The American Heritage Dictionary of the English Language identifies room temperature as around 20–22 °C (68–72 °F), while the Oxford English Dictionary states that it is “conventionally taken as about 20 °C (68 °F)”.

A period 1 element is an element in the first period (row) of the periodic table. It means that elements in the same group have similar properties. The first period has less elements than any other periods in the periodic table. There are only two elements in the first period: hydrogen and helium.

Some substances exist as gases at room temperature (oxygen and carbon dioxide), while others, like water and mercury metal, exist as liquids. Most metals exist as solids at room temperature. All substances can exist in any of these three states.

The simplest way to determine if something is a liquid is to ask this question: If I try and move it from one container to another (i.e. by pouring), will it conform to or take on the shape of the new container? One property of water is that it conforms to the shape of a container.

Water is, by far, the most common liquid on Earth. The density of a liquid is usually close to that of a solid, and much higher than in a gas. Therefore, liquid and solid are both termed condensed matter. On the other hand, as liquids and gases share the ability to flow, they are both called fluids.

The process of a liquid becoming a gas is called boiling (or vapourization), while the process of a gas becoming a liquid is called condensation.

Freezing, or solidification, is a phase transition in which a liquid turns into a solid when its temperature is lowered to or below its freezing point. All known liquids, except helium, freeze when the temperature is low enough. Crystalline SolidModel of closely packed atoms within a crystalline solid.

Some solids can even become a gas without first becoming a liquid; this is called “sublimation”. For instance, ice in a freezer slowly disappears, since it’s subliming into a gas.

condensation

Solutions having solvent in solid-state and solute in the gaseous state are called gas-solid solution. Hydrogen is a gas at STP and platinum is solid. Hence, Hydrogen gas adsorbed on the surface of platinum is an example of gas in solid solution.

Some examples of solutions are salt water, rubbing alcohol, and sugar dissolved in water. When you look closely, upon mixing salt with water, you can’t see the salt particles anymore, making this a homogeneous mixture. Let’s make use of our salt water example to talk about the two main parts of a solution.

The solutions are of two forms, depending on whether the solvent is water or not.

• Aqueous solution – When a solute is dissolved in water the solution is called an aqueous solution.
• Non-aqueous solution – When a solute is dissolved in a solvent other than water, it is called a non-aqueous solution.