Problem 23 - Chemistry: The Central Science

Question

How many protons, neutrons, and electrons are in the following atoms: (a) \({ }^{40} \mathrm{Ar}\), (b) \({ }^{65} \mathrm{Zn}\), (c) \({ }^{70} \mathrm{Ga}\), (d) \({ }^{80} \mathrm{Br}\), (e) \(^{184} \mathrm{~W}\), (f) \({ }^{243} \mathrm{Am}\) ?

Step-by-Step Solution

Answer

(a) \(^{40}\mathrm{Ar}\): 18 protons, 22 neutrons, 18 electrons; (b) \(^{65}\mathrm{Zn}\): 30 protons, 35 neutrons, 30 electrons; (c) \(^{70}\mathrm{Ga}\): 31 protons, 39 neutrons, 31 electrons; (d) \(^{80}\mathrm{Br}\): 35 protons, 45 neutrons, 35 electrons; (e) \(^{184}\mathrm{W}\): 74 protons, 110 neutrons, 74 electrons; (f) \(^{243}\mathrm{Am}\): 95 protons, 148 neutrons, 95 electrons.

Step 1: Periodic Table Lookup

(a) Argon (Ar) has atomic number Z = 18. (b) Zinc (Zn) has atomic number Z = 30. (c) Gallium (Ga) has atomic number Z = 31. (d) Bromine (Br) has atomic number Z = 35. (e) Tungsten (W) has atomic number Z = 74. (f) Americium (Am) has atomic number Z = 95. **Step 2: Determine the number of neutrons**

Step 2: Region for neutrons

Using the mass number (A) and atomic number (Z), we can find the number of neutrons (N) using the formula: N = A - Z (a) For \(^{40}\mathrm{Ar}\): N = 40 - 18 = 22 neutrons (b) For \(^{65}\mathrm{Zn}\): N = 65 - 30 = 35 neutrons (c) For \(^{70}\mathrm{Ga}\): N = 70 - 31 = 39 neutrons (d) For \(^{80}\mathrm{Br}\): N = 80 - 35 = 45 neutrons (e) For \(^{184}\mathrm{W}\): N = 184 - 74 = 110 neutrons (f) For \(^{243}\mathrm{Am}\): N = 243 - 95 = 148 neutrons **Step 3: Determine the number of electrons**

Step 3: Region for electrons

For neutral atoms, the number of electrons is equal to the number of protons (Z): (a) \(^{40}\mathrm{Ar}\): 18 electrons (same as the atomic number) (b) \(^{65}\mathrm{Zn}\): 30 electrons (same as the atomic number) (c) \(^{70}\mathrm{Ga}\): 31 electrons (same as the atomic number) (d) \(^{80}\mathrm{Br}\): 35 electrons (same as the atomic number) (e) \(^{184}\mathrm{W}\): 74 electrons (same as the atomic number) (f) \(^{243}\mathrm{Am}\): 95 electrons (same as the atomic number)

Key Concepts

Protons

Protons are positively charged particles found in the nucleus of an atom. Every element has a unique number of protons, known as its atomic number (Z), which determines its identity and place on the periodic table. The atomic number is crucial because it tells us how many protons are in an atom of a particular element. When you look at the periodic table, the atomic number of an element is usually found above the element's symbol.

For example, Argon (Ar) has an atomic number of 18, which means it has 18 protons. Similarly, Zinc (Zn) has an atomic number of 30, indicating 30 protons, and so on for other elements.

Understanding protons helps us identify elements and predict their chemical behavior. Since protons carry a positive charge, they contribute to the overall charge of the nucleus, balancing with electrons, which are negatively charged.

Neutrons

Neutrons are neutral particles, meaning they carry no charge and are also found in the nucleus alongside protons. They play a vital role in the stability of an atom. Without neutrons, the positively charged protons in the nucleus would repel each other, causing the nucleus to fall apart.

The number of neutrons in an atom can be determined using the formula: \[ N = A - Z \]where \( N \) is the number of neutrons, \( A \) is the mass number (total number of protons and neutrons), and \( Z \) is the atomic number (the number of protons).

For instance, to find the number of neutrons in \(^{40}\mathrm{Ar}\), you subtract the atomic number from the mass number: \[ 40 - 18 = 22 \ ext{neutrons} \] This calculation is repeated for each element, helping us understand isotopes, which are atoms with the same number of protons but different numbers of neutrons.

Electrons

Electrons are negatively charged particles that orbit the nucleus in various energy levels or shells. In a neutral atom, the number of electrons is equal to the number of protons, ensuring that the overall charge is balanced.

These tiny particles are crucial for chemical reactions and bonding. Electrons can be transferred or shared between atoms, leading to the formation of chemical compounds. They determine the atom's reactivity and the types of bonds it can form.

For neutral atoms in this exercise:

• Argon (\(^{40}\mathrm{Ar}\)) has 18 electrons.
• Zinc (\(^{65}\mathrm{Zn}\)) has 30 electrons.
• Gallium (\(^{70}\mathrm{Ga}\)) has 31 electrons.
• Bromine (\(^{80}\mathrm{Br}\)) has 35 electrons.
• Tungsten (\(^{184}\mathrm{~W}\)) has 74 electrons.
• Americium (\(^{243}\mathrm{Am}\)) has 95 electrons.

Understanding electrons gives insight into why elements behave differently and how they interact with each other.