Element \(X\) reacts with sodium to form the compound \(\mathrm{Na}_{2} X\) and is in the second period on the periodic table. Identify this element.

Chemical bonding is a fundamental concept in chemistry that explains how atoms combine to form compounds. At the core of bonding is the idea that atoms form bonds in order to achieve a more stable electron configuration, often resembling the nearest noble gas. In the context of the given exercise, the bonding between a metal (sodium, Na) and a non-metal (element X) typically results in the formation of an ionic compound.

Sodium, being a metal, loses electrons to achieve a full outer shell and becomes a positively charged ion or cation (Na+). Conversely, the non-metal X must gain electrons to achieve stability, becoming a negatively charged ion or anion. The charge of the anion is determined by how many electrons are gained. In the sodium compound \( \mathrm{Na}_{2} X \), we have two sodium ions each with a charge of +1, leading to a need for the non-metal X to have a charge of -2 to balance the overall charge and keep the compound neutral.

The periodic table is a powerful tool in chemistry that organizes all known chemical elements in a structured way based on their atomic number and electronic configuration. Elements in the same period, or row, have the same number of electron shells. The exercise specifies that element X is in the second period of the periodic table, which means it must have two electron shells.

With this information, we can conclude that element X is among the few elements located in the second row, such as lithium (Li), beryllium (Be), boron (B), carbon (C), nitrogen (N), oxygen (O), fluorine (F), and neon (Ne). These elements have varying properties and charges when they form ions. However, the identity of X can be narrowed down because we know it forms a 2- ion, connecting this information with the concept of valence electrons.

Valence electrons are the outermost electrons of an atom and are essential in determining an element's chemical properties and reactivity. They are the electrons involved in forming chemical bonds. For instance, in non-metals, atoms typically obtain a full outer shell by gaining electrons, resulting in a negative charge.

Element X must have six valence electrons to gain an additional two from sodium to achieve a stable octet, a principle known as the octet rule. The second period element that fits this description is oxygen (O), which naturally has six valence electrons. By gaining two electrons, oxygen forms an oxide ion (O^2-), satisfying the condition of the compound \( \mathrm{Na}_{2} X \) where X is a 2- anion. Thus, the logical conclusion based on the given information and understanding of valence electrons is that element X is oxygen.