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the periodic table., Eg. chlorine + potassium bromide --> potassium…
the periodic table.
Dmitri Mendeleev
Dmitri Mendeleev created a periodic table in 1869, which arranged the elements in order of increasing atomic weights. He also took into account the properties of the elements and their compounds. This meant that the table had gaps in it, to leave space for elements which had not yet been created, Mendeleev's periodic table grouped elements with similar properties together.
He also discovered an element, which he named mendelevium.
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The modern periodic table's elements are arranged in rows, called periods, in order of increasing atomic number.
Group 0
Elements in Group 0 are known as the noble gases. They have a full outer shell of electrons, meaning they are very unreactive due to their very stable electron configuration. Their boiling points increase down the group.
Group 1
The elements in Group 1 are known as the alkali metals:
- they have one electron in their outer shell
- they have low melting and boiling points that decrease down the group
- they become more reactive down the group because the outer electron gets further away from the nucleus, and the bond becomes weaker, so the electron is lost more easily.
Alkali metals must be stored in oil because they react very vigorously with oxygen and water, including moisture in the air.
When alkali metals react with water, a metal hydroxide is formed and hydrogen gas is given off. Group 1 metals have a low density - lithium, sodium and potassium are less dense than water, so float on top of it.
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Group 7
The Group 7 metals are non-metals and are known as the halogens. They have seven electrons in their outer shell and the elements in this group are diatomic, meaning the electrons travel in pairs, eg. Cl2, O2, Br2.
Reactivity decreases down the group because the outer shell gets further away from the nucleus and means it's less easy to gain an electron. The further down the Group 7 element is, the higher its melting and boiling point.
Halogens react with metals to produce ionic salts. When this happens, the halogen atom gains one electron to form a halide ion with a negative charge (-1).
Displacement reactions: A more reactive halogen will displace a less reactive halogen from an aqueous solution of its salt.
Transition elements
The transition elements are in the centre of the periodic table, between Group 2 and 3. They form coloured compounds. They have ions with different charges, eg. Fe2+ and Fe3+.
They can be used as catalysts to speed up chemical reactions. Transition metals are good conductors of heat and electricity, and can be bent easily or hammered into shape.
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