Question

An unknown element contains 33 protons, 36 electrons, and has a mass number 76. 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 33, the element is arsenic (As), it contains 43 neutrons, the charge is -3 making it an anion, and the symbolic notation is \( ^{76}_{33}\text{As}^{-3} \).

Step-by-step solution

Determine the Atomic Number

The atomic number is equal to the number of protons in an atom. Since the unknown element has 33 protons, its atomic number is 33.

Identify the Element

Using the atomic number obtained in Step 1, refer to the periodic table to identify the element. The element with atomic number 33 is arsenic, with the symbol As.

Calculate Neutrons

The number of neutrons in an atom can be calculated by subtracting the atomic number from the mass number. For this element: Neutrons = Mass Number - Atomic Number = 76 - 33 = 43.

Determine the Charge

The charge of an ion is determined by the difference between the number of protons and electrons. This element has 33 protons and 36 electrons, thus it has 3 more electrons than protons. Therefore, the charge is -3. Since the ion has more electrons than protons, it is an anion.

Write Symbolic Notation

The symbolic notation for this element consists of the element's symbol, the mass number as a superscript, the atomic number as a subscript, and the charge as a superscript on the right. For this element, it is written as \( ^{76}_{33}\text{As}^{-3} \).

Key concepts

Atomic Number

The atomic number is a fundamental property of an element and provides significant information about its characteristics. In simple terms, the atomic number is the number of protons found in the nucleus of an atom. Since each element has a unique number of protons, the atomic number effectively serves as an identification number for that element.

For instance, in our exercise, the unknown element with 33 protons has an atomic number of 33. This is crucial not just for identification but also for understanding an element's position on the periodic table and its chemical behaviour. Elements are arranged in the periodic table in order of their atomic numbers, which means the element in our problem is located in the 33rd place on the table.

Periodic Table

The periodic table is not just a chart; it's a gateway to exploring the elements that make up our universe. This organised table provides a visual representation of all known elements arranged according to their atomic number, electron configurations, and recurring chemical properties. Groups (columns) and periods (rows) systematically categorise elements, making it easier to predict an element's properties and its reactivity with other elements.

In relation to our exercise, once we know the atomic number of an element, we can easily find it on the periodic table. This tool told us that the element with atomic number 33 is arsenic, which is denoted by the symbol 'As'. Understanding how to effectively use the periodic table can significantly enhance one's ability to study and comprehend chemistry.

Neutrons Calculation

Neutrons, along with protons, form most of the mass of an atom. Despite being neutral particles (having no charge), they play a vital role in the mass and stability of an atom. To determine the number of neutrons, you subtract the atomic number from the mass number (which is the sum of protons and neutrons). This simple calculation uncovers yet another layer of an atom's identity.

In our example, the mass number of the element is 76. To find the number of neutrons, we calculate 76 (mass number) - 33 (atomic number) which equals 43 neutrons. This understanding is indispensable for students as they delve into atomic structures and isotopes, where neutron count is integral for identifying different forms of the same element.

Ion Charge

An ion is an atom or molecule that has an unequal number of protons and electrons, causing it to have a net positive or negative electrical charge. If an atom has more electrons than protons, it's negatively charged and is called an anion. Conversely, if there are fewer electrons than protons, the atom is positively charged and is known as a cation.

Our exercise reveals an ion where the number of electrons (36) exceeds the number of protons (33) by three, giving this ion a charge of -3. Recognizing the charge and type of ion is essential for predicting the behavior of atoms in different chemical contexts, such as bonding and electrical conductivity.

Symbolic Notation

Symbolic notation is a compact way to convey an atom's or ion's physical characteristics at a glance. This shorthand includes the element's symbol, its mass number and atomic number, and if applicable, its ionic charge. It’s a universal language that allows chemists to quickly understand and communicate complex information.

In our exercise, the symbolic notation for arsenic with a mass number of 76 and a -3 charge is written as \( ^{76}_{33}\text{As}^{-3} \). Mastering symbolic notation is fundamental for students in expressing atomic constituents without resorting to wordy explanations, thereby making written communication in science precise and efficient.