Nuclear

• Helium's nucleus has two neutrons and two protons. Though protons have positive charges, and the protons naturally repel each other, the four particles are nonetheless stuck together by what physicists call the strong force. Of the four fundamental forces recognized by physics, strong, weak, electromagnetic and gravity, the strong force has the most power, but acts only over distances of about 10^-15 meters, or the size of an average nucleus. This force holds the nuclei of all atoms together, except hydrogen, as it has only a single proton.
  
  

London Dispersion

• A weakly attractive force, called the London dispersion force, allows helium to become a liquid at minus 452 F. When its two orbiting electrons are momentarily on the same side of the atom, this produces a short-lived electrical polarity, having the positive protons on one side and the negative electrons on the other. Without this small force, helium would remain a gas at all temperatures.
  
  

Electric

• Under normal conditions, helium is electrically neutral, with the charges of its two protons and two electrons balancing each other out. However, outside forces can remove one or both of its electrons and make helium positively charged. In this state, it repels other positive particles, attracts any nearby free electrons and becomes neutral again.
  
  

Pressure

• Helium exerts pressure against containers as does any other gas. For the same volume and increasing temperature, pressure increases. For the same temperature and shrinking volume, pressure also increases. The Ideal Gas Laws describe and formulate the behavior of helium under most conditions.