What new characteristic did john dalton add to the model of the atom? (a) an atom is a round, solid mass.(b) an atom has a massive, positive center. (c)an atom is made up of smaller particles.(d) an atom can join with other kinds of atoms.

The right answer is D.

John Dalton is a British chemist and physicist who developed the atomic theory on which modern physical science was based.

The atom is, for chemists, the fundamental constituent of matter. The term comes from elsewhere a Greek word that means "indivisible", although it is known for a long time that this element is not.

The atom may be associated with other atoms, similar or different, to form a molecule (two oxygen atoms to form O2, or two hydrogen atoms with an oxygen atom to form H2O)

Basically he explained the principle of what is a molecule. He was wrong thinking that atoms are indivisible particles.

explanation:

metals have excess of electrons whereas non-metals have deficiency of electrons. thus, in order to gain stability metals easily donate their electrons to the non-metals.

for example, electronic configuration of sodium is and electronic configuration of phosphorous is .

when a phosphorous atom and sodium atom combine together then sodium will donate is extra one electron to the phosphorous atom. as a result there will be formation of ionic bond between sodium and phosphorous.

the reaction will be as follows.

there, are three sodium sodium atoms and each of them will donate its one extra electron to phosphorous atom. thus, the sub-shell of phosphorous gets completely filled.  

thus, we can conclude that electrons are transferred from atoms of sodium to atoms of phosphorous. this transfer makes the sodium atoms donate one electron and the phosphorous atoms to gain one electron. as a result, the sodium and phosphorus atoms strongly attract each other.

the answer is b & c i believe : )