chemistry

• atoms contain protons neutrons and electrons
• all substances are made of atoms
• the nucleus is in the middle of the atom and contains protons and neutrons
• the nucleus has a positive charge because of the protons
• electrons move around the nucleus in electron shells
• electrons are negatively charged and they are small, but cover a lot of space
• electrons have no mass
• atoms are neutral, they have no overall charge
• atoms are neutral because they have the same number of protons as electrons
• the charge on the electrons is the same size as the charge on the protons, but opposite so the charge cancels out
• the nuclear symbol of an atom tells you it’s atomic number and mass number
• the atomic number tells you how many protons there are
• the mass number tells you the total number of protons and neutrons in the atom
• to get the number of neutrons, subtract the atomic number from the mass number
• an ion is an atom or group of atoms that has lost or gained electrons
• the number of protons in the nucleus decides what type of atom it is
• if a substance only contains atoms with the same number of protons, it’s called an element
• so all the atoms of a particular element have the same number of protons and different elements have atoms with different numbers of protons
• when elements react, atoms combine with other atoms to form compounds
• compounds are substances formed from two or more elements
• making bonds involves atoms giving away,taking or sharing electrons
• it’s difficult to separate the original elements of a compound so a chemical reaction is needed to do this
• a compound which is formed from a metal and non-metal consists of ions
• a compound formed from non-metals consists of molecules
• in a mixture, there’s no chemical bond