Chemistry 3 Key Ideas

Periodic Table 1. Newlands arranged elements in order of atomic weight, octaves; Mendeleev arranged elements according to how they reacted, this resulted in gaps (for undiscovered elements). 2. Now elements are arranged in order of atomic number. 3. Groups = columns; elements have the same number of electrons in the outer shell. Periods = rows; outer electrons in the same shell. 4. Group 1: reactivity increases down the group because the outer shell is further from the positive nucleus so electrons are lost more easily 5. Group 7: reactivity decreases down the group because the outer shell is further from the positive nucleus so electrons are gained less easily 6. Transition metals are less reactive than group 1 and have higher melting points and densities.

Water 7. Hard water contains Ca2+ and Mg2+ ions. Temporary hard water contains HCO3- ions 8. Scale is CaCO3 and forms when temporary hard water is boiled. 9. Scum is calcium/magnesium stearate and forms when hard water reacts with soap. 10. To remove hardness, Ca2+ and Mg2+ ions have to be replaced by Na+ or H+ ions. 2 options = add washing soda or use an ion-exchange column 11. Water treatment involves filtering to remove solids and adding chlorine to kill microorganisms.

Energy 12. Simple calorimetry is when a substance is heated and the rise in temperature is measured. 13. Q = m x c x ∆T; energy is measured in J or kJ. 14. Energy is supplied to break bonds (endothermic) and is released when bonds are made (exothermic). 15. ∆H is the overall change in energy for the reaction. If ∆H is negative = exothermic. 16. Catalysts lower the activation energy for a reaction.

Analysis 17. Positive ions are identified using flame tests (distinctive colours) and by adding NaOH (precipitates). You need to know the results! 18. Negative ions are identified by adding reagents and looking for specific results. Learn them! 19. Titrations: pipette, burette, conical flask, indicator, swirl, endpoint 20. Concentration = no. moles ÷ volume; unit is mol/dm3

Equilibrium 21. Equilibrium occurs when the rate of the forward reaction equals the rate of the backward reaction. 22. The amount of yield produced can be affected by changing temperature or pressure. 23. If the forward reaction is exo, lower the temp; if the forward reaction is endo; increase the temp. 24. Nitrogen + hydrogen ⇌ ammonia 25. The raw materials are air and methane; the conditions are 450oC, 200atm and iron catalyst.

Organic Chemistry 26. Alcohols have the functional group –OH. 27. Alcohols are used in drinks, as solvents and as fuels. 28. Carboxylic acids have the functional group –COOH. 29. Carboxylic acids are weak acids and react with alcohols to form esters. 30. Esters have the functional group –COO-.