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What Are the Different Ways Atoms Form Molecules?

On the most basic level, every physical thing in existence is made up of atoms. These atoms then form into molecules, which are groupings of two or more atoms. Generally these molecules are bonded through the sharing of electrons --- negatively charged particles which occupy the space around the atom's nucleus. There are three basic types of chemical bonds that may form between atoms, depending on the atoms which are being bonded.

Valence Electrons
- The three most common types of chemical bonds which are formed between atoms depend on the sharing of electrons. The specific electrons used in bonding are those found in the outermost expanse of an atom, where the pull of the nucleus is weakest. Although in the case of simple atoms like hydrogen, where there is only one electron present, it's these valence electrons that make chemical bonds possible for more complex atoms and molecules, where an abundance of valence electrons help hold a number of atoms together.
Covalent Bonds
- Covalent bonds form when atoms share a pair of electrons. While the electrons are not completely pulled away from the original atom's nucleus toward the other, the sharing forms a balance of attraction and repulsion which bonds the atoms to each other. In its simplest form, a covalent bond uses one electron from each atom in the bond to create a stable balance. Covalent bonding creates a variety of chemical attraction, such as pi bonds and sigma bonds, which are the strongest type of covalent bonds. Covalent bonds exist between atoms of similar electronegativity.
Ionic Bonds
- Ionic bonds occur when an atom gains an electron from another atom. This form of bonding turns each atom into an ion --- an atom with either a negative or positive charge, caused by an imbalance in the number of electrons to protons. The atom which donates the electron becomes a positively charged ion (cation), while the one which receives the electron becomes a negatively charged one (anion). These atoms have a large difference in electronegativity, which attracts the bonds to each other, as each atom seeks a balance.
Metallic Bonds
- The third common type of bonding, metallic bonding, happens most often in metals like copper and iron. Metals of a specific type have a certain arrangement of each atom within the molecules. This arrangement allows the valence electrons to move between the different atoms contained in the metal, pulled between the positive charge of each atom's nucleus. The atoms are then held together tightly by the mass sharing of electrons, leading to the dense and hard structure of metals.

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