Chemical Bonds and Substance Classification

Chemical Bonds and Substance Types

The enormous variety of substances is possible thanks to the fact that the atoms of most elements have a great ability to join other atoms, either among different elements or atoms of the same element. These forces are known as chemical bonds. The result of chemical bonding ranges from a discrete group of atoms, called a molecule, to a structure of millions of atoms ordered regularly in space, forming a lattice or crystal.

Classifying Chemical Substances

Elements and Compounds

If atoms of the same element join, they form an elemental substance, whereas if they are different elements, they form a chemical compound.

Molecular Substances

Substances which are formed by molecules are called molecular substances. The union of atoms to form molecules always involves covalent bonds, given the name of covalent bond. Molecular substances are characterized by their relative molecular mass, Mr, which we can calculate by adding the relative atomic masses of the elements that form them. This is written as the atomic mass, without units.

Atomic Substances

Sometimes, atoms form crystal networks instead, leading to atomic substances. The properties of atomic substances derive from the nature of this crystal network, called an atomic crystal, formed by an infinite number of atoms linked by strong covalent bonds.

Metallic Substances

Metallic Substances include only atoms of metallic elements. In these substances, most external electrons are weakly held by the nucleus and form an electron cloud around the atoms, which can move freely among them.

Understanding Chemical Bonds

Covalent Bonds

The union of atoms by sharing electrons is given the name of covalent bond.

Ionic Bonds

An ion with a positive charge or cation occurs when an atom loses electrons. An ion with a negative electric charge or anion occurs when an atom gains electrons. Ionic bond: oppositely charged ions attract and remain united.

Metallic Bonds

Metallic bond: occurs between metallic elements and is characterized by positive ions immersed in a structure arranged within an electron cloud with weak holding forces.

Representing Chemical Substances

Molecular Formulas

A chemical substance formed by molecules is represented by a molecular formula. The molecular formula indicates the exact number of atoms of each element that exists in the molecule.

Empirical Formulas

A chemical substance formed by a crystal network is represented by an empirical formula. The empirical formula indicates only the relative ratio between the atoms of each element in the crystal network.

Crystal Structures

Lattices and Crystals

The result of chemical bonding can be a structure of millions of atoms ordered regularly in space, forming a lattice or crystal.

Atomic Crystals

Atomic substances form an atomic crystal, formed by an infinite number of atoms linked by strong covalent bonds.

Metallic Crystals

The arrays of atoms in metallic substances bind together to form a compact crystal network within the electron cloud, called a metallic crystal. This electron cloud, common in all metals, is mainly responsible for the properties and similar appearance of all metals.