chemistry

• elements are pure substances composed of one type of atom. They cannot be separated by any physical or chemical processes.
• Compounds are pure substances which contain two or more types of atoms, which are chemically bonded together in a fixed ratio. They cannot be separated by any physical processes, but they can be chemically separated into the elements they contain.
• Mixtures are impure substances which contain various elements and compounds which are NOT all chemically bonded to each other. The proportions of each part of the mixture may vary enormously.
• The Lithosphere is the solid part of the Earth. It is mostly made of rocks which are a mixture of minerals.
• The hydrosphere is the liquid part of the Earth. It is a mixture of water and various dissolved elements and compounds notably salt.
• The atmosphere is a mixture of gases, the most abundant being oxygen and nitrogen.
• Homogenous mixtures appear to have a uniform composition and are not obviously composed of different parts/fractions.
• Heterogenous mixtures are obviously composed of different parts or "phases".
• Every mixture contains different parts, each with different properties. This makes it fairly easy to separate the "fractions" by simple physical processes such as filtering, distillation and evaporation.
• Gravimetric analysis is the method of finding the composition of a mixture, by separating a mixture and weighing the fractions accurately as they are collected.
• All atoms are composed of 3 types of particles: protons, neutrons and electrons.
• Electrons are negatively charged particles that orbit around the nucleus of an atom.
• Protons are positively charged particles found in the nucleus of an atom.
• Protons and electrons are always equal/have the same atomic number.
• Atomic number is the number of protons in the nucleus of an atom, which determines its place in the periodic table.
• Neutrons have no charge but are attracted to both positive and negative charges.
• Isotopes are different forms of the same element with the same number of protons but differing numbers of neutrons.
• protons + neutrons = mass number
• Mass number is also known as Nucleon Number
• Electrons are not counted in the number of protons in an atom because the mass of electrons are so small its insignificant.
• A mass number is integer because there are whole number of nucleons.
• Isotopes chemistry are the same.
• Isotopes have different number of neutrons in atomic structure.
• Radioisotope an isotope which is unstable and emits radiation asit decays into a more stable form
• 3 types of nuclear radiation are Alpha, Beta and Gamma.
• If an isotope undergoes alpha decay the nucleus is too large for the “strong nuclear force” (very short-range) to hold it all together.
• If an isotope undergoes alpha decay the Mass No. of the atom decreases by 4, and the Atomic No. decreases by 2.
• If an isotope undergoes beta decay the ratio between protons : neutrons is beyond the “balance” necessary for stability.
• If an isotope undergoes beta decay the Mass No. of the atom has no charge, and the Atomic No. goes up by 1.
• How can radiations cause ionisation?

  
  

  Radiation may strike an electron & give it so much energy that it is knocked out of orbit. This turns that atom into an electrically charged ion.
• The radiation with the highest ionising ability is Alpha and the lowest is Gamma.
• The radiation with the highest penetrating ability is Gamma and the lowest Alpha.
• Artificial radioisotopes are produced by placing an appropriate element inside a nuclear reactor is one method. Atoms will be struck by the huge flux of neutrons. Some neutrons may stick in the atomicnucleus. This creates a new isotope.
• Gamma radiation - γ
• Alpha radiation - ⁴₂He
• Beta radiation - ⁰-¹e
• $²⁰⁵₁₃Al --> ²⁰¹₁₁Na +$$⁴₂He$