You are given a gray substance that melts at 700 °C; the solid is a conductor of electricity and is insoluble in water. Which type of solid (molecular, metallic, covalent-network, or ionic) might this substance be?

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Identify the properties of the substance: it is gray, melts at 700 °C, conducts electricity as a solid, and is insoluble in water.

Consider the types of solids: molecular, metallic, covalent-network, and ionic.

Recall that molecular solids typically have low melting points and do not conduct electricity, so this is unlikely.

Consider metallic solids: they are often gray, have high melting points, conduct electricity, and are insoluble in water.

Conclude that the substance is most likely a metallic solid based on its properties.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Types of Solids

Solids can be classified into four main types: molecular, metallic, covalent-network, and ionic. Each type has distinct properties based on the nature of the bonding and structure. Molecular solids consist of molecules held together by intermolecular forces, metallic solids consist of metal atoms sharing electrons, covalent-network solids have atoms connected by covalent bonds in a continuous network, and ionic solids are composed of ions held together by electrostatic forces.

Electrical Conductivity

Electrical conductivity refers to a material's ability to conduct electric current. In solids, this property is influenced by the presence of free-moving charged particles. Metallic solids are good conductors due to the mobility of delocalized electrons, while ionic solids conduct electricity when melted or dissolved in water, as ions can move freely. The gray substance in the question is a conductor, suggesting it may be metallic.

Melting Point and Solubility

The melting point of a substance provides insight into its bonding and structure. A high melting point, like 700 °C, typically indicates strong bonding forces, such as those found in metallic or covalent-network solids. Additionally, solubility in water can help differentiate between types; for instance, ionic solids are often soluble, while metallic and covalent-network solids are generally insoluble. The gray substance's high melting point and insolubility suggest it is likely a metallic solid.