Atoms, Elements and Molecules Y7 Chemistry

• Substances can be made of single atoms or molecules
• Molecules are small groups of atoms bonded together
• Mixtures can be pure (one substance) or mixtures (two or more substances not joined together)
• Elements are simple substances made up of only one kind of atom
• There are about 90 different types of atoms found on Earth, resulting in about 90 different elements
• Compounds contain more than one kind of atom bonded together
• The periodic table lists all 118 known elements, described by symbols of one or two letters
• Metals have high melting points, are malleable, ductile, shiny, and good conductors of heat and electricity
• Non-metals have low melting points, are brittle, not shiny, and poor conductors of heat and electricity
• Compounds are formed when elements react and atoms join together
• Chemical reactions form new substances and can be identified by colour changes, gas production, solid formation, or energy changes
• Some reactions start by mixing substances, some need heat to start, and others need a continuous energy supply
• Word equations represent chemical reactions, showing reactants turning into products
• Thermal decomposition reactions involve breaking down compounds using heat
• Data can be sorted and presented in tables, bar charts, line graphs, scatter graphs, or pie charts depending on the type of variable and what is being shown
• Gases in the air include nitrogen (78%), oxygen (21%), and other gases like carbon dioxide (0.04%)
• The metals that react with water produce: METAL + WATER ---> METAL HYDROXIDE + HYDROGEN
• The metals that react with dilute acid produce: METAL + ACID ---> METAL SALT + WATER
• The metals that react with oxygen produce: METAL + OXYGEN ---> METAL OXIDE