Question

Identify the following elements: (a) A member of the same period as selenium but with two fewer protons than selenium. (b) A transition metal in group \(6,\) period 6 . (c) An alkaline earth with 38 protons. (d) A post-transition metal in group 15 .

Short answer

Question: Identify the elements based on the given information: (a) This element has two fewer protons than selenium and is in the same period as selenium. (b) This is a transition metal in group 6 and period 6. (c) This is an alkaline earth metal with 38 protons. (d) This is a post-transition metal in group 15. Answer: (a) Germanium (Ge) (b) Chromium (Cr) (c) Strontium (Sr) (d) Bismuth (Bi)

Step-by-step solution

Understanding the terms in the exercise

Make sure to have a basic understanding of the periodic table and the associated terms. In this problem, we need to identify elements based on their position in the periodic table and the atomic number (number of protons). - A period refers to the horizontal row of the periodic table. Elements in the same period have the same number of electron shells. - A group refers to the vertical column of the periodic table. Elements in the same group have similar chemical properties and share the same number of valence electrons. - Transition metals are the elements found in groups 3-12. - Alkaline earth metals are found in group 2. - Post-transition metals are elements in groups 13-16.

Identifying elements based on the atomic number and period

Use the periodic table and the information provided to identify elements as described below: (a) The element we are looking for has two fewer protons than selenium. First, we need to find the atomic number of selenium. Selenium (Se) has an atomic number of 34. Therefore, the element we are looking for has 34 - 2 = 32 protons. The element with 32 protons is Germanium (Ge), which belongs to the same period (period 4) as selenium. (b) We are looking for a transition metal in group 6 and period 6. Using the periodic table, the element that we find at the intersection of group 6 and period 6 is Chromium (Cr). (c) The element we are looking for is an alkaline earth metal with 38 protons. Alkaline earth metals are found in group 2 of the periodic table. The element with an atomic number of 38 is Strontium (Sr), which belongs to group 2, making it an alkaline earth metal. (d) The element we are looking for is a post-transition metal in group 15. Using the periodic table, we can determine that the element in group 15 and period 5 is Bismuth (Bi).

Key concepts

Atomic Number

The atomic number is a fundamental property of an element that determines its identity. Simply put, it's the number of protons found in the nucleus of an atom of that element. It's crucial because it not only uniquely identifies an element but also gives us information about its properties. For instance, every atom of carbon has exactly 6 protons in its nucleus, giving it an atomic number of 6.

When we're trying to identify an element related to another, like one with 'two fewer protons than selenium,' we subtract 2 from selenium's atomic number, which is 34, landing us at 32. This corresponds to Germanium (Ge), which helps us solve part (a) of our exercise. It's important to remember that elements are arranged on the periodic table in order of increasing atomic number, so this number is always your starting point for element identification.

Transition Metals

Transition metals occupy the central block of the periodic table, specifically in groups 3 through 12. These metals are characterized by their ability to form compounds with variable oxidation states and often exhibit colored compounds and complex behavior. A common example includes iron (Fe), which can exist in both +2 and +3 oxidation states.

In the exercise, identifying a 'transition metal in group 6, period 6' brings us to Chromium (Cr), the first element in this group. Transition metals are significant in many technological and biological processes because of their diverse chemical and physical properties. For students looking at the periodic table, remember, the distinctive 'd-block'—the middle section of the table—is where you'll find these versatile elements.

Alkaline Earth Metals

Just to the left of the transition metals, we find the alkaline earth metals in group 2 of the periodic table. These metals, which include beryllium (Be), magnesium (Mg), calcium (Ca), and others, possess two valence electrons and are highly reactive, though not as much as their neighbors the alkali metals in group 1. They are called 'earth metals' because many of these elements were first isolated from minerals found in the earth.

To address part (c) of our problem, 'an alkaline earth with 38 protons,' we identify the element as Strontium (Sr). Its position in group 2 alongside its reactivity with water and the formation of basic (alkaline) solutions when in contact with water justifies its classification and its 'earthy' moniker.

Post-Transition Metals

Beyond the transition metals, one encounters a group of elements known as post-transition metals, which occupy groups 13 to 16. These metals, such as tin (Sn), lead (Pb), and bismuth (Bi), have properties that fall between the transition metals and the metalloids. They are softer and have lower melting points than transition metals and often form +3 oxidation states, amongst others.

When tasked with identifying a 'post-transition metal in group 15,' we find Bismuth (Bi), a typical representative of this group. Recognizable for its density and low toxicity, bismuth serves as a prime example for part (d) of the exercise. Its usage ranges from cosmetics to pharmaceuticals, highlighting the practical importance of understanding these elements.

Periodic Table Groups and Periods

Mastery of the periodic table's layout is key to success in chemistry. Groups, which run vertically, contain elements with similar chemical properties corresponding to their valence electrons. These shared characteristics such as reactivity and compound formation provide a predictable pattern aiding chemical identification and reaction predictions.

Periods, on the other hand, run horizontally and represent elements with the same number of electron shells, increasing sequentially with atomic number. Elements in the same period showcase a gradual change in properties across the row. For example, as we move across a period, metallic character typically decreases while ionization energy increases. This structured layout of the periodic table into groups and periods forms the backbone for understanding chemical behavior and solving exercises like the ones we've discussed.