Question

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

Short answer

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

Step-by-step solution

Identify the atomic number

For each given element, find the atomic number, which represents the number of protons and electrons. We can find the atomic number using the periodic table.

Calculate the number of neutrons

For each given element, subtract the atomic number from the mass number to get the total number of neutrons.

Write down the protons, neutrons, and electrons for each given element

With the information gathered in steps 1 and 2, we can write down the number of protons, neutrons, and electrons for each element. (a) \({ }^{40} \mathrm{Ar}\) Atomic number of Ar (Argon) = 18 Number of protons = 18 Number of electrons = 18 Number of neutrons = mass number - atomic number = 40 - 18 = 22 (b) \({ }^{65} \mathrm{Zn}\) Atomic number of Zn (Zinc) = 30 Number of protons = 30 Number of electrons = 30 Number of neutrons = mass number - atomic number = 65 - 30 = 35 (c) \({ }^{70} \mathrm{Ga}\) Atomic number of Ga (Gallium) = 31 Number of protons = 31 Number of electrons = 31 Number of neutrons = mass number - atomic number = 70 - 31 = 39 (d) \({ }^{80} \mathrm{Br}\) Atomic number of Br (Bromine) = 35 Number of protons = 35 Number of electrons = 35 Number of neutrons = mass number - atomic number = 80 - 35 = 45 (e) \({ }^{184} \mathrm{W}\) Atomic number of W (Tungsten) = 74 Number of protons = 74 Number of electrons = 74 Number of neutrons = mass number - atomic number = 184 - 74 = 110 (f) \({ }^{243} \mathrm{Am}\) Atomic number of Am (Americium) = 95 Number of protons = 95 Number of electrons = 95 Number of neutrons = mass number - atomic number = 243 - 95 = 148

Key concepts

Atomic Number

The atomic number is a fundamental characteristic of an element, defining its unique identity among all known elements. It is denoted by the symbol 'Z' and indicates the number of protons in an atom's nucleus. Since atoms are electrically neutral, the number of protons (positive charges) is equal to the number of electrons (negative charges), under normal circumstances. For instance, the atomic number of Argon (Ar) is 18, meaning it has 18 protons and, consequently, 18 electrons orbiting the nucleus in its neutral state.

The significance of the atomic number is profound, not only because it informs us about the number of protons and electrons but also because it allows elements to be organized systematically within the periodic table. This organization makes it easier to predict an element's chemical behavior and properties based on its position.

Protons Neutrons Electrons

Understanding atomic structure is key to grasping chemistry fundamentals. An atom is composed of three primary particles: protons, neutrons, and electrons. Protons and neutrons exist in the atom's nucleus, contributing to most of the atom's mass. Electrons, though much lighter, orbit this nucleus and are crucial for chemical bonding and reactions.

Protons carry a positive charge, while electrons are negatively charged, and neutrons are neutral. The number of protons defines an element’s atomic number (Z) and identity. For example, Zinc (Zn) has an atomic number of 30, which means it has 30 protons and 30 electrons in its neutral state. The neutrons provide additional mass and help to stabilize the nucleus; the number of neutrons can vary even within the same element, leading to the formation of isotopes.

Periodic Table

The periodic table is a tabular display of all known chemical elements, organized by increasing atomic number, electron configurations, and recurring chemical properties. Elements are arranged in rows called periods and columns known as groups. The table has periods that run horizontally and groups that run vertically.

Elements with similar characteristics are grouped in the same column. For instance, the noble gases like Argon reside in group 18, known for their lack of reactivity due to a full set of valence electrons. In the periodic table, an element's position not only gives information about atomic structure but also about its potential reactivity, the nature of its bonds, and other physical and chemical properties. It serves as an indispensable tool for students and professionals in the field of science.

Isotopes

Isotopes are atoms of the same element that have the same number of protons (and electrons) but different numbers of neutrons in their nuclei. This difference in neutron number means isotopes have different mass numbers. Despite having varied masses, isotopes of an element exhibit similar chemical behavior because chemical properties are primarily determined by the electron configuration, which remains unchanged between isotopes.

For example, Carbon-12 and Carbon-14 are two isotopes of carbon; both have 6 protons, but Carbon-12 has 6 neutrons, whereas Carbon-14 has 8 neutrons. Isotopes can be stable or radioactive; radioactive isotopes undergo decay over time and are essential in fields such as medicine, archaeology, and energy production. Understanding isotopes is crucial for explaining the atomic weight of elements and for various practical applications like radiometric dating and nuclear reactors.