Select the correct answer from each drop-down menu. Much of the mass of an atom is concentrated in its nucleus. The nucleus contains (blank), and the outer part of the atom contains (blank)

The nucleus of an atom contains a positively charged particles called protons, and the outer part of the atom contains a negatively charge particles called the electrons.

There are many Theories and Models that led to the modern atomic model, that states such idea. The first atomic model about the composition of an atom is from John Joseph Thomson's Plum Pudding Model, that states that an atom contains a positively charged particles, and a negatively charged particles that was scattered about in an atom like raisins in a pudding. This was then followed by Ernest Rutherford's Nuclear Model where he concluded based on his observation from his Gold Foil Experiment. According to Ernest Rutherford's Nuclear Model, an atom is mostly an empty space, it has a dense positively center where he called as the nucleus, and there are negatively charged particles surrounding it.  For Niel Bohr's Atomic Model, he placed the electrons at a specific energy levels, that move around the nucleus, or the center of an atom, much like planets revolve around the sun. Lastly, there is also the Quantum Mechanics model, where it states that the location of an electron cannot be easily identified. The electron in the model was represented as a clouded region, and the higher the energy in that region, the more possible that there are many electron in there.

All these models have led to the formulation of the Modern Atomic Model, which states that an atom contains a positively charged nucleus, and a large negatively charged region in which there are enough electrons to make the atom neutral.