Chemical bonds are forces that hold atoms together to form molecules. There are three types of bonds between atoms: metallic, ionic, and covalent. Thanks to these bonds, all the compounds that exist in nature are formed.
In addition, there are forces that hold molecules together, which are known as intermolecular bonds, such as: dipole-dipole forces and hydrogen bonds.
Next, we explain each of these links.
Types of chemical bond Characteristic Examples
Metal
Metal ions float in a sea of moving electrons. Metallic elements: sodium, barium, silver, iron, copper.
Ionic
Transfer of electrons from one atom to another. Sodium chloride Na+Cl-
Covalent
Nonpolar Share electrons equally between two atoms. Molecular hydrogen HH or H2 Polar Shares electrons unequally between two atoms. Water molecule H2O Simple Shares one pair of electrons. Chlorine molecule Cl2 Cl-Cl Double Shares two pairs of electrons. Oxygen molecule O2 O=O Triple Share three pairs of electrons. Nitrogen molecule N≣N or N2 Dative Only one of the atoms shares the electrons. Bond between nitrogen and boron in the ammonia-boron trifluoride compound.
intermolecular forces
Hydrogen bonding The hydrogens of one molecule are attracted to the electronegative atoms of another molecule. Hydrogen bonds between the hydrogen of one water molecule with the oxygen of another water molecule. Dipole-dipole Molecules with two electric poles attract opposite poles of other molecules. Interactions between methanal H2C=O molecules
The metallic bond is the force of attraction between the positive ions of metallic elements and the negative electrons that are free to move between the ions. Metal atoms are tightly packed, this allows electrons to move within the lattice of atoms.
In metals, valence electrons are released from their parent atom and form a “sea” of electrons that floats around the entire metal structure. This causes the metal atoms to transform into positively charged metal ions that pack together.
The metallic bond is established between metallic elements such as sodium Na, barium Ba, calcium Ca, magnesium Mg, gold Au, silver Ag and aluminum Al.
When the electrons in a metal “delocalize,” the metal’s nucleus becomes positive, and the metal is held together by negative electrons moving through the structure.
ionic bond
The ionic bond is the force that unites a metallic element, such as sodium or magnesium, with a non-metallic element, such as chlorine or sulfur. The metal loses electrons and becomes a positive metal ion called cation. These electrons pass to the non-metallic element and it becomes a negatively charged ion called anion.
The cations and anions combine to form a three-dimensional lattice that is held together by the forces of electrostatic attraction between the differently charged ions. These forces form ionic compounds.
The earth’s crust is made up mainly of ionic compounds. Most rocks, minerals, and gemstones are ionic compounds. For example:
Sodium Chloride NaCl: the metallic element is sodium that transfers an electron to chlorine, which is the non-metallic element.
Magnesium Chloride MgCl2: magnesium Mg donates two electrons to two chlorine atoms, as shown in the figure below:
Magnesium has two electrons in its outer shell that it can transfer to two chlorine atoms to form magnesium chloride MgCl2.
See also Difference Between Cations and Anions.
Covalent bond
Covalent bond is formed when two non-metal atoms share electrons. This bond can be of several types depending on the affinity for the electrons of the atoms and the number of shared electrons.
nonpolar covalent bond
The nonpolar covalent bond is the bond that forms between two atoms where the electrons are shared equally. This bond normally occurs in symmetrical molecules, that is, molecules made up of two identical atoms, such as the hydrogen molecule H2 and the oxygen molecule O2.
Two hydrogen atoms share their electrons in a nonpolar covalent bond.
polar covalent bond
The polar covalent bond is formed when two atoms share electrons but one of them has a greater attraction for the electrons. This causes the molecule to have a more negative “pole” with a greater number of electrons and the opposite pole is more positive.
Molecules with this distribution or imbalance of electrons are known as polar. For example, in hydrogen fluoride HF, there is a covalent bond between hydrogen and fluorine, but fluorine has higher electronegativity, so it attracts shared electrons more strongly.
The fluorine atom more strongly attracts the electrons it shares with hydrogen, giving the bond a polar character.
single covalent bond
When two atoms share two electrons, one coming from each other, the covalent bond formed is called a single covalent bond.
For example, chlorine is an atom that has seven valence electrons in its outer shell, which can be filled with eight electrons. One chlorine can combine with another chlorine to form the chlorine molecule Cl2 which is much more stable than the separate chlorines.
A pair of electrons is shared between two chlorine atoms, forming a single bond.
double covalent bond
The double covalent bond is the bond where four electrons (two pairs) of electrons are shared between two atoms. For example, oxygen has 6 electrons in its last shell. When two oxygens combine, four electrons are shared between the two, causing each to have 8 electrons in the last shell.
When two oxygen atoms bond together, they share four electrons between them, forming a double bond.
triple covalent bond
The triple covalent bond is formed when two atoms share 6 electrons (or three pairs). For example, in the hydrogen cyanide molecule HCN, a triple bond is formed between carbon and nitrogen, as shown in the figure below:
In the hydrogen cyanide molecule, carbon and nitrogen share six electrons, forming a triple bond.
coordinate or dative covalent bond
The coordinate or dative covalent bond is the bond that is formed when only one of the atoms in the bond contributes a pair of electrons. For example, when ammonia NH3 reacts with boron trifluoride BF3, nitrogen bonds with two electrons directly to boron, which has no electrons available to share. In this way, both nitrogen and boron are left with 8 electrons in their valence shell.
Nitrogen shares its two available electrons with the boron atom which has no electrons to share in the NH3BF3 molecule.
See also Organic and inorganic compounds.
Dipole-dipole bonds or forces
Weak intermolecular bonds can be established between polar molecules when the negative poles are attracted to the positive poles and vice versa. For example, methane H2C =O is a polar molecule, with a partial negative charge on oxygen and a partial positive charge on hydrogens. The positive side of one methane molecule attracts the negative side of another methane molecule.
The methane molecule has two poles: positive and negative. The positive pole of one methane molecule is attracted to the negative pole of another methane molecule.
hydrogen bonds or bonds
The hydrogen bridge or hydrogen bond is a bond that is established between molecules. It occurs when a hydrogen in the molecule is covalently bonded to oxygen, nitrogen, or fluorine. Oxygen, nitrogen and fluorine are atoms with greater electronegativity, therefore they attract electrons more strongly when they share them with another less electronegative atom.
There are hydrogen bonds between the water molecules H2O and ammonia NH3 as shown in the figure:
Hydrogen bonds in ammonia form between the partially positively charged hydrogen of one molecule and the partially negatively charged nitrogen of another molecule.
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References
Zumdahl, SS, Zumdahl, SA (2014) Chemistry. Ninth Edition. Brooks/Cole. Belmont.
Commons, C., Commons, P. (2016) Heinemann Chemistry 1. 5th edition. Pearson Australia. Melbourne.