Science exams revision

• Atoms


  The basic building blocks of all matter and the materials we use
• Atoms are defined as different things in chemistry
• Types of atoms


  • 118 types of atoms in the world
  • 20 lab made atoms
• Atoms are so small that they cannot be seen
• Each atom has its own chemical symbol
• Humans are a carbon-based species
• Molecules


  Atoms can combine with other atoms to form Molecules - Molecules are made up of two types of atoms
• Substance


  A substance made of 2 or more atoms, chemically combined - same or different
• Atoms need to be stable to be a molecule - there are some exceptions
• Elements


  Substances are only made up of one type of atom
• Compounds


  Substances made up of 2 or more different atoms, chemically combined
• Mixtures


  A substance that has different things mixed up but NOT chemically combined with each other
• Mixtures


  • Salt water (boil water leaves the salt) - you can separate again
• Subatomic particles


  • Neutrons
  • Protons
  • Electrons
• Nucleus


  The center of the atom which contains neutrons and protons
• Electron cloud


  Holds the electrons around the nucleus
• If you add or take away protons


  It changes the element, e.g. carbon (6 protons) + 2 protons = oxygen (8 protons)
• The number of electrons and protons in an atom is equal
• Atoms are neutral in charge (0 = neutral)
• Atomic number


  Number of protons
• Mass number


  Number of protons and neutrons in the nucleus
• Number of neutrons


  Mass number - protons
• The number of electrons and protons in an atom is the same
• Isotopes


  All atoms of the same element have the same amount of protons, but sometimes the same element can have a different mass because they have different numbers of neutrons
• Stable


  Protons and neutrons are held strongly together
• Unstable


  Protons and neutrons are not held strongly together, meaning they will be radioactive
• Isotopes


  Have the same number of protons but different number of neutrons
• Radioactive


  Unstable and can decay
• Alpha particles


  Represented as helium's nuclear symbol because they are ejecting the same number of protons and neutrons, they don't have electrons, so they have a charge of +2
• Alpha particles


  • Can't penetrate very far into other materials
  • Can easily knock of any electrons off any atoms they collide with (ionizing)
• Beta particles


  Just electrons with a charge of – 1 and basically no mass
• Beta particle emission


  1. The neutron decays into a proton

  2. The electron is emitted out at high speed
• Beta particles


  • Penetrate moderately far into materials
• Gamma rays


  • Not particles, but energy, waves of electron magnetic radiation
  • Have no mass or charge
• Alpha particles


  • The Helium atom has 2 protons and 2 neutrons
  • It ejects a helium nucleus
  • This is an Alpha particle: it has 2 protons and 2 neutrons
  • Positive charged: there are no electrons to make it neutral
  • Can't travel through particles easily (not even paper)
  • Serious damaged if breathed in
• Beta particle


  • High energy electron
  • Negative charge
  • Small mass
  • 90% of speed of light
• Gamma rays


  • Not particles but a burst of energy
  • Released after alpha and beta particles are released
  • Speed of light
  • Highly penetrating
  • Stopped by thick concrete or lead
• Nuclear radiation


  • The spontaneous breakdown of an unstable atomic nucleus
  • It releases energy and matter from the nucleus through radiation
  • This radiation can be either alpha, bet or gamma rays
• Isotopes


  Atoms of the same element that have the same amount of protons but different numbers of neutrons
• All atoms of the same element have the same amount of protons