Atomic Size
With the above image, courtesy of Webelements, it is rather easy to tell the general trend of atomic size as we move through the periodic table.
Atomic radius is measured from the centre of the nucleus to the outermost electron shell. The general trend of atomic radius is that it increases as you move down a group, and decreases as you move to the right across a period.
Atomic radius can be linked to core charge. CORE CHARGE = PROTONS - NON-VALENCE ELECTRONS. The core charge is simply an expression of the attractive force that the centre of the nucleus gives off to the valence electrons. As this number gets higher, the valence electrons are pulled closer to the nucleus, therefore decreasing the atomic size of the atom. This equation fits perfectly with the above diagram and explains why the atoms get smaller as they travel across the period. However as we go down the group the situation of the equation is reversed and so our atoms become larger as their core charge gets smaller.
On the bottom of the table we see a slight bump in the trend. Two elements decrease and then increase again, seemingly throwing the trend off. This is an example of how these elements behave differently, and a reminder that trends do not necessarily apply to every instance.
Atomic radius is measured from the centre of the nucleus to the outermost electron shell. The general trend of atomic radius is that it increases as you move down a group, and decreases as you move to the right across a period.
Atomic radius can be linked to core charge. CORE CHARGE = PROTONS - NON-VALENCE ELECTRONS. The core charge is simply an expression of the attractive force that the centre of the nucleus gives off to the valence electrons. As this number gets higher, the valence electrons are pulled closer to the nucleus, therefore decreasing the atomic size of the atom. This equation fits perfectly with the above diagram and explains why the atoms get smaller as they travel across the period. However as we go down the group the situation of the equation is reversed and so our atoms become larger as their core charge gets smaller.
On the bottom of the table we see a slight bump in the trend. Two elements decrease and then increase again, seemingly throwing the trend off. This is an example of how these elements behave differently, and a reminder that trends do not necessarily apply to every instance.