Question

What is the correct symbol for the species that contains 18 neutrons, 17 protons, and 16 electrons?

Short answer

The correct symbol for the species that contains 18 neutrons, 17 protons, and 16 electrons is \(^{35}Cl^{+}\).

Step-by-step solution

Determine the Element

The atomic number of an atom is equal to the number of protons. Here the number of protons is 17, which means the atom belongs to the element Chlorine(Cl) because Chlorine has an atomic number of 17.

Calculate the Mass Number

The mass number of an atom is found by adding the number of protons and neutrons together. Here, protons are 17 and neutrons are 18. Therefore, the mass number would be \(17 + 18 = 35\).

Identify the Charge

The charge of the ion is determined by the difference between the number of protons and electrons. If there are more protons than electrons, the ion has a positive charge. If there are more electrons than protons, it has negative charge. Here, protons are 17 and electrons are 16, so it has a charge of \(+1\). The difference is \(17 - 16 = +1\).

Key concepts

Atomic Number

The atomic number is a fundamental characteristic of an element, representing the number of protons in the nucleus of an atom. It's like the element's unique fingerprint. In the periodic table, elements are arranged by increasing atomic number, thus affecting their chemical behavior and properties.
For example, in our original exercise, knowing that the atomic number is 17 immediately identifies the element as Chlorine (Cl), because Chlorine has 17 protons in its nucleus.
This is crucial since the atomic number defines the identity of the element. So whether the atom is electrically neutral, a positive ion, or a negative ion, the atomic number remains unchanged, consistently identifying it as the same element.

Mass Number

The mass number of an atom provides the total count of protons and neutrons within its nucleus. These subatomic particles account for nearly all the mass of the atom, unlike electrons, which have negligible mass.
You calculate the mass number by simply adding the number of protons and neutrons. In the exercise, Chlorine has 17 protons and 18 neutrons, leading to a mass number of 35 ( 17 + 18 = 35 ).
It's important to distinguish that the mass number is different from the atomic mass found on the periodic table, as the latter considers isotopes. The mass number is always a whole number and is specific to an isotope of an element, providing insight into the isotope's composition.

Ion Charge

Ion charge relates to the difference between the number of protons and electrons in an atom. Atoms generally start electrically neutral, meaning they have equal numbers of protons and electrons. However, when there is an imbalance, ions form.
An ion that has more protons than electrons will have a positive charge, known as a cation. Conversely, an ion with more electrons than protons is negatively charged and referred to as an anion. In the case of our initial problem, there are 17 protons and 16 electrons, resulting in a positive charge of +1. This is because there is one more proton than there are electrons, giving the ion a positive charge overall (17 protons - 16 electrons = +1).
Understanding ion charge is crucial for predicting the chemical behavior of elements, especially in reactions and bonding, as ions seek to achieve a stable electronic configuration.