chemistry

• There are millions of different substances, a substance is a material that has specific structure and properties.
• A chemical reaction occurs when the atoms in a substance rearrange to form new substances.
• In a physical change no new substances are made.
• The protons and neutrons are found in the nucleus (the middle) of the atom. These are what give the atom mass.
• The electrons are found in shells (rings) around the nucleus.
• The first shell can hold up to 2 electrons, and the next two shells can hold up to 8 electrons. This rule only really works for the first 20 elements.
• An element is made of only one type of atom
• The periodic table shows relationships between different elements.
• The elements are grouped based on their properties.
• An atom is the smallest particle of a chemical element (the building blocks of all chemical substances.)
• A molecule is a particle made of many atoms bonded together.
• A compound is made of more than one type of atom
• Water is a compound because its particles are made of more than one type of atom.
• atoms are made of three different types of particles

  1. positive protons
  2. negative electrons
  3. neutral neutrons
• The number of protons determines which element it is. This is called the atomic number
• The mass number is the number of protons plus the number of neutrons
• Chemical reactions occur so that atoms have a full outer shell. This can be achieved by sharing electrons or transferring electrons from one atom to another (to form ions)
• Number of neutrons = mass number - atomic number