bonding p1,2 Flashcards
what are ions?
charged particles that are formed when an atom loses or gains electrons
what is the charge of an ion when electrons are gained?
negative
positive when lost
what are molecular ions?
covalently bonded atoms that lose or gain electrons
which electrons are lost when as atom becomes a positive ion?
electrons in the highest energy levels
do metals usually gain or lose electrons?
lose electrons
which are the 4 elements that don’t tend to form ions and why?
Beryllium, boron, carbon and silicon
requires lots of energy to transfer outer shell electrons
what are the 3 main types of chemical bonds?
ionic, covalent, metallic
ionic bonding
electrostatic attraction between positive nucleus and negative ions
what determines the strength of an ionic bond?
- ionic radius
- ionic charge
- ionic bonding is stronger and the melting points higher when the ions are smaller and have higher charges
what is the trend in ionic radius down a group?
increases down the group
because the ions have more shells of electrons and thus the outermost electron experiences less pull from positive nucleus
what are the physical properties of ionic compounds?
- high melting points
- non conductor of electricity when solid
- conductor when in solution or molten
- brittle
in a solution of CuCrO4 with connected electrodes which electrode will the 2 ions (Cu2+ & CrO2-) migrate to?
Cu2+ - migrates to negative electrode
CrO2- - migrates to positive electrode
covalent bonding
electrostatic attraction between a shared pair of electrons and the nuclei
metallic bonding
electrostatic attraction between the positive metal ions and the sea of delocalised electrons
why do giant ionic lattices conduct electricity when liquid but not when solid?
in solid state the ions are in fixed positions and thus cannot move
when in liquid state the ions are mobile and thus can freely carry charge
giant ionic lattices have high melting and boiling point. why?
large amount of energy is required to overcome the electrostatic bonds
what type of solvents do ionic lattices dissolve in?
polar solvents
e.g. water
why are ionic compounds soluble in water?
water has a polar bond
hydrogen atoms have a 1+ charge and oxygen atoms have a 2- charge
these charges are able to attract charged ions
what is it called when atoms are bonded by a single pair of shared electrons?
single bond
what is the effect of multiple covalent bonds on bond length and strength?
double/triple bonds exert greater electron density therefore the attraction between nucleus and electron is greater resulting in a shorter and stronger bond
what is a lone pair?
electrons in the outer shell that are not involved in the bonding
what is formed when atoms share two pairs of electrons?
double bond
what is a dative covalent bond?
a bond where both of the shared electrons are supplied by one atom
how are oxonium ions formed?
formed when acid is added to water
H3O+
what does expansion of the octet mean?
when a bonded atom has more than 8 electrons in the outer shell
what are the types of covalent structure?
- single molecular lattice
- giant covalent lattice
describe the bonding in simple molecular structures
atoms within the same molecule are held by strong covalent bonds and different molecules are held by weak intermolecular forces
why do simple molecular structures have low melting and boiling points?
small amount of energy is enough to overcome the intermolecular force
can simple molecular structures conduct electricity?
no - no free charged particles to move around
simple molecular structures dissolve in what type of solvent?
non polar solvents
examples of giant covalent structures
diamond, graphite, silicon dioxide
properties of giant covalent structures?
- high melting and boiling point
- non conductors (except graphite)
- insoluble in polar and non polar solvents
how does graphite conduct electricity?
delocalised electrons present between the layers are able to move freely carrying the charge
why do giant covalent structures have high melting and boiling points?
strong covalent bonds within the molecules need to be broken which requires lots of energy
describe the structure of diamond
3D tetrahedral structure of C atoms, with each C atom bonded to 4 others
what does the shape of a molecule depend on?
number of electron pairs in outer shell, number of electrons which are bonded/lone pairs
2 bonded pairs shape
linear
180*
3 bonding pairs shape
trigonal planar
120*
4 bonded pairs shape
tetrahedral
109.5*
5 bonded pairs shape
trigonal bipyramid
90* and 120*
6 bonded pairs
octahedral
90*
3 bonded pairs 1 lone pair shape
pyramidal
107*
2 boned pairs and 2 lone pairs shape
non linear (bent)
104.5*
by how many degrees does each lone pair reduce the bond angle?
2.5*
electronegativity
the ability of an atom to attract a (bonding) pair of electrons in a covalent bond
what scale is electronegativity measured on?
Pauling scale
which direction of the periodic table does electronegativity increase?
top right, towards fluorine
what does is mean when a bond is non-polar?
the electron in the bond are evenly distributed
how is a polar bond formed?
bonding atoms have different electronegativities
why is H2O polar and not CO2?
CO2 is symmetrical so there is no overall dipole
intermolecular force
attractive force between neighbouring molecules
what are the 3 types of intermolecular forces?
hydrogen bonding, permanent dipoles, London forces
permanent dipole-induced dipole interactions
when a molecules with a permanent dipole is close to other non polar molecules it causes the non polar molecule to become slightly polar leading to attraction
permanent dipole-permanent dipole interactions
some molecules with polar bonds have permanent dipoles
forces of attraction between those dipoles and those of neighbouring molecules
London forces
- caused by random movements of electrons
- leads to instantaneous dipoles
- instantaneous dipole induces a dipole in nearby molecules
- induced dipoles attract one another
are London forces greater in smaller or larger molecules?
larger due to more electrons
does boiling point increase or decrease down the noble gas group? why?
increases
the number of electrons increases and hence the strength of London forces also increases
what conditions are needed for hydrogen bonding?
between hydrogen atom and a highly electronegative atom - O, N, F
why is ice less dense than liquid water?
in ice the water molecules are arranged in an orderly pattern
it has an open lattice with hydrogen bonds
in water the lattice is collapsed and the molecules are closer together
why does water have a higher melting/boiling point than expected?
hydrogen bonds are stronger than other intermolecular forces so extra strength is required to overcome the forces
what type of intermolecular forces do alkanes have? why?
London force
induced dipole-dipole interaction becuase the bonds are non polar
what happens to the boiling point as alkane chain length increases? why?
boiling point increases bc there is more surface area and so higher number of induced dipole-dipole interactions
therefore more energy required to overcome the attraction
does a branched molecule have lower or higher boiling point compared to equivalent straight chain? why?
branched molecule has a lower boiling point bc they have smaller surface area and hence less induced dipole-dipole interactions
are alkanes soluble in water?
insoluble because hydrogen bonds in water are stronger than alkane’s London forces
what kind of intermolecular forces do alcohols have?
Hydrogen bonding due to the electronegativity difference in the OH bond
London forces
how do alcohols’ melting point and boiling point compare to other hydrocarbons’ of similar C chain lengths?
higher due to hydrogen bonding being stronger than London forces
are alcohols soluble in water? why does solubility depend on chain length?
soluble when short chain - OH hydrogen bonds to hydrogen bond in water
insoluble when long chain - non-polar C-H bond
explain the trend of boiling temperatures of hydrogen halides HF to HI
general increase of boiling point from HCl to HI which is caused by increasing London forces becuase of increasing number of electrons
there is a big drop from HF to HCl becuase F is very electronegative therefore the hydrogen bonding is much stronger
