GCSE AQA Chemestry unit C3 1.1-1.5 key points

GCSE AQA Chemestry unit C3 1.1-1.5 key points

1. C3 1.1

   • The periodic table of elements developed as chemists tried to classify the elements. It arranges them in a pattern in which similar elements are grouped together.
   • Newlands table put the elements in order of atomic mass but failed to take account of elements that were unknown at that time.
   • Mendeleev's periodic table left gaps for the unknown elements, and so provided the basis for modern periodic table.

2. C3 1.2

   • The atomic (proton) number of an element determines its place in the periodic table
   • the number of electrons in the outer shell (highest energy level) of an atom determines its chemical properties
   • the group number in the periodic table equals the number of electrons in the outermost shell
   • we can explain trends in reactivity as we go down a group in terms of
     • The distance between the outermost electrons and the nucleus
     • the number of occupied inner shells (energy levels) in the atoms

3. C3 1.3

   • the elements in group 1 of the periodic table are called the alkali metals
   • Their melting points and boiling points decrease going down the group
   • the metals all react with water to produce hydrogen and the alkaline metal solution containing the metal hydroxide
   • They form 1+ ions in reactions to make ionic compounds. these are generally white and dissolve in water, giving colourless solutions
   • The reactivity of alkali metals increase going down the group

4. C3 1.4

   • Compared with the alkali metals, transition metals have much higher melting points and densities. They are also stronger and harder but are much less reactive.
   • The transition metals do not react vigorously with oxygen or water.
   • a transition element can from ions with different charges, in compounds that are often coloured.
   • Transition elements and their compounds are important industrial catalysts.

5. C3 1.5

   • The halogens all form ions with a single negative charge in their ionic compound with metals.
   • The halogens form covalent compounds by sharing electrons with other non-metals
   • a more reactive halogen can displace a less reactive halogen from ma solution of one of its salts.
   • The reactivity of halogens decreases as you go down the group