All elements have same number of valence electrons and similar properties

Groups

Explanation:

Groups(row going up and down) All have the same amount of valence electrons) Ex: First group the alkali metals all have 1 valence electron and are all very highly reactive.

The only ones that this rule does not work for is the smaller column in the middle called transitional metals and the amount of valence electron that each one has differs

the atomic mass is the bottom number on the element.

-steel jelly

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.