How were atomic models developed when no one has seen an atom?

Experiments

Explanation:

Models of the atom are developed by experiments in which evidences that support various models are obtained via ingenious means. For instance, in Rutherford's experiments, he made use of a thin gold foil. The foil contains gold atoms though they cannot be seen with naked eyes. The inferences deduced from the experiments can be generalized to all atoms since atoms of all elements posses essentially the same structure even though the energy levels are different for each atom.

the number of valence electrons for each molecule or ion is shown beneath the structure. remember hydrogen will not have more than two electrons. this hydrogen is part of a covalent bond (sharing two electrons). a double bond here would cause hydrogen to share four electrons with phosphorus.

a. energy is absorbed in the reaction.

if in a given reaction the energy of products is greater than the energy of reactants it means that reaction is endothermic and during the reaction, the energy is absorbed by reactants. in an endothermic reaction, the products have more stored chemical energy than the reactants. and in this reaction the reactants are more stable than products before the compounds with less energy are always more stable.