Question

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

Explanation:

John Dalton's atomic theory proposed that atoms are the smallest units of matter and that atoms of different elements can combine with each other in simple whole - number ratios to form compounds. His model did not suggest atoms were made of smaller particles (discovered later), nor did it describe a massive positive center (Rutherford's discovery). He considered atoms as round, solid masses, but the key new characteristic was that atoms could combine with other kinds of atoms.

Answer:

An atom can join with other kinds of atoms.