Year 8 Chemistry 2024 PDF

Atoms bond together to make molecules and compounds Lesson 2 – Year 8 Chemistry 2024  Learning Intentions Molecules are groups of two or more atoms that are bonded together. When the atoms are different elements bonded together, they can also be called compounds. Elements and compounds can be r...

Atoms bond together to make molecules and compounds Lesson 2 – Year 8 Chemistry 2024  Learning Intentions Molecules are groups of two or more atoms that are bonded together. When the atoms are different elements bonded together, they can also be called compounds. Elements and compounds can be represented by chemical formulas, while mixtures cannot. Success criteria Define molecule, compound, bonded, molecular element, molecular compound and polymers, and provide an example of each Explain the difference between an element, molecule, compound and mixture Glossary Terms 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 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) 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 molecules 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. Pure substances Elements and compounds can be pure substances. Pure substances means all the particles in the substances are identical to each other. Water is an example of this. Pure water contains many molecules of H20 (water molecules). Molecular compounds are different to mixtures When sugar (C6H1206) is mixed with water (H20), there are two different compounds in the mixture. Because the two compounds are not chemically bonded to each other, they can be easily separated. This means mixtures cannot be represented by chemical formulas. Summary of elements and molecules Remember and understand 1 Identify two elements that exist as molecules rather than single atoms. Summary of elements and molecules 2 Compare (the similarities and differences between) molecules and compounds. 3 Contrast (the differences between) the following terms: a atoms and molecules b elements and compounds c diatomic and monatomic d molecule, polymer and lattice. Apply and analyse 4 Identify which of these diagrams show (i) A mixture of an element and a compound, (ii) a mixture of two elements, and (iii) a pure element. Justify your decision (by defining each term and describing how this matches the diagram). 5 Ammonia is a gas that contains molecules with the formula NH3. Identify the elements that are present in ammonia and the number of each type of atom in each ammonia molecule. Evaluate and create 6 A student claimed that ‘all elements are molecules, but not all molecules are elements.’ Evaluate this statement by: > defining the terms ‘molecules’ and ‘elements’ > deciding whether the first part of the claim is correct > deciding whether the second part of the claim is correct.