What was the early periodic table based on?
Their physical / chemical properties and their atomic mass
What did Newland set out for his periodic table?
Newland’s law of octaves – every 8th element had similar properties
What did Mendeleev do with his periodic table?
Mendeleev left gaps and predicted new elements – he put known ones in order of atomic mass
Why were the gaps so important in Mendeleev’s periodic table?
The gaps predicted the properties of undiscovered elements
What is the modern periodic table based on?
Electron structure – this can predict the element’s chemical properties (group number is equal to the number of electrons in the outer shell)
What are the alkali metals and what properties do they have?
Alkali metals are group 1 elements – they become more reactive down the group (outer e- further from nucleus) and have lower melting and boiling points
They also have a low density (Li, Na and K less dense than water)
How many electrons in the outer shell are present in group 1 elements (alkali metals)?
1 electron – making them very reactive and forming ionic compounds with non-metals (which produce white compounds that dissolve in water forming colourless solutions)
How do the alkali metals react when placed in water?
They react vigorously producing hydrogen gas and form hydroxides that dissolve producing alkaline solutions
2Na (s) + 2H2O (l) → 2NaOH (aq) + H2 (g)
2K (s) + 2H2O (l) → 2KOH (aq) + H2 (g)
What are the group 7 elements known as and what are their properties?
Halogens – they are non-metals with 7 outer electrons and become less reactive (as it is harder to gain an e- as the outer shell is further from the nucleus) and have higher melting and boiling points
What colour vapours do the halogens fluorine, chlorine, bromine and iodine form?
Fluorine = yellow gas; chlorine = green gas; bromine = red-brown liquid; iodine = dark grey solid / purple vapour
What do the halogens form with metals?
Ionic bonds with metals (1- ions) called halides
What will more reactive halogens do too less reactive ones?
A more reactive halogen will displace a less reactive halogen from an aqueous solution of its salt
Cl2 (g) + 2Kl (aq) → I2 (aq) + 2KCl (aq)
Cl2 (g) + 2KBr (aq) → Br2 (aq) + 2KCl (aq)
What are the transition elements?
Transition elements are positioned between group 2 and 3 and are good conductors of heat and electricity; dense, strong, and shiny
What are the properties of the transition metals?
Transition metals often have more than one ion (e.g. Fe+2, Fe+3), form colourful compounds and make good catalysts
What is hard water and what does it make?
Hard water makes scum and scale (instead of lather with soap) due to calcium and magnesium ions dissolved in the water (scale is mostly calcium carbonate which is a thermal insulator and making heating elements less efficient)
*But calcium ions are good for teeth / bones and it is suggested minerals in hard water reduce heart disease
What ions cause hardness in water?
Calcium ions (Ca+2) and Magnesium ions (Mg+2)
How is hard water made soft?
The calcium and magnesium ions are removed
What is temporary / permanent hardness caused by and how is this removed?
Temporary hardness is caused by HCO3- and can be removed by boiling (HCO3- decomposes to insoluble CO3)
Permanent hardness can only be softened using washing soda (Na2CO3) where the carbonate ions react with the Ca+2 and Mg+2 ions
How can the hardness of water be compared?
Titrations – soap solution can be added to the water until a lasting lather was created
How can water quality be improved?
Filtration (removal of materials) and chemicals added to kill microbes
Why are chlorine / fluoride added to water and what problems may these cause?
Fluoride is added to drinking water to help reduce tooth decay and chlorine is added to prevent disease
Some studies have linked fluoride and chlorine to increased cancer
What is a reversible reaction?
A reversible reaction is one where the products of the reaction can themselves react to produce the original reactants
What happens if a reversible reaction takes place in a closed system?
Equilibrium is reached – the amounts of reactants and products will reach a balance
How can the position of the equilibrium in a reversible reaction be changed?
The temperature and pressure can be changed
How does temperature affect and exothermic and endothermic reaction?
All reactions are exothermic reaction in one direction and endothermic in the other
- Temp. raise causes endothermic reaction to increase (use up the extra heat)
- Temp. fall causes exothermic reaction to increase (give out more heat)
How does pressure affect an exothermic and endothermic reaction?
Many reactions have a greater volume on one side (either reactants or products)
- Pressure raise encourages the reaction will produces less volume
- Pressure fall encourages the reaction will produces more volume
What does a catalyst do to the equilibrium position?
Catalysts do not change the equilibrium position – they speed up both the forward and reverse reactions by the same amount
What is the Haber process?
Nitrogen + Hydrogen Ammonia
N2 (g) + 3H2 (g) 2NH3 (g)
What conditions are needed for the Haber process?
Nitrogen from air and hydrogen from natural gas at 200 atmosphere pressure and 450oC with an iron catalyst
How does the Haber process recycle its ‘waste’?