The Early Periodic Table
- The periodic table of the elements developed as an attempt to classify the elements.
- It arranges them in a pattern according to their properties.
- Early versions of the periodic table failed to take account of the fact that not all elements had been discovered yet.
- Dmitri Mendeleev's table took account of unknown elements, and so provided the basis for the modern periodic table
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The Modern Periodic Table
- The group that an element is in is determines by its proton number (atomic number).
- The number of electrons in the highest energy level/outer shell of an atom determines its chemical properties.
- We can explain trends in reactivity as we go down a group according to the number of energy levels (shells) in the atoms.
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Group 1: Alkali Metals
- The group 1 elements are called the alkali metals.
- They are very reactive and their reactivity increases going down the group.
- They have a low density and are very soft.
- They are silvery and shiny, but go dull when they react with the air.
- They melt and boil at low temperatures.
- They all react with water to produce hydrogen and an alkaline solution containing the metal hydroxide.
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Group 7: Halogens
- They have low melting and boiling points.
- They are poor thermal and electrical conductors.
- The halogens exist as diatomic molecules.
- The halogens all form ions with a single negative charge.
- The halogens form covalent compounds by sharing electrons with other non-metals.
- The reactivity of he halogens decreases going down the group.
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- Most of the transition elements have high melting and boiling points. They also have a high density.
- The transition metals are strong and hard, making them useful for making alloys.
- The transition metals do not react vigorously with oxygen or water, making them useful as structural metals.
- They have metallic structures with delocalised electrons, making them good electrical and thermal conductors.
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