Solids Liquids and Gases

Solids, Liquids, and Gases on the Periodic Table

Before diving into the periodic table, you need to remember that matter is anything that has mass and occupies space. The functional unit of matter is an atom, at least for chemistry. The simplest type of matter in chemistry is called an element, and an element is composed of only one type of atom!

Now, let's look at the periodic table, showing the state of the elements in nature. At room temperature (25 °C) and under standard pressure (1 atm) conditions, most elements are found in nature in the solid state. Some nonmetals such as nitrogen, oxygen, fluorine, chlorine, and hydrogen are found as gases, whereas bromine and mercury are found in the liquid state.

Now, let's dive into what solids, liquids, and gases are.

Facts about Solids, Liquids, and Gases

Elements can exist in three states of matter: solids, liquids, and gases. Molecules in these states of matter differ in their physical properties.

The state of matter of an element and the energy required to change from one state of matter to another is directly related to the strength of its intermolecular forces.

Intermolecular forces are responsible for influencing the physical properties of a chemical compound. Some of the physical properties that can be affected by these forces are states of matter, mass, density, volume, hardness, boiling point (BP), and melting point (MP).

Let's start by looking at solids.

Solids

Solids have a fixed shape and volume. They are not compressible because their particles are tightly arranged together. They also have a fixed position, and can only vibrate in place. Solids usually have strong intermolecular forces, and they can be classified as either Crystalline or Amorphous solids.

There are 4 different types of crystalline solids:

• Ionic solids
• Molecular solids
• Covalent network solids
• Metallic solids

Ionic Solids

Ionic solids have ionic bonds as their attractive forces. Their smallest units are ions. Solids in this category are brittle, hard, and have high melting and boiling points. Ionic solids can only conduct electricity in a water solution or molten state.

Molecular Solids

Molecular solids have intermolecular forces between the individual molecules keeping everything together. The attractive forces holding the molecules together depend on their polarity.

• Polar molecular solids have dipole-dipole and London dispersion forces present.
• Nonpolar molecular solids only possess London dispersion forces.

Solids in this group have soft textures because the intermolecular forces holding the molecules together are weak compared to the chemical bonds found in other types of solids. Their melting point (MP) varies but generally is low. Nonpolar molecular solids generally have low melting points, while polar molecular solids tend to have slightly higher melting points.

Covalent Network Solids

Covalent network solids have covalent bonds holding atoms together. These solids have hard textures due to their strong covalent bonds. Covalent network solids also have very high melting points. Usually, solids in this category are insoluble in water. They also tend to be poor conductors of heat and electricity, although there are some exceptions.

Metallic Solid

Metallic solids have metallic bonds. As the name suggests, the smallest unit in metallic solids are metal atoms. Metallic solids are shiny, possess variable hardness, and have high melting points They are also good at conducting heat and electricity, are malleable, and ductile. Metallic solids are not soluble in water.

Amorphous Solids

In amorphous solids, the smallest unit can be an ion, atoms, molecules, or even polymers. The electrostatic forces present in amorphous solids can vary.

Amorphous solids have no distinct melting points, so parts of an amorphous solid melt at different temperatures. Since its particles can randomly arrange, amorphous solids lack an organized structure/pattern such as the ones we see in crystalline solids. Examples of amorphous solids include glass, obsidian (volcanic glass), and even rubber bands.

Liquids

Liquids assume the shape of the container, but not the volume. Although liquid particles can move around the container, they are still very close to one another, and there is not much space available. So, liquids are slightly compressible. Liquids also have intermolecular forces, but they are usually slightly weaker than solids.

Liquids can have different viscosity, and the greater the viscosity, the slower the liquid will flow. For example, water and honey are liquids, but water flows faster than honey because honey has a greater viscosity.

Another property that affects liquids is surface tension. In liquids, the intermolecular forces pull the molecules into the liquid,

Gases

Gases assume the shape and volume of the container. Since gas particles are spread out in the container, they are highly compressible when pressure is applied. In this state of matter, gases vibrate and can move freely in random directions.

Some factors affecting gases include temperature, pressure, and volume.

• When the temperature rises, particles move faster.
• When pressure increases, volume decreases since the particles are now closer together.
• When volume increases, pressure decreases.

Kinetic Energy in Solids, Liquids, and Gases

Anything that moves has kinetic energy. For example, water falling down a waterfall contains kinetic energy, and so does a bird flying! And, why does atoms and molecules have kinetic energy? Because they are always moving!

The kinetic energy of gases can be calculated using the following equation:

$KineticEnergy(K.E)=\frac{1}{2}\times mass\times {\left(velocity\right)}^2$

Let's look at a simple example!

When a particle has high kinetic energy, it will be able to move around faster.

• Solids have very low kinetic energies because their particles are tightly packed and do not vibrate as much.
• Liquids have intermediate kinetic energies because they can move between each other in the little empty space.
• Gases tend to have high kinetic energies because they can freely move around in the empty space.

Activities of Solids, Liquids, and Gases

Another term that you need to be familiar with is the activity (α) of a species, chemists use the term activity to describe the deviation of ideal gases and solutions from ideal behavior.

When dealing with gases, they depend on pressure. So, the activity of gas is considered to be the ratio of the actual partial pressure of the gas to its ideal partial pressure.

${\alpha }_{gas}=\frac{P_{\mathit{g}\mathit{a}\mathit{s}}}{P_{\mathit{g}\mathit{a}\mathit{s}\mathit{,}\mathit{}\mathit{i}\mathit{d}\mathit{e}\mathit{a}\mathit{l}}}$

This can sound confusing, so let's look at an example. Let's say that you were asked to calculate the pressure for one mole of ethane at 295.15 K behaving as an ideal gas (using the ideal gas law equation) and as a non-ideal gas (using the real gas equation). You found that the pressure for ethane as ideal gas was 24.47 atm, whereas the pressure for ethane as a real gas was 20.67 atm. The activity of ethane would be:

${\alpha }_{gas}=\frac{20.67}{24.47}=0.8447$

Now, when it comes to solids and liquids, we deal with concentrations. Therefore, activity is used to tell chemists the difference between how many particles appear to be present in the solution, and the number of particles actually present in the solution. The activity of solutions can be estimated using concentration. In general, for relatively dilute solutions, the activity of a substance and its molar concentration is roughly equal.

The activity of pure solids and liquids is always equal to 1 because, per unit volume, the concentration of a pure solid or liquid is always the same. For example, the activity of liquid water is 1, and the activity of 5 grams of aluminum metal is also 1.

Comparing Solids, Liquids, and Gases

To make this simple and easier, let's make a table comparing the three states of matter using the information discussed in this article.