Paper 1&2- Bonding Flashcards
(35 cards)
Why is ice less dense than water?
Hydrogen bonds hold molecule apart in an open lattice structure
How do hydrogen bonds form?
Hydrogen is bonded to a very electronegative element (N,F, or O). H becomes positive and other element becomes partially negative. The partially positive hydrogen is attracted to a lone pair of electrons on another molecule
How do permanent dipole-dipole forces arise?
The delta positive and delta negative charges on polar molecules cause weak electrostatic forces of attraction between opposite charges.
How do Van-der-Waals forces arise?
Electrons constantly moving so at any point can be unevenly distributed, causing a temporary dipole. This induces dipoles in neighbouring molecules causing a weak electrostatic attraction between them.
What affects the strength of Van-der-Waals forces?
Bigger molecules means more electrons so larger induced dipole and stronger electrostatic attraction.
List the 3 types of intermolecular forces starting with the smallest
Van-der-Waals
Dipole-dipole
Hydrogen bonding
Define electronegativity
The power of an atom to draw electron density in a covalent bond towards itself
How and why does electronegativity change down a group?
It decreases
Atomic radius increases and so does shielding, meaning there is a weaker electrostatic attraction between the nucleus and the bonding electrons
How and why does electronegativity change across a period?
It increases
Shielding is constant, atomic radius decreases, and nuclear charge increases, meaning a stronger electrostatic attraction between the nucleus and bonding electrons
Why don’t noble gases have a value for electronegativity?
They don’t bond
Explain the melting points of ionic compounds
They are high
Strong electrostatic attraction in all directions between oppositely charged ions in a giant lattice structure
Why are ionic compounds hard?
Many strong ionic bonds
Why are ionic compounds brittle?
Force is applied causing layers to shift. Repulsion between like charges causes structure to shatter
Can ionic compounds conduct electricity?
Only when molten or dissolved
Contain charged particles but need to be free to move
Two disadvantages of the ball and stick model
Show spaces between ions
Doesn’t show forces going in all directions
Explain the melting points of simple molecular structures
Low
Only weak intermolecular forces between molecules
Can simple molecular substances conduct electricity and why?
No
No charged particles
Why are simple molecular structures weak?
Only weak intermolecular forces between molecules
What type of crystal structure is diamond/ silicon dioxide?
Macromolecular
Explain the melting/ boiling point of diamond/ silicon dioxide
High
Many strong covalent bonds
Explain the strength of diamond/ silicon dioxide
Strong- many strong covalent bonds
Can diamond and silicon dioxide conduct electricity?
No
No charged particles
Explain the strength of graphite
Soft
Weak intermolecular forces between layers of carbon atoms so can slide over each other
Explain the melting point of graphite
High
Many strong covalent bonds
