Topic P1- Matter Flashcards
When and what did J J Thompson theorise about the atomic structure?
- In 1887
- J J Thompson figured out that atoms weren’t solid spheres.
- His measurement of charge and mass showed that an atom must contain smaller negatively charged particles called electrons.
- From his results, he made a model of the atom, known as the ‘plum pudding model.’
- This model shows the electrons spread though the positive ‘pudding’ that made up most of the atom.
When and what did Ernest Rutherford theorise about the atomic structure?
- In 1909
- Ernest Rutherford, working with Hans Geiger and Ernest Marsden
- conducted the famous gold foil experiment.
- They fired positively charged alpha particles at an extremely thin sheet of gold.
- From the plum pudding model, they expected the particles to pass straight through the gold sheet, only to be slightly deflected.
- Although most particles went straight through the sheet,
- some were deflected more than they expected to
- and a few were deflected straight back the way they came
- the plum pudding model had no evidence to support this.
- Rutherford came up with a new theory of the nuclear atom
- In his model, most of the mass of an atom is concentrated in a tiny, positively charged nucleus at the centre
- surrounded by a ‘cloud of negative electrons
- most of the atom consists of empty space.
- his model was flawed, as scientists recognised that electrons in a ‘cloud’ around the nucleus of an atom like this would be attracted to the nucleus, causing the atom to collapse.
When and what did Neils Bohr theorise about the atomic structure?
- In 1913
- Niels Bohr proposed a new model where the electrons are in shells.
- He suggested that electrons can only exist in these shells (fixed orbits)
- and not anywhere in between.
- Each shell has a fixed energy.
- His theory was similar to the modern-day model.
What does the nucleus contain?
What is the overall charge of the nucleus?
- Nucleus contains protons ( + charge) and neutrons ( neutral charge),
- which gives it an overall positive charge.
What is the nuclear radius and the whole mass of the atom?
- Nuclear radius is 1 x 10^-15m
- whole mass of atom is about 1 x 10^-23, depending on the element.
What is the diameter of an atom?
1 x 10^-10
How small is the nuclear radius compared with the atomic radius?
The nuclear radius is around 10 000 times smaller than the atomic radius.
What are the relatives masses for a proton, neutron and an electron?
Proton = 1 Neutron = 1 Electron = 0.0005
What are the relative charges for a proton, neutron and an electron?
Proton = +1 Neutron = 0 Electron = -1
What is density?
-Density is a measure of the mass per unit of volume.
What is the formula for calculating density?
Density = mass ÷ volume
triangle:
m ----------- p x V
What does the density of an object depend on?
- What it is made of!
- It DOES NOT vary with size or shape.
What determines if an object floats or sinks in water?
- The object’s average density of an object- it needs to have a lower average density than the liquid, in order to float.
- If it has a higher average density than the liquid it is submerged in, than it will sink.
Describe an experiment used to measure the density of solids and liquids::
1) An object submerged in water will displace a volume of water equal to its own volume
2) Use a eureka can (Archimedes)
3) Fill eureka can so that water level is just under the spout.
4) Slightly over-fill the can then let the extra water drain away
5) Place a measuring cylinder under the spout, then gently lower your object in the can, using a thin, strong thread.
6) The displaced water will start to come out of the spout.
7) Wait for the spout to stop dripping, then measure the volume of water collected in the cylinder.
8) This is the volume of water displaced by the object which is equal to the volume of the object.
9) Repeat three times and calculate a mean.
How can you work out the volumes of:
- a liquid
- a solid cuboid
- a solid cylinder
1) To measure the density of a substance, measure the mass and volume of a substance (use formula)
2) You can measure the mass using a mass balance.
3) To measure the volume of a liquid, pour the liquid into a measuring cylinder
4) 1ml = 1cm3
5) To measure the volume of a solid cuboid, measure its length, width and height than multiply them together.
6) To find the volume of a solid cylinder, measure the diameter of one face of the circle, then halve this to give a radius.
7) Measure the cylinder’s height, and use the formula volume = π x radius^2 x height.
Describe what the particle theory says about solids as a state of matter:
- Strong forces of attraction hold the particles close together in a fixed, regular arrangement
- The particles don’t have much energy in their kinetic energy stores
- so they only vibrate about their fixed positions.
Describe what the particle theory says about liquids as a state of matter:
- The forces of attraction between the particles are weaker (than solids)
- The particles are close together,
- but can move past each other
- and from irregular arrangements
- they have more energy in their kinetic energy stores than the particles in a solid
- they move in random directions at low speeds.
Describe what the particle theory says about gases as a state of matter:
- There are almost NO forces of attraction between the particles
- Particles have more energy in their kinetic energy stores than those in liquids.
- and are free to move
- and travel in random directions
- at high speeds.
What are the physical changes between solid to liquid and liquid to solid called?
Solid to Liquid - melting
Liquid to Solid - freezing
What are the physical changes between liquid to gas and gas to liquid called?
Liquid to gas - evaporating
Gas to Liquid - condensing
