Ethanol, or Ethyl Alcohol (\(\text{C}_2\text{H}_5\text{OH}\)), is a molecule found in alcoholic beverages and industrial fuel. Ethanol is classified as a covalent compound, meaning its atoms are linked by shared electrons rather than transferred ones. Understanding this structure requires examining the basic forces that hold chemical matter together.
Defining Chemical Bonds
Chemical bonds are the attractive forces that hold atoms together to form molecules and compounds. The two primary types of bonds, ionic and covalent, are distinguished by how atoms manage their valence electrons.
Ionic bonding occurs when electrons are essentially transferred from one atom to another, a process that typically happens between a metal and a non-metal. This transfer results in one atom becoming a positively charged ion (cation) and the other becoming a negatively charged ion (anion). These oppositely charged ions are then held together by strong electrostatic forces.
In contrast, covalent bonding involves the sharing of valence electrons between atoms. This type of bond predominantly forms when two non-metal atoms interact. The shared electrons orbit the nuclei of both atoms, effectively linking them together to form a stable molecule.
Analyzing the Atomic Structure of Ethanol
To determine the bonding type in ethanol, we examine its elements: Carbon (C), Hydrogen (H), and Oxygen (O). All three are classified as non-metals. Since a compound formed entirely of non-metals relies on the sharing of electrons, the internal bonds within the \(\text{C}_2\text{H}_5\text{OH}\) molecule are covalent.
The structure of ethanol is a two-carbon chain with a hydroxyl (\(\text{-OH}\)) group attached. This structure contains multiple single covalent bonds, specifically C-C, C-H, C-O, and O-H bonds. The atoms within the molecule arrange themselves in three-dimensional space to maximize the distance between their shared electron pairs.
The Role of Polarity and Hydrogen Bonding
While all internal bonds of ethanol are covalent, many are polar covalent bonds. Polarity arises from the difference in electronegativity, which is an atom’s ability to attract shared electrons toward itself. Oxygen is significantly more electronegative than both Carbon and Hydrogen.
The high electronegativity of oxygen pulls electron density in the C-O and O-H bonds closer to itself. This unequal sharing creates a molecular dipole moment, where the oxygen end develops a partial negative charge and the hydroxyl hydrogen develops a partial positive charge. This charge separation classifies ethanol as a polar molecule.
This polarity is responsible for strong intermolecular attractions known as hydrogen bonds. The partial positive charge on the hydroxyl hydrogen of one molecule is strongly attracted to the partial negative charge on the oxygen of a neighboring molecule. This attraction explains properties like ethanol’s high boiling point.
Hydrogen bonding is also responsible for ethanol’s complete miscibility (ability to mix) with water. Since both ethanol and water are polar, they can form hydrogen bonds with each other. This ability to interact with both polar substances (via the OH group) and non-polar substances (via the \(\text{C}_2\text{H}_5\) chain) makes ethanol a versatile solvent.