Question

Write the appropriate symbol for each of the following isotopes: (a) \(Z=11, A=23\); (b) \(Z=28, A=64\); (c) \(Z=50, A=115\); (d) \(Z=20, A=42\).

Short answer

(a) \( ^{23}_{11}\text{Na} \); (b) \( ^{64}_{28}\text{Ni} \); (c) \( ^{115}_{50}\text{Sn} \); (d) \( ^{42}_{20}\text{Ca} \).

Step-by-step solution

Understand the Meaning of Symbols Z and A

The symbol \(Z\) represents the atomic number, which is the number of protons in the nucleus of an atom. The symbol \(A\) is the mass number, the sum of protons and neutrons in the atom. The element symbol is represented by the chemical symbol of the element, typically written with \(A\) as a superscript on the left and \(Z\) as a subscript on the left.

Identify the Element Using Z

To identify the chemical element, look up the atomic number \(Z\) on the periodic table. This number determines the element. For instance, when \(Z = 11\), the element is Sodium (Na). When \(Z = 28\), the element is Nickel (Ni). When \(Z = 50\), the element is Tin (Sn). When \(Z = 20\), the element is Calcium (Ca).

Write the Isotope Symbol

Using the formula \( ^A_Z ext{X} \), where \(X\) is the element symbol, substitute the identified elements and given \(A\) and \(Z\):- (a) \(Z = 11\), \(A = 23\): The isotope is \( ^{23}_{11}\text{Na} \).- (b) \(Z = 28\), \(A = 64\): The isotope is \( ^{64}_{28}\text{Ni} \).- (c) \(Z = 50\), \(A = 115\): The isotope is \( ^{115}_{50}\text{Sn} \).- (d) \(Z = 20\), \(A = 42\): The isotope is \( ^{42}_{20}\text{Ca} \).

Key concepts

Atomic Number

The atomic number, denoted by the symbol "Z," is a fundamental property of an element. It tells us the number of protons found in the nucleus of an atom. Since protons have a positive charge, the atomic number also determines the element's overall charge neutrality when balanced by electrons. In essence, the atomic number uniquely identifies a chemical element, as no two elements will share the same number of protons. This number can be found on the periodic table next to the element's symbol.

For example:

• If an element has an atomic number of 11, it has 11 protons, and its element is Sodium (Na).
• If the atomic number is 28, it correlates to Nickel (Ni) with 28 protons.

Thus, understanding the atomic number is crucial in distinguishing and identifying different elements.

Mass Number

The mass number, symbolized by "A," is the sum of an atom's protons and neutrons within its nucleus. While the atomic number defines the element, the mass number tells us about the isotope of that element. Because neutrons do not typically affect the chemical properties of the element, isotopes behave largely the same in chemical reactions but differ in mass due to the neutrons.

To calculate mass number:

• Sum the total number of protons and neutrons in the atom.
• For instance, if an atom has 11 protons and 12 neutrons, the mass number would be 23.

Keep in mind that the mass number is not found on the periodic table, as it varies from isotope to isotope for a given element.

Chemical Symbols

Chemical symbols are shorthand notations derived from an element's English or Latin name. These symbols are used worldwide, providing an easy and universal way of identifying elements in the periodic table and chemical reactions. Each element's symbol consists of one or two letters, where the first letter is always capitalized, and the second, if present, is lowercase.

Examples:

• Sodium is represented as Na, derived from its Latin name 'Natrium'.
• Nickel is represented as Ni.

This standardized system allows scientists to easily communicate and denote substances without language barriers, simplifying chemical equations and reactions.

Periodic Table Elements

The periodic table is an organized arrangement of all known chemical elements, displayed in order of increasing atomic number. It is a powerful tool for chemists and students alike due to its ability to predict the properties of elements based on their position.

Key features of the periodic table include:

• Rows, known as periods, where elements increase sequentially by atomic number.
• Columns, known as groups or families, which contain elements with similar properties.

The periodic table helps quickly identify an element's properties through its placement. For instance, elements with similar chemical behaviors are grouped together, aiding in their study and utilization in various applications.