Which scientist proposed that electrons orbit the nucleus in fixed energy levels?

Who proposed the nuclear model of the atom based on the gold foil experiment?

What did John Dalton propose about atoms?

Which subatomic particle was discovered by J.J. Thomson?

What is the term for a positively charged ion?

What is the term for two or more different atomic nuclei with the same mass number but different atomic numbers?

What is the term for a negatively charged ion?

Which term describes elements with the same number of protons but different numbers of neutrons?

Which type of chemical formula shows the actual number of atoms of each element in a molecule?

What is the name of the smallest unit of a compound that retains its chemical properties?

What is a mole fraction?