Chemical Change

Elements

Substance made up of only one type of atom and cannot be broken down by chemical means

Neutrons

Neutrons are found in the nucleus and are neutral.

Nitrogen Dioxide

A brown gas with a strong smell. It is poisonous and can cause acid rain.

Chemical change

A chemical change occurs when chemicals combine together in different ways to form new chemical substances which have completely different properties (both physical and chemical). Chemical changes are very hard to reverse.

Ionic compounds

A compound can also form when positive metal ions and negative non-metal ions join together. These compounds are called ionic compounds

Molecule

A molecule consists of at least two atoms that do not have to be different, joined together.

Mixtures

A substance made by mixing other substances together

Reactants

Are the substances that you start with and are things that react and make a new substance

Magnesium Activity

Collect a 5cm strip of magnesium ribbon and use tongs to hold one end of the strip in the hot part of a bunsen flame. Magnesium is a bendy, shiny, silver coloured solid that burns with an intensely bright white light and leaves behind a brittle white powder.

Electrons

Electrons are found moving rapidly around the nucleus and are grouped in different shells around the nucleus. The first shell has a maximum of 2 electrons, the second shell has a maximum of 8 electrons, and the third shell has a maximum of 8 electrons. Depending on how many electrons are in each shell determines where the element is on the periodic table.

Three parts of an atom

Electrons, protons and neutrons. The protons and neutrons are found in the nucleus, whereas the electrons are found moving rapidly around the nucleus

Making Oxygen

Place a small amount of manganese dioxide powder in a test tube. Pour a few mLs of hydrogen peroxide into the test tube.

Making carbon dioxide

Place two or three marble chips in a boiling tube and then cover them with hydrochloric acid. It bubbled and the boiling tube got warmer.

Testing for carbon dioxide

Place two or three marble chips in a boiling tube and then cover them with hydrochloric acid. Seal the boiling tube with the stopper and tubing, and place the other end of the tubing into a test tube half filled with lime water. The lime water becomes cloudy showing after reacting with the carbon dioxide.

Products

The new chemical that is made after the reaction, which has different properties to the reactants

Nitrogen

This gas makes up most of the air and doesn't react much. A burning splint will go out in this gas.

Painting

This is a common way of protecting large structure such as bridges and cars.

Oiling or greasing

This is used on many moving machinery parts. Oil or grease can be used to protect and store garden tools.

Valence electrons

Valence electrons are the electrons in the outer shell of the atom.

Group 18 elements

All the elements in Group 18 are unreactive because they already have a full shell. They are inert/noble gases

Carbon dioxide

About 0.03% of the air is carbon dioxide. It is a colourless gas with no smell. It is more dense than air so it sinks to the ground.

Oxygen

About 20% of the air is oxygen. It is a colourless gas with no smell and it is very reactive.

Group 17 elements

All elements in Group 17 are very reactive non-metals because they only need to gain one electron to have a full shell.

Group 1 elements

All the elements in Group 1 are soft metals and alkali metals and are very reactive because they only need to lose their one valence electron to achieve a full shell.

Atomic Structure

An atom consists of three types of sub-atomic particles, the protons, neutrons and electrons. The overall charge of an atom is zero, it is neutral

Compounds

Compounds are substances that contain different elements chemically combined or bonded together. Compounds can only be separated into the separate elements by a chemical reaction

Why chemical reactions happen

Elements react together to try and achieve a full outer shell of electrons. Elements can achieve this by either losing or gaining electrons to form ionic compounds or by sharing electrons to form covalent compounds.

How does Carbon Dioxide put out a fire?

For a fire to burn, it needs fuel, oxygen and heat. Carbon Dioxide creates a barrier between the fire and the oxygen, starving the flame of oxygen so then is will die out.

Ways of recognising chemical change

Gives off a gas, new product, process cannot be reversed easily, smells, temperature change, new properties, colour changed, and gives off heat.

Hydrogen

Hydrogen is a colourless, odourless gas. It is lighter than any other substance and is highly flammable and reacts so violently with oxygen in the air that it explodes

Alloying

Iron can be mixed with another element to form a solid mixture called an alloy. The alloy corrodes much less easily. An example of an alloy is stainless steel.

Testing for oxygen

Light a wooden splint and then blow out the flame leaving a glowing tip, and then immediately hold the tip in the test tube of oxygen. The wooden splint relights on fire/bursts back into flames.

Reactions of metals and oxygen

Most metals, except very unreactive ones such as silver or gold, will react with oxygen to form metal oxides.

Covalent Compounds

Non-metal atoms join together by sharing their electrons to form bonds between the atoms. The particles formed are often referred to as molecules.

Testing for hydrogen

Place a few pieces of magnesium in a test tube. Add some dilute hydrochloric acid to the test tube and put your thumb over the test tube to prevent any gas escaping. When you feel the pressure building on your thumb, hold a burning splint to the mouth of the test tube. The lighted splint will go out with a squeaky pop.

Protons

Protons are found in the nucleus and have a positive electric charge that is the same amount as an electron

Molecules

Some non-metal atoms exist joined together in groups called molecules. If the atoms in a molecule are the same, it is an element. If the atoms in a molecule are different, it is a compound.

Oxygen reactant

Steel wool will burn readily if it is burnt in a jar contain 100% pure oxygen, rather than in air (with only 21% oxygen). It burns more vigorously, faster, with a lot of energy being given out and has a brighter white light.

Atomic number

The atomic number of an element is the number of protons in the nucleus. Because the atom is overall neutral, it will have the same number of electrons as protons.

Ions

When atoms lose or gain electrons they form ions, which have different properties to the original atoms, as they are no longer neutral. Metal atoms undergo chemical reactions in which they lose electrons to form positive ions.

Word equations

A chemical reaction can be described by a word equation. The chemicals you start off with are called the reactants and are written on the left hand side of the equation. The chemicals you finish up with are called the products, and are written on the right hand side of the equation.

Making hydrogen

Place a few pieces of magnesium in a test tube. Add some dilute hydrochloric acid to the test tube and put your thumb over the test tube to prevent any gas escaping.

Preventing rusting

Rusting can be slowed or stopped by preventing oxygen or water reaching the iron surface. The method that is chosen depends on the way the iron is to be used after it has been protected. The size of the object and the cost of the method of protection is also important.

Rusting

The reaction of iron with oxygen is commonly called 'rusting' and produces a reddish-brown solid product as a surface coating.

Atoms

The smallest particle that can exist on its own is an atom. All matter is made up of either single atoms, groups of atoms (called molecules) or atoms that have undergone a change to form ions.

Plating

In this method, iron is coated with a thin layer of another metal that can act as a protective coating. When the metal coating is zinc, the process is called galvanising. Galvanised iron is used to make buckets and playground equipment such as jungle gyms. Another metal, chromium, is used to is used to produce a shiny coating on objects such as kettles and taps.

Mass number

The mass number is the number of protons plus the number of neutrons in the nucleus. The number of neutrons is the same as (or slightly greater than) the number of protons. In comparison to the neutrons and protons, the electrons are so light they do not contribute to the mass of the atom.

Periodic Table

There are 118 elements on the periodic table so far.

Argon

This gas does not react at all and is used in light bulbs so that it can get very hot without burning.

Helium

This gas is very light, so we use it in balloons. It doesn't react at all, and will put out a flame.

Fire Triangle

Fuel, oxygen and heat.