How To Read Chemical Formula

Any time y'all're reading nigh chemistry, you're going to come across chemical formulae and equations. You might well think these from high school chemistry, but if it feels similar a afar memory then this refresher might be useful. This post goes out to the BH Unlimited subscribers attempting the outset instalment of The H2o Course. At that place is a fair fleck of chemical science in in that location so this post will make the perfect primer.

Formulae

Whatever molecule tin can be represented by a formula that lists all the atoms in that molecule. Each element is represented by its atomic symbol in the Periodic Table – e.g. H for hydrogen, Ca for calcium. If more than one atom of a particular element is present, then information technology's indicated by a number in _subscript after the atomic symbol — for instance, H_iiO ways in that location are 2 atoms of hydrogen and 1 of oxygen.

If at that place is more than than 1 of whole groups of atoms, and so that's shown with a bracket effectually them. For case, calcium hydroxide has one calcium (Ca) for every ii hydroxides (OH), so is written as Ca(OH)₂.

If a accuse is present, information technology's indicated in ^superscript, with a sign (+/-) and a number if more than than one charge is nowadays. For example, calcium ions have two positive charges so are written Ca^two+.

Structural Formulae

Sometimes a formula tin can exist written in a style that gives an indication of the structure. For example, acetic acrid contains two carbons, 4 hydrogens, and 2 oxygens, and so could exist given as C₂H_ivO₂ — only is more ordinarily written as CH₃COOH, to emphasise the structure:

Equations

A chemical equation shows a reaction taking place. On the left-hand side are the reactants, the molecules that take part in the reaction. On the right-hand side are the products, the molecules that are created in the reaction. Each side must contain the aforementioned number of each kind of cantlet. An arrow betwixt them indicates the direction the reaction is expected to occur:

Ca + Cl_ii→ CaCl₂

Calcium + chlorine → Calcium chloride

If there are two or more than of any molecules, that'due south indicated with a number in front of the molecule:

CH₄ + 2O_two → CO₂ + 2H₂O

One methane molecule + two oxygen molecules → 1 carbon dioxide molecule and two h2o molecules

Phases

An equation may sometimes specify which stage each molecule is in – whether it's solid, liquid, or gas, or if it's dissolved. This is written in brackets after the molecule – (s) for solid, (l) for liquid, (grand) for gas, and (aq) for 'aqueous', meaning dissolved in water. For case, solid calcium carbonate reacts with carbonic acid in h2o to class calcium bicarbonate, which is much more soluble so becomes dissolved in water:

CaCO₃(s) + H₂CO₃(aq) → Ca(HCO₃)₂(aq)

Solid calcium carbonate + dissolved carbonic acrid → dissolved calcium bicarbonate

Equilibriums

All chemical reactions can really go along in either management. Most of the fourth dimension, ane direction is expected to accept place more strongly, so the arrow is written in that direction. However, many mutual reactions happen in both directions simultaneously, creating an equilibrium where the reactions are taking identify simply in that location is no net change in concentration from one side to the other. This is indicated with the symbol ⇌.

For case, carbonic acid in water is continually breaking down into bicarbonate and hydrogen ions – but the ions are besides continually joining back together.

H_twoCO_three ⇌ HCO_iii ^– + H⁺

^{Carbonic acid} ^⇌ ^{bicarbonate + hydrogen ions}