Chemistry Unit 3

Unit 3 Chemistry key notes

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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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Transition Elements

  • 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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