Question

An element X reacts with oxygen to form \(\mathrm{XO}_{2}\) and with chlorine to form \(\mathrm{XCl}_{4} . \mathrm{XO}_{2}\) is a white solid that melts at high temperatures (above \(1000^{\circ} \mathrm{C}\) ). Under usual conditions, \(\mathrm{XCl}_{4}\) is a colorless liquid with a boiling point of \(58^{\circ} \mathrm{C}\). (a) \(\mathrm{XCl}_{4}\) reacts with water to form \(\mathrm{XO}_{2}\) and another product. What is the likely identity of the other product? (b) Do you think that element \(\mathrm{X}\) is a metal, nonmetal, or metalloid? (c) By using a sourcebook such as the CRC Handbook of Chemistry and Physics, try to determine the identity of element X.

Short answer

The other product formed when XCl₄ reacts with water is hydrochloric acid (HCl). Element X is likely a nonmetal or a metalloid, and the most probable identity of element X is Silicon (Si).

Step-by-step solution

(a) Determine the other product formed when XCl₄ reacts with water.

The given information is that XCl₄ reacts with water to form XO₂ and another product. In general, when a compound with a halogen (such as chlorine) reacts with water, one of the products is a hydrogen halide. Therefore, we can write the reaction as follows: \(XCl_{4} + H_{2}O \longrightarrow XO_{2} + 4H^{+} + 4Cl^{-}\) The other product formed is hydrochloric acid (HCl). The balanced equation for the reaction is: \(XCl_{4} + 4H_{2}O \longrightarrow XO_{2} + 4HCl\)

(b) Identify if element X is a metal, nonmetal, or metalloid.

We know that XO₂ is a white solid with a high melting point and XCl₄ is a colorless liquid with a boiling point of 58°C. Based on these properties, we can deduce the following: - XO₂ has a high melting point, which is indicative of a compound with strong ionic or covalent bonding. High melting points are usually observed in ionic compounds of metals and nonmetals or covalent compounds of nonmetals. - XCl₄ is a liquid at room temperature, which implies that it has relatively weak intermolecular forces, consistent with covalent bonds. This suggests that X is a nonmetal or a metalloid. Considering the properties of XO₂ and XCl₄ and the fact that X has a valence of +4, we can conclude that element X is likely a nonmetal or a metalloid.

(c) Determine the identity of element X.

Referring to a sourcebook such as the CRC Handbook of Chemistry and Physics, we can find elements that tend to form compounds with a +4 valence state and examine their properties. Possible candidates include: - Tin (Sn): Forms SnO₂ and SnCl₄; however, Sn is a metal, and we deduced that X is likely a nonmetal or metalloid. - Silicon (Si): Forms SiO₂ and SiCl₄. Silicon is a metalloid and has properties consistent with the unknown element X. Based on this information, the identity of element X is likely Silicon (Si).

Key concepts

Element Identification

Identifying an unknown element often includes analyzing the products formed when it reacts with other substances. In the given exercise, element X reacts with oxygen to form \(\mathrm{XO}_{2}\), and with chlorine to create \(\mathrm{XCl}_{4}\). These reactions provide critical information about X's properties.

• The reaction with oxygen resulting in \(\mathrm{XO}_{2}\) suggests that X forms compounds that are stable and potentially ionic with oxygen.
• The reaction with chlorine to form \(\mathrm{XCl}_{4}\) yields a liquid, indicating weaker forces between molecules, which are usually seen in covalent compounds.

Element X's behavior in forming different compounds can lead us to infer that it is more likely a nonmetal or metalloid. By examining these reactions in more detail and referencing additional chemical data, we can narrow down the identities of element X to certain elements like metalloids Silicon (Si) and nonmetals that commonly exhibit similar valence and bonding characteristics.

Compound Properties

The properties of compounds formed with element X give us a window into the nature of chemical bonding involved. For example, the compound \(\mathrm{XO}_{2}\) being a white solid with a high melting point hints towards a strong bonding. This is typical in covalently bonded networks or ionic solids.

• High melting points typically indicate strong interaction forces in the structure of the compound, whether ionic or covalent.
• Color and physical state provide insights into the types of elements involved; many covalent network structures like \(\mathrm{SiO}_{2}\) are solid and white.

Conversely, \(\mathrm{XCl}_{4}\) being a liquid at room temperature suggests weaker van der Waals forces between its molecules despite having covalent bonds internally. These insights into compound properties further support elements with potential covalent bonding tendencies, such as some nonmetals or metalloids.

Valence State

The valence state of an element refers to its potential to combine with other elements, forming different compounds with specific bonding capacities. Element X shows a valence of +4 as seen in its compounds\(\mathrm{XO}_{2}\)and\(\mathrm{XCl}_{4}\). This means it shares or transfers four electrons when reacting, an important feature of certain elements in the periodic table.

• Elements like carbon, silicon, and germanium typically exhibit a +4 valence state due to their electron configuration.
• The ability to form different compounds like \(\mathrm{SiO}_{2}\) and \(\mathrm{SiCl}_{4}\) is characteristic of elements that can bond to multiple other atoms with similar valencies, supporting possibilities like silicon.

Understanding such valence states offers a deeper comprehension into how elements engage in various chemical reactions based on their available bonding electrons. This knowledge is fundamental in pinning down element X's identity, pointing towards metalloid properties with significant covalent character.