Chapter 6 - Flashcards
expanding the octet?
- the bonding atoms will have more than 8 electrons in the outer shells
- this can occur in Group 15-17, period 3 downwards
Group 15 Non metals can form?
3 or 5 covalent bonds
Group 16 non metals can form?
2,4, or 6 covalent bonds
group 17 non metals can form?
1,3,5,7 covalent bonds
what is electronegativity?
the ability of an atom to attract the bonding electrons in a covalent bond
how is electronegativity measured?
on the Pauling scale
electronegativity trends ?
increases across a period, up a group
* IN ALL DIRECTIONS TOWARDS FLUORINE
why does electronegativity increase across a period ?
as the charge on the nucleus increases across a period, the number of protons in nucleus increases, therefore is increased attraction for the outer electrons , the bonded pair of electrons are attracted more strongly
why does electronegativity increase up a group?
- bc down the group, the boning pair of electrons is held increasingly further away from the nucleus bc. the no. of shells increases and so the distance of the outer electrons from the nucleus increases
- the bonded pair of electrons are attracted less strogly
Polar covalent bonds?
- if the 2 bonding atoms are different diff elec neg., ethir attraction for the shared pair of electrons is unequal
- more elctronegative atom has a a greater atttraction for the bonded pair of electrons
non polar bonds ?
- if the 2 bonding atoms are the same or have same/similar electronegativity, their attraction for the shared pair of electrons is equal
- the electrons are equally distributed between the bonding atoms
- the bond is PUREcovalent
dipoles?
- the differing attraction for the pair of electrons allows there to be a small charge difference between the atoms
delta pos, delta neg
electron density?
relates to the probability of finding electron at a particular position of space
- can be imagined as a cloud of electrons around a nucleus, like contour lines
spectrum of bonds - ionic
- the diff in electronegativity is so great that one atom effectively takes tehe electrons from another
spectrum of bonds - polar covalent?
- the diff in electronegativity is small
- the atoms share the electrons unequally
- the bond is polarised
spectrum of bonds - covalent?
- no difference in electronegativity
- the molecule is electronically similar
molecules containing polar bonds are not always polar…
the symmetry of polar bonds can cancel out the effect of any permanent dipole
non symmetrical?
- e.g. h20
- a diff in charge exists across the molecule, there is an overall dipole, molecule is polar
symmetrical?
- e.g.CO2
- the symmetry of the molecule means that the effect of any permanent dipole is cancelled out
- linear, tetrahedral or trigonal planar shape
- all atoms attached to central atom are identical
- no diff in charge exists across the molecule
non - polar bond definition?
the 2 bonding atoms are identical and the electrons are equally distributed between the bonding atoms
polar bonds definition?
the 2 bonding atoms are different and their attraction for the shared pair of electrons is unequal
intramolecuar forces ?
act WITHIN molcules
- ionic, covalent
Intermolecular forces ?
forces of attractraction BETWEEN molcules
- non bonded interactions
- don’t involve transfer of electrons
intermolecular forces are the result of?
the constant an random movement of electrons within the shells of atoms
3 main types of intermolecular forces?
London forces
- permanent dipoles
- hydrogen bonds
INDUCED DIPOLE?
- rather than electrons existing statically within orbitals, they are constantly moving within the clouds of charge
- at any moment, it is likely that there are more electrons on one side of the atom than the other
- temp, the charge is unequally distributed
- the temp dipole can induce a temp dipole in neighbouring atoms
- 2 dipoles will be attracted to each other
the scale of london forces?
- occur on more than just an atomic scale, occur molecular scale too
- occur between almost everything
- in addition to other intermolecular forces
permanent dipoles?
- if correctly aligned, the 2 mols will attract each other
- however, as mols are randomly and constantly moving, they do not always align
london forces occur between?
- induced dipole, induced dipole
dipole - dipole interactions?
- permanent - permanent
- permanent - induced
permanent dipoles are much ____ interactions
weaker
hydrogen bonds are?
strong permanent dipole- permanent dipole forces of attraction that always involves Hydrogen bonded to Oxygen, Nitrogen, Fluorine
hydrogen bonds occur between?
- an electron deficient hydrogen and Oxygen, Fluorine, or Nitrogen
- and a lone pair of electrons on a highly electronegative atom on another molecule
when does an electron deficient hydrogen occur?
when H is bonded to a more electonegative element
all compounds containing an N-H bond are able to form
intermolecular H bonds
the only fluroide containing compound with intermolecular H bonding is
hydrogen fluoride
hydrogen bonding gives water these interesting properties?
- ice is less dense than liquid water
- high b.p and m.p
- high surface tension - the lattice is strong and flexible
strength of intermolecular forces?
london -> permanent dipoles -> hydrogen bonds
types of intermolecular forces - b.p. Noble gases
trend; gradual increase in b.p
- only weak Van der Waals forces of attraction exist
- Van der Waals forces od attraction increase as electrons increase
- B.p. increases down the group
types of intermolecular forces - b.p.- H20, HF, NH3
trend: higher bp than expected
- H bods exist which are stronger than Van Der Waals Forces
SHAPES OF MOLECULES: always write
the shape of a molecule is determined by the repulsion between pairs of electrons.
a double bond is classed as 1 ……
region of electrons
energy required to break induced dipole forces?
2-4 KJmol(^-1)
explain trend in BP of halogens as ⬇ group
gas - fewer weak induced dipole forces as fewer electrons
- more stronger induced dipoles due to more electrons
when the atoms which are bonded together attract the bonding electrons unequally, the bonds are said to be ?
POLAR
energy required to break permanent dipole forces?
10KJmol(^-1)
what is a polar molecule?
one side delta + and other delta -
energy needed to break Hydrogen bonds ?
40KJ per mole
hydrogen bonds hold water molecules together in a ____ _________ ______
simple molecular lattice
the density of ice is less than water bc
the H bonds hold the water molecules apart in an open lattice structure
- so molecules in ice are further apart than in water
H bonds & MP, BP in water
- water has a high MP &BP than molecules of a similar size with just induced dipole or permanent dipole foces
water also has
high surface tension - pond skaters walk on a raft of H bonds
structure of iodine (I 2 )
- simple molecular lattice or covalent lattice
- iodine is a dark grey cystalline solid that sublimes to form a purple vapour
- very very slightly soluble in water, but dissolves in organic solevents
MP: 114 (under pressure) BP: 184
iodine typical properties?
- sublimes on gently heating at room pressure
- no electrical conductivity
- soluble in organic solvents - like dissolves like
giant covalent structures - diamond?
4 strong covalent bonds with each carbon in a tetrahedral arrangement
covalent bonds in ALL directions
MP: very high, lots of strong covalent bonds = lots of energy to break
Conductivity: no mobile charged particles in diamond, non conductor
giant covalent structures - gpraphite?
- 3 strong covalent bonds around each carbon atom within the layers
- trigonal planar arrangement
- 4th electron is delocalised between the layers holding them together
- NO INTERMOLECULAR FORCES - NOT BETWEEN MOLECULES
MP: very high, lots of strong covalent bonds, lots of energy to break
Conductivity: 4th e is delocalised so can move to carry current = conductor
Why is the formula of silicon dioxide SiO2 not SIO4?
- each O is bonded to 2 Si
- half of O goes to each Si
= 2 O for each
giant covalent structures covalent bonds are
BROKEN
electron pair repulsion theory?
electrons repel each other so that they are arranged as far apart as possible
what does a solid line represent?
a bond in the plane of the paper
a solid wedge?
comes out of the plane of the paper
a dotted wedge?
goes into the plane of the paper
lone pairs repel more strongly than a bonded pair bc?
a lone pair of electrons is slightly closer to the central atom, and occupies more space, than a bonded pair
repulsions between lone pairs and bonded pairs scale?
bonded pair/bonded pair < bonded pair/ lone pair < lone pair/ lone pair
why does the way the bonded electron pair is shared
change when the 2 atoms are not of the same element?
- the nuclear charges are different
- the atoms may be different sizes
- the shared pair of electrons may be closer to one nucleus than the other
why are noble gases not included in the Pauling scale?
- they tend not to form compounds
a bond is polar if these 5 elements are tehre?
F, O , N , S, Cl
covalent bond electronegativity difference =?
0
polar covalent bond electronegativity difference =?
0 - 1.8
ionic bond electronegativity difference =?
greater than 1.8
a dipole in a polar covalent bond is a?
permament dipole
intermolecular forces responsible for ? but covalent determine ?
inter = physical properties - MP &BP covalent = identity and chemical reactions of molecules
what effect does having more electrons in each molecule have on induced dipole?
- the larger the instantaneous and induced dipoles
- the greater the induced dipole-dipole interactions
- the stronger the attractiev forces between molecules
larger number of electrons =
larger induced dipoles
- more energy needed to break, increasing BP
when ice lattice breaks ? but when water boils ?
ice lattice breaks = rigid arrangement of H bonds is broken
water boils = H bonds break completely
Soubility of diamond and graphite?
Bith don’t dissolve in polar/covalent solvents
Lots of strong covalent bonds need to be broken
Giant covalent structures - graphene
Like graphite :- triginal planar arrangement around C atom
- 3 cov bonds
- 4 e delocalised along structure
MP: high- 3 covalent bonds = lots of energy
Conductivit= 4th e delocalised = good electrical conductivity
why do covalent substances not really dissolve in both organic substances too?
covalent bonds too strong, lots of energy needed to break
why is the 4th electron in graphite delocalised?
- 4th e is held in a p orbital
- C atoms close enough to let the p orbitals overlap
why is graphite soft and slippery?
- layers can slide over each other
- so is used in pencil
- layers of graphite slide onto the paper
graphite can also be used in?
lubricant
nanotubes?
- layers of graphene rolled into a tube
- diameter of the tube is one billionth of a metre
- drug delivery
buckminsterfullerene?
- hollow cages of C
- Drug delivery, drug trapped within the balls
