Question

Draw a diagram of the arrangement of protons, neutrons, and electrons in an atom of each of the following isotopes: (a) \(^{31} \mathrm{P}\) (b) \(^{35} \mathrm{Cl}\) (c) \({ }^{40} \mathrm{Ar}\) (d) 131 I

Short answer

Isotopes (\(^{31} \mathrm{P}\), \(^{35} \mathrm{Cl}\), \(^{40} \mathrm{Ar}\), \(^{131} \mathrm{I}\)): 15p/16n, 17p/18n, 18p/22n, 53p/78n for protons/neutrons.

Step-by-step solution

Understanding Isotopes

An isotope is an atom of the same element with the same number of protons but different numbers of neutrons. Each isotope is represented with its mass number, symbolized as A, such as in \(^{31}\mathrm{P}\), where 31 is the mass number.

Finding Element Information

To draw a diagram of the isotopes, we first need the atomic number and average atomic mass for each element. These values can be found on the periodic table. The atomic number gives the number of protons and electrons in a neutral atom.

Identifying Protons, Neutrons, and Electrons for \(^{31}\mathrm{P}\)

\(\mathrm{Phosphorus (P)}\) has an atomic number of 15. This means it has 15 protons and 15 electrons. To find the number of neutrons in \(^{31} \mathrm{P}\), subtract the atomic number (15) from the mass number (31): \(31 - 15 = 16\) neutrons.

Drawing Diagram for \(^{31}\mathrm{P}\)

Draw the nucleus and represent it with 15 protons and 16 neutrons inside, typically protons with a '+' symbol and neutrons as plain circles. Surround the nucleus with 3 shells containing electrons: 2 in the first shell, 8 in the second, and 5 in the third.

Identifying Protons, Neutrons, and Electrons for \(^{35}\mathrm{Cl}\)

\(\mathrm{Chlorine (Cl)}\) has an atomic number of 17. It has 17 protons and 17 electrons. For the isotope \(^{35} \mathrm{Cl}\), calculate the neutrons as: \(35 - 17 = 18\) neutrons.

Drawing Diagram for \(^{35}\mathrm{Cl}\)

In the nucleus place the 17 protons and 18 neutrons. Draw electron shells around the nucleus: 2 electrons in the first, 8 in the second, and 7 in the third shell.

Identifying Protons, Neutrons, and Electrons for \(^{40}\mathrm{Ar}\)

\(\mathrm{Argon (Ar)}\) has an atomic number of 18, indicating 18 protons and 18 electrons. For \(^{40} \mathrm{Ar}\), find the number of neutrons: \(40 - 18 = 22\) neutrons.

Drawing Diagram for \(^{40}\mathrm{Ar}\)

Represent the nucleus with 18 protons and 22 neutrons. Draw electron shells holding 2 electrons in the first, 8 in the second, and 8 in the third shell, as argon is a noble gas with full outer shells.

Identifying Protons, Neutrons, and Electrons for \(^{131}\mathrm{I}\)

\(\mathrm{Iodine (I)}\) has an atomic number of 53. Assume it has 53 protons and 53 electrons. For \(^{131} \mathrm{I}\), the number of neutrons is calculated as: \(131 - 53 = 78\) neutrons.

Drawing Diagram for \(^{131}\mathrm{I}\)

In the nucleus, place 53 protons and 78 neutrons. Draw electron shells with 2 in the first shell, 8 in the second, 18 in the third, 18 in the fourth, and 7 electrons in the fifth to complete the diagram.

Key concepts

Isotopes

Isotopes play a fascinating role in the atomic structure as they are variations of the same element. They have the same number of protons but differ in the number of neutrons. The concept of isotopes allows scientists to understand why elements can exist in different forms. For example, while both

• Protons determine the identity of an element, making isotopes of the same element chemically identical.
• Neutrons vary between isotopes, causing different mass numbers.

These isotopic differences are crucial in fields like medicine and archaeology for dating materials and diagnostics.

Protons

Protons lie at the heart of atomic structure, residing in an atom's nucleus. Each element on the periodic table is defined by its number of protons. This constant number is known as the atomic number. For example,

• Phosphorus (P) has 15 protons.
• Chlorine (Cl) has 17 protons.
• Argon (Ar) has 18 protons.
• Iodine (I) has 53 protons.

Protons have a positive charge, balancing the negative charges of electrons to ensure the atom's overall neutrality when the atom is in its ground state.

Neutrons

Neutrons are the uncharged particles found in an atom's nucleus. They play an essential role in stabilizing the nucleus. Without neutrons, the repulsive forces of positively charged protons would make many nuclei unstable. The number of neutrons determines the isotope of an element. For instance:

• Phosphorus (P) with its 16 neutrons makes it the isotope ^{31}P.
• Chlorine (Cl) has 18 neutrons in ^{35}Cl.
• Argon (Ar) features 22 neutrons in ^{40}Ar.
• Iodine (I) includes 78 neutrons in ^{131}I.

Overall, neutrons are pivotal in defining the mass and various isotopes of an element.

Electrons

Electrons are fundamental particles that occupy the space around an atom's nucleus. They are negatively charged and much lighter than protons and neutrons. Electrons inhabit energy levels or shells. Their arrangement defines the atom's chemical properties. In neutral atoms, the number of electrons equals the number of protons:

• In the case of phosphorus, the electrons are arranged in three shells: 2, 8, and 5.
• Chlorine's electrons fill shells as: 2, 8, and 7.
• Argon's stable shell configuration is: 2, 8, 8.
• Iodine distributes electrons through five shells: 2, 8, 18, 18, and 7.

Electrons determine how an atom interacts with others, making them essential for forming chemical bonds and reactions.