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