OCR 21st Century C4

• Elements are arranged in order of Proton number. ( also called atomic number) 

• This is also the number of Protons in each atom. ( Its the number written below each element in the Periodic table.)
  
  
• The relative atomic mass is the mass of one atom of an element relative to a carbon atom.

• Elements on the left are metals, elements on the right are non-metals.
• Groups= Columns

• Patterns and trends can be identified due to the way the Periodic table is arranged. E.g Group 1 metals' melting point decreases as you go down the group.

• As you go from left to right the elements get less metallic. 

Group 1 properties- Alkali metals.

• Li , Na, K are all soft metals which are easily cut and shiny till they "tarnish" ( become dull) as the metal reacts with oxygen in the air and water in the air. Storage in oil prevents oxidisation.
• There is increasing reactivity as you go down the group. 
• As a result of their reactivity, alkali metals must not be touched because they  react with water in sweat so gloves and goggles may be worn. 

Physical properties 

• Melting & Boiling point decreases as you go down the group .
• Density ( g/cm3 ) generally increases as you go down the group.
• Alkali metals are soft. Hardness decreases as you go down the group.

Reaction with water : 

• Hydrogen (g) + metal hydroxide is produced .
• Speed and violence of reaction increases as you go down the group.
• Lithium : 2Li(s) + 2H₂O(l) → 2LiOH(aq) + H₂(g)
  Sodium: 2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g) 
• Potassium: 2K(s) + 2H₂O(l) → 2KOH(aq) + H₂(g) 
• Hydroxides dissolve in water to form corrosive alkali solutions

Reaction with chlorine : 

• Each reaction with chlorine gas produces a white crystalline salt.
• Reactivity increases as you move down the group.
• 2Li(s) + Cl₂(g) → 2LiCl(s) 
• 2K(s) + Cl₂(g) → 2KCl(s)  

Halogens- diatomic molecules (exist in two's e.g Br₂ in Group 7).

• Melting & Boiling points increase as you go down the group.
• State trends- Gas to liquid to solid as you go down the group ( fluoride and chlorine are gases, bromine is liquid ,iodine and astatine are solid) 
• Darker as you go down the group. Fluorine , Chlorine is yellow green,Bromine is red-brown ,Iodine is shiny purple , astatine is black.

Reactions and uses of halogens

• React with metals to make salts called metal halides. metal +hydrogen = metal halide. e.g 2Na(s) + Cl₂(g) → 2NaCl(s) 
• Reactions become less vigorous as you move down the group. 

Bleaching agents to remove colours  e.g Cl₂  used to bleach wood pulp for paper. Or killing bacteria            e.g swimming pools. Halogens are very reactive and poisonous so they are handled with care e.g Chlorine is used only in a fume cupboard. 

A more reactive halogen displaces a less reactive halogen from a solution of one of its salts.

• E.g chlorine (as a gas or dissolved in water) + sodium bromide solution the chlorine takes the place of the bromine. Because chlorine is more reactive than bromine, it displaces bromine from sodium bromide. The solution turns brown. This brown colour is the displaced bromine. The chlorine has gone to form sodium chloride.

Cl₂(aq) + 2NaBr(aq) → 2NaCl(aq) + Br₂(aq)

Hazards ( Without the images)

• Corrosive, Irritant, Toxic , Harmful, Highly flammable and Oxidising.  
• For each , gloves, eye protection or a face shield may be worn.
• Fume cupboards - Toxic substances , Clothing - Oxidising substances.

Chemicals reacted together - Reactants. Chemicals made - Productants.

Halides of group 1 :                 Hydroxides of Group 1 metals 

sodium chloride - NaCl              Sodium Hydroxide - NaOH Potassium Bromide- KBr           Potassium Hydroxide - KOH Lithium iodide - LiI               Lithium Hydroxide - LiOH State symbols : 2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g) : solid, liquid, aqueous ( dissolved in water) , gas.
Writing chemical equations (  Higher ) 

• Word equation, Formula, Symbol equation, then Balancing by putting the correct numbers in front of each element.  
• There must be thesame number of atoms of each element on each side.  e.g  2Na + 2H₂O → 2NaOH + H₂ 

Atoms are the basic unit of a chemical element.

 Electrons are contained in shells and total no of electrons = total number of protons. Protons have +1 charge, Neutrons 0, and electrons -1. Relative masses of protons and neutrons are 1:1 and electron mass is trace. 

 Neutrons carry no electrical charge.

Flame colours- 
Li - red , Na - Yellow, K - lilac

• All atoms give off light when heated. 
• A prism can be used to split the light to form a spectrum 
• This technique is called spectroscopy. 
• rubidium and caesium were discovered through spectroscopy.

• Electrons are arranged in shells.
• As you go through each row of the periodic table, proton no ( and therefore electron no) increases by 1. 
• The first shell holds 2 electrons, second shell holds 8 , third holds 8 and the fourth holds 2 . 
• A dot and cross diagram can be shown like the diagram below .   Calcium has 20 electrons. 2 + 8+ 8+2 = 20
  The way electrons are arranged is called the electronic structure.
• the number of shells is the same as the period number. 
• the number of electrons in the outermost shell is the same as the group number. as you move down the groups.
• Each element in a group therefore has the same number of electrons in its outer shell.  

• Group 1 alkali's all have 1 electron in the outer shell
• In a reaction with a non-metal, each alkali metal atom loses its outer electron and becomes an ion with a single positive charge, +1.
• Electrostatic force between nucleus and electrons in outer shells become weak as you increase the number of shells. 
• which is why the outer electron is more easily lost.
• The further away the outer electron of an atom from its nucleus the more reactive the element is. E.g K is more reactive then Li.

Group 7- 7 electrons in the outer shell , willing to gain one .