Why is it useful for scientist to develop models for the structure of atoms

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Atomic models are important because, they help us visualize the interior of atoms and molecules, and thereby predicting properties of matter.

Explanation:

indium, and thallium have three electrons i think

periodic trends is an atom that gets larger as the number of electronic shells increase, the radius of atoms increases as you go down a certain group in the periodic table of elements. in general, the size of an atom will decrease as you move from left to right of a certain period.