Chemistry Igcse Gcse topics

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• Chemistry

• Periodic table

• The Periodic Table is a way of arranging what we know about the chemical elements

• Each element in the Periodic Table is a different type of atom

• The Periodic Table is arranged in atomic number order

• Compounds are formed when two or more chemical elements react together.

• An atom has a central nucleus. A nucleus contains one or more protons.

• The number of protons in the atomic nucleus gives the atomic number. An atom contains one or more electrons. The electrons are arranged in shells.

• The elements are arranged in rows in the Periodic Table.The rows of elements are called periods. The higher the atomic number of an element, the higher the period. The number of shells of electrons determines the period an element is in.

• Physical properties of elements often change in a pattern down the group

• States of matter

• There are three different states of matter

• Solid

• Liquid

• Gas

• Arrangment

• Close together

• Far apart

• Regular

• Random

• Movement of particles

• Vibrate on the spot

• Move around each other

• Move quickly in all directions

• Heat must be apllied to a substance for it to

• A substance must be cooled for it to freeze or condense

• A gas will also liquefy (turn into a liquid) if its pressure is increased enough. This is because the particles are moved close enough for bonds to form between the particles.

• Atomic structure

• A solution is made when a solute dissolves in a  solvent

• If the solute is white (eg sodium chloride) then the solution is colourless. This is because the individual particles (in this case,

• If the solute is coloured then the solute with have colour.  

• When chemicals, like the smell of perfume or burning toast, are let loose in a room, the particles mix with the air particles. The particles of smelly gas are free to move quickly in all directions. They eventually spread throughout the whole room. This is called diffusion

• Diffusion is much quicker in gases, especially hot gases

• Diffusion can also happen in liquids. This is because the particles in liquids can move around each other, which means that eventually they are evenly mixed.

• diffusion in liquids is slower than gases

• Diffusion doesn't happen in solids due to there being no movements apart from vibrating.

• definitions

• Atom

• the smallest component of an element having the chemical properties of the element, consisting of a nucleus containing combinations of neutrons and protons and one or more electrons bound to the nucleus by electrical attraction; the number of protons determines the identity of the element.

• Molecule

• the smallest physical unit of an element or compound, consisting of one or more like atoms in an element and two or more different atoms in a compound.

• Element

• one of a class of substances that cannot be separated into simpler substances by chemical means.

• Compound

• a pure substance composed of two or more elements whose composition is constant.

• Mixture  

• an aggregate of two or more substances that are not chemically united and that exist in no fixed proportion to each other.

• Acid

• a compound usually having a sour taste and capable of neutralizing alkalis and reddening blue litmus paper, containing hydrogen that can be replaced by a metal or an electropositive group to form a salt, or containing an atom that can accept a pair of electrons from a base. Acids are proton donors that yield hydronium ions in water solution, or electron-pair acceptors that combine with electron-pair donors or bases.

• Alkali

• any of various bases, the hydroxides of the alkali metals and of ammonium, that neutralize acids to form salts and turn red litmus paper blue.

• Acids and Alkalis

• Characterisiticy of acids

• 1. They are liquids. 2. They are solutions of compounds in water. 3. If concentrated they can be corrosive. 4. Acids taste sour (for example, vinegar). 5. Turn blue litmus paper red - this is an easy test for an acid! 6. Usually react with metals to form salts. 7. Acids contain hydrogen ions. 8. Turn Universal Indicator from green to red, and have a pH less than 7. Examples of acids: are vinegar (ethanoic acid) and lemon juice (citric acid)

• Properties of alkalis

• 1. They feel soapy to touch. 2. They are soluble bases. 3. Like acids, they can burn the skin. 4. They turn red litmus blue - this is how you test for an alkali! 5. Alkalis contain hydroxide ions (OH-). 6. They taste bitter. 7. Turns Universal Indicator from green to blue or purple.

• Ram (Realative Atomic mass)

• The realtive atomic mass shows s the mass of  that atom compared to the mass of other atoms.  For example if an atom had a relative atomic mass of 4. This would be compared to other atoms

• Relative formulae mass (RFM)

• Relative atomic masses can be used to find the relative formula massof a compound. To find the relative formula mass (Mr) of a compound, you add together the relative atomic mass values (Ar values) for all the atoms in its formula.

• The relative formula mass of a substance, shown in grams, is called one mole of that substance. So one mole of carbon monoxide has a mass of 28 g, and one mole of sodium oxide has a mass of 62 g.

• MOLES