Which of the following has larger size and why? 1) Be or Mg 2) Li or Na
You should use the periodic to see that Be and Mg are in the same family (they’re both alkaline earth metals, so will have the same number of valence electrons). However, since magnesium is one period lower than Beryllium, it will have an additional few energy shells, there for, magnesium is than beryllium.
The same reasoning can be used to show that sodium is larger than lithium.
Hopefully this helps!
Got a Periodic Table...?
Of course you do.... Atomic size decreases ACROSS a Period, a ROW of the Periodic Table, FROM LEFT to RIGHT as we face the Table; INCREASES down a Group, a column of the Table...
Does the diagram agree with what we have asserted? Incomplete electronic shells SHIELD the nuclear charge very ineffectively...once the shell is filled (at the right as we face the page) at the Noble Gases, shielding becomes fairly effective, and the next Period starts with a valence shell that is REMOVED from the nuclear core at a new and GREATER distance of separation.
And so for (i) third Period magnesium is CLEARLY LARGER than second Period beryllium. (ii) third Period sodium is CLEARLY LARGER than second Period lithium. Got it?