Question

Indicate the number of protons, neutrons, and electrons in each of the following species: \({ }^{15} \mathrm{~N},{ }_{16}^{33} \mathrm{~S},{ }_{29}^{63} \mathrm{Cu},{ }_{38}^{84} \mathrm{Sr}\). \({ }_{56} \mathrm{Ba},{ }_{74}^{136} \mathrm{~W},{ }^{202} \mathrm{Hg}\).

Short answer

For each species, protons, neutrons, and electrons are: - \( ^{15}\mathrm{N} \): 7p, 8n, 7e - \( _{16}^{33}\mathrm{S} \): 16p, 17n, 16e - \( _{29}^{63}\mathrm{Cu} \): 29p, 34n, 29e - \( _{38}^{84}\mathrm{Sr} \): 38p, 46n, 38e - \( _{56}\mathrm{Ba} \): 56p, 81n, 56e - \( _{74}^{136}\mathrm{W} \): 74p, 62n, 74e - \( ^{202}\mathrm{Hg} \): 80p, 122n, 80e.

Step-by-step solution

Understanding the Notation

Chemical species are written in the form \( _{Z}^{A}\text{Element} \), where \( A \) is the mass number and \( Z \) is the atomic number. \( A \) represents the sum of protons and neutrons, while \( Z \) indicates the number of protons.

Counting Protons

The number of protons in each species corresponds directly to \( Z \), the atomic number, on the lower left segment. Here are the species and their proton numbers:- \( ^{15}\mathrm{N} \) has 7 protons (Nitrogen's atomic number)- \( _{16}^{33}\mathrm{S} \) has 16 protons- \( _{29}^{63}\mathrm{Cu} \) has 29 protons- \( _{38}^{84}\mathrm{Sr} \) has 38 protons- \( _{56}\mathrm{Ba} \) has 56 protons- \( _{74}^{136}\mathrm{W} \) has 74 protons- \( ^{202}\mathrm{Hg} \) has 80 protons (Mercury's atomic number)

Counting Neutrons

Neutrons can be calculated by subtracting the atomic number from the mass number, \( N = A - Z \). Perform these calculations:- \( ^{15}\mathrm{N} \): \( 15 - 7 = 8 \) neutrons- \( _{16}^{33}\mathrm{S} \): \( 33 - 16 = 17 \) neutrons- \( _{29}^{63}\mathrm{Cu} \): \( 63 - 29 = 34 \) neutrons- \( _{38}^{84}\mathrm{Sr} \): \( 84 - 38 = 46 \) neutrons- \( _{56}\mathrm{Ba} \): \( 137 - 56 = 81 \) neutrons- \( _{74}^{136}\mathrm{W} \): \( 136 - 74 = 62 \) neutrons- \( ^{202}\mathrm{Hg} \): \( 202 - 80 = 122 \) neutrons

Counting Electrons

For neutral atoms, the number of electrons is equal to the number of protons. Thus:- \( ^{15}\mathrm{N} \) has 7 electrons- \( _{16}^{33}\mathrm{S} \) has 16 electrons- \( _{29}^{63}\mathrm{Cu} \) has 29 electrons- \( _{38}^{84}\mathrm{Sr} \) has 38 electrons- \( _{56}\mathrm{Ba} \) has 56 electrons- \( _{74}^{136}\mathrm{W} \) has 74 electrons- \( ^{202}\mathrm{Hg} \) has 80 electrons

Key concepts

Protons

Protons are subatomic particles found in the nucleus of an atom. They have a positive electric charge and are denoted by the symbol \( p^+ \). A crucial aspect of protons is that they define the identity of an element. For example, an element like oxygen has 8 protons, no matter what isotope or ion it's in.
The number of protons in an atom is known as the atomic number, represented by \( Z \). This number is unique for each element, and you can find it in the periodic table.

• For neutral atoms, protons equal electrons, keeping the atom electrically balanced.
• In ions, the number of protons remains the same, while electrons change, leading to a charge.

Protons, being positively charged, play a significant role in keeping electrons bound to the nucleus via electromagnetic forces. This balances the opposite charges across the atomic structure.

Neutrons

Neutrons are neutrally charged particles located in an atom's nucleus alongside protons. They do not carry any charge and are symbolized as \( n^0 \). The presence of neutrons is pivotal in stabilizing the nucleus. This is because they help offset the repulsive forces between positively charged protons.
Neutrons come into play particularly in isotopes. Isotopes of an element have the same number of protons but differ in their number of neutrons. This variation affects the atomic mass but not the chemical behavior of the element. Neutrons are calculated by the formula:
\[ N = A - Z \]
where \( N \) is the number of neutrons, \( A \) is the mass number (protons + neutrons), and \( Z \) is the atomic number.

• The stability of an atom is often determined by the ratio of protons to neutrons.
• Radioactive isotopes result when the nucleus has an excess or shortage of neutrons.

Electrons

Electrons are tiny, negatively charged particles orbiting the nucleus of an atom. They are represented by the symbol \( e^- \). Electrons are a fundamental part of chemistry because they participate in forming chemical bonds and reactions.
Electrons orbit around the nucleus in regions called electron shells. The distribution and arrangement of electrons in these shells determine the atom's chemical properties and how it interacts with other atoms. Importantly, for a neutral atom, the electron count equals the number of protons:

• Electrons reside in energy levels or shells around the nucleus.
• The number of electrons in the outer shell determines an atom's reactivity.
• Ions form when electrons are gained or lost, altering the charge.

In chemical reactions, it's the electrons that are often transferred or shared between atoms, forming the basis for all chemical bonding.