Chemistry Flashcards
What is the atomic number ?
the number of protons in the atom
What is the atomic mass?
The number of protons + number of neutrons
Electron configuration: What is present in n=1, 2, 3 and 4.?
n=1: 2 electrons max in 1 subshell type 1s2
n=2: 8 electrons max in 2 subshell types 2s2 2p6
n=3: 18 electrons max in 3 subshell types 3s2 3p6 3d10
n=4: 32 electrons max in 4 subshell types 4s2 4p6 4d10 4f14
What is present in group 1, 2, 13, 14, 15, 16, 17, 18 of the periodic table ?
1= alkali metals e.g. lithium and sodium 2= alkaline earth metals e.g. magnesium and calcium 13= B and Al 14= C, Si 15= N, P 16= O, S 17= halogens, Fluorine, chlorine, bromine 18= noble gases, heliu
What is an ionic bond?
atoms exchange electrons to give ions that form strong electrostatic bonds.
bond strength increases with increasing charge and smaller ions
What are ionic crystals?
inorganic salts with giant lattice structures
What are strong ionic bonds?
solid at room temp with high melting and boiling points
What are ionic solutions?
conduct electricity when molten or dissolved in water
What are covalent bonds?
atoms share one or more electron pairs to achieve a full outer shell
Define: molecular covalency
number of shared electron pairs
What are metallic bonds?
atoms are packed together tightly, surrounded by a sea of electrons (de-localised)
What are the properties of a metallic bond?
- most have high melting points (strong bonds)
- good electrical and thermal conductivity (highly mobile outer electrons)
- high strength, especially when alloyed with other metals
What is electronegativity?
this is the ability of atoms to attract electrons - concept links ionic and covalent bonding
What does a large difference, >2, in electronegativity indicate?
favours ionic bonds
What does similar electronegativities indicate ?
favour covalent bonds
What does intermediate electronegativities indicate?
form polar compounds that display both types of bonding
Define mole:
one mole of any substance contains 6.022x 1023 particles of the substance
What are the 4 neutralisation chemical reactions ?
1) acid + base goes to metal salt + water
2) acid + carbonate/hydrogen carbonate goes to metal salt + water + carbon dioxide
3) acid + ammonia goes to ammonium salt + water
4) acid + metal goes to metal salt + hydrogen
OILRIG:
Oxidation is LOSS = add oxygen/remove hydrogen/loss of electrons
Reduction is GAIN = remove oxygen/add hydrogen/gain of electrons
What is a combustion reaction ?
oxidation of each element in the compound
What is a composition reaction?
A + B goes to AB
What is a decomposition reaction?
AB goes to A + B
What is a dissociation reaction ?
AB goes to A+ + B-
What is a substitution reaction ?
swap an atom, ion or group in a molecule
What is a hydrolysis reaction ?
add water molecule
What is a condensation reaction ?
remove water molecules
What is a 1M concentration?
1 mole of solute in 1 litre of solution
What is another way of expressing pH?
-log10 molecules H+/L
How is rate represented in reaction rates?
rate= k[A]x[B]y
How is a zero order reaction represented?
x+y=0 rate =k (k is the rate constant)
How is a first order reaction represented?
x+y=1 rate k[a] or k[b]
How is a second order reaction represented ?
x+y=2 rate k[a]2, k[b]2 or k[a][b]
What can increase the rate of a reaction ?
increasing temperature
addition of a catalyst
greater surface area
How does increased temp increase the rate of a reaction ?
molecules have more kinetic energy, a greater proportions overcome the activation energy
How does a catalyst increase the rate of a reaction ?
lowers the activation energy for the reaction. Faster equilibrium but position unchanged
What is Le chatelier’s principle?
Exothermic and endothermic reactions
What is an exothermic reaction?
Heat energy is released. Enthalpy of reaction is negative
deltaH
What is an endothermic reaction?
Heat energy is absorbed. Enthalpy of reaction is positive
delta H>0
-heat added from surroundings
e.g. liquid to gas and bond breaking (cools down)m
Define Le Chatelier’s principle:
for a system in equilibrium, when a change is made to the conditions the equilibrium will shift so as to oppose the change
Le chatelier’s principle: Temperature
it increases and the reaction shifts to absorb heat
reduce it and the reaction shifts to produce more heat
Le Chatelier’s principle: pressure
increase it and the reaction shifts to lower it and vice versa
Le Chatelier’s principle: concentration
increase the concentration of a molecule and the reaction shifts to decrease it and vice versa
What are the properties of a gas?
very low density no shape weak bonds particles diffuse to fill any volume easy to compress pressure of a gas is a linear function of temperature -PV i constant at constant temperature
What are the properties of liquids?
much more dense than gases
usually less dense than when in the solid state (water/ice is the notable exception)
constant volume (incompressible for most practical purposes)
take on the shape of the container
particles are bonded locally
expand much less than gases when heated
What are the properties of solids?
usually the most dense state
incompressible, though depends on the structure
strong bonds between particles- rigid form
expand less than liquids on heating
all metals, mercury excepted, are solids at room temperature
What is the melting point?
solid to liquid - heat energy absorbed
What is freezing point?
liquid to solid- heat released
What is vaporisation?
liquid to gas - heat absorbed
What is condensation?
gas to liquid - heat released
What is sublimation ?
solid to gas
What is deposition ?
gas to solid
What are the properties of a temperature vs pressure graph?
solid to liquid to gas with increasing temperature and gas to liquid to solid with increasing pressure
In a temperature vs pressure graph, what is the triple point?
all 3 states in equilibrium
In a temperature vs pressure graph what is the critical temperature?
above this a gas cannot be condensed to liquid by increased pressure
What do impurities do ?
impurities such as grit or salt lower the freezing point and increase the boiling point
What is electrochemistry?
chemical reaction can give rise to electricity (batteries) and vice versa
What are conductors?
metals, and carbon in the form of graphite
What are insulators?
non-metals (glass/ceramics, polymers, rubber)
What are semi-conductors ?
silicon “chips” (metalloids)
What are electrolytes?
conduct electricity when molten or dissolved in water (e.g. salts, acids and alkalis)
What are electrodes?
positive (anode) and negative (cathode) terminals
What is electrolysis?
when an electrical current is passed through an electrolyte, cations migrate to the cathode, where electrons are added (reduction) and anions migrate to the anode, where electrons are removed (oxidation)
What does Faraday’s law of electrolysis state?
states that the amount of aluminium deposited at the cathode or oxygen liberated at the anode is directly proportional to the amount of current passed
1 Faraday= 1 mole of electrons= 96500 coloumbs
What do more electropositive metals displace?
displace less electropositive metals from solution
What are carbons 3 main allotropes?
graphite
carbon
fullerenes (buckyball)
allotrope= same elements in a different physical form with a different molecular structure
What is graphite like?
an electrically conducting soft powder, giant non-crystalline sheets that slide over each other
3 strong covalent bonds in 2d hexagonal planes and one weak bond between the planes
What is diamond like?
very hard, giant structure with 4 strong covalent bonds
What are fullerenes like >?
hollow spherical clusters of carbon atoms
e.g. carbon 60
What are alkanes?
carbon-carbon single bonds
saturated hydrocarbons
combust completely in air to produce water and carbon dioxide or carbon monoxide if combustion incomplete
What are alkenes?
carbon- carbon double bonds
What are alkynes?
carbon-carbon triple bonds
What is fractional distillation?
separates a mixture into its constituents according to their boiling points.
in fractional distillation of crude oil the alkanes with shorter carbon chains are lighter, boil off first and are highly flammable
the larger molecules are less volatile, highly viscous and are more difficult to ignite
What does cracking do ?
(with steams) breaks less useful, longer hydrocarbon chains into more useful shorter chains
What does polymerisation of alkenes do ?
builds short chains to long chains
What does reforming do?
changes straight chain hydrocarbons into aromatic hydrocarbons
What are isomers?
isomers have the same formula but a different arrangement of atoms
