Bonding and Solid Structures - 1.4 and 1.5 Flashcards
What is ionic bonding between?
metals and non-metals / cations and anions
What is ionic bonding made up of?
strong electrostatic forces of attraction between oppositely charged ions
Are electrons shared in ionic bonding?
No, electrons are transferred
Why do ionic bonds have high m.p?
lots of strong ionic bonds require lots of energy to break
When does ionic bonding conduct elec?
when molten or dissolved
Are ionic bonds soluble in water?
Yes
Why don’t ionic bonds collapse into each other?
ions exist in a balanced position between electron-electron repulsion and ionic attractions between positive and negative ions
What is the coordination number of sodium chloride?
6, Na+ each surrounded by 6 Cl- ions and vice versa
what is the configuration of sodium chloride?
face centred cubic
What is the coordination number of caesium chloride?
8, Cs+ each surrounded by 8 oppositely charged ions
What is the configuration of caesium chloride?
body centred cubic
What is covalent bonding between?
non-metal - non-metal
Are electrons shared in covalent bonding?
yes they share electrons
Why is the m.p between covalent bonds low?
as weak intermolecular forces between molecules
What are the forces of attraction within a molecule?
nuclei + electrons (opposite charges attract)
What are the forces of repulsion within a molecule?
electron + electron (same charges repel)
do covalent bonds conduct elec?
No they don’t
What are physical properties reliant on?
The bonding between molecules (intermolecular forces)
Why does iodine vaporise easily on warming?
weak VDW forces between molecules which require little energy to overcome
What are the two examples of giant covalent structure?
Diamond and graphite
why do giant covalent structure have high m.p?
lots of strong covalent bonds which require lots of energy to break
Do giant covalent structure conduct elec?
Diamond doesn’t, graphite does due to free delocalised electrons between the layers
What is the bond angle of diamond?
109.5 degrees
What is coordinate bonding?
both electrons forming bond pair come from the same atom
Define electronegativity
the ability of an atom to attract a pair of electrons in a covalent bond
What does the degree of an ionic or covalent character depend on?
the difference in electronegativity between the bonded atoms
Finish the sentence:
The higher the electronegativity value…
the better the element can attract bonding electrons
When does electronegativity across a period increase?
- nuclear charge increases
- shielding has little change
When does electronegativity decrease down a group?
- atomic radius decreases
- shielding increases therefore ENC decreases
What is the most electronegative element?
Fluorine
What is the least electronegative element?
Francium
If the value is less than 0.4 what will the bond be?
non-polar covalent bonds
If the value is between 0.4 and 1.9 what will the bonding be?
polar covalent bond
If the value is 2.0 or more what will the bond be?
ionic
If a bond is formed between group 1 and group 7, what will the bond be? Why?
form an ionic bond b/c big electronegativity difference
What does intermolecular bonding govern?
physical properties
What does intramolecular bonding govern?
chemistry eg reactivity
What are the two types of VDW’s forces?
- Temporary dipoles
- Permanent dipoles
How are temporary dipoles formed?
electrons are in constant motion around the nuclei and therefore at any particular moment the distribution of the electron cloud around the nuclei will not be symmetrical
What factors affect the strength of VDW forces?
- size of the molecule/atom as more electrons so more opportunity for temporary dipoles to form
- shape of the molecule as long straight chains will have more points of contact so more VDW forces
What are permanent dipoles?
small positive and negative charges on polar molecules
Do permanent dipoles have stronger intermolecular forces than temporary dipoles? if so why?
Yes as the greater the polarity of a bond or molecule, the stronger the permanent dipole-dipole interactions.
What are hydrogen bonds?
extra strong dipole-dipole attraction bonded to small, very electronegative elements which have lone pairs (fluorine, oxygen or nitrogen)
How does charge density increase in hydrogen bonds between fluorine, oxygen or nitrogen?
b/c F, O, N are highly electroneative and the H atom is small, the positive charge in bonded H atom is spread over a small volume.
What are the effects of H-bonding in terms of boiling points?
Because hydrogen bonds are rather strong intermolecular interactions, breaking them requires a great deal of energy.
What are the effects of H-bonding in terms of ice vs water?
when water freezes, additional H bonds form which hold molecules in a more uniform structure, so therefore the distance between molecules is larger, this causes ice to be denser than water
As boiling point of hydrides increases, what happens to the mr?
mr increases
why is the volume for water and ammonia much higher than other hydrides?
b/c extra energy is needed to break H-bonds between molecules
What is the general strongest relative strength from the forces?
Ionic/covalent > hydrogen > VDW’s
What are patterns of solubility determined by?
the type of intermolecular force, H-bonds or VDW’s forces
In terms of solubility what is important to remember?
Like dissolves like
(eg polar dissolves polar)
The dissolving process can be considered to be 2 processes, these are:
- the breaking of the electrostatic attraction between ions in the ionic lattice
- the formation of aqueous ions w/attractive forces being established between the water molecules and these ions
Why is NaCl soluble in water?
bc the energy released as the water molecules that bind to the NaCl ion is sufficient to overcome the energy needed to break the ionic bonds between Na and Cl
Why are some salts like BaSO4 insoluble?
bc the hydration energy released is NOT sufficient to overcome the energy required to break the ionic bonds in BaSO4
Why does ethanol dissolve in water?
as ethanol possesses an O-H bond which is highly polar so H can bond to adjacent H2O molecules
Why are hydrocarbons insoluble?
do not bave O-H bonds, only force of attraction are VDW which are too weak to overcome bonding with water molecules
Why can hexane dissolve in propane?
both molecules only exhibit weak VDW forces therefore they are soluble and form similar intermolecular forces between propane and hexane hydrocarbon molecules
What is the VSEPR theory?
- the shape of a molecule/ion is governed by the no. of pairs of e-s in the outer shell
- pairs arrange themselves around the central atom as far apart as possible from each other so that the repulsion between them is at a min
What is a lone pair?
a pair of electrons not included in bonding
What is a bonding pair?
a pair of electrons involved in bonding
What is the molecule called with 2 bonded pairs? What is the bond angle? Why?
Linear
180 degrees as a pair of electrons gives max repulsion and bond angle is 180
What is the molecule with 3 bonded pairs? What is the bond angle?
Trigonal planar
120 degrees
What is the molecule with 4 bonded pairs? What is the bond angle?
Tetrahedron
109.5 degrees
What is the molecule with 5 bonded pairs? What is the bond angle?
Trigonal bipyramidal
90 degrees and 120 degrees
What is the molecule with 6 bonded pairs? What is the bond angle?
Octahedron
90 degrees
Why does a lone pair affect the shape?
lone pairs of electrons will repel other electron pairs
Why do lone pairs exert the greatest repelling effect?
bc the orbital of the lone pair of electrons is concentrated closer to the nucleus of the central atom
Arrange these in terms of repulsive strength:
Lone pair + lone pair
Bond pair + bond pair
Lone pair + bond pair
lp + lp > lp + bp > bp + bp
What is the name of the shape which has 3 bonding pairs of electrons and 1 one pair? Why? What is the bond angle? Give an example of a molecule with this bonding?
Pyramidal
as lone pair of electrons are concentrated closer to the nucleus of the central atom than the bonding pairs
107.4
NH3
What is the name of the shape which has 2 bonding pairs of electrons and 2 lone pairs? Why? What is the bond angle? Give an example of a molecule with this bonding?
Bent
as the 2 lone pairs exert a greater repulsive effect than the lone in NH3
bond angleis 104.5
H2O
