How many electrons are present in an atom of mercury whose atomic number is 80 and whose mass number is 201?

Understanding the concept of electrons in an atom is fundamental to grasping atomic structure. Electrons are subatomic particles with a negative charge, and they occupy the space around the nucleus of an atom. The number of electrons an atom has directly influences its chemical properties and behavior.

In the case of mercury, or any other element, the atomic number tells us exactly how many protons are in the nucleus of the atom. Since atoms are electrically neutral in their stable state, this same number also reveals how many electrons are present in a neutral atom. Therefore, with mercury having an atomic number of 80, it possesses 80 electrons swirling in its electron cloud. The electron configuration of these electrons determines how mercury interacts chemically with other elements.

The mass number of an atom is equal to the total number of protons and neutrons in its nucleus. Unlike the atomic number, which is always a whole number unique to each element, the mass number can vary because atoms of the same element can have different numbers of neutrons. These different versions are known as isotopes.

For the mercury atom in our example, the mass number is 201. Since we know the atomic number (which equals the number of protons) is 80, we can deduce the number of neutrons by subtracting the atomic number from the mass number: \( 201 - 80 = 121 \) neutrons. This information is crucial for understanding the isotopic composition and atomic weight of elements, which can affect their stability and physical properties.

A neutral atom is one in which the number of protons in the nucleus is exactly balanced by the number of electrons surrounding it. This balance ensures that the positive and negative charges cancel each other out, leading to no overall electrical charge.

In every atom, protons carry a positive charge and electrons carry a negative charge. If an atom has an equal number of protons and electrons, the charges balance and the atom is neutral. For mercury with an atomic number of 80, we recognize that it has 80 protons. In order to maintain neutrality, it must also contain 80 electrons because each proton's positive charge is balanced by an electron's negative charge. A neutral atom is the most stable state, and in chemical reactions, atoms tend to gain or lose electrons to return to or maintain this state.