Problem 27 - Chemistry: The Central Science in SI Units, Global Edition

Question

How many protons, neutrons, and electrons are in the following atoms? (a) \({ }^{84} \mathrm{Kr}\), (b) \({ }^{200} \mathrm{Hg}\), (c) \(^{59} \mathrm{Co}\), (d) \({ }^{55} \mathrm{Mn}\), (e) \(^{239} \mathrm{U},(\mathbf{f})^{181} \mathrm{Ta}\).

Step-by-Step Solution

Answer

The number of protons (Z), neutrons (N), and electrons (E) for each atom are: (a) Krypton (Kr): Z=36, N=48, E=36 (b) Mercury (Hg): Z=80, N=120, E=80 (c) Cobalt (Co): Z=27, N=32, E=27 (d) Manganese (Mn): Z=25, N=30, E=25 (e) Uranium (U): Z=92, N=147, E=92 (f) Tantalum (Ta): Z=73, N=108, E=73

Step 1: To find the atomic number (Z), refer to the periodic table for each element symbol. The atomic number represents the number of protons in each atom. #Step 2: Calculate the number of neutrons#

Use the given mass number (A) and the atomic number (Z) determined in step 1 to calculate the number of neutrons (N) in each atom. The formula to calculate the number of neutrons is: \(N = A - Z\). #Step 3: Determine the number of electrons#

Step 2: In a neutral atom, the number of electrons is equal to the number of protons (Z). Now, let's apply these steps to each of the given atoms: (a) \({}^{84} \mathrm{Kr}\) #Step 1: Identify the atomic number (Z) for Kr#

The atomic number (Z) of Krypton (Kr) is 36. #Step 2: Calculate the number of neutrons for Kr#

Step 3: Using the mass number (A) 84 and the atomic number (Z) 36, find the number of neutrons: \(N = A - Z = 84 - 36 = 48\) neutrons. #Step 3: Determine the number of electrons for Kr#

There are 36 electrons in a neutral Krypton atom (same as the atomic number). (b) \({}^{200} \mathrm{Hg}\), (c) \(^{59} \mathrm{Co}\), (d) \({}^{55} \mathrm{Mn}\), (e) \(^{239} \mathrm{U},(\mathbf{f})^{181} \mathrm{Ta}\) Following the same steps for the remaining atoms: (b) Mercury (Hg): Z=80, N=120, E=80 (c) Cobalt (Co): Z=27, N=32, E=27 (d) Manganese (Mn): Z=25, N=30, E=25 (e) Uranium (U): Z=92, N=147, E=92 (f) Tantalum (Ta): Z=73, N=108, E=73 So, the number of protons (Z), neutrons (N), and electrons (E) in each atom are: (a) Krypton (Kr): Z=36, N=48, E=36 (b) Mercury (Hg): Z=80, N=120, E=80 (c) Cobalt (Co): Z=27, N=32, E=27 (d) Manganese (Mn): Z=25, N=30, E=25 (e) Uranium (U): Z=92, N=147, E=92 (f) Tantalum (Ta): Z=73, N=108, E=73

Key Concepts

protons

Protons are fundamental building blocks found in the core of an atom, known as the nucleus. They carry a positive electrical charge. The number of protons in an atom determines its identity and place in the periodic table, referred to as the atomic number (Z).
This number is crucial as it defines the element we are dealing with. For instance,

• Krypton (Kr) has 36 protons
• Mercury (Hg) has 80 protons
• Cobalt (Co) has 27 protons
• Manganese (Mn) has 25 protons
• Uranium (U) has 92 protons
• Tantalum (Ta) has 73 protons

These protons reside in the nucleus and contribute significantly to the mass of the atom. The presence of a unique number of protons means each element has distinct properties, distinguishing it from others. Moreover, protons are stable particles, making the atomic number a consistent identifier for elements.

neutrons

Neutrons are another type of subatomic particle that, alongside protons, make up the nucleus. Unlike protons, neutrons carry no charge, which is why they are referred to as neutral particles.
The number of neutrons in an atom can vary even within atoms of the same element, leading to different isotopes. The presence of neutrons adds mass to the atom but does not affect the chemical properties. To find the number of neutrons (N), subtract the atomic number (Z) from the mass number (A):

• Krypton (Kr) has 48 neutrons, calculated as 84 - 36
• Mercury (Hg) has 120 neutrons, 200 - 80
• Cobalt (Co) has 32 neutrons, 59 - 27
• Manganese (Mn) has 30 neutrons, 55 - 25
• Uranium (U) has 147 neutrons, 239 - 92
• Tantalum (Ta) has 108 neutrons, 181 - 73

By understanding neutron count, we can grasp the concept of isotopes, which are atoms with the same number of protons but different numbers of neutrons.

electrons

Electrons are the negatively charged subatomic particles orbiting the nucleus. Their arrangement in an atom determines the atom's chemical behavior and conductivity. In a neutral atom, the number of electrons equals the number of protons to balance the charges. This balance makes the atom electrically neutral. For the atoms we considered:

• Krypton (Kr) has 36 electrons
• Mercury (Hg) has 80 electrons
• Cobalt (Co) has 27 electrons
• Manganese (Mn) has 25 electrons
• Uranium (U) has 92 electrons
• Tantalum (Ta) has 73 electrons

The electrons arrange in shells or energy levels around the nucleus. Chemical reactions mostly involve electrons from the outermost shells participating. Understanding electron distribution is critical in explaining chemical bonding and reactions, as they often share, lose, or gain electrons during reactions.