physical chem; bonding Flashcards
define the term ionic bonding
it’s the electrostatic force of attraction between oppositely charged ions formed electron transfer
what charge does group 1 form?
1+
what charge does group 2 form?
2+
what charge does group 3 form?
3+
what charge does group 5 form?
3-
what charge does group 6 form?
2-
what charge does group 7 form?
1-
list the molecular ions
OH⁻ = hydroxide
NO₃⁻ = nitrate
NH₄⁺ = ammonium
SO₄²⁻ = sulfate
CO₃²⁻ = carbonate
do ionic compounds dissolve in water & if so why?
yes
as water molecules are polar they can attract the +ve & -ve ions & break up the structure
explain the features of ionic structures
can conduct electricity when molten or dissolved as e- are free to move around
have high m.p as the structure has many strong electrostatic forces between oppositely charged ions = lots of energy required to overcome the forces
what makes an ionic bond stronger & provide an example
when the ions are smaller/have higher charges
e.g. MgO has a higher m.p than NaCl as MgO’s ions are smaller & have higher charges (2+ & 2-) compared to NaCl (1+ & 1-)
explain the trend of ionic radii in groups & why
increases down a group as ions have more shells of e- down a group
define the term covalent bonding
its an electrostatic attraction between the shared e- & +ve nucleus
what is a dative/coordinate bond?
its a bond where 1 atom donates 2 e- to an atom/ion
give examples of compound that have dative bonds
NH₄⁺
H₃O⁺
NH₃BF₃
give examples of giant covalent structures
graphite
diamond
what is a covalent simple molecular structure & give examples
simple molecular - IMF (van der waals, permanent dipoles, H bonds) between molecules
e.g. iodine, ice, CO₂, H₂O & CH₄
what is a covalent macromolecular structure & give examples
it’s a giant molecular structure held together by many strong covalent bonds
e.g. diamond, graphite, silicon dioxide & silicon
describe the structure of graphite
layers slide easily as there are weak forces between the layers
delocalised e- between layers allow graphite to conduct electricity as they can carry a charge
has low density - as layers are far apart compared to bond length
many strong covalent bonds = high m.p
describe the structure of diamond
good heat conductor - has a tightly packed, rigid arrangement
many very strong covalent bonds = high m.p
doesn’t conduct electricity well as doesn’t have any delocalised e-
describe the similarities in the structures of graphite & diamond
they both and many strong covalent bonds and are both insoluble due to the strength of their bonds
define the term metallic bonding
it’s the electrostatic force of attraction between the metal +ve ions & the delocalised e-
what structures do metals have?
giant metallic structures
describe the structure of giant metallic lattices
they have +ve metal ions which are formed as metals donate e- to form a sea of delocalised e-
describe the features of metallic structures
high m.p - due to strong electrostatic attractions
good electrical conductors - delocalised e- are mobile & can carry electrical currents
good thermal conductors - delocalised e- can transfer KE
are insoluble as metallic bonds too strong to break
what makes a metallic bond stronger & provide an example
the more e- an atom can donate to the delocalised e- system = higher m.p
e.g. Mg has a higher m.p than Na as Mg can donate 2 e- whereas Na can only donate 1 e-
name the structure of a shape & its bond angle with 2 bonding pairs & 0 lone pairs
linear
180º
name the structure of a shape & its bond angle with 3 bonding pairs & 0 lone pairs
trigonal planar
120º
name the structure of a shape & its bond angle with 4 bonding pairs & 0 lone pairs
tetrahedral
109.5º
name the structure of a shape & its bond angle with 5 bonding pairs & 0 lone pairs
trigonal bipyramidal
120º & 90º
name the structure of a shape & its bond angle with 6 bonding pairs & 0 lone pairs
octahedral
90º
name the structure of a shape & its bond angle with 3 bonding pairs & 1 lone pair
pyramidal
107º
name the structure of a shape & its bond angle with 2 bonding pairs & 2 lone pairs
bent
104.5º
name the structure of a shape & its bond angle with 4 bonding pairs & 2 lone pairs
square planar
90º
define the term electronegativity
it’s the ability of an atom to attract a pair of e- in a covalent bond
what is the most electronegative atom?
fluorine
list the most electronegative atoms
F, O, N & Cl
state the general trend of electronegativity in the periodic table
electronegativity increases the further up & right you in the periodic table
state the factors that affect electronegativity
nuclear charge:
increase in no.of protons = increased electronegativity
atomic radius:
its the distance between e- & nucleus - increased atomic radius = decreased electronegativity
shielding:
its the no.of shells & subshells - increased shielding = decreased electronegativity
how do covalent bonds become polar?
when atoms attached have a difference in electronegativity
how do we know if a compound is polar?
atoms will have either a delta +ve (on least electronegative atom) / delta -ve (on most electronegative atom)
how do we know if an atom is non-polar?
if the atoms bonded have the same / similar electronegativities
what causes a bond to be more polar?
the bigger the difference in electronegativity = the more polar a bond will be
what is the difference between intramolecular & intermolecular forces?
intramolecular = forces within a molecule & are usually covalent bonds
intermolecular forces = forces between molecules
give an example of a molecule with intramolecular forces
water
O - H bond within the molecule
give an example of a molecule with intermolecular forces
water
H bond between 2 water molecules
name the types of intermolecular forces from strongest to weakest
H bonding
permanent dipole-dipole forces
induced dipole-dipole forces (AKA van der waals)
how do induced dipole-dipole (van der waals) forces form?
any molecule/atom with e- can form induced dipole when it moves near an atom/molecule
more e- in molecule = higher change induced dipole will form
explain whether an induced dipole-dipole force is permanent/temporary & why
interaction between 2 molecules is temporary & only exists when they are nearby
when they move apart, the interaction is destroyed
state which intermolecular forces can be found in hydrocarbons & how they affect its properties
van der waals
straight, long hydrocarbons have more van der waals = more energy needed to overcome forces - m.p increases
explain how the arrangement of branched hydrocarbons affects its b.p
branched hydrocarbons can’t pack together as close which weakens van der waals = lowers b.p
what are permanent dipole-dipole interactions?
there are weak electrostatic forces that exist in molecules with a polarity
what is the difference between van der waals & permanent dipole-dipole interactions?
permanent dipoles are stronger - have a higher m.p
name the other type of intermolecular forces found in molecules that have permanent dipole-dipole interactions
van der waals
explain how we can identify polar molecules
- place a charged rod near a steady stream of a polar liquid
- if polar molecules are present the liquid will bend towards the rod as the molecules align to face the oppositely charged rod
when does hydrogen bonding occur?
between hydrogen & NOF
name the other types of intermolecular forces found in molecules that have H bonding
van der waals & permanent dipole-dipole interactions
how are H bonds shown in diagrams?
shown by using dotted lines
explain why ice is less dense than water
ice forms a regular structure held by H bonds. & the molecules are further apart which makes it less dense than water
explain the boiling points trend of hydrogen halides using examples
HF has a higher b.p than HCl as it H bonding - more energy is needed to overcome electrostatic forces
there is a slight increase in b.p from HCl to HI due to the increased mass of molecule = bigger e- cloud - more van der waals
