Year 8 Matter - Atoms, Molecules, and Compounds PDF

Atoms bond together to make molecules and compounds Year 8 Matter  Molecules are groups of two or more atoms that are bonded together. When the atoms are Key Ideas different elements bonded together, they can also be called c...

Atoms bond together to make molecules and compounds Year 8 Matter  Molecules are groups of two or more atoms that are bonded together. When the atoms are Key Ideas different elements bonded together, they can also be called compounds. Elements and compounds can be represented by chemical formulas, while mixtures cannot. Last lesson we talked about: Elements and how we organize them. The Periodic Table Molecule vs compound A molecule is a group of two or more atoms bonded together A compound is a substance made up of two or more types of atoms bonded together So what’s the difference? Well essentially a compound is a specific type of molecule. Let’s look at some better definitions for this concept. Two Groups of Molecular Substance molecular element: a molecule that contains two or more of the same atoms bonded together molecular compound: a molecule that contains two or more different atoms bonded together Molecular elements Oxygen is an example of a molecular element. An oxygen molecule consists of two oxygen atoms joined together. Oxygen gas O2 is a substance made of oxygen molecules. Pure oxygen gas consists of millions and millions of oxygen molecules, all exactly alike. This means that the word 'oxygen' can be used in two different ways: 1. Used to describe the element 2. Used as the name of the molecule. When you see the names of chemicals, check the way in which the name is being used. Molecular compounds Remember: Molecules of a compound contain atoms of two or more different elements. Examples: Carbon dioxide is a molecular compound. Its molecules contain one carbon and two oxygen atoms (CO2). Pure carbon dioxide gas consists of millions and millions of carbon dioxide molecules. Water is another molecular compound. A water molecule is made up of two hydrogen (H) atoms and one oxygen (O) atom. This is why water is referred to as H20. Polymers Some compounds are individual molecules, such as water and carbon dioxide. Other compounds are long strings of atoms called polymers. The groups of atoms in these strings repeat over and over - like the beads on a necklace. Plastics are examples of polymers. Other polymers include chemicals found in plants and animals, such as starch and proteins. What do those numbers mean? The small numbers (we call them subscript) after an element tell you how many atoms of that element there are. We call the whole thing a chemical formula. Chemical Formulas tell us which atoms make up different molecular substances and how many of each you have. A glass of water consists of many billions of water molecules. The water molecules are all identical.  Elements and compounds can be pure Pure substances. Pure substances means all the particles in substances the substances are identical to each other. Water is an example of this. Pure water contains many molecules of H20 (water molecules).  When sugar (C6H1206) is mixed with water (H20), Molecular there are two different compounds in the compounds are mixture. Because the two compounds are not different to chemically bonded to each other, they can be easily separated. mixtures This means mixtures cannot be represented by chemical formulas.  Molecule: group of two or more atoms bonded together (e.g. a water molecule) Molecular element: a molecule that contains two or more of the same atoms bonded together Compound: a substance made up of two or more types of atoms bonded together (e.g. water) Molecular compound: a molecule that Glossary contains two or more different atoms bonded together Mixture: a substance made up of two or more pure substances mixed together Polymer: a long-chain molecule formed by the joining of many smaller repeating molecules (monomers) Pure substance: something that contains only one type of substance (e.g. a single element or a single compound)