Atomic Structure Quiz

The electron-cloud model (also known as the quantum mechanical model) is the modern model of the atom used today. It describes the regions around the nucleus where electrons are most likely to be found, rather than fixed orbits like the Bohr model.

Niels Bohr proposed that electrons travel around the nucleus in circular orbits at specific, quantized energy levels. This was a major advancement from previous models, though it was later refined into the electron-cloud model.

Electrons have an extremely small mass of about 1/1836 amu, which is negligible compared to the mass of protons and neutrons (about 1 amu each). Therefore, electrons contribute almost nothing to the overall mass of an atom.

Because the vast majority of alpha particles passed straight through the gold foil without deflection, Rutherford concluded that the atom consists mostly of empty space, with a tiny, dense, positively charged nucleus at its center.

This statement is false because modern atomic theory uses the electron-cloud model, where electrons exist in mathematical probability regions (orbitals) rather than fixed, planetary orbits.

Atoms are electrically neutral because they contain an equal number of positively charged protons and negatively charged electrons. These opposite charges are equal in magnitude and cancel each other out.

Ernest Rutherford discovered the atomic nucleus in 1911 through his famous gold foil experiment, which demonstrated that atoms have a dense, positively charged core.

Dalton's postulate that atoms are indivisible had to be revised after the discovery of subatomic particles (electrons, protons, and neutrons), which showed that atoms are indeed divisible into smaller components.

The ancient Greek philosopher Democritus proposed the existence of ultimate, indivisible particles of matter, which he called 'atomos' (meaning uncuttable or indivisible).