Grade 8 Exam Guide.pdf

Matter Write in your notebook What is Matter? Everything around us that takes up space and has mass is known as matter. Matter has both mass and volume Matter includes solids, liquids and gases. These different forms of a substance are called states of matter. Chemistry is the study of matter. I...

Matter Write in your notebook What is Matter? Everything around us that takes up space and has mass is known as matter. Matter has both mass and volume Matter includes solids, liquids and gases. These different forms of a substance are called states of matter. Chemistry is the study of matter. It is the study of what matter is made of, how matter changes, and what the properties of matter are. What is Matter? Mass can be define as a measure of the amount matter / colour / texture in an object. The greater an object’s mass, the more / less matter it will contain and the heaver / lighter it will be. The amount of space an object takes up is known as its mass / volume. The more matter / volume an object has, the more space it will take. There are two / three / four main states of matter on Earth. These are s________, l________ & g________ Solids, Liquids & Gases Solids o Hold their own shape, are hard to compress and can be smooth or rough Liquids o Do not have shape, they take on the shape of the container they are in o Flow – slowly (like honey) or quickly (like water) Gases o Do not have shape and spread to fill the space they are in Check for Understanding Writing Time 1. Which state of matter can hold its own shape? 2. Which state of matter will always take on the shape of the container it is in? Define the word matter and recall the two main properties of matter When you define something, you show, describe, or clearly state what it is, what its limits are, or what it is like. 3. Which state(s) of matter can be compressed? Two empty balloons are weighed and found to have the same mass. Afterwards, air is added to one balloon, but not the other. 4. Which state(s) of matter cannot be compressed? Describe what you would expect to find if you weighed them again. Water and Matter Identify the state of matter of water in each example Vocab check Particle Theory of matter Atomic Structure and Periodic Table Activity Scientific models The individual particles of water are too small to see, but we do know how water (and ice and steam) behaves. When something is too small to see, scientists use a model to explain the behaviour. To better understand the different forms of water, scientists use a model called the particle model. The Particle Model - Features o All matter is made up of tiny particles o There are spaces between these particles, some big, some small. o The particles that make up matter are always moving o Forces of attraction hold the particles together o Energy makes particles move o Adding heat (energy) makes particles move faster and break free of the forces holding them together The Particle Model - Solids o Particles are tightly packed together o Particles do not move around freely, however, they constantly vibrate o This is why solids have a fixed mass, volume and shape o Cannot be poured (except in granulated form e.g. salt) o They are not able to be compressed The Particle Model - Liquids o Particles in a liquid can slip by one another, able to flow o This means liquids do not have a fixed shape o Liquids have a fixed mass and volume, take the shape of the bottom of the container they are in. o They are not able to be compressed o Can expand with heat and contract when cooled The Particle Model - Gases o Very large spaces between particles, they will spread out to take the shape of the container o Particles move freely o Gases do not have a fixed volume or shape o Can be compressed (pushed in to make them take up a smaller amount of space) Changes of State When Substances Change The world around you is constantly changing. Whether it be the passing of the seasons, a cool breeze or ice-blocks melting in a drink, changes are occurring. Most of these changes can be classified as physical or chemical changes depending on whether any new substances are produced. Changes of State and the Particle Model The particle model explains changes of state It looks at the relationship between how the particles move and the attraction between them. Changes of State o Substances can change from one physical state to another o Particles need to gain or lose heat energy for this to happen so it is measured as a change in temperature o Solids have the lowest energy and gases have the highest Energy out Energy in Changes of State and the Particle Model Melting In a solid, the particles vibrate but are held in position by the forces of attraction between them. As the temperature increases, the vibrations increase and the solid expands. As the temperature is increased further, the solid melts. The vibrations become so energetic that the attraction between the particles can no longer hold them in a fixed position. At this point, the particles become unstuck and start moving freely. However, there is still a small amount of attraction between the particles that holds them together as a liquid. Changes of State and the Particle Model Freezing/Solidification As the free moving particles in the liquid are cooled The particles become slow and less energetic until the attraction between the particles is able to fix them in position Forms a solid. Changes of State and the Particle Model Evaporation Occurs when the particles in a liquid escape to form a gas. The particles in a liquid are stuck together by only weak forces of attraction. As the liquid particles are heated, they move faster until they are able to escape from the surface of the liquid to form a gas. Changes of State and Particle Theory Condensation As a gas is cooled the particles move slower They reach a point where the forces of attraction between the particles can hold and stick them together to form liquid droplets. Pure substance and mixtures A pure substance has only one type of molecules in it. A pure substance consists only of one element or one compound A mixture consists of two or more different substances, not chemically joined together A pure substance has only one type of molecule in it. Identify which of these diagrams show a pure substance Elements    Elements are the simplest pure substances. The smallest particle of an element that has the properties of that element is an atom. Examples:  O-Oxygen  H- Hydrogen  Na- Sodium  C- Carbon  Fe- Iron  Pb- Lead Compounds    Compounds are pure substances that are made of more than one element bound together. A molecule is formed when two or more atoms chemically combine. Examples:  H2O and CO2 Mixtures Homogeneous mixtures   Components cannot be distinguished from each other, appear as one substance Particles distributed evenly throughout Example: air, 10 karat gold, salt water, Mixtures Heterogeneous mixtures All components of the mixture are visible because they do not mix together Particles are not distributed evenly Example: nut mix, vegetable soup, oil and water Identify these items as homogenous or heterogenous mixtures Identify these items as homogenous or heterogenous mixtures Identify these items as homogenous or heterogenous mixtures Habitats, Adaptations and Relationships Habitats   All living things (organisms) have a place where they live called their habitat. To help an organism survive and reproduce, its habitat must provide:       Food Water Shelter and living space A suitable temperature (climate) Mating partners for reproduction Gases such as oxygen The needs of living things can be divided into two groups. Biotic Factors These are the living factors that include:  partners for mating  organisms to eat  organisms they may compete with for food and shelter. Abiotic Factors These are the non-living factors, including:      The amount of light wind, Temperature Soil type Gases present  List the biotic and abiotic factors present in the picture below. Adaptations  Adaptations are characteristics that assist organisms to survive and reproduce.  Adaptations enable animals to:  Protect themselves from predators  Examples include  Camouflage  defences such as poison or stings  built for speed http://www.bbc.co.uk/schools/gcsebitesize/science/ocr_gateway_pre_2011/environment/3_adapt _to_fit1.shtml Can you spot me? Do I scare you?  Survive hot and cold temperatures, and wet and dry seasons.  Move from place to place (flippers, legs and wings)  Catch  Take and eat food in oxygen  Reproduce Describe 6 adaptations that polar bears have. Plant adaptations  Include      the ability to: protect themselves from grazing animals (spines and thorns). take in oxygen and carbon dioxide Take in water (very long roots) Capture light (large leaves) reproduce Relationships  Organisms within ecosystems are interdependent. This means they depend on each other for survival.  There are three main types of interdependence or symbiosis.    Commensalism Mutualism Parasitism Commensalism  Interactions between living things when one benefits and the other is not affected. E.g. Clown fish and anemones. Clown fish gain protection from the anemones(which has stinging tentacles) and some food not eaten by the anemones. The anemone is not affected by this. Mutualism  Interaction where both the organisms benefit.  In many cases neither organism can exist without the other. E.g. the oxpecker (a kind of bird) and the rhinoceros. Oxpeckers land on rhinos and eat ticks and other parasites that live on their skin. The oxpeckers get food and the rhino’s get pest control. Also, when there is danger, the oxpeckers fly upward and scream a warning. Parasitism  Where one organism (the parasite) benefits and the other (the host) is harmed. E.g. tapeworms can live inside an animal, gaining nutrition but causing harm. Predators and Prey  Animals that eat other animals are called predators.  The animal that is eaten is the prey. predator prey  If two or more animals eat the same sort of food and live in the same habitat they are competitors.  Animals can compete for food, living space, shelter, water, and mates. Food chains  All living things require energy.  Plants get their energy from sunlight.  Animals get their energy from the food they eat.  The flow of energy from organism to organism is called a food chain.  Food chains start with the sun.  Plants trap the sun’s energy in their leaves using chlorophyll.  Plants use this trapped energy, along with carbon dioxide (from the air) and water (from the soil) to make glucose (a sugar) and oxygen.  This process is called photosynthesis.  Plants are called producers.  Animals cannot make their own food and must consume (eat) plants and animals to get the energy and nutrients they need.  Animals are also called consumers. Types of consumers  Herbivores: only eat plants  Carnivores: only eat animals  Omnivores: eat both plants and animals  Decomposers: feed off and break down dead/decaying organisms. E.g. include fungi and bacteria Producers and consumers can be described on food chains. Food Webs  Joining a number of food chains from a single habitat makes a food web. Life Cycle of a Star 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 Stars bigger than our sun! At least four times bigger 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. 4 Types of Galaxies Galaxies What are galaxies? • Galaxy - a group of billions of stars and their planets, gas, and dust that extends over many thousands of light-years and forms a unit within the universe. Held together by gravitational forces, most of the estimated 50 billion galaxies are shaped as spirals and ellipses, with the remainder being asymmetric. 4 Types of Galaxies 1. Spiral 2. Irregular 3. Elliptical 4. Lenticular A galaxy is a group of stars, dust and gas. Spiral Galaxy 1. 2. 3. 4. The most common type of galaxy is called a "spiral galaxy." Spiral galaxies look like spirals, with long arms winding toward a bright bulge at the center. About 77% of the observed galaxies in the universe are spiral galaxies. Our own galaxy, the Milky Way, is a typical spiral galaxy Elliptical Galaxies They are generally round but stretch longer along one axis than along the other. ⚫ Elliptical galaxies contain many older stars, up to one trillion, but little dust and other interstellar matter. ⚫ The universe's largest known galaxies are giant elliptical galaxies, which may be as much as two million light-years long. ⚫ Irregular Galaxies ⚫ Approximately 3% of galaxies observed cannot be classified as either ellipsoidal or spirals. ⚫ These galaxies have little symmetry in their structure and are termed irregular galaxies. Lenticular Galaxy ⚫ Lenticular galaxies are disc galaxies (like spiral galaxies) which have used up or lost most of their interstellar matter and therefore have very little ongoing star formation. ⚫ As a result, they consist mainly of aging stars and will produce the least amount of stars.