Chemistry 3 - Water, energy and the perioic table

  • Created by: Alice
  • Created on: 07-04-15 14:25

1st Periodic Tables

Newlands and Mendeleev classified the elements by arranging them in atomic weight order

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Mendeleev overcame problems in his periodic table by leaving gaps for undiscovered elements.

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Modern Periodic Table

In the modern periodic table, elements are arranged in atomic number order.

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Group 1

Group 1 elements are low-denisty metals that react with non-metals to form ionic compounds, and with water to release hydrogen. 
Their hydroxides form alkaline solutions.

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Transition elements

The transition elements are stronger, harder; have highter melting points, and are less reactive. 
They have ions with different charges, form coloured compounds, and are useful as catalysts.

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Group 7

Group 7 elements react with metals to form ionic compounds.  More reactive halogens displace less reactive halogens from aqueous solutions of their salts.

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Contents of Hard Water

Hard water contains dissolved compounds of clacium or magnesium. 
Calcium compounds are good for heart, teeth and bones.

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Hard water - soap and scale

Hard water increases costs because more soap is needed, and scale makes settles and heating systems less efficient.

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Temporary vs Permanent Hard Water

Temporary hard water is softened by boiling. 

Permanent hard water remains hard when it is boiled.

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Softening water - Sodium Carbonate vs Ion Exchange

Hard water can be softened by adding sodium carbonate or by passing it through ion exchange columns.

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Filtering Water

Water is made safte to drink by filtering, and by adding chlorine to reduce microbes. 
Adding fluride may improve dental health.

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Energy Change Equation

The energy change of a chemical reaction can be calculated using the equation q=mc∆t.
∆t is the temperature change of water heated by a burrning fuel, or of reacting solutions.

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Energy-level diagrams

Energy-level diagrams show the elative energies of reactants and products, the activation energy, and then overall energy change of a reaction.

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Chemical Reactions

In chemical reactions, energy is supplied to break bonds, and energy is released when new bonds are formed.

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Catalysts reduce the minimum amount of energy needed to start a chemical reaction (the activation energy).

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Hydrogen can be burnt as a fuel in combustion engines, or used in fuel cells to produce electricity to power vehicles.

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