Year 8 Chemistry Revision Guide PDF

Topics and key ideas to learn for the Chemistry test Substances are of 3 types - Elements, compounds and mixtures Elements and compounds are pure substances while mixtures are a combination of substances Examples of elements= Carbon, Gold, Hydrogen.. Examples of compounds= Water, Sodium chloride...

Topics and key ideas to learn for the Chemistry test Substances are of 3 types - Elements, compounds and mixtures Elements and compounds are pure substances while mixtures are a combination of substances Examples of elements= Carbon, Gold, Hydrogen.. Examples of compounds= Water, Sodium chloride.. Examples of mixtures = Air, Foam, sugar solution, alloys Alloys are solid- solid mixtures eg- steel, bronze, brass.. Elements are organised either as lattices or as monoatomic or diatomic molecules. Neon exists Hydrogen Gold as a molecule exists monoatomic exists as as a element. diatomic lattice Lattices have repeating units with a continuing pattern. The lines between the atoms in a lattice or a diatomic molecule represents attractive forces called chemical bonds. Periodic table Elements are arranged in columns (groups) and rows (periods). In the modern periodic table, elements in a column have similar properties. Most elements in the periodic table are metals and they are mainly located on the left side while nonmetals are on the right side. Noble metals are on the last column and they are least reactive Properties of metals 1. They are shiny 2. They are hard 3. They conduct heat and electricity because they have free electrons moving through their lattice structure 4. They are malleable meaning they can be bent and hammered 5. They are ductile meaning they can be drawn into wires Properties of non-metals 1. They are dull 2. They are brittle 3. They don’t conduct heat and electricity because they don’t have free electrons moving through their lattice structure 4. They are not malleable or ductile. Elements are represented in the periodic table by their chemical formulae. Formula have either one capital letter or a capital letter followed by a lower-case letter. Some elements have the formula beginning with the first letter of their English or common name eg Carbon begins with C, Bromine has the formula Br. However other elements have a Latin name. Eg. Tungsten has a Latin name of Wolfram hence it begins with W. When you look at an element in the periodic table it provides a lot of information as shown in the image below Atoms form the basic unit of matter. Atoms can be further divided into smaller subatomic particles like protons, neutrons and electrons. The number of protons and electrons are always the same for an atom. Proton is positively charged, electron is negatively charged, and the neutron is neutral. The mass of atom is always due to the mass of the nucleus. This is what atomic mass means. Atomic number is the number of protons. Atomic mass can also help you to calculate the number of neutrons. No. of neutrons = Atomic mass (rounded to whole number) – Atomic number Elements combine through chemical bonds to form compounds. They will have different properties to that of the elements. e.g., Copper is brick red or orange in colour, but copper oxide is black and they also have different properties in terms of conductivity. The compounds can also exist as a lattice. E.g. Sodium chloride or salt exists as a lattice. In this lattice for each sodium (Na) atom there will be a chlorine (Cl) atom. So, the formula of the compound is NaCl.