Chemistry Revision

Chemistry Revision

1. Structure of atoms

   • At the centre of an atom is a nucleus containing protons and neutrons. Electrons are arranged around the nucleus in energy levels or shells.

2. Electron configurations

   • The electron configuration of an atom is the representation of the arrangement of electrons distributed among the orbital shells and subshells.

3. Properties of groups

   • Properties of elements in Group 1A, the alkali metals. The alkali metals are the elements Li, Na, K, Rb, Cs, Fr. These elements have relatively low melting points. Cesium, Cs, melts at body temperature, 37oCelsius. They are soft enough that they can be cut with a knife.
   • Properties of elements in Group 2A, the alkaline earth metals. The alkali metals are the elements Be, Mg, Ca, Sr, Ba, Rd. These elements have higher melting points than the alkali metals. They are harder and tougher. Magnesium is used to fabricate car parts like wheels. Calcium metal reacts with water. Magnesium clearly doesn't react with water or else it couldn't be used in car parts.
   • Properties of elements in Group 7A, the halogens. The halogens, F, Cl, Br, I, At, are nonmetals. Halogens have lower melting points than the alkali metals. Fluorine and chlorine are gases at room temperature The halogens are corrosive and so reactive that in nature they are only found combined with other elements
   • Properties of elements in Group 8A, the noble gases. The noble gases, He, Ne, Ar, Kr, Xe, Ra, are nonmetals. The noble gases are very unreactive. They were once called the inert gases. The noble gases are so unreactive they are used to protect materials from reaction. Welding is done using an argon atmosphere to prevent oxygen in the air from reacting with the hot welded metals.

4. Name compounds

   • The least electronegative element is named first.
   • If the compound contains hydrogen, hydrogen is named first.
   • The number of atoms of each element is indicated by a prefix
   • If the first element only has one atom the prefix is not used.

5. Determine type of reaction

   • Combustion: A combustion reaction is when oxygen combines with another compound to form water and carbon dioxide. These reactions are exothermic, meaning they produce heat. An example of this kind of reaction is the burning of napthalene: C10H8 + 12 O2 ---> 10 CO2 + 4 H2O
   • Synthesis: A synthesis reaction is when two or more simple compounds combine to form a more complicated one. These reactions come in the general form of: A + B ---> AB One example of a synthesis reaction is the combination of iron and sulfur to form iron (II) sulfide: 8 Fe + S8 ---> 8 FeS
   • Decomposition: A decomposition reaction is the opposite of a synthesis reaction - a complex molecule breaks down to make simpler ones. These reactions come in the general form: AB ---> A + B One example of a decomposition reaction is the electrolysis of water to make oxygen and hydrogen gas: 2 H2O ---> 2 H2 + O2
   • Single displacement: This is when one element trades places with another element in a compound. These reactions come in the general form of: A + BC ---> AC + B One example of a single displacement reaction is when magnesium replaces hydrogen in water to make magnesium hydroxide and hydrogen gas: Mg + 2 H2O ---> Mg(OH)2 + H2
   • Double displacement: This is when the anions and cations of two different molecules switch places, forming two entirely different compounds. These reactions are in the general form: AB + CD ---> AD + CB One example of a double displacement reaction is the reaction of lead (II) nitrate with potassium iodide to form lead (II) iodide and potassium nitrate: Pb(NO3)2 + 2 KI ---> PbI2 + 2 KNO3
   • Acid-base: This is a special kind of double displacement reaction that takes place when an acid and base react with each other. The H+ ion in the acid reacts with the OH- ion in the base, causing the formation of water. Generally, the product of this reaction is some ionic salt and water: HA + BOH ---> H2O + BA One example of an acid-base reaction is the reaction of hydrobromic acid (HBr) with sodium hydroxide: HBr + NaOH ---> NaBr + H2O

6. REDOX reactions

   • Redox reactions include all chemical reactions in which atoms have their oxidation state changed; in general, redox reactions involve the transfer of electrons between species.
     • The term "redox" comes from two concepts involved with electron transfer: reduction and oxidation.[1] It can be explained in simple terms
       • Oxidation is the loss of electrons or an increase in oxidation state by a molecule, atom, or ion.
       • Reduction is the gain of electrons or a decrease in oxidation state by a molecule, atom, or ion.

7. Metal displacement reactions

   • A metal will displace (take the place of) a less reactive metal in a metal salt solution.
   • iron + copper(II) sulfate arrow iron sulfate + copper.

8. Collision theory (factors affecting the rate of reaction)

   • Surface area of a solid reactant
   • Concentration or pressure of a reactant.
   • Temperature.
   • Nature of the reactants.
   • Presence/absence of a catalyst.