Question

Tell the number of protons, neutrons, and electrons in the following isotopes. (a) \({ }^{54} \mathrm{Fe}\) (b) \({ }^{23} \mathrm{Na}\) (c) bromine-79 \(\left({ }^{79} \mathrm{Br}\right)\) (d) phosphorus-31 \(\left({ }^{31} \mathrm{P}\right)\)

Short answer

(a) ({ }^{54} Fe) has 26 protons, 26 electrons, and 28 neutrons. (b) ({ }^{23} Na) has 11 protons, 11 electrons, and 12 neutrons. (c) ({ }^{79} Br) has 35 protons, 35 electrons, and 44 neutrons. (d) ({ }^{31} P) has 15 protons, 15 electrons, and 16 neutrons.

Step-by-step solution

- Identifying the Number of Protons

The number of protons in an element is equal to the atomic number of that element. For each isotope, this number is constant and specific to each element. It can be found on the periodic table.

- Determining the Number of Electrons

In a neutral atom, the number of electrons is equal to the number of protons. For isotopes, unless they are ions, the number of electrons will be the same as the number of protons.

- Calculating the Number of Neutrons

The number of neutrons can be found by subtracting the atomic number from the mass number (the superscript number in the isotope notation). The formula to calculate the number of neutrons is: Number of Neutrons = Mass Number - Atomic Number.

- Applying the Steps to (a) ({ }^{54} Fe)

Atomic number of iron (Fe) is 26. Therefore, Fe has 26 protons. Since it is neutral, it also has 26 electrons. The number of neutrons = 54 - 26 = 28.

- Applying the Steps to (b) ({ }^{23} Na)

Atomic number of sodium (Na) is 11. Therefore, Na has 11 protons and 11 electrons. The number of neutrons = 23 - 11 = 12.

- Applying the Steps to (c) bromine-79 ({ }^{79} Br)

Atomic number of bromine (Br) is 35. Therefore, Br has 35 protons and 35 electrons. The number of neutrons = 79 - 35 = 44.

- Applying the Steps to (d) phosphorus-31 ({ }^{31} P)

Atomic number of phosphorus (P) is 15. Therefore, P has 15 protons and 15 electrons. The number of neutrons = 31 - 15 = 16.

Key concepts

Understanding Atomic Number

The atomic number is a fundamental property of every element in the periodic table. It is denoted by the letter 'Z' and defines the unique identity of an element. The atomic number indicates the number of protons present in the nucleus of an atom, which also determines the element's placement in the periodic table.

For instance, hydrogen, with an atomic number of 1, has a single proton, making it the lightest and first element on the table. Conversely, carbon, with an atomic number of 6, has six protons. This concept is crucial when identifying an element, as no two elements share the same atomic number. Moreover, in a neutral atom, the number of protons is equal to the number of electrons, establishing the overall electric charge balance.

Neutrons in Isotopes

Isotopes are variants of a particular chemical element, which means they have the same atomic number but different mass numbers due to the variance in the number of neutrons. Neutrons, located in the atom's nucleus alongside protons, do not influence the atom's chemical properties but do affect its mass and stability.

To calculate the number of neutrons in an isotope, one simply uses the following formula:
Number of Neutrons = Mass Number - Atomic Number. For example, carbon-12 and carbon-14 are isotopes of carbon. They both have 6 protons since the atomic number of carbon is 6. However, carbon-12 has 6 neutrons (12 - 6 = 6) and carbon-14 has 8 neutrons (14 - 6 = 8). The difference in neutron number can lead to isotopes having different physical, and sometimes radioactive, properties.

Elements on the Periodic Table

The periodic table is a tabular arrangement of chemical elements, ordered by their atomic number, electron configuration, and recurring chemical properties. Elements are positioned in rows called periods and columns known as groups, with metals placed on the left and non-metals on the right.

Each element on the periodic table has a distinct atomic number, which increases from left to right and top to bottom. The table also provides information about the element's mass number, electron shells, as well as its chemical symbol. For example, iron (Fe) has an atomic number of 26, indicating it has 26 protons, and typically has a mass number of 56 under its most stable isotope (iron-56). Understanding how to read the periodic table is crucial, as it is not only a reference for the identification of elements but also a tool to understand the behavior and properties of each element.