Question

How many protons and neutrons are in the nucleus of each of the following atoms? In a neutral atom of each element, how many electrons are present? a. \({ }^{79} \mathrm{Br}\) b. \(^{81} \mathrm{Br}\) c. \({ }^{239} \mathrm{Pu}\) d. \({ }^{133} \mathrm{Cs}\) e. \({ }^{3} \mathrm{H}\) f. \({ }^{56} \mathrm{Fe}\)

Short answer

a. \(^{79} \mathrm{Br}\): 35 protons, 44 neutrons, and 35 electrons b. \(^{81} \mathrm{Br}\): 35 protons, 46 neutrons, and 35 electrons c. \(^{239} \mathrm{Pu}\): 94 protons, 145 neutrons, and 94 electrons d. \(^{133} \mathrm{Cs}\): 55 protons, 78 neutrons, and 55 electrons e. \(^{3} \mathrm{H}\): 1 proton, 2 neutrons, and 1 electron f. \(^{56} \mathrm{Fe}\): 26 protons, 30 neutrons, and 26 electrons

Step-by-step solution

Finding the Atomic Number and Symbol

First, we need to find the atomic number for each element, which also tells us the number of protons. We can look up the atomic number using a periodic table or by knowing their symbols. Here are the atomic numbers for each element: - Br (Bromine) - atomic number 35 - Pu (Plutonium) - atomic number 94 - Cs (Cesium) - atomic number 55 - H (Hydrogen) - atomic number 1 - Fe (Iron) - atomic number 26 Now we can find the number of protons, neutrons, and electrons for each atom.

a. \({ }^{79} \mathrm{Br}\)

Using the atomic number (35) and mass number (79), we can find the number of neutrons by subtracting the number of protons from the mass number. Number of Protons: 35 Number of Neutrons: 79 - 35 = 44 Number of Electrons: 35 (since the atom is neutral)

b. \(^{81} \mathrm{Br}\)

Using the atomic number (35) and mass number (81), we can find the number of neutrons. Number of Protons: 35 Number of Neutrons: 81 - 35 = 46 Number of Electrons: 35 (since the atom is neutral)

c. \({ }^{239} \mathrm{Pu}\)

Using the atomic number (94) and mass number (239), we can find the number of neutrons. Number of Protons: 94 Number of Neutrons: 239 - 94 = 145 Number of Electrons: 94 (since the atom is neutral)

d. \({ }^{133} \mathrm{Cs}\)

Using the atomic number (55) and mass number (133), we can find the number of neutrons. Number of Protons: 55 Number of Neutrons: 133 - 55 = 78 Number of Electrons: 55 (since the atom is neutral)

e. \({ }^{3} \mathrm{H}\)

Using the atomic number (1) and mass number (3), we can find the number of neutrons. Number of Protons: 1 Number of Neutrons: 3 - 1 = 2 Number of Electrons: 1 (since the atom is neutral)

f. \({ }^{56} \mathrm{Fe}\)

Using the atomic number (26) and mass number (56), we can find the number of neutrons. Number of Protons: 26 Number of Neutrons: 56 - 26 = 30 Number of Electrons: 26 (since the atom is neutral)

Key concepts

Understanding Protons in Atomic Structure

Protons are fundamental particles located in the nucleus of an atom. They are positively charged and play a crucial role in defining the identity of an element. The atomic number of an element, which indicates how many protons are present in the nucleus, distinguishes one element from another. For example, Bromine (Br) has an atomic number of 35, meaning it has 35 protons. This number is consistent across all isotopes of an element.

Since protons carry a positive charge, they contribute significantly to the overall charge of the nucleus. In a neutral atom, the number of protons equals the number of electrons, balancing the charges and resulting in an electrically neutral atom. Identifying the number of protons is essential for understanding the chemical properties and position in the periodic table of an element.

Neutrons and Their Role in Isotopes

Neutrons are neutral particles found in the nucleus along with protons. They have no electrical charge but are similar in size to protons. Neutrons play a vital role in stabilizing the nucleus and adding to its mass without affecting the proton number.

The number of neutrons in an atom can vary, leading to different isotopes of the same element. Isotopes have the same number of protons but different numbers of neutrons. For example, Bromine has isotopes with mass numbers 79 and 81, resulting in different neutron counts (44 and 46, respectively). Neutrons are calculated by subtracting the number of protons from the mass number (e.g., mass number 81 - atomic number 35 = 46 neutrons for _{81}Br). This calculation helps explain variations in atomic mass seen across isotopes.

Electrons and Their Influence on Neutrality

Electrons are negatively charged particles that orbit the nucleus of an atom. They are much smaller than protons and neutrons. In a neutral atom, the number of electrons equals the number of protons, allowing these charges to balance out. If an atom has an atomic number of 26, like Iron (Fe), it has 26 electrons in its neutral state.

Electrons are arranged in specific energy levels or "shells" around the nucleus. Their configuration affects how atoms interact with each other, forming chemical bonds. Electrons play a significant role in the atom's chemical behavior and reactions. Understanding electron distribution is fundamental in predicting how atoms will bond and interact in various chemical processes.