2A: Bonding Flashcards
Use PPQs for spec points: 4, 8, 12, 19
What is ionic bonding?
The strong electrostatic attraction between oppositely charged ions
How do ionic radius and ionic charge affect the strength of ionic bonding?
- Smaller ionic radius and greater ionic charge
- So greater charge density
- So stronger ionic bonding
Describe the formation of ions in terms of electron loss or gain.
Loss of electrons forms positive ions.
Gain of electrons forms negative ions.
Explain the trend in ionic radius down a group.
Ionic radius increases, because more electron shells.
Explain the trend in ionic radius for isoelectronic ions.
Ions with a higher nuclear charge have a smaller ionic radius.
Describe the experiment to show the migration of ions.
Ionic compound on damp filter paper with oppositely charged electrodes.
The opposite ions migrate towards the electrodes.
Proves the existence of ions.
What is covalent bonding
The strong electrostatic attraction between two nuclei and the shared pair of electrons between them
Explain the relationship between bond lengths and bond strengths for covalent bonds?
Shorter bond = stronger bond,
because electrons are closer to the nucleus
State and explain the trend in X-X bond length as you go down group 7.
More electron shells,
so more shielding,
so weaker attraction between the nuclei and the bonding electrons,
so longer bond.
What determines the shape of a simple molecule or ion?
The repulsion between the electron pairs that surround a central atom.
Electron pairs will take a position where repulsion is minimised.
Shape and bond angles of BeCl2
Linear
180
Shape and bond angles of BCl3
Trigonal planar
120
Shape and bond angles of CH4
Tetrahedral
109.5
Shape and bond angles of NH3
Trigonal Pyramidal
107
Shape and bond angle of NH4+
Tetrahedral
109.5
Shape and bond angle of H2O
Bent
104.5
Shape and bond angles of PCl5
Trigonal Bipyramidal
120 and 90
Shape and bond angle of SF6
Octahedral
90
What is electronegativity?
The ability of an atom to attract the bonding electrons in a covalent bond
How is a dipole formed?
When bonding atoms have a large difference in electronegativity, they attract electrons unequally, and one gets a slight positive charge and the other a slight negative charge.
What is a polar molecule?
A molecule with polar bonds creating an overall dipole.
How do you practically check if a substance contains polar molecules?
Electrostatic charge next to a jet of liquid.
Polar molecules will be attracted.
Describe London Forces.
Instantaneous dipole - induced dipole.
Caused by an instantaneous imbalance of electrons in the molecule.
The resultant dipole induces a dipole in a nearby atom or molecule.
Strength increases with number of electrons.
Describe permanent dipole attractions.
Two molecules with permanent overall dipoles.
Attraction between the positive charge in one molecule and the negative charge in the other.
Describe a diagram to show hydrogen bonding.
Lone pair on the O,
delta+ on H and delta- on O,
dashed line between H and the lone pair
What is needed for a Hydrogen Bond to form?
- A large dipole between a H atom and a highly electronegative atom (eg O, N or F)
- A small H atom that can get very close to other molecules
- A lone pair of electrons on the O, N or F atom that the positively charged H atom can line up with
Explain the melting and boiling points of water.
Relatively high temperatures.
Each molecule has 2 hydrogens connected to an oxygen, so it can form 2 hydrogen bonds with other water molecules.
Explain the density of ice compared to water.
Lower density.
As water freezes, the hydrogen bonds pull the water molecules into fixed positions in a comparatively open lattice.
State and explain the trends in boiling temperatures of alkanes with increasing chain length.
As chain length increases,
there are more electrons,
so London forces are stronger,
so boiling point increases.
State and explain the effect of branching in the carbon chain on the boiling temperatures of alkanes
Molecules cannot get as close together,
so London forces are weaker,
so boiling point is decreased.
State and explain the volatility of alcohols compared to alkanes with a similar number of electrons.
The -OH group causes hydrogen bonding,
so boiling point is much higher than alkanes,
so volatility is relatively low.
State and explain the trends in boiling temperatures of the hydrogen halides, HF to HI.
HF has hydrogen bonding, so boiling point is highest.
Down the group from HCl to HI,
number of electrons increases
so London forces are stronger,
so boiling point increases.
Explain why some ionic compounds dissolve in water.
The polar water molecules are attracted to the charged ions.
The water molecules hydrate the ions and break the ionic bonds in the compound.
Explain why simple alcohols dissolve in water.
Alcohols form hydrogen bonds between molecules.
Alcohols also form hydrogen bonds with water molecules.
Bonds formed are similar to bonds broken.
Explain why polar molecules such as halogenoalkanes are insoluble in water.
They are unable to form hydrogen bonds with water.
What compounds would you dissolve in non-aqueous solvents?
Compounds that have similar intermolecular forces to those in the solvent.
What is metallic bonding?
The strong electrostatic attraction between metal ions and the delocalised electrons
What colours would be observed after the electrolysis of copper(II) chromate(VI)?
Cathode: Blue (copper ions)
Anode: Yellow (chromate ions)
