A few facts about elements

An element can be defined as a substance that cannot be broken down into a simpler one by means of a chemical reaction.  Elements (e.g. carbon and oxygen) can often be combined (either by natural means or in a laboratory) to form other substances known as compounds (e.g. carbon dioxide).

The factor that distinguishes one element from another is the number of protons in its nucleus. The most basic element is hydrogen, which has only one proton, hence its “atomic number” is 1.

To date, 118 different elements have been identified, but many of the heavier elements do not occur naturally and have only been created in laboratories. 

Very heavy elements are unstable and readily break apart, releasing particles and/or energy as they do so – these are termed “radioactive”, such as uranium with an atomic number of 92 and plutonium (atomic number 94). 

The term “half-life” has been coined to define the stability of an element, the factor in question being how long it takes for half of a given quantity of the element to decay as the nucleus breaks up and the substance changes into something that is more stable. Some radioactive elements have half-lives of millions of years, whereas some manufactured elements exist for only fractions of a second.

Various elements share certain features in common and so can be grouped together. The standard method of organizing the elements so that these shared features can be tabulated and easily recognised is the Periodic Table (see illustration).

© John Welford

A few facts about electrons

The basic particles of atoms are protons, neutrons and electrons. However, to call an electron a particle is perhaps a bit misleading, given that it can better be described as a packet of energy that whizzes round the nucleus of an atom and more resembles a cloud than an orbiting particle. 

The electron is tiny in comparison to the nucleus of protons and neutrons. The mass of a proton is about 1800 times greater than that of an electron, but the two carry equivalent opposing electric charges, that of the proton being positive and the electron negative. 

There will generally be as many electrons in an atom as there are protons. In a hydrogen atom, which has a single proton, there will be a single electron. However, a carbon atom has six protons and therefore six electrons. 

Multiple electrons are arranged in “shells” at increasing distances from the nucleus, such that the innermost shell can hold a maximum of two electrons, shell 2 can contain up to eight electrons, shell 3 can have up to eighteen electrons, etc. 

An atom of sodium contains 11 protons in its nucleus and therefore has 11 electrons. These are arranged in three shells – two in the first shell, eight in the second, and the final electron being on its own in the third shell. 

Electrons can be gained and lost between atoms. When this happens, the overall electric charge of the atoms will change, thus allowing chemical bonds to be made. Electric currents are created when electrons move between atoms of elements such as copper, which are classed as good conductors of electricity.

© John Welford