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What is an element?
- A pure substance which cannot be broken down into any other substance
- eg: carbon, aluminium,copper,oxygen, sodium and chlorine
What is the periodic table?
A complete list of all the known elements.
Each element has its own symbol made up of one or two letters. What is the symbol for
The symbol for calcium
There are two types of elements, metals and non metals
There are 84 metals and 22 non metals.
What are the properties of metals?
- solid except mercury
- high melting point
- high density
- malleable (able to shape)
- ductile ( able to stretch into wires)
- good conductor of electricity
What are the properties of non metals?
- Can be solid , liquid or gas
- low melting point
- low dinsity
- very brittle (easily broken)
- not ductile cannot be stretched into wires
- poor conductors of electricity
Name some useful products that are made from metals
- Cooking utensils are made from Aluminium
- Electrical wires and plumbing pipes are made from copper
- Thermometers are made with mercury
What are some uses of non metals?
- Nitrogen gas is used to make fertilisers
- Carbon(diamond) for jewellery and cutting tools
What is an Atom?
The smallest piece of a substance
The word atom comes from the Greek word atomos, meaning , which cannot be divided
Can we see atoms?
Yes but only with an electron microscope
What is a molecule?
A small group of atoms linked together
What are lattices?
Larger goups of atoms linked together
What special forces hold the atoms together?
What is a compound?
A number of identical molecules or a lattice containing different atoms joined together
What are chemical formulas?
A shorthand way for scientists to write down which atoms are bonded together in a molecule or a lattice.
What are the subscripts?
They are little numbers used after the element symbol to tell us how many of each atom is in the compound
- Water has two atoms of the element hydrogen and one atom of the element oxygen
What is a mixture?
It is two or more substances mixed together. They are not bonded together and no new substance is formed.
Eg: soft drink or chocolate milk
What is a physical change?
When a substance changes but no new substance is formed.
- Physical change occurs when the state of the substance changes (melting, evaporation, freezing or condensing)
- if a substance is crushed, ground or cut into smaller pieces.
What are some examples of physical change?
- A plate is dropped and shatters
- Ice melts
- Water boils
- Milo dissolves in hot milk
- branches of a tree are mulched
- finger nails are filed down
- breakfast cereal goes soggy
What is a chemical change or chemical reaction?
This is when a new substance is formed
This could mean a change in colour, production of heat or light, a drop in the temperature of the substance
Name some examples of a chemical change
- Wood burns to form charcoal(carbon)
- a green tomatoe ripens and turns red
- an egg is cooked to become a white and yellow solid
- vegetable scraps in the compost bin decompose to form a rich soil
- a dead mouse stuck in a wall begins to smell
- a metal panel on a car rusts
- fireworks explode
- concrete hardens
What are the substances called before a chemical reaction has taken place?
Chemicals formed by a reaction are called
What are the four types of chemical reactions?
- combination reactions
- decomposition reactions
- percipitation reactions
- combustion reactions
What are conmbination reactions?
When two or more reactants join together to form a new substance
Eg: rusting of a metal
- iron and oxygen combine to form iron oxide(rust)
- reactant + reactant -------> Product
What is a decomposition reaction?
Where one reactant breaks down (decomposes) to from two or more products
Eg: Water can be broken down using electrricity to produce oxygen gas and hydrogen gas.
- Water --------> oxygen gas + hydrogen gas
- reactant products
What is a percipitation reaction?
This is when two solutions are mixed together and a solid is formed
Eg: some pecipitates are colourful and are used as paint pigments
What is a combustion reaction?
This happens when ever something burns or explodes.
- Usually there is a release of heat and or light
- It involves two substances reacting with oxygen
eg: carbon + oxygen ---------> carbon dioxide
In word equations what do the following symbols mean?
What ways can we speed up or slow down reaction time?
- by altering the amount or concentration of reactants
- changing the temperature(fruit ripens faster in warmer weather)
- The size of the surface area
- by using a catalysis(helper chemical)
What are enzymes?
- They are special types of catalysts found in our body
- They help break down large starch molecules iinto smaller glucouse molecules
- They do not combine with any other atoms or molecules they just speed up the chemical reactions.
Name the scientists involved in atomic history
We use the Rutherford Bohr model today
Name the structure of the atom
It has a nucleus which contains positively charged particles called protons and neutral particles (no charge) called neutrons
Circling the nucleus at high speeds are smaller negatively charged particles called electrons.
An atom has equal numbers of protons and electrons so the positive and negative charges balance out to form a neutral atom (no charge)
What are the two special numbers used to describe atoms?
- Atomic number
- This is the number of protons in the nucleus and in a neutral atom this is also equal to hte number of electrons
- Mass number
- This is the number of protons and neutrons in the nucleus
Electrons circle the nucleus in areas called shells.
How many electrons are in the first three shells?
- 1st shell max 2
- 2nd shell max 8
- 3rd shell max 8
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