P1a Atoms and Particles

Formulas:

  • Percentage Difference = Measured Value - True Value / True Value x 100

  • Density = Mass / Volume

  • P1V1 = P2V2

Keywords:

Absolute temperature - Temperature measured on the Kelvin Scale where 0k = -273.14•c (lowest temperature)

Alpha particle - A small, positive particle emitted from an unstable, radioactive nucleus

Density - The mass per unit volume

Directly Proportional - If one variable doubles/halves, so does the other. Gives a straight line graph through the origin.

Electron - A very small, negative particle that orbits the nucleus in a shell

Inversely Proportional - When one value increases as the other value decreases in the same ratio.

Kelvin - The unit of temperature on an absolute scale

Massive - An object that contains a lot of mass

Model - A description, idea or equation that helps you to explain the physical world

Neutron - A small, neutral particle found in the nucleus of an atom. It has the same mass as a proton

Nucleus - The small centre of an atom made of protons and neutrons

Proton - A small, positive particle found in the nucleus of an atom

Independent Variable - Variable you change

Dependent Variable - Variable you measure

Control Variable - Variables you keep the same to make a fair test

Hot gas contains a higher pressure because:

  • The higher the temperature, the more kinetic energy the particles have. This means they move at a higher speed

  • At a higher speed, the particles collide with the sides of the container more frequently and with more force

  • More force, means a higher pressure if the surface area remains the same

Crushing Can Demo:

  • Heating the tin causes the gas to expand

  • The expanding gas leaves the can leaving very few particles still inside it

  • When placed in the water, the entrance is sealed and the gas cools rapidly

  • The cool gas exerts very little pressure on the inside of the can because the particles are moving slowly

  • The air pressure outside the can is unchanged and now very high in comparison to their inside and so crushes the can

John Dalton:

  • All matter is made of atoms, and atoms are indestructable and cannot be broken down into pieces

  • All the atoms of a particular element are identical to each other and different from the atoms of other elements

  • Atoms are rearranged in a chemical reaction

  • Compounds are formed when two or more different kinds of atoms join together

JJ Thomson:

  • Studied the rays given out by hot metals

  • These rays were called cathode rays

  • He discovered that they were made of particles that were 2000th the mass of a hydrogen particle

  • These particles are called electrons

  • They must have come from inside the atom

  • The have negative charge

Rutherford:

  • Most alpha particles went straight through the gold foil- most of the atom is made of empty space

  • Some of the particles were deflected at large angles- the centre mass is positively charged and repels the alpha particles when they pass nearby

  • A small number were repelled straight back at the detector- the mass of an atom is mostly concentrated in the centre in a dense nucleus

Niels Bohr:

  • Electrons circle the nucleus at high speed

  • Electrons are kept in certain energy levels in a stable formation around the atomic nucleus

Then in 1917, Rutherford discovered the proton in a new experiment and now realised the nucleus wasn’t just a single, small spherical positive charge

James Chadwick:

  • Discovered the neutron in the nucleus

  • Neutron - subatomic particle. Same mass as a proton but zero charge

The diameter of an atom is known to be approximately 1×10^-10 meters.

The nucleus is 10,000 times smaller than the atom.