Alkanes are gases up to how many carbon atoms?

Alkanes are the simplest saturated hydrocarbons, consisting of carbon and hydrogen atoms connected by single covalent bonds. Their general formula is CₙH₂ₙ₊₂. The physical state of alkanes—whether they are gases, liquids, or solids—depends on the number of carbon atoms present in their molecules.

Alkanes containing one to four carbon atoms (C₁–C₄) are gases at room temperature and atmospheric pressure. These include methane (CH₄), ethane (C₂H₆), propane (C₃H₈), and butane (C₄H₁₀). These gaseous alkanes are colorless, odorless, and combustible, making them commonly used as domestic fuels and liquefied petroleum gases (LPG).

As the number of carbon atoms increases, the molecular weight and van der Waals forces between molecules also increase. This leads to higher boiling and melting points. Therefore, alkanes from pentane (C₅H₁₂) to about hexadecane (C₁₆H₃₄) exist as liquids, while those containing more than sixteen carbon atoms are solids at room temperature, such as paraffin wax.

The gaseous state of lower alkanes is due to their small molecular size and weak intermolecular attractions, allowing them to move freely as gases. This trend demonstrates how molecular size directly influences physical properties within the homologous series.

Understanding this property is important in organic chemistry and fuel technology, as it explains why methane and propane are used for heating and cooking, while higher alkanes serve as components of gasoline, diesel, and lubricating oils.

Hence, alkanes remain gaseous up to four carbon atoms, after which they exist as liquids or solids depending on molecular size.