bond angle is the second biggest
lone pair/bonding pair
which bond angle is the smallest?
bonding pair/bonding pair
how to find number of electron pairs
step 1
find central atom (one all other atoms are bonded to)
how to find number of electron pairs
step 2
work out how many electrons are in outer shell of central atom (group number)
how to find number of electron pairs
step 3
add 1 electron for every atom that the central atom is bonded to
how to find number of electron pairs
step 4
if it is an ion add 1 electron for each negative charge/subtract 1 for each positive charge
how to find number of electron pairs
step 5
add up all the electrons and divide by 2 to find the number of electron pairs
how to find number of electron pairs
step 6
calculate number of BP and LP
central atom with 2 electron pairs
- linear shape
- bond angle of 180
- pairs of bonding electrons want to be as far away from each other as possible
central atom with 3 electron pairs
3BP 0LP
shape
trigonal planar
central atom with 3 electron pairs
3BP 0LP
bond angle
120
central atom with 3 electron pairs
3BP 0LP
explanation
repulsion of charge clouds is the same between each pair
central atom with 3 electron pairs
2BP 1LP
shape
bent/non linear
central atom with 3 electron pairs
2BP 1LP
bond angle
104.5
central atom with 4 electron pairs
4BP 0LP
shape
tetrahedral
central atom with 4 electron pairs
4BP 0LP
bond angle
109.5
central atom with 4 electron pairs
4BP 0LP
explanation
charge clouds all repel each other equally
central atom with 4 electron pairs
3BP 1LP
shape
trigonal pyramidal
central atom with 4 electron pairs
3BP 1LP
bond angle
107
central atom with 4 electron pairs
3BP 1LP
explanation
lone pair/bonding pair repulsion will be greater than the bonding pair/bonding pair repulsion. smaller bond angles between bonding pairs of electrons and larger bond angles between the lone pair and bonding pairs
central atom with 4 electron pairs
2BP 2LP
shape
bent/non linear
central atom with 4 electron pairs
2BP 2LP
bond angle
104.5
central atom with 4 electron pairs
2BP 2LP
explanation
lone pair/lone pair repulsion squishes bond angle even further
central atom with 5 electron pairs
5BP 0LP
shape
trigonal bipyramidal
central atom with 5 electron pairs
5BP 0LP
bond angle
3 will be 120 and other 2 atoms will be at 90 to them
central atom with 5 electron pairs
5BP 0LP
explanation
repulsion between bonding pairs means 3 of the atoms will form a trigonal planar shape and the other 2 will be at 90 to them
central atom with 5 electron pairs
4BP 1LP
shape
seesaw
central atom with 5 electron pairs
4BP 1LP
bond angle
120 and 86.5
central atom with 5 electron pairs
4BP 1LP
explanation
lone pair is always positioned where 1 of the trigonal planar atoms would be in a trigonal bipyramidal molecule
central atom with 5 electron pairs
3BP 2LP
shape
T shaped
central atom with 5 electron pairs
3BP 2LP
bond angle
87.5
central atom with 6 electron pairs
6BP 0LP
shape
octahedral
central atom with 6 electron pairs
6BP 0LP
bond angle
90
central atom with 6 electron pairs
5BP 1LP
shape
square pyramidal
central atom with 6 electron pairs
5BP 1LP
bond angle
90
central atom with 6 electron pairs
4BP 2LP
shape
square planar
central atom with 6 electron pairs
4BP 2LP
bond angle
90
awkward molecules
if a molecule has multiple bonds, treat each multiple bond as if it was 1 single bond when working out the shape
awkward molecules example
carbon dioxide
- 4BP, 0LP
- treat it as 2BP and 0LP
- linear shape, bond angle 180
awkward molecules example
sulfur dioxide
-4BP, 1LP
- treat as 2BP, 1LP
- bent/non linear shape
- bond angle 120
what is electronegativity
the power of an atom to attract the pair of electrons in a covalent bond.
what is electronegativity measured on?
Pauling scale
what does a higher electronegativity mean?
higher number means an element is better able to attract the bonding electrons
what is the most electronegative element?
fluorine
where are the most electronegative elements found
top right of periodic table
where are the least electronegative elements found
bottom left of periodic table
electronegativity trends across periods
electronegativity generally increases as you move from left to right across a period
electronegativity trends down groups
electronegativity generally decreases as you move down a group.
are covalent bonds in diatomic gases polar or non polar
non polar as atoms have equal electronegativities
elements with similar electronegativities
some elements e.g. carbon and hydrogen have similar electronegativities so bonds between them are essentially non polar
polar bonds
in covalent bond between 2 atoms of different electronegativities, bonding electrons are pulled towards the more electronegative atom which makes the bond polar
how does difference in electronegativities affect how polar a bond is
greater difference in electronegativity = more polar bond
how is dipole caused
difference in electronegativity between the 2 atoms causes a dipole
what is a dipole
a dipole is a difference in charge between the 2 atoms caused by a shift in electron density in the bond
what determines whether a molecule will have a permanent dipole
if charge is unevenly distributed over a whole molecule, the molecule will have a permanent dipole
what are molecules that have a permanent dipole called
polar molecules
what does whether or not a molecule is polar depend on?
-if it has any polar bonds
- its shape
simple polar molecules
e.g. HCl, one polar bond means charge is distributed unevenly across the whole molecule so it has a permanent dipole
what happens if polar bonds are arranged symmetrically?
if polar bonds are arranged symmetrically, the dipoles cancel each other out so the molecule has no permanent dipole and is non polar
example of a molecule with polar bonds arranged symmetrically
carbon dioxide
what happens if polar bonds are arranged not symmetrically?
if polar bonds are arranged so they all point in roughly the same direction and don’t cancel each other out, then charge will be arranged unevenly across the whole molecule which results in a polar molecule which has permanent dipole
what are intermolecular forces
forces between molecules
strength of intermolecular forces
much weaker than covalent, ionic or metallic bonds
types of intermolecular forces
(from weakest to strongest)
- Van der Waals forces
- permanent dipole-dipole forces
- hydrogen bonding
Van der Waals forces:
what do they cause
all atoms and molecules to be attracted to each other
Van der Waals forces:
how is temporary dipole formed
electrons in charge clouds are always moving very quickly. at any given moment, the electrons in an atom are likely to be more to 1 side than the other so at this moment the atom has a temporary dipole
Van der Waals forces:
how does one dipole cause more dipoles
this dipole causes another temporary dipole in the opposite direction on a neighbouring atom . 2 dipoles are then attracted to each other. 2nd dipole causes another dipole in a 3rd atom
Van der Waals forces:
as electrons are constantly moving, dipoles are being created and destroyed all the time. even though dipoles keep changing, overall effect is for the atoms to be attracted to each other
are all Van der Waals forces the same strength
no- larger molecules have larger electron clouds, meaning stronger Van der Waals forces
does shape of molecules affect the strength of Van der Waals forces
yes
how does a molecule’s shape affect Van der Waals forces
long straight molecules can lie closer together than branched ones - closer together 2 molecules are, the stronger the forces between them
Van der Waals forces and bp
stronger Van der Waals forces = higher boiling point
what are permanent dipole dipole forces
weak electrostatic forces of attraction between the slightly + and slightly - charges on neighbouring molecules
what substances have permanent dipole dipole forces
in substances made of molecules with permanent dipoles
what happens if you put an electrostatically charged rod next to a stream of polar liquid
if you put an electrostatically charged rod next to a stream of polar liquid e.g. water then the liquid will move towards the rod
what is the explanation for what happens when you put an electrostatically charged rod next to a stream of polar liquid
polar liquids contain molecules with permanent dipoles. the polar molecules in the liquid can turn around so the oppositely charged end is attracted towards the rod
relationship between polarity and how much stream is deflected
more polar liquid = stronger electrostatic attraction between the rod and the stream = greater deflection
when does hydrogen bonding occur
when hydrogen is directly bonded to oxygen, fluorine or nitrogen
explanation for hydrogen bonding only happening with these 3 elements
fluorine, nitrogen and oxygen are very electronegative so draw the bonding electrons away from the hydrogen atom
explanation for hydrogen bonding
bond is so polarised, and hydrogen has such a high charge density as it’s so small , that the hydrogen atoms form weak bonds with lone pairs of electrons on the F,N or O atoms of other molecules
do substances with hydrogen bonds have high or low melting and boiling points
higher boiling and melting points
explanation for bp/mp for substances with hydrogen bonding
extra energy compared to other molecules needed to break the hydrogen bonds
why does water have a higher bp than the other group 6 hydrides
as it has hydrogen bonding
what happens as water forms ice
as liquid cools to form ice, the molecules make more hydrogen bonds ad arrange themselves into a regular lattice structure
why is ice less dense than water
as H bonds are relatively long, the avg distance between H2O molecules is greater in ice than in liquid water so ice is less dense than liquid water
simple covalent compounds:
bonds within molecules/forces between molecules
simple covalent compounds have strong covalent bonds within molecules but weak forces between the molecules
simple covalent compounds:
electrical conductivity
don’t conduct electricity as there are no free ions or electrons to carry the charge
simple covalent compounds:
melting point
low MP as weak forces between molecules are easily broken
simple covalent compounds:
solubility
some simple covalent compounds dissolve in water depending on how polarised the molecules are
