atoms, bonding and moles

There are around 100 different elements from which all substances are made. The Periodic Table is a list of all the elements known to man.

• Each element is made up of 1 type of atom.
• Compounds contain more that 1 element.
• Atoms have tiny nucleuses surrounded by electrons.

The elments in The Periodic Table are arranged in columns, called groups. The element in a group usually have similar properties.

Chemical equations show the reactants and the products in a reaction.

Word equations give the name of the reactants and the products only.

Hydrogen + oxygen ----> water 

    H2        +     O     ----> H2O

In chemical reactions the atoms get rearranged. Atoms are not created nor destroyed in a chemical reaction. The number and types of atoms remain the same before and after the reaction.

When writing a chemical equation you sould always balance the equation. A balanced symbol equation has the same number of each type of atom on both sides of the equation. use multivilers to ensure symbol equation balance.

You can include state symbols in balanced equations. These are (S) solids, (l) liquids, (g) gases and (aq) aqueos solutions.  

The law of conservation of mass states that no atoms are lost or made during a chemical reaction, so the mass of the products equals the mass of the reactants. 

In some reactants, the las seems to be broken because the mass appears to change. this is usually when gases are reactants or products.

A mixture is made up of 2 or more substances that are not chemicly reacted toghether.

Amixture can be seperated by physical means, such as filtration, crystilisation and simple distilation.

Compounds

Compounds have a fixed composition.

Chemical reaction must be used to separate the elements in a compound.

There are chemical bonds between atoms of different elements in the compound.

Mixtures

Mixtures have no fixed composition.

The different elements or compounds in a mixture can be separated again more easily.

There are no chemical bonds between atoms of different substances in a mixture.

distilation

In simple distilation, a solution is heated and boiled to evaporate the solvent the vapour given off then enters a cindencer. Hot vapour is cooled and condensated back into a liquid ready for collection.

filtration

The teqnique of filtration is used to speprate substances that are insoluble in a particular solvebt from those that are soluble in the solvent. The sand you collect on the filter paper can be washed.

crystilisation

To obtain a samole of pure salt from the salt solution following filtration you would need to seperate sodium chloride in the solution from the water. you evaporate the water from the sodium chloride solution.

fractional distilation is a way to seperate mixtures of misciblr liqueds, for example, ethenol and water. miscible liqueds dissolve in each other, mixing completely. Then do not form layers.

The liquids have different boiling points. The liquids with the lowest boiling point will be collected first. 

Paper chromatography is a way to seperate substances from mixtures in solution. it works compounds are more soluble than others in the solvent.