P1 Revision

P1 Revision:

The History of the Atom and Atomic Structure:  J J Thomson discovered that Dalton's theory was not entirely correct and that atoms are not solid spheres. His measurements of mass and charge showed that an atom must contain a smaller. negatively charged particles - the electron. This is when the 'plum pudding model' was discovered.  Rutherford worked with Geiger and Marsden to fired positively charged alpha particles at a thin layer of gold. They expected particles to pass straight through due to the findings of Thomson, but they found that whilst most passed through, some were deflected and some deflected backwards! This confirmed that the atom's mass is concentrated into the centre in a positively charged nucleus and that most of the atom is empty space with electrons in clouds around it.  Bohr later tested the theory after realising that a nucleus in the centre with clouds of negative charge around it would cause the atom to collapse. Surely enough, he proposed that electrons should be in electron shells in orbit around the nucleus. Each shell has fixed energy and his model was accepted as what we know today.    Protons, Neutrons and Electrons:  The nucleus contains protons and neutrons, giving it an overall positive charge. The nucleus is tiny with almost the whole mass of the atom concentrated into it.  The rest of the atom is mostly empty space. The electrons orbit around the outside of the nucleus in electron shells. They give the atom its overall size.  Atoms can join together to form molecules. Small molecules are roughly the same size as an atom - 10 x 10^-10 m.     

Density:  Density = measure of the compactness of a substance.  Density = mass/volume  The density of an object depends on what it's made of and doesn't vary with size or shape. The average density of an object determines whether it sinks or floats - a solid object will float on a fluid if it has a lower average density than the fluid.    How do you measure the density of solids and liquids?  To measure the density of a substance, measure the mass and volume of a sample of the substance and use the equation above. You can measure the mass of an object using a mass balance. To measure the volume of a liquid, you can just pour it into a measuring cylinder.  If you want to measure the volume of a solid cuboid, measure its length, width and height then multiply them together. To find the volume of a solid cylinder, measure the diameter of one of the bases, then halve this to find the radius. Measure the height and then use volume = pi x radius^2 x height.  An object that is submerged in water will displace a volume of water equal to its own volume. Use the Eureka can to do this.    Eureka Can Experiment:  You need the eureka can to be filled so that the water level is just under the spout.  Place a measuring cylinder under the spout, then gently lower your object into the can.  Wait for the spout to stop dripping, then measure the volume of the water collected. This is the volume of the water displaced by the object which is equal to the volume of the object.  Repeat this three times and calculate a mean to find the average volume of an irregular object. 

Specific Heat Capacity:  Specific Heat Capacity = the amount of energy needed to raise the temperature of 1 kg of matter by 1 degree Celsius.  It takes more energy to increase the temperature of some materials than others. Materials that need to gain lots of energy to warm up also release lots of energy when they cool down again. They store a lot of energy for a given change in temperature.  The change in the energy stored in a substance when you heat it is related to the change in its temperature by its specific heat capacity.  Change in thermal energy (J) = mass (kg) x specific heat capacity (j/kgdegreecelsius) x change in temperature (degreecelsius) 

Specific Latent Heat:  Specific Latent Heat = the change of energy when 1 kg of a substance changes state without changing temperature.  When a substance is melting or evaporating, you are still putting in energy, but the energy is used for breaking bonds between particles rather than raising the temperature.  When a substance is condensing or freezing, bonds are forming between particles, which releases energy. This means that the temperature doesn't go down until all the substance has turned into a liquid or a solid.  Thermal energy for a change in state (J) = mass (kg) x Specific Latent Heat (J/kg) 

Pressure Of Gases:  Colliding gas particles create pressure:  Matter is made up if very small, constantly moving particles. The warmer something is, the more these particles are moving.  In a gas, these particles are free to move around in random directions. As gas particles move about, they randomly bang into each other and whatever else gets in the way such as the walls of their container. When they collide with something, they exert a force on it.  All of these collisions cause a net force on the inside surface of the container. This force is pressure. The more particles there are in a given volume, the more often they will collide with the walls of the container and each other, so the pressure will get higher.  Changing the temperature changes the pressure:  The pressure a gas exerts on its container also depends on how fast the particles are going and how often they hit the walls. If you hold gas in a sealed container with a fixed volume and heat it, they move faster. This means that the particles hit the container walls harder and more frequently, creating more pressure.