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Periodic Table - Trends in the Periodic Table

By now you will be aware that a good knowledge of the periodic table is essential for students of GCSE Chemistry. This is one of a series of quizzes on the topic and it looks at some of the patterns or trends between elements which can be observed in the periodic table.

Several scientists came up with the idea of the periodic table, but the one thing they all had in common was that they looked for patterns. A full understanding was beyond these people as they had no knowledge of atomic structure. Russian scientist Dimitri Mendeleev was the scientist who finally came up with a periodic table that worked. Like others before him, he arranged the known elements in order of atomic mass, starting a new line after each eight elements, but sometimes he swapped the order of elements and also left gaps, realising that there were probably other elements to discover. This meant that some of them were 'out of order' in terms of their atomic mass but his table seemed to work.

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When the first 'missing' element was discovered, it fitted the pattern that Mendeleev had predicted, which was good evidence that he had been on the right track. When protons were discovered, scientists worked out the atomic number of each element and arranged them in atomic number order. When they did this they discovered that the order of elements corresponded to Mendeleev's table.

Mendeleev's clever insight meant that definite patterns could be seen, patterns that now we take for granted. The biggest pattern is perhaps concerning the original classification of the elements into metals and non-metals by French scientist Antoine de Lavoisier. We can see that the metals appear on the left hand side of the table whilst the much smaller group of non-metals is to the right. Metals all have similar basic properties, for example they conduct heat and electricity, they are malleable and ductile, they are shiny when freshly cut and so on. These properties can easily be explained now that we know the atomic structure - metallic bonding, with its 'sea of delocalised electrons' explains most of them.

All of the scientists who contributed to the development of the periodic table arranged groups of similar elements in vertical columns. You need to know a little about several of these groups, particularly groups 1, 7 and 0. These have 'trivial names' - the alkali metals, the halogens and the noble gases. The patterns in the periodic table are usually referred to as trends because the patterns are not exact and in some cases, you can't measure them directly e.g. reactivity of the alkali metals with water. Whilst there are some trends that run along the rows, the most important trends are found when you go down the groups.

PLEASE NOTE: There are different ways of numbering the groups of the periodic table. Most UK exam boards still follow the convention that the number of electrons in the outer shell = number of group. If you study chemistry to higher levels, you will find that this is no longer the case other than for groups 1 and 2. We follow the numbering that is currently taught in most UK schools.

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  1. As you go down group 1, from lithium to francium, what happens to the reactivity of the elements?
    Lithium is the least reactive of the group 1 metals. Francium hasn't actually been made in large enough quantities to be tested but the expectation is that it would explode fiercely, covering the vicinty of the explosion in radioactive materials
  2. As you go down group 7, from fluorine to astatine, what happens to the reactivity of the elements?
    Fluorine is the most reactive halogen. It is so reactive that it can form compounds with some of the noble gases
  3. As you move across the periods of the periodic table, which of the following statements is true?
    The chemistry of metals and non-metals is usually opposite to one-another, for example, metals lose electrons but non-metals gain them
  4. What property can explain the changes in reactivity as you go down a group of elements?
    The more electron shells, the easier to lose electrons AND the harder to gain electrons
  5. As you go across a period of the table, what do the elements have the same number of?
    This is one of the few horizontal patterns
  6. What are the elements arranged in order of in the periodic table?
    In the modern periodic table, elements are arranged by their atomic number, early attempts to produce a periodic table were based on atomic mass
  7. What happens to the density of group 1 metals as you go down the group?
    Lithium is the least dense group 1 metal
  8. What happens to density as you go down group 8?
    This is one pattern for metals and non-metals that is the same!
  9. Why does the atomic radius of an element increase as you go down a group?
    Increasing the number of electron shells around the nucleus increases the radius of the atom
  10. What happens to the reactivity as you go down group 8?
    Group 8 elements do not react, they are the noble gases. As far as the GCSE is concerned, this group is unreactive therefore the reactivity is the same from element to element i.e. zero. Since the 1960s, a few compounds have been made, but with difficulty. So far, no compounds of helium or neon are known and so technically, elements lower down the group are more reactive which is not typical for non-metals

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