Indicate the number of protons, neutrons, and electrons in each of the following species: $$ { }_{7}^{15} \mathrm{~N},{ }_{16}^{33} \mathrm{~S},{ }_{29}^{63} \mathrm{Cu},{ }_{38}^{84} \mathrm{Sr},{ }_{56}^{130} \mathrm{Ba},{ }_{74}^{186} \mathrm{~W},{ }_{80}^{202} \mathrm{Hg} $$

Understanding atomic notation is key for anyone diving into the world of chemistry. Atomic notation is a concise way to communicate the fundamental properties of an atom. This standard representation includes two essential numbers: the atomic number (Z) and the mass number (A).

In atomic notation, the atomic number is written as a subscript to the left of the chemical symbol, while the mass number is written as a superscript. For instance, the atomic notation for carbon could look like \( { }_{6}^{12} \mathrm{C} \), where 6 is the atomic number, and 12 is the mass number. The atomic number tells us the number of protons, which defines the type of element, while the mass number is the sum of both protons and neutrons in the nucleus.

• Atomic Number (Z): Indicates the number of protons and uniquely identifies the chemical element.
• Mass Number (A): The total number of protons and neutrons in the atom's nucleus.

The chemical symbol itself represents the element, such as 'C' for carbon, 'N' for nitrogen, and so forth.

The number of protons in an atom is a fundamental characteristic that defines the atom's identity as an element. Protons are positively charged particles located within the nucleus of an atom. Each element on the periodic table has a unique number of protons, known as the atomic number (Z). It's this count that dictates where the element stands in the periodic table and its chemical properties.

When observing the atomic notation (e.g., \( { }_{7}^{15} \mathrm{N} \) for nitrogen), the subscript number represents the atomic number which directly gives us the count of protons. Therefore, a nitrogen atom has 7 protons. The number of protons within an atom remains unchanged; even when an atom gains or loses electrons and becomes an ion, the proton count - and thus the atomic number - stays constant.

Neutrons are the other type of particle found in the nucleus of an atom along with protons. Unlike protons, neutrons carry no electric charge. The number of neutrons is not directly indicated in the atomic notation, but it can be calculated by subtracting the atomic number (Z) from the mass number (A).

To illustrate, let's use the nitrogen isotope \( { }_{7}^{15} \mathrm{N} \): this notation reveals that its atomic number (Z), and consequently its number of protons, is 7, while its mass number (A) is 15. To find the number of neutrons, subtract the atomic number from the mass number: \(15 - 7 = 8\) neutrons. The number of neutrons is crucial because it can vary even within atoms of the same element, resulting in different isotopes. These isotopes have different physical properties due to variations in neutron count.

Electrons are negatively charged particles that orbit the nucleus of an atom at various energy levels. The number of electrons in a neutral atom is equal to the number of protons. This balance maintains the atom's overall electrical neutrality.

For example, a neutral nitrogen atom (\( { }_{7}^{15} \mathrm{N} \) as given in the exercise) has 7 protons and, therefore, must also have 7 electrons. However, atoms can lose or gain electrons through chemical reactions, forming ions that carry a positive or negative charge. In such cases, the atomic notation might be amended with a charge notation, such as \( { }_{7}^{15} \mathrm{N}^{3+} \) indicating a loss of 3 electrons or \( { }_{7}^{15} \mathrm{N}^{3-} \) indicating a gain of 3 electrons. It's essential for students to remember that while the number of protons and neutrons can inform us about the atomic mass and isotopes, the number of electrons dictates an atom's reactivity and the types of chemical bonds it can form.