Grade 7 Chemistry Study Guide 2025 (PDF)

Chemistry Essentials Atoms and Elements An Element: a substance that cannot be split into any other identifiable substance. Eg: Carbon cannot be divided into anything other than 2 smaller pieces of carbon An Atom of carbon is the smallest possible piece of carbon. Atoms: The small...

Chemistry Essentials Atoms and Elements An Element: a substance that cannot be split into any other identifiable substance. Eg: Carbon cannot be divided into anything other than 2 smaller pieces of carbon An Atom of carbon is the smallest possible piece of carbon. Atoms: The smallest possible particle of an element. Compounds Compound: a substance made up of 2 or more elements whose atoms are bonded chemically. Eg: Carbon dioxide is made up of the elements of carbon and oxygen. The smallest possible piece of carbon dioxide is a molecule consisting of 1 carbon atom with 2 oxygen atoms attached to it. Eg: Water: is made up of the elements hydrogen and oxygen. The smallest possible piece of water is a molecule consisting of 1 oxygen atom with 2 hydrogen atoms attached to it. Molecules Molecules: atoms bonded together chemically. Elements often exist naturally as molecules (in ‘molecular’ form) eg Oxygen occurs in the atmosphere in pairs of atoms: O2. The smallest unit of a compound has to be a molecule (or it will not be a compound any longer if it is split up further into its elemental atoms) Chemical Formulae Symbols for elements always have a capital starting letter and the second is a small letter (if there is one) Subscript numbers determine the number of the element written just before it. Mixtures The substances in mixtures are not bonded chemically and can be separated out by physical methods. Mixtures can contain elements and compounds. Sometimes these are in ‘measured’ amounts, like cordial but the components are not combined so that the atoms ‘bond’ together. Physical Change Is when a substance appears different but no new substance is formed A change in shape A change in state (solid or liquid or gas) A change by dissolving Chemical change Is when a NEW substance is formed The process is called a chemical reaction. The ingredients for the new substance are called the reactants The new substances are called the products New substances are never created from nothing Signs of chemical change The new substance behaves very differently Colour change Temperature change Production of a gas (bubbling or fizzing) Production of light  HELIUM ATOM Shell proton + N - + - N electron neutron What do these particles consist of?  ATOMIC STRUCTURE Particle Charge Mass proton + ve charge 1 neutron No charge 1 electron -ve charge nil  ATOMIC STRUCTURE 2 He Atomic number the number of protons in an atom 4 Atomic mass the number of protons and neutrons in an atom number of electrons = number of protons (Re)Teach When we conduct science investigations it is important to know about variables We look at three types of variables » Independent Variables are what we change » We want to measure the effect that have on something else » Dependent Variables are what we measure » We want to see how the independent variable affects it » Control Variables are things we keep the same. » We do this to make sure that the only thing affecting the dependent variable is the independent variable Retrieve When we conduct science investigations it is important to know about variables We look at three types of variables » Independent Variables are what we change » We want to measure the effect that have on something else » Dependent Variables are what we measure » We want to see how the independent variable affects it » Control Variables are things we keep the same. » We do this to make sure that the only thing affecting the dependent variable is the independent variable Apply (I Do) Identify the independent variable, the dependent variable and some possible control variables. A study was done to find if different tyre treads affect the braking distance of a car Independent Variable: Tyre treads Dependent Variable: braking distance of a car Control Variables: Same car, same road surface, indoors to prevent wind resistance etc. Apply (We Do) Identify the independent variable, the dependent variable and some possible control variables. Aim: To determine if the height of bean plants depends on the water they receive Independent Variable: Water volume Dependent Variable: height of bean plants Control Variables: Same size pot, same sunlight, same fertiliser etc. Apply (You Do) Identify the independent variable, the dependent variable and some possible control variables. Aim: To determine if lemon trees receiving the most water grow the most lemons Independent Variable: Water volume Dependent Variable: number of lemons Control Variables: same sunlight, same soil, same fertiliser, same type of lemon tree. Apply (You Do) Identify the independent variable, the dependent variable and some possible control variables. Aim: To determine whether diesel or petrol cars produce more pollution Independent Variable: type of fuel/car Dependent Variable: amount of pollution Control Variables: same size car, same driving speed, same conditions etc. Retrieve Select the option(s) that matches the variables to their definitions 1. Dependent Variable i. Kept the same 2. Independent Variable ii. Changed during the experiment 3. Controlled Variable iii. What you are measuring A. 1 & i B. 2 & ii C. 3 & iii D. 1 & ii E. 2 & iii F. 1 & iii Apply (We Do) Thinking hats on Think of some variables that are likely to affect the: 1. Amount of sugar that will dissolve in a cup of tea 2. Growth of a plant 3. Time taken to cook a potato Apply (You Do) The Year 8s have been experimenting with bouncing balls and they recorded the following results: Ball Surface Drop height (cm) Bounce heigh (cm) Tennis Sand 30 1 Squash Concrete 300 30 Golf Gravel 100 5 On the basis of his results, he claimed Volleyball Grass that squash 50 balls bounced better 10 than tennis balls. What is the most likely dependent variable that was being tested? A. How high a ball bounces C. How long it takes for a ball to fall B. How high a ball is dropped from D. Which kind of ball bounces highest? Apply (You Do) The Year 8s have been experimenting with bouncing balls and they recorded the following results: Ball Surface Drop height (cm) Bounce heigh (cm) Tennis Sand 30 1 Squash Concrete 300 30 Golf Gravel 100 5 Which of the following Volleyball show the independent Grass variables 50 that were changed? 10 A. Type of ball B. Type of surface C. Height of drop D. Height of bounce Apply (You Do) The Year 8s have been experimenting with bouncing balls and they recorded the following results: Ball Surface Drop height (cm) Bounce heigh (cm) Tennis Sand 30 1 Squash Concrete 300 30 Golf Gravel 100 5 The Year 8s didn’tVolleyball do a very good job. Grass Finish the sentence 50 10 This was not a fair test because….. Apply (You Do) Three bears returned home and found someone had been eating their porridge. Being scientific bears, they were interested in how fast different sized bowls cooled. They filled them with hot porridge and measured the temperature every minute. Their results are shown in the table. Time Temperature of Papa Bear’s Temperature of Mama Bear’s Temperature of Baby Bear’s (min) porridge (°C) porridge (°C) porridge (°C) 0 60 58 61 1 55 48 50 2 39 48 3 45 31 30 4 40 20 Which bowl cooled the fastest? A. Papa B. Mama C. Baby Apply (You Do) Time Temperature of Papa Bear’s Temperature of Mama Bear’s Temperature of Baby Bear’s (min) porridge (°C) porridge (°C) porridge (°C) 0 60 58 61 1 55 48 50 2 39 48 3 45 31 30 Which of the following 4 variables 40 are unlikely to have much effect on 20 the cooling of the porridge? A. Size of the bowl C. Amount of sugar in the porridge B. Amount of porridge D. starting temperature of the porridge Apply (You Do) Time Temperature of Papa Bear’s Temperature of Mama Bear’s Temperature of Baby Bear’s (min) porridge (°C) porridge (°C) porridge (°C) 0 60 58 61 1 55 48 50 2 39 48 3 45 31 30 Baby bear misread4 his thermometer 40 once. Identify which of his readings 20 is probably wrong. A. 50°C C. 30°C B. 48°C D. 20°C Apply (You Do) Time Temperature of Papa Bear’s Temperature of Mama Bear’s Temperature of Baby Bear’s (min) porridge (°C) porridge (°C) porridge (°C) 0 60 58 61 1 55 48 50 2 39 48 3 45 31 30 Papa bear forgot to4 read his thermometer 40 once. Identify the most likely 20 missing temperature. A. 31°C C. 53°C B. 18°C D. 50°C Apply (You Do) Time Temperature of Papa Bear’s Temperature of Mama Bear’s Temperature of Baby Bear’s (min) porridge (°C) porridge (°C) porridge (°C) 0 60 58 61 1 55 48 50 2 39 48 3 45 31 30 Mama bear also forgot 4 to read40her thermometer. Identify the most 20likely missing temperature. A. 30°C C. 20°C B. 24°C D. 18°C Apply (You Do) Time Temperature of Papa Temperature of Mama Temperature of Baby (min) Bear’s porridge (°C) Bear’s porridge (°C) Bear’s porridge (°C) 0 60 58 61 1 55 48 50 2 50 39 48 3 45 31 30 A Mama Bear sketched the line graphs to show 4 40 24 20 what was happening. Temperature (°C) B Which one shows Papa Bear’s Porridge? C A B C D D Time (min) Apply (You Do) Time Temperature of Papa Temperature of Mama Temperature of Baby (min) Bear’s porridge (°C) Bear’s porridge (°C) Bear’s porridge (°C) 0 60 58 61 1 55 48 50 2 50 39 48 3 45 31 30 A Mama Bear sketched the line graphs to show 4 40 24 20 what was happening. Temperature (°C) B Which one shows Mama Bear’s Porridge? C A B C D D Time (min) Apply (You Do) What would be the best title for this A graph? A. Rate of cooling for bowls Temperature (°C) B B. Porridge C. Cooling C D. Rate of cooling for bowls of porridge E. Bowls D F. Rate of cooling for porridge Time (min) G. Temperature Metamorphic Rocks How a little bit of heat & pressure transform rocks! What is a metamorphic rock? ◼ The term "metamorphic" means "to change form." ◼ Any rock (igneous, sedimentary, or metamorphic) can become a metamorphic rock. If rocks are buried deep in the Earth at high temperatures and pressures, they form new minerals and textures all without melting. If melting occurs, magma is formed, starting the rock cycle all over again. Summary Summary IGNEOUS ROCKS  CHARACTERISTICS OF IGNEOUS ROCKS  Hard: Because the minerals they contain are hard  Strong: Because the mineral crystals that make them are strong  Made of interlocking cr ystals that have grown into each other and lock together.  Igneous rocks are classified according to how they were formed and the texture and colour of the rock.  WEATHERING Weathering is the term used to describe the physical or chemical break down of rocks.  Physical Weathering:  Chemical Weathering ▪ Caused by;  Caused by: ▪ Temperature change  Water and the chemicals in ▪ The action of ice and water the water and air reacting ▪ Crystallisation of salts with rock and changing it. ▪ Wind ▪ Living plants  EROSION AND SEDIMENTATION  Erosion is when the small particles of weathered rock are carried away by wind, water and ice.  Sedimentation describes the process by which the eroded rock particles are deposited at a particular location.  Sedimentation usually occurs where the moving water, wind or ice carrying the particles slows down.  SEDIMENTARY ROCKS  Sedimentary rocks are rocks made from sediments.  They are formed when the sediments are cemented together under pressure.  Sedimentary rocks are classified by the type of sediments they are made of.  There are three main types of sediments: ▪ From pieces of weathered rock ▪ From minerals crysalising in solution ▪ From dead plant or animal material  WEATHERED ROCK SEDIMENTS  These sediments come from the weathering of all types of rocks.  They form sedimentary rocks called clastic sedimentary rocks.  Sediments form rocks when the natural cements (chemicals in water) surrounding the sediments set, holding them together.  The cements set because pressure from the weight of all the sediment layers above squeezes out the water in the bottom sediment layer causing the cementing agent to solidify.  CHEMICAL SEDIMENTS  Chemical sedimentary rocks form when materials dissolved in water come out of solution, form a solid and sink to the bottom.  This process is Crystallisation, in which the dissolved minerals turn into solid crystals as the water evaporates.  Characteristics: ▪ Contain crystals ▪ Quite soft ▪ Rarely have layers ▪ Only some have fossils  ORGANIC SEDIMENTS  Organic sedimentary rocks form when dead plant matter or animal debris accumulate and is cemented together.  Characteristics: ▪ Can be layered ▪ Are usually soft but come can be hard. ▪ Example: coal  USES OF SEDIMENTARY ROCKS  Due to the wide variety of sedimentary rocks they have many uses:  Examples:  Sandstone is used in buildings, walls and pavers  Limestone is used in making cement, glass and steel  Gypsum is used to make plaster  Coal is used for energy supply.  METAMORPHIC ROCKS  Metamorphic = change form  Metamorphic rocks form when high temperatures and pressure alter existing igneous and sedimentary rocks.  Changes can be physical or chemical and include the formation of new minerals not seen in the original rock.  T YPES OF METAMORPHISM  Regional metamorphism ▪ This occurs over a wide area and is generally due to layers of rock deep underground being exposed to extreme heat and pressure. ▪ It can also be caused by the movement of tectonic plates. ▪ When the tectonic plates move around on top of the mantel they can collide and scrape past each other, and are heated up and compressed in the process.  Contact metamorphism ▪ Occurs in particular local areas on a much smaller scale. ▪ Occurs when rocks come in contact with hot magma as it pushed through the mantle and crust. T YPES EXAMPLES OF METAMORPHIC ROCKS ROCK CYCLE Life Cycle of a Star Waves, Atoms and Space Overview Stage 1 Protostars Protostars Huge clouds of gas (hydrogen) in which stars are made. Many thousands of times bigger than our solar system As the clouds collapse stars are born in them  Stage 2 Main sequence star Main Sequence Star E.g. Our Sun Sequence lasts for about 10 000 million years Our Sun is about half way through it’s main sequence Stage 3 Red Giant Red Giant As the sun runs out of hydrogen the outer layers of the sun will become cooler They will also expand massively. The Earth (along with Mercury, Venus and Mars) will be swallowed up. Stage 4 White Dwarf White Dwarf Gravity will cause the red giant to collapse The sun is now much cooler and it collapses into a small white star It still has the same mass as the original sun! Stage 5 Black Dwarf Black Dwarf The sun cools more and more Eventually it will become a black mass emitting no light It will then spend the rest of eternity drifting silently through space  Stage 4 (for a big star) Red Supergiant  Stage 5 (for a big star) Supernova Supernova! The largest and most powerful explosions in the universe. The red supergiants literally blow themselves apart! Supernova All the atoms we are made from came originally from these giant supernova explosions.  Stage 6 (for a big star) Black hole Black hole After the supernova a huge mass is left behind. There is so much mass its gravity prevents even light from leaving it Black holes can suck in nearby stars and solar systems.