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But teacher, we don't know what is atom radius yet.
Today we are going to talk about atom radius and atomic size.
Atom radius is one half of the distance between the nuclei of two atoms of the same element when they join together.
Oh, so atom size is decided by the atom radius?
Partly yes. And if we look at the periodic table, we can find out a pattern of the atom size.
By looking at the periodic table?!
Yes, and this called the periodic trend. By studying the periodic trend, we can easily find out the atom size is getting bigger or smaller.
So look at the board. The periodic trend for the stom size is that in a period,the size of atom decreases; in a group, the size of atom increases.
And i am going to explain the reason for you now.
In a period, the number of protons andelectrons is increasing, and the number of shells stays the same
Once the nuclei has more protons, it means that the nuclei has more force to pull the electrons closer,therefore the size of atom decreases.
In a group, the number of protons and electrons is increasing while the number of shells is also increasing.
Okay, got it!
The nuclei does not have much force to pull the electrons of the outest shell closer, therefore the size of atom increases.
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