Writing Chemical Formulae

 

Writing Chemical Formulae

Compounds

• When two or more elements chemically combine in a fixed ratio by mass, the obtained product is known as a compound.
• Compounds are substances consisting of two or more different types of elements in a fixed ratio of its atoms.

Ions

• An ion is defined as an atom or molecule which has gained or lost one or more of its valence electrons, giving it a net positive or negative charge.
• A negatively charged particle is called an anion, and a positively charged particle is called a cation.

Ionic Compounds: Chemical Formula

Each constituent element in a chemical formula is identified by its chemical symbol, along with the relative number of atoms that make up each element. These ratios are used in empirical equations to start with a key element and then assign atom counts for the remaining elements in the compound in relation to the key element.

• Ionic compounds are chemical compounds in which ions are held together by specialised bonds called ionic bonds.
• An Ionic compound always contains an equal amount of positive and negative charge.
• For example: In calcium chloride, the ionic bond is formed by oppositely charged calcium and chloride ions.
  The calcium atom loses 2 electrons and attains the electronic configuration of the nearest noble gas (Ar). By doing so, it gains a net charge of +2.
  The two chlorine atoms take one electron each, thus gaining a charge of -1 (each) and attain the electronic configuration of the nearest noble gas (Ar).