Write the symbol of the ion that has (a) 11 protons, 13 neutrons, and 10 electrons; (b) 13 protons, 14 neutrons, and 10 electrons; (c) 34 protons, 45 neutrons, and 36 electrons; (d) 24 protons, 28 neutrons, and 22 electrons.

The atomic number of an element is a fundamental characteristic that defines its identity. It is represented by the letter Z and indicates the number of protons present in the nucleus of an atom. Since atoms are electrically neutral, the atomic number also tells us the number of electrons in an uncharged atom.
For example, in the exercise given, sodium (Na) has an atomic number of 11, which means it has 11 protons. Any atom that does not have exactly 11 protons would not be sodium. It's this precise count of protons that determines the atomic number and consequently, the element to which an atom belongs. The atomic number is also directly linked to the element's position on the periodic table, where elements are arranged in ascending order of their atomic numbers.
Understanding the atomic number is crucial for many chemical concepts, including the formation of ions, as demonstrated in the exercise. This understanding allows us to predict how many electrons an ion must lose or gain to achieve a stable electron configuration, leading to the concept of ionic charge.

In an atom, protons and electrons are subatomic particles with opposite electrical charges. Protons possess a positive charge, while electrons carry a negative charge. In a neutral atom, the number of protons equals the number of electrons, thus canceling out their charges and resulting in a net charge of zero.
When an atom gains or loses electrons, it becomes an ion. The number of protons remains unchanged. For example, when the sodium atom from the exercise loses one electron, it has one more proton than electrons, giving it a positive charge. Conversely, when an atom gains electrons, it will have fewer protons than electrons, and thus, it will have a negative charge.

Importance of Proton-Electron Balance

The balance between protons and electrons determines the electrical neutrality of an atom. If this balance is disturbed, the atom becomes positively or negatively charged, transforming into a cation or an anion, respectively.

The ionic charge of an ion reflects the difference in the total number of protons and electrons. An ion with more protons than electrons has a positive charge (cation), and one with more electrons than protons has a negative charge (anion).
In the given exercise, we see that the sodium ion, which has one fewer electron than protons, is denoted as Na+, signifying a charge of +1. Aluminium, with 13 protons and 10 electrons, has a +3 charge, represented as Al³⁺. These positive charges indicate that electrons have been lost. Conversely, selenium, with 34 protons and 36 electrons, has a -2 charge, represented as Se^2-, because it has gained electrons.

Determining Ionic Charge

To find an ion's charge, simply calculate the difference between the number of protons and electrons. This charge is significant because it determines the ion's ability to interact with other ions or molecules, which is the basis of many chemical reactions and the formation of compounds.