The Early Periodic Table
- 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 the time.
- Mendeleev's periodic table left gaps for the unknown elements, and so provided the basis for the modern periodic table.
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The Modern Periodic Table
- The atomic (proton) number of an element determines its position on the periodic table.
- The number of electrons in the outmost 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 outmost shell
- We can explain trends in reactivity as we go down a group in terms of:
- the distance between the outmost electrons and the nucleus
- the number of occupied inner shells (energy levels) in the atoms.
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Group 1 -The Alkali Metals
- 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 an alkaline solution containing the metal hydroxide.
- They form 1+ ions in reactions to make ionic compounds. These are generally white and disolve in water, giving colourless solutions.
- The reactivity of the alkali metals increases going down the group.
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The transition elements
- Compared with the alkali metals, transition elements have much higher melting points and densities. They are also stronger and harder, but are much less reactive
- The transition elements do not react vigorously with oxygen or water
- A transition element can form ions with different charges, in compounds that are often coloured
- Transition elements and their compounds are important industrial catalysts
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Group 7- The Halogens
- The halogens all form ions with a single negative charge in their ionoic compounds 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 a solution of one of its salts
- The reactivity of the halogens decreases going down the group because it is harder for them to gain an electron as they are further away from the nucleus.
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