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Periodic Table

The periodic table

All the different elements are arranged in a chart called the periodic table. A Russian scientist called Dmitri Mendeleev produced one of the first practical periodic tables in the 19th century. The modern periodic table is based closely on the ideas he used:

• the elements are arranged in order of increasing atomic number
• the horizontal rows are called periods
• the vertical columns are called groups
• elements in the same group are similar to each other

                           Learn more at: The Periodic Table

Seperating Mixtures

Separating solids from liquids – filtration

If a substance does not dissolve in a solvent, we say that it is insoluble. For example, sand does not dissolve in water – it is insoluble.

Filtration is a method for separating an insoluble solid from a liquid. When a mixture of sand and water is filtered:

• the sand stays behind in the filter paper (it becomes the residue)
• the water passes through the filter paper (it becomes the filtrate)

The slideshow shows how filtration works:

                                    Learn More At: Separating Mixtures

Pure and Impure Chemical Substances

Pure chemical substances

A glass of mineral water is not pure water

Food and drink may be advertised as ‘pure’. For example, you may see cartons of ‘pure orange juice’ or ‘pure mineral water’. This means that nothing else was added to the orange juice or mineral water during manufacture. However, these substances are not pure to a scientist. In science, a pure substance contains only one element or compound.

Mineral water is mostly water, but there are other substances mixed with it. These are the ingredients that you see listed on the bottle’s label.

                                                      Learn More At: Pure and Impure Substances

Atoms, Elemnts, and Compounds

Atoms

Everything is made from atoms, including you. Atoms are tiny particles that are far too small to see, even with a microscope. If people were the same size as atoms, the entire population of the world would fit into a box about a thousandth of a millimetre across.

We usually imagine atoms as being like tiny balls:

                                                      Learn More At: Atoms, Elements, and Compounds

Heating And Cooling Curves

Changing state

A substance must absorb heat energy so that it can melt or boil. The temperature of the substance does not change during melting, boiling or freezing, even though energy is still being transferred.

A heating curve is a graph showing the temperature of a substance plotted against the amount of energy it has absorbed. You may also see a cooling curve, which is obtained when a substance cools down and changes state.

                                               Learn More At: Heating And Cooling Curves

Solids, Liquids,Gas

Solids

Steel, plastic and wood are solids at room temperature. Ice is solid water. The particles in a solid are:

• close together
• arranged in a regular way

Particles in a solid

Strong forces, called bonds, attract the particles towards each other. This means that the particles in a solid:

• can vibrate in a fixed position
• cannot move from place to place

The table shows some of the properties of solids and why they are like this:

Property	Reason
They have a fixed shape and cannot flow	The particles cannot move from place to place
They cannot be compressed (squashed)	The particles are close together and have no space to move into

Solids such as concrete are useful for buildings and their foundations because they cannot be compressed.

                                                                            Learn More At: Solids, Liquids,Gas 

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