Dalton stated that

all atoms of the same element are identical
atoms combine in one-to-one ratios to form compounds
all atoms are the same size
which one is it

What happens to isotopes that are unstable?

13. a covalent bond between two atoms is likely to be polar if: a. one of the atoms is much more electronegative than the other. b. the two atoms are equally electronegative. c. the two atoms are of the same element. d. the bond is part of a tetrahedrally shaped molecule. e. one atom is an anion.

Correct relationship between molecular formula and empirical formula