Year 8 Science: Chemistry Materials on Earth PDF

# Materials on Earth ## Year 8 Science: Chemistry [Unit 4] ### Lesson Objectives - Describe the Rutherford model of the structure of an atom. - Know that electrons have negative charge, protons have positive charge and neutrons have no charge. - Know that the electrostatic attraction between positi...

# Materials on Earth ## Year 8 Science: Chemistry [Unit 4] ### Lesson Objectives - Describe the Rutherford model of the structure of an atom. - Know that electrons have negative charge, protons have positive charge and neutrons have no charge. - Know that the electrostatic attraction between positive and negative charge is what holds together individual atoms. - Know that purity is a way to describe how much of a specific chemical is in a mixture. # Atomic Theory - A Brief History ### Atoms - All substances are made of tiny particles of matter called atoms which are the building blocks of all matter. - Each atom is made of subatomic particles called protons, neutrons, and electrons. A diagram shows the structure of a carbon atom with the sub-atomic particles labeled. # Atoms ### Definition: - The basic unit of a chemical element/ the smallest part of an element - The smallest piece of matter - Matter is anything that can be touched physically. All matter is made of atoms. ### Different Types of atoms - 94 Types occur naturally in the universe - 24 made in laboratories ### Atoms: The Building Blocks of Matter - Atoms are the building blocks of all matter. Everything is made of atoms - even yourself. - Atoms are the smallest particle of an element, which are far too small to see. Even the most powerful microscopes cannot visualise a single atom. If the earth's population of 7 billion people were the size of an atom, they would take up less than 1mm of space. - A diagram shows that these rings are made from pure silver. # Elements - Some substances are made up of just a single kind of atom. - A substance made of just one kind of atom is called an element. - A diagram shows samples of Carbon, Gold and Silver. ### What is an atom like? - Scientists have discovered that atoms are made up of even smaller particles, called sub-atomic particles. Atoms are made up of three kinds of particles: protons, neutrons and electrons. - The particles are arranged in a similar way in all atoms. - The protons and neutrons are grouped closely together in the center of the atom. They form the nucleus of the atom. (Be careful not to confuse the nucleus of a cell with the nucleus of an atom). - The electrons more around the nucleus. A simple diagram shows the structure of an atom with the electron shells around the nucleus. # Purity ### Pure Products - Often, when scientists carry out a chemical reaction, it is important that they obtain a pure product. For example if they are carrying out a chemical reaction to make a medicine, impurities in the product could stop the medicine from working, or it could harm the patient. - In some simple reactions there is only one product. For example: Magnesium + Oxygen → Magnesium Oxide. - In other reactions, there may be more than one product. For example: - Silver Nitrate + Sodium Chloride → Sodium Nitrate + Silver Chloride - Sulfuric Acid + Sodium Hydroxide → Sodium Sulfate + Water - Barium Chloride + Sodium Sulfate → Barium Sulfate + Sodium Chloride - Lead Nitrate + Potassium Iodide → Potassium Nitrate + Lead Iodide - Copper Carbonate + Hydrochloric Acid → Copper Chloride + Water + Carbon Dioxide. - When there is more than one product, they are mixed up together. These products need to be separated and purified to produce whichever pure product you want. The products may also be mixed up with some of the reactants if they have not all been used up in the reaction. ### Exam Tips - Pure substances are made from only one chemical element or one compound. For example, salt is a pure substance made only of sodium chloride. - Elements are listed on the periodic table. - Elements are made from one type of atom. - A compound is made from two or more elements bonded together. # Pure Elements - If an element is pure, it means that every one of its atoms is exactly the same and made of just one type of atom. For example, pure gold is made of gold atoms. - When you buy gold, it is usually marked to state if it is pure gold (24 carat) or an alloy such as 18 carat or 9 carat. This is a measure of its purity. The more gold it has, the higher its purity. 18 carat gold has 18 parts out of 24 that are gold; the rest (6 parts out of the 24) is made up of other metals such as silver or copper. 18 carat gold has a purity of 75%. A diagram shows different samples of carat gold. # Seawater - Seawater is made up of water and various salts, such as sodium chloride. If you want to obtain sodium chloride from seawater you can evaporate off the water. In some countries, this is done by letting seawater fill flat and shallow areas called beds, and allowing the water to evaporate in the heat from the Sun. - If you take 1000 g of seawater, about 35 g (or 3.5%) of it is made up of salts. Of this 35 g, about 68% is sodium chloride; the rest is made up of magnesium chloride, sodium sulfate, calcium chloride and some other salts. If you want pure sodium chloride, you need to do some work to remove the other salts. A diagram shows the process of extracting salt from seawater in Vietnam. - A pie chart shows the percentage composition of salts in seawater. Diagram shows a pure diamond and a yellow diamond. - The salt that is obtained from this seawater is only 68% sodium chloride. - The mass of sodium chloride in 1000g seawater is: 68/ 100 * 35 = 23.8g - Salts are compounds made from acids. The names tell you which acid has been used to form them. For example, sodium chloride is formed from hydrochloric acid and sodium sulfate is formed from sulfuric acid. # Video - What is an Atom? - A video link is shown. - A diagram shows a table of the subatomic particles with their relative charges. - The three different particles in an atom have different properties. - Protons and neutrons have much more mass than the electrons. In fact, electrons have almost no mass. - Protons and neutrons have the same mass - Protons have a positive electrical charge. - Neutrons have no electrical charge. - Electrons have a negative electrical charge. - There is a lot of empty space between parts of the atom. This space really is completely empty; there is nothing in it at all. - There is an attraction between the positive and negative charges. This electrostatic attraction between the positive charge on the protons and the negative charge on the electrons is what holds individual atoms together.