Grade 7
Science e-Book
Grade 7 Chemistry
Term 1: Matter
Short notes to remember:
Matter is defined as anything which has mass and occupies space (has volume). Mattercan be solid, liquid or gas.
Matter can exist as solid, liquid or gas. These are called the three states of matter and they have different properties.
A solid has a fixed volume and a fixed shape. It does not flow and cannot be compressed.
A liquid has a fixed volume but no fixed shape. It takes the shape of the container in which it is placed. It flows and it cannot be compressed.
A gas has no fixed shape and no fixed volume. It fills the container in which it isplaced. It flows and it can be compressed.
Matter can undergo two types of change: physical change and chemical change.
A physical change is one during which no new substances are formed and it is reversible.
A chemical change is one during which new substances are formed and it is irreversible (not reversible)
All changes of states are physical changes.
Explore further:
https://quizlet.com/161416572/science-grade-7-introduction-to-matter-flash-cards/
https://quizlet.com/162334825/grade-7-matter-flash-cards/
https://quizlet.com/162334825/grade-7-matter-flash-cards/
Term 2: Elements, compounds and mixtures
Short notes to remember:
• Matter can exist as elements, compounds or mixtures.
• An element is a substance which cannot be broken down into simpler substances.
• Each element is represented by a short-hand form called a symbol.
• Elements are arranged in a special chart called a periodic table.
• Elements can be classified as metals or non-metals depending on their properties.
• Metals and non-metals have important uses.
• A compound is made of two or more elements chemically combined together. A compound has properties which are different from the properties of its constituent elements. The constituent elements of a compound cannot be easily separated.
• Some examples of compounds are water, sugar, kitchen salt and rust.
• A mixture consists of two or more components which are not chemically combined together. The components of a mixture retain their individual properties and can be easily separated from the mixture.
• Some examples of mixtures are air, sea water, stainless steel and salads.
Further explore
http://www.chemistryforkids.net/compounds
http://www.chemistryforkids.net/mixtures
Term 3: Air
Short notes to remember:
• The atmosphere is a layer of air that surrounds the earth.
• Pure air is colourless, odourless and tasteless.
• Air is a mixture of gases. The main gases and their approximate percentage composition are as follows: nitrogen 78%, oxygen 21%, carbon dioxide 0.03%. Air also contains about 0.96% of argon, traces of other noble gases and water vapour (variable amount).
• The other noble gases present in air are neon and helium. They are found in very small quantities in air.
• The amount of water vapour in air is variable. Humidity in air is due to the presence of water vapour in the air.
• Water vapour present in air condenses on cold surfaces forming liquid water.
• Air is important for burning. Without air, combustion does not occur.
• Oxygen is used up during burning.
• Burning occurs faster in pure oxygen than in air.
• Air is also important to living things for respiration. During respiration, oxygen is taken in by living things and carbon dioxide is given off.
• Photosynthesis is another important process which needs air. During photosynthesis, plants absorb carbon dioxide from air and release oxygen into the air.
• The two processes respiration and photosynthesis help to maintain the composition of oxygen and carbon dioxide in air.
• Both photosynthesis and respiration are examples of chemical changes.
• Oxygen can be prepared in the school laboratory using hydrogen peroxide and the catalyst manganese (IV) oxide. A catalyst is a substance which makes a reaction proceed faster.
• Oxygen is odourless and colourless.
• Oxygen has many uses, some of which are:
- In hospitals for patients having breathing problems and during operations
- In space shuttles
- For breathing in space
- By divers
• Oxygen gas can be tested using a glowing splint. The glowing splint relights in the presence of oxygen.
• Carbon dioxide can be prepared in laboratory using hydrochloric acid and calcium carbonate.
• Carbon dioxide is colourless and odourless.
• Carbon dioxide turns lime water milky and it does not support combustion.
• Lime water can be used to test for the presence of carbon dioxide.
• Carbon dioxide is used in fire extinguishers, in the making of fizzy drinks and in refrigeration.
• Nitrogen is used to make fertilisers, dyes, explosives and nylon thread and fabrics.
• Argon is used in light bulbs; helium is used to fill weather balloons, air ships and decorative balloons; and neon is used in red advertising lights.
Further exploration :
• http://www.sciencekids.co.nz/sciencefacts/chemistry/oxygen.html
• http://photosynthesiseducation.com/photosynthesis-for-kids/
Assignments
Coming soon!