T4: Bonding Flashcards
metallic structure
giant lattice (regular arrangement of particles)
metallic bonding
strong metallic bonds
metallic structure and bonding definition
strong electrostatic attraction between positive metal ions surrounded by a sea of delocalised electrons
comparing the strength of metallic bonds (the bonding in Mg is stronger than in Na)
- Mg2+ has a greater charge of 2+
- Mg2+ ions are smaller
- attraction between the Mg2+ ions and the delocalised e- is stronger
properties of metals conductivity
they have delocalised e-
properties of metals strength of the metal
strong electrostatic attraction between the positive metal ions and delocalised e-
properties of metals malleable and ductile
layers of metal ions can slide past one another
properties of metals melting and boiling points
strength of the metallic bonds
covalent structure
macromolecular or simple molecular
covalent bonding
strong covalent bonds
covalent structure and bonding definition
a shared pair of electrons between 2 atoms
How does sharing e- hold atoms together
The attraction forces are stronger than the repulsion forces and therefore the atoms are held together
3 macromolecular structures
- carbon
- silicon
- silicon dioxide
2 macromolecular crystals
- diamond
- graphite
diamond characteristics
- each C has 4 covalent bonds
- tetrahedral shape
- very high mp
- very hard
- non-conductor
graphite characteristics
- layers with 3 covalent bonds to each C
- high mp
- each C has delocalised e-
- layers held together by weak intermolecular forces
- soft layers can slide over each other
- conductor (has delocalised e-)
examples of simple molecular structures
H2O (water)
NH3 (ammonia)
Cl2 (chlorine)
O2 (oxygen)
CH4 (methane)
example of drawing simple molecular structure (I2)
3 molecules each with 2 atoms covalently bonded with intermolecular forces between the molecules
forces and properties of simple molecular structures
- intermolecular forces act between molecules
- simple molecular substance boils intermolecular forces break
- intermolecular forces weaker than covalent bonds so simple molecular compounds have low mp
ionic structure
giant lattice
ionic bonding
strong ionic bonds
ionic structure and bonding definition
an ionic bond is the strong electrostatic attraction between oppositely charged ions
drawing the structure of an ionic compound
physical properties of ionic compounds high mp + bp
strong electrostatic attraction
physical properties of ionic compounds electrical conductivity
solid -> ions fixed in lattice so cannot move
aqueous / molten -> ions can now move and conduct electricity
structural properties tend to be brittle + shatter easily
when an external force is applied the layers of ions shift and like charges repel causing the crystal to crack
molecule definition
a group of atoms which are covalently bonded to 1 another
coordinate bond definition
a shared electron pair which have both come from the same atom
covalent bond =
bonded pair
coordinate bond =
lone pair
model ans lone pair donation question
lone pair of electrons on the X+ / X- is donated to Y
valence definition
the outer shell of electrons (e- used in bonding)
to minimise their (bonding and lone pairs) repulsion…
the e- pairs repel each other as far apart as possible
strength of repulsion between lone and bonding pairs equation
lone pair to lone pair > lone pair to bond pair > bond pair to bond pair
strength of repulsion between lone and bonding pairs
- lone pairs repel more than bonding pairs
- the strength of the repulsions determines the bond angles between the bond to bond pairs
VSEPR theory - draw the shapes of molecules and ions, name them and give the bonding angles
electronegativity definition
the power of an atom to attract the pair of electrons in a covalent bond
which element has the highest electronegativity
F - 4.0
what are the next elements with the highest electronegativity
O - 3.5
N - 3.0
Cl - 3.0
Br - 2.8
I - 2.5
S - 2.5
P - 2.1
the 3 factors which determine how electronegative elements are
- nuclear charge
- atomic radius
- shielding
elements with high electronegativity have…
- high nuclear charge
- relatively low atomic radius
- low amount of shielding
(EN) covalent bonding =
small difference in EN
(EN) ionic bonding =
large difference in EN
across Period 2 the EN increases because…
- number of protons increase
- same shielding
- ability to attract electrons in a covalent bond increases
polarity in Cl2
Molecules made of atoms with no difference in EN have their electrons distributed evenly
Bond = non polar
polarity in HCl
Bond is unsymmetrical
1 atom that is more EN
H (δ+) - Cl (δ-)
This creates what’s called a ‘dipole’
polarity of BF3 (molecule)
- Molecule is symmetrical
- Dipoles cancel out
- NON-POLAR
polarity of NH3 (molecule)
- Molecule is not symmetrical
- Dipoles don’t cancel out
- POLAR
polarity of CHCl3 (molecule)
- Molecule is not symmetrical
- Dipoles don’t cancel out
- POLAR
where do imf found
between molecules
3 intermolecular forces
- H bonding
- permanent dipole-dipole
- induced dipole-dipole (van der waals forces)
how do you know if it has H bonding
H bonded to F, N, O
how do you know if it has permanent dipole dipole forces
- not H bonded to F, N, O
- polar molecule
how do you know if it has induced dipole dipole forces (van der waals forces)
- not H bonded to F, N, O
- non-polar molecule
what happens to the stronger intermolecular forces
- have a higher mp + bp
- more energy to overcome the imf
what is special about I2 (imf)
- i.d.d forces
- large molecule (lots of e-)
- solid at room temp
- stronger imf than H bonding in water
BF3 (identifying imf)
- non-polar
- i.d.d forces between molecules
- least energy required to overcome forces between molecules
NH3 (identifying imf)
- H bonding between molecules
- strongest attraction between molecules
CHCl3 (identifying imf)
- polar
- p.d.d between molecules
bp comparison (how to write it)
NH3 > CHCl3 > BF3
H bonding when it occurs
- strongest intermolecular attraction
- occurs between H (bonded to N, O, F) and a lone pair on a N, O, F atom on another molecule
H bonding how does it arise
- N, O, F are highly electronegative
- there is large difference in electronegativity between O + H (state atoms) creates a dipole on O-H bond (state bond)
- lone pair on O atom (state atom) in 1 molecule strongly attracts a partially positive H atom on another molecule
H bonding how to draw it
P.D.D forces when it occurs
- generally weaker than H bonding
- occurs between polar molecules
P.D.D forces how does it arise
- difference in EN leads to bond polarity
- dipoles do not cancel out therefore the molecule has an overall permanent molecule
- there is an attraction between δ+ on 1 molecule and δ- on another
P.D.D forces how to draw it
I.D.D forces when it occurs
- generally weakest force (stronger than H and PDD if large molecular)
- occurs between all molecules (and atoms of noble gases) important force in non-polar molecules - don’t have any other i.m.f
I.D.D forces how does it arise
(RUTID)
R -> Random movement of e- in 1 molecule (atom) leads to an…
U -> Uneven distribution of e-, creating a…
T -> Temporary dipole in 1 molecule (atom). This…
I -> Induces a induced dipole in a neighbouring molecules (atom)
D -> Dipole attract
I.D.D forces how to draw it
i.m.f in molecules containing H
(graph shows bp of molecules changes as the central atoms get bigger)
key points to note from the graph
- H2O, HF, NH3 all have H bonding between molecules
- other molecules increase in bp as size increases
- bigger molecules have stronger I.d.d forces between molecules
The importance of H bonding in ice
Ice less dense than water
H bonds in ice hold the molecules further apart
The importance of H bonding in proteins
Proteins held in complex 3D shapes by H bonds
N-H group on 1 amino acid and H bonding to the C=O group on another
the importance of H bonding in DNA
- 2 strands double helix DNA held by H bonds
- H bonds strong enough to hold strands together
- weak enough to enable DNA helix to separate for DNA replication when cells divide
physical properties of period 3 elements (trends in mp and bp) -> what 3 things should you talk about
1 Na to Mg to Al
2 Silicon
3 P, S, Cl and Ar
phosphorus chemical formula
P4
silicon chemical formula
S8
chlorine chemical formula
Cl2
argon chemical formula
Ar
physical properties of period 3 elements (trends in mp and bp) -> Na to Mg to Al
mp increases Na to Mg to Al as strength of metallic bonding increases
Na only forms +1 ions, Mg forms +2 ions, Al forms +3 ions
Na ions are largest whereas Al ions are smallest so stronger metallic bonding for Al
physical properties of period 3 elements (trends in mp and bp) -> Silicon
- high mp -> macromolecular -> held by strong covalent bonds that require lots of energy to break
physical properties of period 3 elements (trends in mp and bp) -> P, S, Cl and Ar
- simple molecular -> I.D.D increase for bigger molecules
- S8 biggest strongest VdW higher mp and bp
- P4 next in size order slightly lower mp and bp
- Cl2 smallest of 3 weakest VdW lowest mp and bp
- Ar single atoms weakest VdW forces of non-metals lowest mp and bp of all period 3 elements
physical properties of period 3 elements (trends in mp and bp) -> silicon has the highest mp but aluminium has the highest bp
Si strong covalent bonds -> high temp needed once
Molten relatively little more energy is then needed to vapourise it -> bp not much higher then the mp
compared to Al once molten a lot of energy is still needed to overcome strong electrostatic metallic bonds -> Al has very high bp
comparison question 1
- Br is simple molecular
- Mg is metallic
- Br has weak VdW forces between molecules
- more energy is needed to overcome the stronger metallic bonds
- Mg has a much greater liquid range because forces of attraction in liquid are stronger
comparison question 2
HCl -> p.d.d between molecules
I2 -> i.d.d between molecules
I2 is a bigger molecule so stronger i.d.d forces between molecules
comparison question 3 [6m]
HF -> simple molecular -> H bonding between molecules -> strongest attraction of 3 -> requires most energy to break
CH3Cl -> simple molecular -> p.d.d forces between molecules
Ne -> simple atomic -> i.d.d forces between atoms -> weakest attraction of the 3 -> requires least energy to break