Summary
Highlights
This video will teach you an easy trick to find the group, subgroup, period, and block number of any element, crucial for college and entry tests. Remember to click the subscribe button for access to hundreds of free unique lectures.
For elements where the last orbital is 's', the block is 's'. The highest principal quantum number gives the period. The number of electrons in the last 's' orbital indicates the group number. If the last orbital is 's' or 'p', the subgroup will always be 'A'. Examples include Sodium (1s) and Calcium (2s).
If the last orbital is 'p', the block is 'p'. The highest principal quantum number gives the period. To find the group number for 'p' or 'd' orbitals, add the electrons in 'p' and 's' orbitals. For instance, Nitrogen (2p3) has 3 electrons in 'p' and 2 in 's', totaling a 5th group. Subgroup is 'A' for 's' or 'p' blocks.
When the last orbital is 'd', the block is 'd'. The highest principal quantum number determines the period. To find the group, add the number of electrons in the 'd' and 's' orbitals. For example, Iron (3d6, 4s2) has 6 + 2 = 8 electrons, placing it in the 8th group. If the last orbital is 'd' or 'f', the subgroup is always 'B'.
For elements like Zinc (3d10, 4s2), where the 'd' orbital is completely filled with 10 electrons, do not add the electrons from 'd' and 's' orbitals. The group number is simply the number of electrons in the 's' orbital (2 for Zinc), making it the 2nd group. The subgroup remains 'B'.
For elements like Nickel (3d8, 4s2), adding the 'd' and 's' electrons gives 8 + 2 = 10. Since there is no 10th group in the periodic table (according to Roman numerals), any sum greater than 8 means the group number is 8th. The subgroup is 'B'.
For elements like Bromine (4p5, 4s2, 3d10), when finding the group number for a 'p' block element with a 'd' orbital in between, always 'cross out' the 'd' orbital and add the electrons from the 'p' and 's' orbitals. So, 5 + 2 = 7, placing Bromine in the 7th 'A' group (since it's a 'p' block element).