Write the symbol of the ion that has (a) 9 protons, 10 neutrons, and 10 electrons; (b) 12 protons, 12 neutrons, and 10 clectrons; (c) 52 protons, 76 neutrons, and 54 clectrons; (d) 37 protons, 49 neutrons, and 36 electrons.

The atomic number is a fundamental property of an element, defined as the number of protons found in the nucleus of an atom of that element. It not only identifies the element but also indicates its position in the periodic table. For instance, an atom with an atomic number of 9 always refers to fluorine (F), and this is consistent regardless of the number of neutrons or electrons.

It's important for students to recognize that the atomic number remains unchanged when an atom forms an ion, which is an atom or molecule with a net electric charge due to the loss or gain of one or more electrons. When writing the symbol of an ion, as we do in the exercise, we start by identifying the element using its atomic number, which leads us directly to the correct element symbol.

Ions are charged entities, and their net charge is a critical concept to grasp. The net charge is determined by the difference between the number of protons and electrons within an atom. When an atom loses electrons, it becomes a positively charged ion or cation; conversely, if it gains electrons, it becomes a negatively charged ion or anion.

For educational purposes, let's delve into an example: a sodium atom normally has 11 electrons, but when it loses one electron, it forms a sodium ion with a net charge of +1, represented as Na⁺. Furthermore, understanding the net charge is essential when it comes to predicting the chemical behavior of ions, especially their interactions and bonding with other ions or molecules.

Writing ion notation involves a combination of the element's symbol, derived from its atomic number, and its net charge. Getting this right is vital for accurately conveying the properties of the ion. The format is straightforward: place the element's symbol first followed by a superscript indicating the net charge.

The charge is written with a number, representing the magnitude of the charge, and a plus (+) or minus (-) sign, denoting whether it is a cation or anion. For example, Mg²⁺ is a magnesium ion with a +2 charge because it has lost two electrons. Students can practice this skill by writing out the symbols for various ions, ensuring they pay attention to the balance of protons and electrons to find the net charge.