Everything you interact with is made of combinations of the chemical elements. The periodic table is the complete list of every element found in nature, arranged so their mass increases from left to right and from top to bottom. Lighter elements are more widespread than heavier ones, and finding out about them offers an illuminating introduction to the elements and their varying properties. The lightest four elements are hydrogen, helium, lithium and beryllium.
TL;DR (Too Long; Didn't Read)
Hydrogen, helium, lithium and beryllium are the lightest four elements, with one, two, three and four protons, respectively. Hydrogen has no neutrons, helium has two, lithium has four and beryllium has five, and the masses of the elements increase in that order.
Hydrogen and helium are gases, whereas lithium and beryllium are metals.
The Periodic Table and the Masses of Elements
You can easily identify the lightest elements by checking the periodic table (see Resources). The atomic number, the top number on each element’s square, tells you the number of protons in the element; the mass number, the bottom number on each square, tells you the relative atomic mass of the element. Both of these increase together, so an element with an atomic number of 10 (neon) is more massive than an element with an atomic number six (carbon). You can always use the periodic table to find the lightest and heaviest elements.
Hydrogen is the lightest and most common element in the universe, consisting of just a single proton and a single electron, with the chemical symbol H. It is colorless and odorless, and exists as a gas at everyday temperatures. However, most of the hydrogen on the Earth is bound up with oxygen as part of water. Organic chemistry, which is the chemistry of life, based around carbon, depends heavily on hydrogen, although most of the reactions don’t directly involve it. Hydrogen was originally formed in the big bang and is part of the fusion process that powers stars like our Sun.
Helium consists of two protons, two neutrons and two electrons, and has the chemical symbol He. Like hydrogen, it is a colorless and odorless gas. However, it is an unreactive element, and the lightest of the group called the “noble gases.” It therefore doesn’t play a role in biology, and isn’t used in many chemical processes in industry (aside from as an inert substance), although magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) machines use it as a superconducting material. Helium is the second most common element in the universe, and as well as being formed in stars and during the big bang, it’s also created during radioactive decay processes.
Lithium contains three protons, four neutrons and three electrons, with the chemical symbol Li. It is the lightest alkali metal, with a silvery color and a soft but solid consistency. Lithium is a highly reactive element, particularly so with water. It doesn’t have much of a role in biology, though lithium carbonate is a standard treatment for bipolar disorder. It can be toxic except when given in tiny amounts. Lithium does have several uses, though, most importantly as a key part of lithium-ion batteries. Compounds containing lithium, including lithium oxide, lithium chloride, lithium stearate and lithium carbonate are used in a wide range of applications, from the production of glass and ceramic to pharmaceuticals. Lithium is formed in stars and some was also formed in the early stages of the universe, around the time of the big bang.
Beryllium is the fourth-lightest element, with four protons, five neutrons and four electrons, and the chemical symbol Be. It’s a metal, with a silver-white color and a soft consistency. Beryllium and compounds containing it are dangerous to humans, with toxic and carcinogenic effects, but it does have practical uses in industry. Mixing beryllium with copper and nickel creates alloys that are more conductive for heat and electricity, and these alloys are made into electrical contacts, springs, gyroscopes and tools that won’t spark. There are many other uses for beryllium too, including in x-ray lithography and in nuclear reactors. Beryllium is formed in stars, and trace amounts were created in the aftermath of the big bang.