The 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 together molecules, which are known as intermolecular bonds, such as dipole-dipole forces and hydrogen bonds.
Here are some of these links.
| Type of chemical bond | Feature | Examples | |
|---|---|---|---|
| Metallic | 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 | No polar | It shares electrons evenly between two atoms. | Molecular hydrogen HH or H2 |
| Polar | It shares electrons unevenly between two atoms. | Water molecule H2O | |
| Simple | It shares a pair of electrons. | Chlorine molecule Cl2 Cl-Cl | |
| Double | It shares two electron pairs. | Oxygen molecule O2 O = O | |
| Triple | It shares three pairs of electrons. | N≣N or N nitrogen molecule2 | |
| Dative | Only one of the atoms shares electrons. | Binding between nitrogen and boron in the ammonia-boron trifluoride compound. | |
| Intermolecular forces | Hydrogen bridge | Hydrogens in one molecule are attracted to the electronegative atoms of another molecule. | Hydrogen bridges between the hydrogen of one water molecule and the oxygen of another water molecule. |
| Dipole-dipole | Molecules with two electric poles attract the opposite poles of other molecules. | Interactions between methanal molecules H2C = O | |
The metal bond is the force of attraction between the positive ions of the metal elements and the negative electrons that are free moving between the ions. Metal atoms are heavily packaged, which allows electrons to move within the network of atoms.
In metals, the valence electrons are released from their original atom and form a “sea” of electrons that floats around the entire structure of the metal. This causes the metal atoms to transform into positively charged metal ions that are packed together.
The metal bond is established between metal elements such as sodium Na, barium Ba, calcium Ca, magnesium Mg, gold Au, silver Ag and aluminum Al.
Ionic bond
The ionic bond is the force that binds a metallic element, such as sodium or magnesium, to a non-metallic element, such as chlorine or sulfur. The metal loses electrons and transforms into a so-called positive metal ion cation. These electrons pass to the non-metallic element and are transformed into a negatively charged ion called anion.
Cations and anions combine to form a three-dimensional lattice held by electrostatic attraction forces between ions with different charges. 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 the sodium that transfers an electron to chlorine, which is the non-metallic element.
- Magnesium chloride MgCl2: Mg magnesium gives two electrons to two chlorine atoms, as shown in the figure below:
See also Difference between cations and anions.
Covalent bond
The covalent bond is formed when two non-metallic atoms share electrons. This bond can be of various types depending on the affinity for the electrons of the atoms and the number of electrons shared.
Non-polar covalent bond
The non-polar covalent bond is the bond that is formed between two atoms where electrons are shared equally. This bond usually occurs in symmetric molecules, that is, molecules made up of two equal atoms, such as the hydrogen molecule H2 and the oxygen molecule O2.
Polar covalent bond
The polar covalent bond is formed when two atoms share electrons but one has more attraction to electrons. This makes the molecule have a more negative “pole” with more electrons and the opposite pole is more positive.
Molecules with this electron distribution or imbalance are known as polars. For example, in HF hydrogen fluoride, there is a covalent bond between hydrogen and fluorine, but fluorine has more electronegativity, so it attracts more strongly shared electrons.
Simple covalent bond
When two atoms share two electrons, one from each, the covalent bond formed is called a simple covalent bond.
For example, chlorine is an atom that has seven valence electrons in its outer layer, 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 chlorines separately.
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 layer. When two oxygens are combined, four electrons are shared between the two, each having 8 electrons in the last layer.
Triple covalent bond
The triple covalent bond is formed when 6 electrons (or three pairs) are shared between two atoms. For example, in the HCN hydrogen cyanide molecule, a triple bond is formed between carbon and nitrogen, as shown in the figure below:
Coordinated or dative covalent bond
The coordinated or dative covalent bond is the bond that is formed when only one of the atoms in the bond provides a pair of electrons. For example, when NH ammonia reacts3 with boron trifluoride BF3, nitrogen binds 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 the valence shell.
See also Organic and inorganic compounds.
Dipole-dipole bonds or forces
Weak intermolecular bonds can be established between polar molecules when negative poles are attracted to positive poles and vice versa. For example, the metanal H2C = O is a polar molecule, with a negative partial charge on oxygen and a positive partial charge on hydrogen. The positive side of one methanal molecule attracts the negative side of another methanal molecule.
Hydrogen bonds or bridges
The hydrogen bridge or hydrogen bond is a bond established between molecules. It occurs when a hydrogen in the molecule is covalently attached to an oxygen, nitrogen, or fluorine. Oxygen, nitrogen and fluorine are atoms with more electronegativity, so they attract electrons more strongly when they share them with another less electronegative atom.
There are hydrogen bonds between water molecules.2O and NH ammonia3 as shown in the figure:
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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.