What is a Chemical Compound?

Kate Onissiphorou

by Kate Onissiphorou

6th April 2022

An image of boiling water. Water is a liquid state at room temperature and boils at 100°C.

A chemical compound is a substance containing two or more different elements that are chemically bonded together.

Chemical bonds are grouped into four main categories: covalent bonds, molecular bonds, ionic bonds, and metallic bonds. Other types of bonds exist, but these are the most common and most stable bonds. They provide sufficient stability for compounds within certain physical limits.

Alloys, solutions, suspensions, colloids, and other types of mixtures are not classed as compounds – but they could be a combination of compounds.

Compound stability 

A compound’s stability is mainly determined by its bonds, which, put simply, is the way valence electrons are distributed among the elements. Illustration of the four types of chemical bonds - covalent, ionic, molecular, and metallic bonding.

Many bio-organic compounds have relatively low decomposition temperatures. Most proteins start to become denatured at 41°C. Carbon monoxide has the highest known decomposition temperature at ≈3870 °C.

External factors can also affect a compound’s stability. Chemical bonds can be broken in several ways, such as by a change in pressure or temperature. For example, if you open a soda can, you will observe bubbles forming, which may sometimes become frothy. This is actually a result of chemical bonds breaking due to a change in pressure.

As you open the soda can, you release the pressure inside. This causes the chemical bonds of carbonic acid to break, decomposing the compound into smaller compounds of carbon dioxide and water. See the illustration below.

An illustration of carbonic acid

As you can see, the reaction is in dynamic equilibrium or, in other words, it’s reversible. However, this is only true if the pressure is maintained. 

Other chemical bonds can be broken by radiation, such as in the case of skin cancers. In this example, exposure to UV rays damages the chemical bonds in DNA molecules, which can potentially cause skin cancer. Melanoma - a malignant tumor of the skinComplex and large bio-organic compounds are particularly sensitive to radiation. This is the main reason why most of the complex living organisms, as far as we know, can only survive within a certain narrow range of environmental conditions.

Is Water a Chemical Compound?

Water is a polar compound that’s made up of two hydrogen atoms and one oxygen atom per molecule. It’s in a liquid state at room temperature but freezes at about 0°C and boils at 100°C. An image of boiling water. Water is a liquid state at room temperature and boils at 100°C.Water has a molar mass of 18.01528 g/mol, while pure water at standard conditions has a density of 1000 kg/m3.

Water plays a central role in chemical reactions, especially biochemical reactions. Without water in liquid form, complex organisms such as humans probably wouldn’t exist. 

Where is Energy Stored in Chemical Compounds?

Chemical reactions mainly involve the valence or outermost electrons. These electrons are responsible for the bonding and affinities of various elements and compounds. That means the energy of chemical compounds is contained within the outermost energy levels that correspond to the orbitals of the electrons.

During a chemical reaction, bonds are either broken or created, or sometimes both. As a result, energy – particularly in the form of heat and light – is released or absorbed.

It’s released when an electron from a higher energy level moves to a lower energy level. Conversely, energy is absorbed when an electron jumps from a lower energy level to a higher energy level, such as in the case of photosynthesis 

Are Compounds Chemically Bonded?

The chemical bonds between different elements are the defining characteristic of compounds. 

These bonds can determine a compound’s molecular structure and its chemical and physical properties. For example, the chemical bonds in alkanes or saturated hydrocarbons make them nonpolar and insoluble in water.

How is a Chemical Compound Different from an Element?

Unlike compounds, elements cannot be further chemically broken down to combine with other elements or react with compounds. Compounds, on the other hand, have to break their chemical bonds when reacting with elements or other compounds.

There are 118 chemical elements, 92 of which are naturally occurring. Technetium (Tc) and promethium (Pm) are elements with atomic numbers below 92. They’re byproducts of nuclear reactors and are also radioactive. The Periodic Table

Synthesised elements that have atomic numbers above 92 are all radioactive and unstable. Their nuclei are too large so they decay easily.

Elements are the fundamental chemical units of all compounds. However, not all elements form compounds. Neither are they all chemically reactive. This is particularly true for the noble gases: helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon (Rn). These are inert elements and do not have any naturally occurring compounds.

How do you Form Chemical Compounds?

There are several ways to form chemical compounds, although the most common and simplest way is via the reactions between elements. For example, in chemical manufacturing the combustion of hydrogen produces water.

Another way to form compounds is through the decomposition of larger and more complex compounds into simpler compounds. This typically occurs in chemicals that aren’t very stable or highly reactive. For instance, hydrogen peroxide typically decomposes into water and oxygen when taken out of the container. The balanced chemical equation for this reaction is shown below.

2 H2O2 → 2 H2O + O2

Reactions between two different compounds can also produce new compounds, such as in the neutralisation reaction between acids and bases. See the example below, which is the balanced chemical equation of the reaction between sulphuric acid and potassium hydroxide.

H2SO4 (aq.) + 2 KOH(aq.) → K2SO4 (aq.) + 2 H2O(l)

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