BRAINCAKEThe Periodic Table
Mendeleev arranged the (approx) 60 known elements in order of "atomic weight" in groups with similar properties and left gaps for undiscovered elements. When protons were discovered in the 1900s the reason for the pattern became clear.
The modern periodic table has 114 elements arranged in order of atomic number in vertical columns called groups and rows called periods.
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Key terms in this lesson
- Atomic number
- The number of protons in the nucleus of an atom.
- Ionisation
- The loss or gain of electrons by an atom or molecule to form a charged ion.
- Electron shell
- A main energy level occupied by electrons, given a principal quantum number n, with n = 1 closest to and lowest in energy relative to the nucleus.
- Electron configuration
- The notation showing the arrangement of an atom's electrons in shells and sub-shells, such as 1s2 2s2 2p6.
More in Periodicity
- Electron Configuration
- Ionisation Energy
- Successive Ionisation Energies
- Trends in First Ionisation Energies Across a Period
- Trends in First Ionisation Energies Down a Group
- Beryllium and Boron
- Nitrogen and Oxygen
- Metallic Bonding
All 14 lessons in Periodicity · All OCR AS-level Chemistry topics