Element X is a grey solid.
It combines with chlorine to form a polar molecule with the formula XCl . In this compound, element X has an oxidation state of +1.
In potassium iodide solution, it dissolves to form a coloured solution.
At 500 °C, it becomes a coloured vapour.
What is the identity of element X?
A. manganese
B. fluorine
C. iodine
D. carbon
E. lithium
X+Cl → XCl
What is X?
Oxidative state +1
From this we can make some hypotheses: it could be an alkali metal, hydrogen, or a less electronegative non-metal, typically group 7.
We know that it cannot be an alkali metal because we have been told it forms a polar compound. Polar means that there is an uneven distribution of charge and this is characteristic of covalent molecules because they share their electrons. In ionic compounds, there is the donation of electrons, so they become more fixed around one of the atoms in the compound.
Electronegativity
In terms of electronegativity values, we cannot yet eliminate hydrogen (2.1) because it is less electronegative than Chlorine (3.0). This rules out B, fluorine, which is the most electronegative element.
We were also told it is a grey solid but forms a coloured vapour.
Grey solid
Iodine at room temperature is a dark grey (almost black)
remember halogens go from:
(gases)
F
Cl
(Liquids)
Br
(Solids)
I
As
This is not as complicated to remember as you think because the phases are changing as you move down the family (it is in order from lowest atomic number to highest)
The ability to form coloured vapours in a property of halogens
(500°C does not really tell us much if we haven’t memorized the boiling points of all elements, but we should note that boiling point increases down a group for halogens because of stronger London dispersion forces).
Now that we have examined all of the evidence, we know that it is a halogen less electronegative than chlorine because it has the oxidation number +1, a polar covalent bond, and it forms coloured vapours. Based on everything, we can conclude that iodine is the mystery element.
Iodine is a chemical element with the symbol I and atomic number 53. It is a nonmetal and halogen, which means that it is a highly reactive element that readily forms compounds with other elements. Iodine is a solid at room temperature, and it has a characteristic bluish-black color. It has a high melting and boiling point, and it is easily sublimated, which means that it can be converted directly from a solid to a gas without passing through the liquid state. Iodine is highly soluble in water and other polar solvents, and it readily dissolves in potassium iodide solution to form a colored solution. It has a number of important industrial and medical uses, including the production of iodized salt and the treatment of thyroid conditions.
Based on the information provided, it appears that element X is iodine. This can be inferred from the fact that element X combines with chlorine to form a polar molecule with the formula XCl, and that element X has an oxidation state of +1 in this compound. Additionally, the fact that element X dissolves in potassium iodide solution and becomes a colored vapour at 500 °C is consistent with the known properties of iodine. Therefore, the correct answer to the question is option C, iodine.
Hi, I’m getting a little confused, I was just reviewing question 48 and there you said " water and salt are both polar"
the salt was NaCl, which is indeed polar, but it is also ionic, so why do we eliminate the possibility of XCl being an ionic compound in this question?
To answer your question, I would proceed as follows:
(1). First of all, Manganese is a transition metal and attains variable oxidation states from +2 to +7. If Manganese reacted with chlorine it would NOT attain a +1 oxidation state. Hence, we eliminate it from the answer choices.
(2). Moreover, consider Lithium. Lithium has an oxidation state of +1 when combined with LiCl, that is true. HOWEVER, lithium does not become a vapor at 500 C and it is neither colored. Metals have VERY high melting points due to the strong electrostatic attractions between the metal cations and the delocalized electrons in the lattice. Hence, 500 C celsius for a boiling seems low for the compound being a metal. This eliminates element X being a metal from the answer choices.
(3). Recall that Iodine is a solid since it contains stronger London forces due to its higher molar mass compared to Fluorine.
(4). Most importantly, I would suggest for further questions to think of the concept of “ionic” bonding not in terms of metal and non-metal, but in terms of a type of bonding between a very electronegative element (non-element) and a less electronegative element (metal). The difference is around >= 1.8 to be considered ionic. The idea of ionic binding is analogous to the concept of heterolytic fission.
Most of the time ionic bond is polar.
Covalent bond is polar only when the difference of electronegativities is larger than 0.5