PHYSICS YEAR 10

• An atom has a positively charged nucleus containing protons and neutrons, surrounded by negatively charged electrons in shells.
• An atom contains equal numbers of protons and electrons
• Atoms have no overall electrical charge because the number of positive

  protons is equal to the number of negative electrons.
• number of protons = atomic number
• All atoms of an element have the same number of protons in the nucleus. This number is unique to that element.
• PROTONS

  mass= 1

  charge= positive

  location= nucleus
• NEUTRONS

  mass= 1

  charge= no charge

  location= shells
• ELECTRONS

  mass= 1/1835

  charge= negative

  location= shells
• The total number of protons

  and neutrons in an atom is

  called its mass number.

  FOR EXAMPLE

  Oxygen has a mass number of

  16. If it has 8 protons it must

  therefore have 8 neutrons to

  make a mass number of 16.
• Atoms are electrically neutral

  so there must be the same

  number of electrons as

  protons.
• atomic number= amount of protons
• The nucleus holds

  99% of the mass of

  the atom
• density= mass/volume
• To find the density of an irregular shaped object, you need to determine its volume. To do this, it is placed in a known volume of

  water and the amount of water displaced

  equals the volume of the object.
• pre 1900- sphere

  before the discovery of the electron

  atoms were thought to be tiny indivisible spheres
• pre 1911- plum pudding model

  JJ Thompson

  the atom is a sphere of evenly distributed positive charge with negative electrons embedded in it

  
• 1911-present - the nuclear model

  RUTHERFORD: atom has a small positively charged nucleus surrounded by electrons.

  NEILS BHOR: electrons orbit nucleus in shells

  JAMES CHADWICK: provided evidence for existence of neutrons in nucleus

  
• conclusions to rutherfords experiment:

  most of the atom is empty space

  the nucleus is positive

  the nucleus is very small compared to the size of the atom and most of the mass in the atom is found in the nucleus.
• diameter of nucleus: 1x 10−15 m
• diameter of an atom: 1 × 10−10
• the nucleus has a positive charge because it contains positively charged protons
• isotopes: atoms of the same element that have the same number of protons but different number of neutrons
• atomic mass (larger number)= number of protons +number of neutrons
• number of neutrons= atomic mass - atomic number
• an elastic material changes shape when you apply a force to it but returns to its original shape when the force is removed
• rutherfords experiment:

  •rutherford shot alpha particles at thin gold foil

  •they should’ve all pass though unaffected

  • most of them did but some bounced back
• what rutherford proved:

  •the atom must have a very small positively charged nucleus

  •the nucleus contained most of the mass in the atom

  •electrons orbit the nucleus
• SPRING CONSTANT: tells you how much force is needed to stretch / compress the spring by a certain distance (measured in K)
• directly proportional: straight line passing through 0,0

  
• linear graph: straight line

  
• non- linear graph: curve

  
• HOOKES LAW:

  the force needed to extend or compress a spring by some distance is proportional to that distance
• change in thermal energy= mass (Kg) x specific heat capacity (J/Kg K) x change in temp (K)
• specific heat capacity= amount of energy needed to heat up 1 Kg of a substance by 1 K
• the specific latent heat is the energy required to cause 1Kg of material to change state at a constant temperature
• temperature in C + 273 = temperature in K