Open the PhET States of Matter Simulation (http://openstaxcollege.org/l/16phetvisual) to answer the following questions:

(a) Select the Solid, Liquid, Gas tab. Explore by selecting different substances, heating and cooling the systems, and changing the state. What similarities do you notice between the four substances for each phase (solid, liquid, gas)? What differences do you notice?

(b) For each substance, select each of the states and record the given temperatures. How do the given temperatures for each state correlate with the strengths of their intermolecular attractions? Explain.

(c) Select the Interaction Potential tab, and use the default neon atoms. Move the Ne atom to the right and observe how the potential energy changes. Select the Total Force button, and move the Ne atom as before. When is the total force on each atom attractive and large enough to matter? Then select the Component Forces button, and move the Ne atom. When do the attractive (van der Waals) and repulsive (electron overlap) forces balance? How does this relate to the potential energy versus the distance between atoms graph? Explain.

A substance is defined as a material with certain features and makeup.

A substance is a pure compound or element. Water is a pure material made up of hydrogen and oxygen. A homogenous substance is free of impurities. Elements and compounds are the two kinds of pure substances.

• In a simulation, we can see four different atoms/molecules in a confined container: neon, argon, oxygen, and water.
• We can also change the temperature of a container's interior.

Let's have a look at how the four chemicals compare and contrast in each phase.

Similarities

• In the solid state, all particles are closely packed, things retain their shape, and particles cannot move freely but can vibrate.
• Particles are loosely packed when substances are in a liquid state, Substances take the shape of a container, and the particles can flow around within their constant volume. When substances are in a gaseous state, particles are so loosely packed that substances have neither a specific shape nor a specific volume, and the particles can freely move around.
• As the temperature rises, so does the movement of particles (and the phase changes from solid to liquid and from liquid to gaseous).
• And as the temperature drops, so does the movement of particles (and the phase changes from gaseous to liquid and from liquid to solid).

Differences

Let's look at how the temperatures of each state correspond to the intensity of their intermolecular interactions.

• A substance's phase is determined by the intermolecular forces and the kinetic energy of its atoms/molecules.
• Intermolecular interactions tend to keep particles close together, but kinetic energy tends to counteract attractive forces (intermolecular forces) and increase the distance between particles, resulting in phase transitions (from solid to liquid and from liquid to gaseous).

The kinetic energy increases in proportion to the temperature rise.

As a result, the higher a substance's melting/boiling point (temperature), the greater the intermolecular forces.

As a result, the higher a substance's melting/boiling point (temperature), the greater the intermolecular forces.

The order of strength of intermolecular forces for four given substances is

\({\rm{ Water }} > {\rm{ Argon }} > {\rm{ Oxygen }} > {\rm{ Neon }}\)

• In a simulation, we have two neon atoms separated by a distance that we may modify and a graph of potential energy vs. distance.
• We can also be the attractive/repulsive force's strength (shown by the size of the arrows).

(1) There are no attractive forces (because there is no interaction between atoms) when two neon atoms are very far apart and the potential energy is zero.

(2) When two atoms are relatively far away (or relatively close), they will attract one another, resulting in negative energy in the system (attractive force \( > \) repulsive force).

(3) Proton-proton and electron-electron repulsion occur when two atoms are sufficiently near that their nuclei meet. Because a system's energy is very high (potential energy is positive), they will resist one another (repulsive force attractive force).

(4) When two atoms are at the correct distance apart, attraction forces equal repulsive forces, and a system's energy is at its lowest, a bond is formed. A molecule's bond length is that distance.