CHEM - The Periodic Table

🚨 Understanding how elements are arranged in the periodic table is very important for IGCSE Chemistry 🚨

All elements are arranged in the periodic table in order of increasing atomic number. 

• Hydrogen (atomic number = 1) is placed first on the periodic table, and then helium (atomic number = 2), and then lithium (atomic number = 3), and so on.

Periods:

• Periods are horizontal rows in a periodic table.
• Period number shows the number of electron shells an atom has.
  • Carbon is period 2, therefore has 2 electron shells.
  • Calcium is in period 4, therefore has 4 electron shells

Groups:

• Groups are vertical columns in a periodic table.
• Group number shows the number of electrons in the outermost shell of an atom. 
  • Magnesium is in group 2, therefore has 2 electrons in the outermost shell.
  • Oxygen is in group 6, therefore has 6 electrons in the outermost shell.
• Elements in group 0 have a full outermost electron shell.
  • Helium has 2 electrons in the outermost shell.
  • Other elements in group 0 have 8 electrons in the outermost shell.
• Since elements in the same group all have the same number of outer electrons, elements in the same group have similar chemical properties.
  • Group 1 alkali metals react vigorously with water.
  • Group 7 halogens react with group 1 or group 2 metals to form ionic compounds.
  • Group 0 noble gases are very stable and do not react with other elements because they have a full outermost electron shell.

If you know the position of an element in the periodic table, you can easily figure out the electronic configuration of the atom!

• Fluorine is in period 2, group 7. It has two electron shells and 7 electrons in the outermost shell, which is the second shell. Therefore, the electron configuration of fluorine is (2, 7).
• Potassium is in period 4, group 1. It has 4 electron shells and 1 electron in the outermost shell, which is the fourth shell. Therefore, the electron configuration of potassium is (2, 8, 8, 1).

Metals and non-metals:

☝️ Elements to the left of the red line are metals, and elements to the right of the red line are non-metals. ☝️

Metals:

• Good conductors of electricity
• Oxides of metals dissolve in water to form basic solutions.
• Examples of metals: lithium, magnesium, calcium

• Bad conductors of electricity
• Oxides of non-metals dissolve in water to form acidic solutions.
• Examples of non-metals: sulfur, phosphorous, chlorine

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