KEY POINTS:
- In atomic theory development you will have read of the electrons existing in shells (energy levels) around a central nucleus.
- The arrangement of the electrons is indicated by the position of an element in the periodic table. A column in the table is a group, a row in the table a period.
- The group number tells us how many electrons are in the outer shell of an element. The period number indicates the number of occupied energy levels (shells).
- Sulphur is in period three, group six. Therefore it has three occupied shells, and six electrons in the outermost shell.
- Reactivity is dictated by the number of electrons in the outer shell. All the elements in a group behave in a similar way because of this e.g. how the alkali metals (group one) react with water.
- The underlying principle of every chemical reaction is that EVERY ELEMENT WANTS TO OBTAIN A FULL OUTER SHELL OF ELECTRONS.
- Reactions involve the transfer, sharing and movement of electrons in order to obtain a full outer shell.
THINK OUTSIDE THE BOX:
- How many different elements can you identify in the laboratory using simple chemical tests?
- How many pieces of evidence do you think are required to say with absolute certainty what the identity of an unknown substance is?