Chemistry Higher 3 GCSE Flashcards
arrangement of particles in solid, liquid, gas
regular, random, random
relative distance between particles in solid, liquid, gas
very close, close, far apart
main movement of particles in solid, liquid, gas
vibrate in fixed positions, move around each other and move quickly in all directions
at what state can you not compress a substance
solid or liquid
Because there is no space for the particles to move into. A substance in its solid shape has a fixed shape and cannot flow, because the particles vibrate around in fixed positions and cant move from place to place.
what is an atom
a small piece of matter
how big is an atom
Helium atoms are the smallest and they are 62pm (62 *10-12 (to the power of -12))
what are electrostatic forces
forces of attraction between positive and negative charges.
limitations of the particle model
doesn’t show:
forces between the particles
the size of particles
the space between particles
relative mass of an electron
0.0005
isotopes
different number of neutrons
ion
different number of electrons
Atomic model
DaTe RnBo
relative atomic mass/ formula mass
the mean mass of an atom/ formula compared to 1/12 the mass of a 12 6 Carbon atom
pure
consists of only 1 element
what is an alloy
a mixture of a metal and one or more element
how do you know what a substance is impure
the m.p is often less than that of a pure substance
it melts over a range of temperatures
how can you find the m.p
heat slowly
stir the substance as you melt it
How does crystallisation work
You have to heat a solution, until it becomes a saturated solution. Then allow to cool, and crystallisation should form
stationary phases in PC
absorbent paper
mobile phases in PC
solvent like water or propane
stationary phases in TLC
thin layer of silica or alumina powder spread over the glass plate
Thin layer chromatography method
- put solvent in the chromatography tank to a depth of 1cm. (make sure there are no naked flames if it is flammable)
- add a small amount of the sample to the baseline
- let the solvent travel through the powder and take out the plate before it reaches the top
- analyse the pattern
gas chromatography stationary phase
silica or alumina powder in metal column
gas chromatography mobile phase
unreactive carrier as like nitrogen
what is the solvent front
how far the water/ solvent has actually reached
explanation for gas chromatography
the sample is turned into a gas and injected into the column. The carrier gas pushes the sample through the column. The different components take different times to travel through the column, depending on how strongly they bond to the stationary phase.
advantages of TLC
quicker
more sensitive- so less sample
large range of stationary phases to choose from
what ions do metals form
they form positive ions as they lose electrons
what ions do non-metals form
they form negative ions as they gain electrons
do metals react with each other
no, but non-metals can react with each other
metal oxides produce what
alkaline solutions
non-metal oxides produce what
acidic solutions
structure and bonding in ionic compounds
ions are held together by ionic bonds, which act in all directions. ionic bonds are strong electrostatic forces between the oppositely charged ions
structure and bonding in covalent compounds
involve electrostatic forces, but the forces are between the nucleus of each bonded atom and the shared electrons. The covalent bonds are strong, but the IMF are weak
2 types of polymers
thermosoftening - tangled chains that are easy to seperate
thermosetting- chains joined with covalent bonds- called cross linking
metallic bonds
electrons leave their outer shells of the metal atoms, forming a ‘sea of delocalised electrons’ around the positively charged ions. They have strong electrostatic forces of attraction between the delocalised electron and the ions
Why can carbon form so many compounds
its atoms have 4 electrons, so it can form 4 covalent bonds
What can carbon form
CHAINS AND RINGS
What is an allotrope
different forms of the same element in different arrangements
Diamond
exists as a giant covalent structure, in which each carbon atom is joined to 4 others. Can’t transfer electricity. High melting point and very hard
Graphite
Giant covalent structure where each carbon atom is joined to 3 others. Has 1 delocalised electron that can carry the charge
why is graphite slippery
even though the covalent bonds between in the graphite are strong. The forces between the layers is quite weak, so the layers can easily slide over each other
Graphene
A layer of graphite
Transparent
Strong
Conducts electricity
Fullerenes
Large family of carbon allotropes. Nanotube: a sheet of graphene rolled into a tube.
Buckyball: Graphene closed to make a hollow ball.
what elements are in the solid state at r.t
metals
ionic compounds
giant covalent
Brittle
Cracks under pressure
Malleable
be bent
how big are nanoparticles
1nm- 100 nm
nanoparticles uses
paints
cosmetics
what is a mole
a unit for amount of substance
What is Avogadro’s constant
6.02 * 10 (-23) / mol
The number of entities in one mol
acid + carbonate
salt + water + carbon dioxide
acid + metal
salt + hydrogen
dilute acid
contains a low ratio of acid to volume of solution
concentrated acid
contains a higher ratio of acid to volume of solution
weak acids
they partially ionise
strong acids
they fully ionise
explanation behind weak and strong acids
acids release Hydrogen ions in aqueous solutions. As the concentration of H+ ions increases by a factor of 10, by pH decreases by 1.
electrolysis of water anode
4H+(aq) + 4e- -> 2H2 (g)
electrolysis of water cathode
4OH-(aq) -> 2H20(l) + O2(g) + 4e-
when is hydrogen produced
at the anode, unless there is an atom of a metal less reactive than hydrogen, then it will form
when is oxygen produced
at the cathode, unless there is a group 7 element there (bromine, chlorine, iodine?)
non-inert electrodes
will change
inert electrodes
will not change
in electroplating, what is the cathode
the object you want to coat
in electroplating, what is the anode
the metal you want to coat with
in electroplating, what is the electrolyte
has atoms of the metal you want to coat with
how does electroplating work
atoms lose electrons at the anode and then they gain electrons at the cathode, so they move and stay on the cathode.
how is copper purified
both electrodes are made from copper.
The anode is the impure one and the cathode is the pure one. Copper(2) sulfate solution is usually used as the electrolyte. The cathode will gain copper atoms, and the anode will lose the electrons.
what type of particle is present in covalent bonding
a molecule
why might a covalent compound have a low melting point
because it still had weak intermolecular forces
