Mendeleev · science lesson
Isoelectronic series
Isoelectronic species have the same number of electrons but different proton counts.
Start with the idea
Isoelectronic species have the same number of electrons but different proton counts.
A concrete example
O²⁻, F⁻, Ne, Na⁺ and Mg²⁺ each have ten electrons; increasing nuclear charge changes their size.
Mendeleev
Mendeleev’s tip
Do not start with a formula. Identify what changes, what stays constant and which quantity you are trying to explain or calculate.
Go one step deeper
For O²⁻, F⁻, Ne, Na⁺ and Mg²⁺, electron count stays at 10 while proton count rises from 8 to 12.
Common trap
A trend or model is not an exceptionless law. Always check the quantity’s definition and the conditions being compared.
Check your understanding
Can you explain the phenomenon in your own words before looking at an equation?