Elements at Room Temperature

Introduction

Look around you and almost every element you can name is a solid: the iron in a railing, the copper in a cable, the carbon in pencil lead. Yet the air you breathe is mostly two gaseous elements, and a thermometer may still contain a shiny liquid element. Of all the known elements, only a handful are gases or liquids at room temperature. This page shows which ones they are and how to predict the state of any element from its melting and boiling points.

Core explanation

Room temperature. Chemists usually take room temperature to be about 20–25 °C. The state of an element at this temperature depends on where room temperature falls compared with its melting and boiling points.

Gaseous elements. Eleven elements are gases at room temperature:

- hydrogen, nitrogen, oxygen, fluorine and chlorine; - the six noble gases: helium, neon, argon, krypton, xenon and radon.

All of them are non-metals, and all have boiling points far below room temperature. Oxygen boils at −183 °C and nitrogen at −196 °C, which is why they are gases in the air.

Liquid elements. Only two elements are liquids at room temperature:

- bromine , a dense, red-brown non-metal that gives off an orange vapour; - mercury , a silvery metal, which melts at −39 °C and boils at 357 °C.

Two other metals come very close. Caesium melts at about 28 °C and gallium at about 30 °C, so a lump of gallium held in a warm hand slowly melts.

Solid elements. Every other element is a solid at room temperature. This includes almost all metals and non-metals such as carbon, sulfur, phosphorus and iodine. Their melting points vary enormously: sulfur melts at about 115 °C, iron at about 1538 °C and tungsten at about 3422 °C, the highest of any metal.

Predicting the state. Use this rule for any temperature:

- below the melting point, the element is a solid ; - between the melting and boiling points, it is a liquid ; - above the boiling point, it is a gas .

Step-by-step reasoning

To find the state of an element at 25 °C:

1. Find its melting point and boiling point in a data table. 2. Compare 25 °C with the melting point. If 25 °C is lower, the element is solid. 3. If 25 °C is higher than the melting point, compare it with the boiling point. 4. If 25 °C is lower than the boiling point, the element is liquid; if higher, it is a gas.

Visual explanation

Imagine a number line of temperatures with a marker at 25 °C. Each element is a bar running from its melting point to its boiling point. If the whole bar lies to the right of the marker, the element is solid. If the marker falls inside the bar, it is liquid. If the whole bar lies to the left, it is a gas.

Real-world analogy

Think of a room temperature "gate" at 25 °C. Elements with melting points above the gate are still locked in solid form. Elements whose boiling points are below the gate have already escaped as gases. Only elements whose liquid range straddles the gate, like mercury and bromine, are caught in the middle as liquids.

Real-world example

Liquid nitrogen, used to freeze warts and to store biological samples, has to be kept in insulated flasks at −196 °C. As soon as it warms up, it boils away, because room temperature is far above its boiling point. Gallium, by contrast, is sold as a novelty metal that melts in your palm because its melting point is just above room temperature.

Why?

Why are most elements solids? In most elements, the particles are held together by strong forces, such as metallic bonding or giant networks of covalent bonds, and a lot of energy is needed to break them apart. The gaseous elements consist of single atoms or small molecules with only very weak forces between them, so little energy is needed to separate the particles.

Common misconception

"Bromine and mercury are liquids, so they must both be metals." Only mercury is a metal. Bromine is a non-metal from the same family as chlorine and iodine. The state of an element does not tell you whether it is a metal or a non-metal.

Worked example

Question: Chlorine melts at −102 °C and boils at −34 °C. Iodine melts at 114 °C and boils at 184 °C. State the physical state of each at 25 °C.

Reasoning: For chlorine, 25 °C is above the boiling point of −34 °C, so it is a gas. For iodine, 25 °C is below the melting point of 114 °C, so it is a solid.

Answer: Chlorine is a gas; iodine is a solid.

Quick check

1. Name the two elements that are liquids at room temperature. Answer: Bromine and mercury.

Exam focus

You may be given a table of melting and boiling points and asked for the state at a stated temperature. Watch the negative signs carefully: −34 °C is lower than −7 °C. Always compare the given temperature with both the melting point and the boiling point before answering.

Advanced insight

Within a family of elements, states often change in a clear pattern. In Group 7, fluorine and chlorine are gases, bromine is a liquid and iodine is a solid. The molecules get larger down the group, so the weak forces between them become stronger and the melting and boiling points rise. Carbon, meanwhile, does not melt at ordinary pressure at all: it turns straight into a gas at about 3600 °C.

Summary

At room temperature (about 20–25 °C), eleven elements are gases — hydrogen, nitrogen, oxygen, fluorine, chlorine and the six noble gases — and only two, bromine and mercury, are liquids. All the rest are solids. The state of any element at a given temperature is found by comparing that temperature with its melting and boiling points.

Practice questions

1. Why is oxygen a gas at room temperature? Answer: Its boiling point (−183 °C) is far below room temperature. 2. Gallium melts at about 30 °C and boils at about 2400 °C. What is its state at 20 °C and at 40 °C? Answer: Solid at 20 °C; liquid at 40 °C. 3. Name three gaseous elements that are not noble gases. Answer: Any three of hydrogen, nitrogen, oxygen, fluorine and chlorine. 4. Element Y melts at −7 °C and boils at 59 °C. What is its state at 25 °C, and which element is it likely to be? Answer: Liquid, because 25 °C lies between −7 °C and 59 °C; it is bromine.