Write the empirical (or molecular) formulas of compounds that the elements in the third period (sodium to chlorine) should form with (a) molecular oxygen and (b) molecular chlorine. In each case indicate whether you would expect the compound to be ionic or molecular in character.

The empirical formula represents the simplest whole-number ratio of the elements within a compound. It is a foundational concept in chemistry that provides a basic understanding of the composition of ionic and molecular compounds.

For example, the empirical formula for water, H₂O, indicates that for every oxygen atom in water, there are two hydrogen atoms. This contrasts with the molecular formula, which might show multiple units of the empirical formula. For instance, the molecular formula of glucose is C₆H₁₂O₆, but its empirical formula, which represents the simplest ratio, is CH₂O. Understanding empirical formulas is crucial when predicting and writing formulas for compounds formed by elements, as we often look at in exercises involving periodic table elements like sodium (Na) or chlorine (Cl).

When working with exercises that involve formulating compounds, it's essential to deduce the empirical formula first. For instance, Sodium Oxide has a simple empirical formula of Na₂O, which indicates that the compound consists of two atoms of sodium for every one atom of oxygen.

Chemical bonding is the force that holds atoms together in compounds, and this can manifest in two primary forms: ionic and molecular (covalent) bonds.

Ionic compounds are formed between metals and non-metals, where there is a transfer of electrons from the metal to the non-metal, creating ions. Metals lose electrons and become positively charged cations, while non-metals gain electrons and become negatively charged anions. These oppositely charged ions attract each other, forming the ionic bond. Ionic compounds like Sodium Chloride (NaCl) and Magnesium Oxide (MgO) are typically solid at room temperature, have high melting and boiling points, and can conduct electricity when melted or dissolved in water.

Molecular compounds, on the other hand, are formed between non-metals and involve the sharing of electrons, resulting in covalent bonds. Covalent bonds are directional and form when two atoms share electrons to attain a full valence shell, achieving greater stability. Compounds such as Silicon Dioxide (SiO₂) and Sulfur Dichloride (S₂Cl₂) exhibit molecular bonding. Molecular compounds typically have lower melting and boiling points compared to ionic compounds and do not conduct electricity.

The periodic table is a tabular arrangement of elements, ordered by their atomic number, electron configuration, and recurring chemical properties. Elements are grouped into periods and groups, and the third period specifically contains elements from sodium to argon.

Understanding the periodic table is crucial for predicting and explaining the chemical bonding behavior of elements. Elements in the third period have varying tendencies to lose or gain electrons, which directly affect the types of compounds they can form. For example, sodium, being an alkali metal, readily loses one electron to form ionic compounds such as Na₂O and NaCl. On the other end of the period, chlorine, being a halogen, tends to gain an electron and forms covalent compounds like Cl₂O₇ and S₂Cl₂.

Noble gases, such as argon, have a complete valence shell and are generally inert, not typically forming compounds. This aligns with their position on the periodic table and the trends observed across periods and groups—demonstrating the interconnectedness of periodic table placement and chemical bonding.