Question

Of the elements calcium, Ca, beryllium, Be, barium, Ba, and strontium, Sr, arrange in order of decreasing atomic radii. Explain your answer using the terms electron and energy level.

Answer 1

Order these elements Ca, Be, Ba, and Sr:

If we take a look at the periodic table trends we will see that the atomic radii increases from left to right and from top to bottom.

So let's look for our elements:

Be: atomic number 4

Ba: atomic number 56

Ca: atomic number 20

Sr: atomic number 38

They are all Alkaline Earth Metals, they are in the same group.

So we said that the atomic radii increases from top to bottom. If we have to arrange them in order of decreasing atomic radii, we have to put first the largest one. The Barium is the one that is in a lower position, then Sr, then Ca and finally Be.

So the order of our problem is Ba, Sr, Ca and Be.

Which is the explanation?

As we move down in the periodic table the number of electrons increases. They all have 2 electrons in the outer shell. But let's look at the electronic configuration of two of them:

Ca:

Ba: