unit 2 knowledge points Flashcards
(49 cards)
What are London forces?
- diagram
- instantaneous dipole-induced dipole interaction
The three features of London forces?
- the attractive force increases with increasing number of electrons in the molecule
- they depend on the shape and size of the molecules
- London forces are always present between molecules (whether there is permanent dipole or hydrogen bond)
What are permanent dipoles?
permanent dipole-permanent dipole interaction
1. permanent dipole-permanent dipole
2. permanent dipole-induced dipole
What is van der Waals force？
sum of all the intermolecular interactions between molecules
What is hydrogen bond?
an intermolecular interaction (in which there is some evidence of bond formation) between a hydrogen atom of a molecule (or molecular fragment) bonded to an atom in the same or a different molecule
Boiling temperatures of unbranched alkanes?
boiling temperature increases with increasing molecular mass
1. molecular mass increases, the number of electrons increases, instantanrous and induced dipoles increase
2. length of carbon chain increases, the number of points of contact between adjacent molecules increases, because instantaneous dipole-induced dipole forces exist at each point of contact between molecules, so greater London force
Boiling temperature of branched alkanes?
the more branching in the molecule, the fewer points of contact between adjacent molecules, leads to a decrease in the overall intermolecular force of attraction between molecules and a decrease in boiling temperature
Boiling temperature of alcohols?
when the chain is short, the predonminant bonding in alcohols is hydrogen bonding, London forces eventually predominate as the chain length incareases
Boiling temperatures of the hydrogen halides?
HF>HI>HBr>HCl
1. the increase from HCl to HI is the result of the increasing number of electrons
2. the London force is weaker in HF, but the hydrogen bonding is significantly greater because of the high electronegativity of fluorine
Two important anomalous properties of water?
- It has a relatively high melting and boiling temperature for a molecule with a few electrons
- the density of ice at 0℃ is less than that of water at 0℃
Why the hydrogen bond strength for HF is greater
Two conditions for a substance to dissolve
- the solute particles must be separated from each other and then become surrounded by solvent particles
- the forces of attraction between the solute and solvent particles must be strong enough to overcome the solvent-solvent forces and the solute-solute forces
What is redox reaction?
a reaction that involves both reduction and oxidation
What is a disproportion reaction?
a reaction involving the simultaneous oxidation and reduction of an element in a single species
What is oxidation number?
the charge that an ion has, or the charge that it would have if the species were fully ionic
The common oxidising agent?
potassium manganate (Ⅶ)
The trend in ionisation energy for Groups 1 and 2
decrease down the group
1. the nuclear charge increases, the force of attraction for the electron being removed increases
2. the quantum shell is added, energy of the outermost electrons increases
3. the number of filled inner shells increases, the force of repulsion on the electron being removed increases
The trend in reactivity for Groups 1 and 2?
a general increase in reactivity down the group
What is basic oxides?
oxides of metals that react with water to form metal hydroxides, and with acids to form salts and water
The trend in solubility of the Group 2 hydroxides?
increases down the group
What is thermal stability?
a measure of the extent to which a compound decomposes when heated
The thermal stability of nitrates?
Group 1: Li has a greater decomposition, other have lesser decomposition
Group 2: all have greater decomposition
greater: metal oxide + NO₂ + O₂
lesser: metal nitrite + O₂
How to detect oxygen?
glowing splint (relights)
The stability of carbonates?
Group 1: only Li has decomposition, other have not
Group 2: all decomposition
metal oxide + CO₂
