Question

Which of the following statements is/are always true? Never true? Usually true? (a) Compounds containing chlorine can be either molecular or ionic. (b) An ionic compound always has at least one metal. (c) When an element in a molecule has a "di" prefix, it means that the element has a +2 charge.

Short answer

Answer: The "di" prefix in a chemical compound indicates that there are two atoms of that element present in the molecule. It does not provide information about the charge of the element.

Step-by-step solution

Statement (a): Compounds containing chlorine can be either molecular or ionic.

Take note that molecular compounds consist of atoms bonded together by covalent bonds, while ionic compounds consist of charged particles (ions) that attract each other as a result of opposite electric charges. Now, let's consider this specific statement about compounds containing chlorine. Chlorine is a non-metal that forms covalent bonds with other non-metals to form molecular compounds. However, it can also form ionic compounds when it gains an electron from a metal, creating a chloride ion (Cl-). Therefore, this statement is always true, as compounds containing chlorine can indeed be either molecular or ionic.

Statement (b): An ionic compound always has at least one metal.

Ionic compounds result from the transfer of electrons between atoms, leading to the formation of positively charged cations and negatively charged anions. Metals tend to lose electrons and take on a positive charge (cation), while non-metals tend to gain electrons and assume a negative charge (anion). Since ionic compounds require the presence of both cations and anions, it is logical to say that they consist of at least one metal and one non-metal. Hence, this statement is also always true.

Statement (c): When an element in a molecule has a "di" prefix, it means that the element has a +2 charge.

The "di" prefix refers to the number of atoms of the element present in the compound rather than the charge of the element. Specifically, "di" indicates that there are two atoms of that element in the molecule. For instance, in the compound H2O (water), it means there are two hydrogen atoms and one oxygen atom. An element's charge is determined by the number of electrons it has compared to the number of protons within the atomic nucleus. This statement is, therefore, never true, as the "di" prefix does not provide information about the charge of the element.

Key concepts

Ionic Compounds

When we talk about ionic compounds, we're delving into the world of chemistry where atoms form compounds by transferring electrons. This creates ions: atoms or groups of atoms with a net positive or negative charge. An ionic compound is a chemical compound composed of these ions, held together by the strong electrostatic forces known as ionic bonds.

Imagine a dance between metals and non-metals. Metals, with their propensity to lose electrons, become positively charged cations. Non-metals, on the flip side, tend to grab those electrons and become negatively charged anions. This is like a cosmic give-and-take, with electrons being the hot potato that gets passed around. The result? A stable crystal lattice structure that we recognize as salt is one of the most common ionic compounds.

• Ionic compounds have high melting and boiling points, making them solid at room temperature.
• They often dissolve well in water, breaking down into their individual ions.
• Their conductivity depends on their state; they conduct electricity when molten or dissolved but not when solid, due to the mobility of ions.

Covalent Bonds

Covalent bonds are all about sharing. Atoms form these bonds by sharing pairs of electrons, rather than losing or gaining them outright. This sharing allows each atom to attain the equivalent of a full outer shell, hitting the sweet spot for stability that all elements crave.

A classic example of covalent sharing is found in water (H2O), where hydrogen and oxygen atoms share electrons to achieve a stable configuration. These bonds are like mutual partnerships, and the strength of these partnerships varies. Some covalent bonds are stronger and require more energy to break, while others are weaker.

• Covalent compounds, also known as molecular compounds, typically have lower melting and boiling points than ionic compounds.
• These compounds might not conduct electricity, as they don't have free ions or electrons traveling around.
• They can be gases, liquids, or solids at room temperature depending on the strength of their bonds.

Molecular Compounds

Molecular compounds are distinct from ionic compounds. They consist of molecules formed by atoms joined together by covalent bonds, which involve that electron-sharing we talked about. These molecules can be made up of different numbers of atoms and different elements, creating the vast diversity of compounds we see in chemistry and in our daily lives.

When it comes to prefixes like 'di', 'tri', 'tetra,' and so on in molecular compounds, it's vital to recognize their purpose. They're there to tell us how many atoms of a particular element are in a molecule. For the record, 'di' means two—it has nothing to do with the charge but is an indicator of quantity.

• Molecular compounds usually have lower melting and boiling points compared to ionic compounds.
• They can be composed of a variety of elements, which opens up a universe of possibilities for chemists and nature alike.
• The way atoms are arranged in molecular compounds—also known as their molecular structure—is essential for determining the properties and behaviors of the compound.