Textbook Question
Which of the following is the expected product of the reaction of K(s) and H2(g)? (i) KH(s), (ii) K2H(s), (iii) KH2(s), (iv) K2H2(s), or (v) K(s) and H2(g) will not react with one another.
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Ch.7 - Periodic Properties of the Elements
Chapter 7, Problem 105
Zinc in its 2+ oxidation state is an essential metal ion for life. Zn2+ is found bound to many proteins that are involved in biological processes, but unfortunately, Zn2+ is hard to detect by common chemical methods. Therefore, scientists interested in studying Zn2+-containing proteins frequently substitute Cd2+ for Zn2+, since Cd2+ is easier to detect. On the basis of the properties of the elements and ions discussed in this chapter and their positions on the periodic table, describe the pros and cons of using Cd2+ as a Zn2+ substitute. Proteins that speed up (catalyze) chemical reactions are called enzymes. Many enzymes are required for proper metabolic reactions in the body. One problem with using Cd2+ to replace Zn2+ in enzymes is that Cd2+ substitution can decrease or even eliminate enzymatic activity. Can you suggest a different metal ion that might replace Zn2+ in enzymes instead of Cd2+? Justify your answer.
Verified step by step guidance1
Step 1: Understand the context of the problem. Zn2+ is an essential metal ion in biological systems, often found in proteins and enzymes. However, it is difficult to detect, leading scientists to use Cd2+ as a substitute due to its easier detectability.
Step 2: Analyze the pros and cons of using Cd2+ as a substitute for Zn2+. Pros include its detectability, but cons include potential toxicity and the possibility of altering or inhibiting enzymatic activity due to differences in ionic radius and chemical properties.
Step 3: Consider the periodic table and the properties of elements. Zn and Cd are both in group 12, which means they have similar properties, but Cd is larger and more toxic. Look for another element in the same group or nearby that might have similar properties to Zn2+.
Step 4: Evaluate other potential metal ions. Consider ions like Mg2+ or Mn2+, which are also biologically relevant and might mimic the coordination chemistry of Zn2+ without the toxicity of Cd2+. These ions are also involved in biological processes and might be less disruptive to enzymatic activity.
Step 5: Justify your choice based on chemical properties. For example, Mg2+ is smaller and less toxic than Cd2+, and it is involved in many biological processes, making it a potentially better substitute for Zn2+ in enzymes. Consider the ionic radius, charge density, and coordination preferences when making your justification.
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Oxidation States and Metal Ions
Oxidation states indicate the degree of oxidation of an atom in a compound, reflecting its electron loss or gain. Zinc commonly exists in a +2 oxidation state (Zn2+), which is crucial for its role in biological systems, particularly in enzyme function. Understanding oxidation states helps in predicting how metal ions interact with proteins and their biological significance.
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Oxidation Numbers in Ions
Enzyme Function and Metal Ion Role
Enzymes are biological catalysts that accelerate chemical reactions in living organisms. Many enzymes require metal ions, like Zn2+, as cofactors to maintain their structure and activity. The presence of the correct metal ion is essential for the enzyme's catalytic function, and substituting it with a different ion, such as Cd2+, can disrupt this activity, leading to decreased or lost function.
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Periodic Table Trends and Element Properties
The periodic table organizes elements based on their atomic structure and properties, influencing their reactivity and interactions. Elements in the same group often exhibit similar chemical behaviors. Understanding these trends is vital when considering substitutions of metal ions, as properties like ionic radius, electronegativity, and coordination ability can affect how well a substitute, like Cd2+, can mimic Zn2+ in biological systems.
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00:59Main Group Elements: Periodic Trends Example
Related Practice
Textbook Question
A historian discovers a nineteenth-century notebook in which some observations, dated 1822, were recorded on a substance thought to be a new element. Here are some of the data recorded in the notebook: 'Ductile, silver-white, metallic looking. Softer than lead. Unaffected by water. Stable in air. Melting point: 153 °C. Density: 7.3 g>cm3. Electrical conductivity: 20% that of copper. Hardness: About 1% as hard as iron. When 4.20 g of the unknown is heated in an excess of oxygen, 5.08 g of a white solid is formed. The solid could be sublimed by heating to over 800 °C.' (a) Using information in the text and the CRC Handbook of Chemistry and Physics, and making allowances for possible variations in numbers from current values, identify the element reported.
Textbook Question
We will see in Chapter 12 that semiconductors are materials that conduct electricity better than nonmetals but not as well as metals. The only two elements in the periodic table that are technologically useful semiconductors are silicon and germanium. Integrated circuits in computer chips today are based on silicon. Compound semiconductors are also used in the electronics industry. Examples are gallium arsenide, GaAs; gallium phosphide, GaP; cadmium sulfide, CdS; and cadmium selenide, CdSe. (a) What is the relationship between the compound semiconductors' compositions and the positions of their elements on the periodic table relative to Si and Ge?