Question

The formulas for the fluorides of the third-period elements are \(\mathrm{NaF}, \mathrm{MgF}_{2}, \mathrm{AlF}_{3}, \mathrm{SiF}_{4}, \mathrm{PF}_{5}, \mathrm{SF}_{6},\) and \(\mathrm{ClF}_{3}\). Classify these compounds as covalent or ionic.

Short answer

NaF, MgF2, and AlF3 are ionic; SiF4, PF5, SF6, ClF3 are covalent.

Step-by-step solution

Define Ionic and Covalent Compounds

Ionic compounds are made up of metals and non-metals and involve the transfer of electrons, resulting in the formation of positive and negative ions. Covalent compounds typically consist of non-metals sharing electrons.

Analyze Each Formula

List each compound and identify the elements:- \(\mathrm{NaF}\): Na is a metal, F is a non-metal.- \(\mathrm{MgF}_2\): Mg is a metal, F is a non-metal.- \(\mathrm{AlF}_3\): Al is a metal, F is a non-metal.- \(\mathrm{SiF}_4\): Si shares electrons with F, Si is a metalloid.- \(\mathrm{PF}_5\): P and F are non-metals.- \(\mathrm{SF}_6\): S and F are non-metals.- \(\mathrm{ClF}_3\): Cl and F are non-metals.

Classify as Ionic or Covalent

Using the definitions and the elements involved:- \(\mathrm{NaF}\) is ionic (metal + non-metal).- \(\mathrm{MgF}_2\) is ionic (metal + non-metal).- \(\mathrm{AlF}_3\) is ionic (metal + non-metal).- \(\mathrm{SiF}_4\) is covalent (metalloid forming molecules with non-metals).- \(\mathrm{PF}_5\) is covalent (non-metals).- \(\mathrm{SF}_6\) is covalent (non-metals).- \(\mathrm{ClF}_3\) is covalent (non-metals).

Key concepts

Understanding Ionic Compounds

Ionic compounds are fascinating structures formed from metals and non-metals. These compounds result from a fascinating process called electron transfer. In ionic compounds, atoms transfer electrons to achieve stability, forming charged particles called ions. This electron transfer creates a strong electrostatic attraction between positively charged ions and negatively charged ions.
This bond forms a solid, crystalline structure at room temperature.

• Example: Sodium fluoride (\(\text{NaF} \)) is an ionic compound. Sodium (Na) transfers one electron to fluorine (F), resulting in a positively charged sodium ion and a negatively charged fluoride ion.

By giving up electrons, metals like sodium, magnesium, and aluminum form compounds like \(\text{NaF}, \text{MgF}_2,\) and \(\text{AlF}_3\). These are stable, solid materials due to the strong attraction between oppositely charged ions.

Exploring Covalent Compounds

Covalent compounds form when non-metal atoms come together and share electrons instead of transferring them. This sharing allows each atom involved to achieve a full outer electron shell, which provides stability.
These compounds often exist as gases or liquids at room temperature and have distinct molecular shapes. Covalent bonding is particularly important in organic chemistry where complex molecules are formed.

• Example: Phosphorus pentafluoride (\(\text{PF}_5 \)) is a covalent compound, where phosphorus and fluorine atoms share electrons to form stable, neutral molecules.

Compounds such as \(\text{SiF}_4, \text{PF}_5, \text{SF}_6,\) and \(\text{ClF}_3\) consist of non-metal to non-metal bonding typified by electron sharing.

Delving into Electron Sharing

Electron sharing is the hallmark of covalent bonds found in covalent compounds. This process involves two non-metal atoms coming close enough to share pairs of electrons, ensuring that each atom achieves a filled outer electron shell required for stability.
This shared electron pair creates a bond that holds the atoms together, resulting in discrete molecules with specific properties and structures.
The phenomena of electron sharing can lead to single, double, or even triple bonds depending on how many pairs of electrons are shared between the atoms.

• Single bonds involve one shared pair, such as in hydrogen gas (\(\text{H}_2 \)).
• Double bonds, like in oxygen gas (\(\text{O}_2 \)), involve two shared pairs.
• Triple bonds involve three pairs, like in nitrogen gas (\(\text{N}_2 \)).

Overall, electron sharing allows for a wide variety of molecular geometries and bonding strengths.

The Process of Electron Transfer

Electron transfer is central to the formation of ionic compounds. When an atom gives up one or more electrons, it becomes a positively charged ion, known as a cation. Conversely, atoms that accept electrons become negatively charged ions, known as anions.
The transfer of electrons enables atoms to reach a stable electronic configuration, often resembling the nearest noble gas.

• Example: In magnesium fluoride (\(\text{MgF}_2 \)), magnesium (Mg) transfers two electrons, forming a \(\text{Mg}^{2+} \) ion, while each fluoride ion (\(\text{F}^{-} \)) gains one electron.

The robust electrostatic forces between these oppositely charged ions create a solid lattice that makes ionic compounds like \(\text{NaF} \) and \(\text{AlF}_3 \) durable and with high melting points, characteristic of their solid crystalline nature.