Chemistry- Trends

• Catalysts can be added to reaction to speed them up. They work by lowering the activation energy and providing an alternative route for the reaction to happen which takes less energy so its easier to achieve
• The collision theory states a chemical reaction can only happen if the reacting particles collide with enough energy.
• When energy is transferred to the surroundings, this is called an exothermic reaction and the temperature of the surroundings increase. Examples of exothermic reaction include: combustion reactions and rusting
• When energy is taken in from the surroundings, this is called an endothermic reaction and the temperature of the surroundings decrease. An example of an endothermic reaction include: thermal decomposition
• The elements in group 1, on the left of the periodic table, are called alkali metals. They can easily obtain a full outer shell by losing 1 electron. They all lose their outer shell electron in reactions to form positive ions with a +1 charge

  
• The size of the element's atoms and the number of full electron shells, increases down the group. This means that down the group, the electron in the outer shell gets further away from the nucleus and is shielded by more electron shells. The further away an electron is from the positive attraction of the nucleus, the easier it can be lost in reactions. This means the reactivity increases with the size of the atom
• Lithium + water --> lithium hydroxide

  Sodium + water --> sodium hydroxide

  Potassium + water --> potassium hydroxide
• The elements in group 7 of the periodic table, are called halogens
• All halogens have 7 electrons in their outer shell. This means that they can easily obtain a full outer shell by gaining 1 electron. This forms a negative ion with a -1 charge.
• The reactivity of halogens decreases down the group. This is because they get larger going down the group, the outer shell gets further away from the nucleus and is shielded away by more electron shells.
• Metals are found on the left side on the periodic table
• All metals are malleable, have a high melting point and are good conductors of heat and electricity
• Alkali metals are unique because they are very reactive
• A displacement reaction is a reaction where a more reactive element will displace a less reactive element from its compound

  e.g. Lead chloride + magnesium --> magnesium chloride + lead

  
  

  This happens because magnesium is more reactive than lead