Problem 38 - Chemistry The Molecular Science

Question

Predict which compounds are ionic. Explain your answers. (a) \(\mathrm{CF}_{4}\) (b) \(\mathrm{SrBr}_{2}\) (c) \(\mathrm{Co}\left(\mathrm{NO}_{3}\right)_{3}\) (d) \(\mathrm{SiO}_{2}\) (e) \(\mathrm{KCN}\) (f) \(\mathrm{SCl}_{2}\)

Step-by-Step Solution

Answer

SrBr extsubscript{2}, Co(NO extsubscript{3}) extsubscript{3}, and KCN are ionic compounds.

Step 1: Identify the type of elements in each compound (ionic or covalent)

Compounds typically contain ionic bonds if they are composed of a metal paired with a non-metal. Metals are elements found on the left side of the periodic table, while non-metals are on the right side.

Step 2: Analyze each compound

(a) **CF extsubscript{4}**: Carbon and fluorine are both non-metals, which typically form covalent bonds. (b) **SrBr extsubscript{2}**: Strontium (Sr) is a metal and bromine (Br) is a non-metal. This suggests an ionic bond. (c) **Co(NO extsubscript{3}) extsubscript{3}**: Cobalt (Co) is a metal forming a complex with nitrate ions, a common ionic compound structure. (d) **SiO extsubscript{2}**: Silicon (Si) and oxygen (O) are typically not metals and form covalent bonds. (e) **KCN**: Potassium (K) is a metal, cyanide (CN) is often treated as an ionic complex when combined with metals. (f) **SCl extsubscript{2}**: Sulfur (S) and chlorine (Cl) are non-metals, generally forming molecular or covalent bonds.

Step 3: Determine if each compound is ionic

Based on the analysis: - (a) **CF extsubscript{4}** is covalent. - (b) **SrBr extsubscript{2}** is ionic. - (c) **Co(NO extsubscript{3}) extsubscript{3}** is ionic. - (d) **SiO extsubscript{2}** is covalent. - (e) **KCN** is often treated as ionic due to the presence of a metal and an ionic complex. - (f) **SCl extsubscript{2}** is covalent.

Key Concepts

Covalent Bonds

Covalent bonds are formed when two non-metal atoms share electrons. This sharing allows each atom to achieve a stable electronic configuration, usually resembling that of the noble gases. In most cases, non-metals possess similar electronegativities, which leads them to equally share electrons rather than transferring them completely. These types of bonds typically result in the formation of molecules.

In covalent bonding:

• The shared electron pair revolves around the nucleus of both atoms involved.
• The bonds occur between non-metal elements, found on the right side of the periodic table.
• Molecules with covalent bonds exhibit low melting and boiling points due to weaker intermolecular forces compared to ionic compounds.

Analyzing a few compounds from the exercise, we observe that both sulfur and chlorine in (SCl extsubscript{2}) and carbon and fluorine in (CF extsubscript{4}) form covalent bonds, because each pair involves non-metal elements sharing electrons rather than transferring them. Similarly, silicon and oxygen in (SiO extsubscript{2}) also exhibit covalent bonding characteristics due to shared electrons.

Periodic Table

The periodic table is a cornerstone in chemistry, helping us predict the types of bonds elements are likely to form. Elements are organized based on their atomic number, and trends can be observed across periods and groups that inform us about their bonding behaviors. Metals and non-metals are distinctly separated on this table, aiding in the prediction of ionic or covalent bonds.

Here are some key points about the periodic table:

• Metals are generally located on the left and center of the periodic table, while non-metals are found on the right side.
• Elements in the same group exhibit similar chemical properties due to having the same number of valence electrons.
• The periodic table indicates the electronegativity of elements, allowing us to predict the bond type when elements combine.

A good understanding of the periodic table allows us to discern that compounds like SrBr extsubscript{2} are ionic, as it involves the combination of a metal from the left (Strontium) and a non-metal from the right (Bromine). On the contrary, (SiO extsubscript{2}) involves non-metals from the right side, thus leading to covalent bonding.

Metal and Non-Metal

Metals and non-metals are fundamental classifications of elements, especially regarding their chemical bonding potential. This division is based on characteristic properties involving conductivity, malleability, and reactivity.

Metals:

• Typically exhibit high electrical and thermal conductivity.
• Are malleable and ductile.
• Tend to lose electrons and form positive ions or cations.

Non-Metals:

• Generally have low conductivity.
• Are brittle in solid state.
• Tend to gain or share electrons, forming negative ions or anions, or covalent bonds.

When metals and non-metals combine, ionic bonds are typically formed. Conversely, combinations of non-metals usually result in covalent bonds. This understanding helps us categorize compounds, for instance, (SrBr extsubscript{2}) and (KCN) where a metal is paired with non-metallic components, indicating ionic bonding.