Florida Biology EOC Practice Test

What causes surface tension in liquids?

1. Gravitational forces

2. Hydrogen Bonding

3. Symmetry in the attractive forces between the liquid molecules

4. Asymmetry in the attractive forces between the liquid molecules

The correct answer is: Asymmetry in the attractive forces between the liquid molecules

Surface tension in liquids is primarily caused by asymmetric attractive forces between the molecules at the surface compared to those in the bulk of the liquid. Molecules within the liquid experience equal attractive forces from all directions, but those on the surface are subjected to stronger cohesive forces from the liquid below them and a lack of similar forces acting upward from the air above. This asymmetry leads to the formation of a 'film' on the surface, which tends to minimize surface area and results in the characteristic behavior of liquids, such as droplets forming and the ability of some objects to float despite being denser than the liquid. While gravitational forces do play a role in overall liquid behavior, they are not responsible for surface tension. Hydrogen bonding is significant in specific liquids like water, influencing their properties, but it's the imbalance of molecular forces, particularly at the surface, that fundamentally generates surface tension. Symmetry in attractive forces would not lead to the unique surface characteristics observed; it is the lack of symmetry that is key to understanding why surface tension exists.