Write the Lewis structure for ethyne, \(\mathrm{C}_{2} \mathrm{H}_{2}\), and tell the bond angles.

Understanding valence electrons is crucial when drawing the Lewis structure of a molecule, such as ethyne (\text{C}_2\text{H}_2). Valence electrons are the electrons in the outermost shell of an atom and are responsible for chemical bonding. For ethyne, each carbon (C) atom brings four valence electrons, while each hydrogen (H) atom brings one.

In total, ethyne has 10 valence electrons, which can be calculated as follows: \( 4 \times 2 + 1 \times 2 = 10 \). These electrons are used to form bonds between atoms and to fulfill the octet rule, which leads to a stable molecular structure.

The octet rule is a chemical rule of thumb that reflects the tendency of atoms to prefer having eight electrons in their valence shell. Fulfilling the octet rule gives an atom the same electron configuration as a noble gas, contributing to its stability. In the case of ethyne, this rule primarily concerns the carbon atoms, as hydrogen is content with two electrons.

When drafting the Lewis structure, we arrange the electrons to ensure that each carbon atom ends up with an octet. This is achieved by forming a triple bond between the two carbon atoms, which shares six electrons, and adding a single bond to each hydrogen. As a result, each carbon atom uses its four original valence electrons to form stable bonds, adhering to the octet rule.

The molecular geometry of a compound like ethyne is determined by the arrangement of its atoms in space. Ethyne has a linear molecular geometry due to its triple bond between the carbon atoms. This bond consists of one sigma bond and two pi bonds, which restrict the rotation and maintain a linear conformation.

The linear shape results in bond angles of 180 degrees, which means the atoms involved are as far apart as possible, minimizing electron repulsion. It is important to note that linear geometry is a consequence of the sp hybridization of the carbon atoms in ethyne. This structural feature is essential for predicting the physical and chemical properties of the compound.