chemistry

• what is an element? a pure substance made up of only one atom
• what is a compound? A compound is a substance made up of two or more different elements chemically bonded together.
• what is a molecule? A group of atoms chemically bonded together in a discrete unit
• all molecules are not compounds but all compounds are molecules
• all matter is made up of small particles called atoms
• atoms consist of 3 subatomic particles: protons, neutrons and electrons
• electrons occupy energy level
• energy levels follow 2,8,8 formation
• neutron number = mass number - atomic number
• mass number = sum of protons + neutrons
• isotopes have the same atomic number but different mass numbers
• isotopes are different forms of the same element with the same atomic number but different mass numbers
• elements are arranged into groups (columns) and periods (rows)
• an atom is stable if the forces between the particles that naje yo the nucleus is balanced
• An atom is radioactive if forces are unbalanced
• radioactivity occurs when an atom decays to become more stable by emitting radiation
• beta decay involves emission of beta particle, which is electron or positron
• alpha decay involves emission of alpha particle, which is helium ion
• the three types of radiation are alpha, beta and gamma
• beta radiation is an electron which can penetrate through paper but not human skin
• gamma ray is high energy electromagnetic wave
• gamma rays have high energy but low penetrating power
• half life is time taken for half of atoms to decay
• alpha rays have low energy but high penetrating power
• daughter nucleas will usually be of a different chemical element to the original isoptope
• radioactive decay is a nuclear rather than a chemical reaction
• the number of protons determines the identity of an atom
• radioactive decay is a random process that occurs in all atoms and is the process by which unstable nuclei become stable
• an alpha particle has two neutrons and two protons, so it is helium-4 (2+)
• gamma radiation is electromagnetic radiation with no mass or charge
• gamma rays can follow beta or alpha decay, gamma

  radiation alone doesn’t change the

  structure of atom
• gamma rays can be Stopped by thick layer of lead or concrete
• Beta particles have negative charges and are stopped by aluminium foil
• alpha particles are positively charged and are stopped by paper
• proton have +1 charge
• electron has -1 charge
• neutron has no charge
• unstable isotopes decay at a steady rate and that this can be displayed in a graph.
• uses of radioactive decay: carbon 14 dating
• that ionic compounds form when cations and anions form ionic bonds between them.