Question

An unknown element contains 56 protons, 54 electrons, and has a mass number 135 . Answer the following questions: (a) What is the atomic number of this element? (b) What are the name and symbol of this element? (c) How many neutrons does it contain? (d) What is the charge on this ion? Is it a cation or an anion? (e) Write the symbolic notation for this element.

Short answer

The atomic number is 56, and the element is Barium (Ba). It contains 79 neutrons. The ion has a charge of +2 and is a cation. The symbolic notation is \[\begin{equation}^{135}_{56}Ba^{2+}\end{equation}\]

Step-by-step solution

Identify the Atomic Number

The atomic number is equal to the number of protons in an atom. Hence, the atomic number of the unknown element is 56.

Determine the Element's Name and Symbol

Using the periodic table, match the atomic number 56 with the element Barium, which has the symbol Ba.

Calculate the Number of Neutrons

The number of neutrons is found by subtracting the atomic number from the mass number: Neutrons = Mass number - Atomic number = 135 - 56 = 79.

Calculate the Ion's Charge

The charge of an ion is determined by the difference between the number of protons and electrons. Charge = Number of protons - Number of electrons = 56 - 54 = +2, indicating it is a cation.

Notation of the Element

The symbolic notation combines the element's symbol with its mass number and atomic number: \[\begin{equation}^{mass number}_{atomic number}Element Symbol\end{equation}\]Inserting the known values, we get \[\begin{equation}^{135}_{56}Ba^{2+}\end{equation}\]

Key concepts

Atomic Number

In the realm of chemistry and physics, the atomic number acts as a fundamental identifier for the elements. Simple yet pivotal, the atomic number is the count of protons within an atom's nucleus. For example, an atomic number of 56 indicates an element with 56 protons, which, consulting a periodic table, is identified as Barium (Ba).

Understanding the atomic number is crucial as it not only determines the element's identity but also its position in the periodic table. Each element has a unique atomic number, and no two elements share the same one, making it easy for students and scientists to classify them. Additionally, the atomic number is directly related to the element's properties and its place in the periodic trends.

Isotopes and Ions

Diving deeper into atomic structure, we encounter isotopes and ions, variants that provide a twist on an element's basic identity. Isotopes of an element share the same atomic number but have different mass numbers due to variations in the number of neutrons.

For instance, our unknown element with mass number 135 and atomic number 56 would have 79 neutrons (135-56=79), which differs from other isotopes of Barium that might have more or fewer neutrons. Ions, on the other hand, are atoms that have gained or lost electrons, resulting in a net charge. A barium atom typically has 56 electrons, but if it loses two, becoming Ba²⁺, it is a cation—positively charged. Anions are the opposite, bearing a negative charge when gaining extra electrons.

Charge Calculation

Calculating the charge of ions is straightforward: subtract the number of electrons from the number of protons. If the result is positive, you have a cation; if negative, an anion. This fundamental concept is critical in understanding chemical reactions and bonding.

Periodic Table

The periodic table is a tabular display of all known elements, organized by increasing atomic number. It is a map of chemical elements, paving the way for students to explore atomic structure, periodic trends, and chemical behavior. Elements are grouped into rows, or periods, and columns, known as groups or families.

Elements within the same group tend to exhibit similar properties and electron configurations. For example, by locating Barium (Ba) with an atomic number of 56, one can deduce its associates in the alkaline earth metal group, which share characteristics such as reacting with water and forming +2 charged ions. The periodic table is not just a classification tool but also a predictive framework that informs us about the potential reactions and compounds certain elements can form.

Using the periodic table, students can infer a wealth of information, such as atomic number, relative atomic mass, and how an element might interact with others. It's a fundamental tool that interconnects all aspects of chemistry.