There are different types of chemical bonds, depending on the chemical properties and attractive forces governing the atoms. In terms of an analogy, just like how good, emotional bonds with those around us creates communities, chemical bonds formed between atoms result in the formation of compounds. Some bonds are weaker than the rest, and can be broken more easily. Atoms form chemical bonds with each other, by either sharing or transferring valence electrons to the other atom, so as to achieve stable noble gas configuration, as per the octet rule. Valence electrons are those electrons found in the outermost orbit of an atom's shell. There are four kinds of chemical bonds: covalent bond, ionic bond, metallic bond, and hydrogen bond. ● Covalent bond is a type of chemical bond in which one or more pairs of electrons, are shared among two or more atoms. ● They are formed between atoms of same element, with no electro-negativity difference (like H-H, Cl-Cl, etc.), or between two atoms of different elements, which have a very small amount of electro-negativity difference (like HCl, CO₂, etc.) ● Since, electrons are shared and no transfer of electrons takes place, no ions are formed. ● Covalent bonds can be of three types, depending on the number of electron pairs shared. The bond energy and bond length increases from single to triple bond. A single covalent bond is that bond in which two atoms share one pair of electrons, by sharing one electron each. The most common example of this bond is the bond between two hydrogen atoms. One H atom contains one electron in its valence shell. When two H atoms come in contact with each other, they share their valence electrons, to attain a stable noble gas configuration. The bond formed by sharing of one electron pair, to become stable is called single covalent bond. A double covalent bond involves sharing of two pair of valence electrons to attain stability. For example, CO₂, O₂, etc. One C atom contains four electrons in its valence shell, and requires four electrons to attain noble gas configuration. One O atom contains 6 electrons in its outer shell and requires two more electrons to attain stability. When one C atom comes in contact with one O atom, C atom shares two of its electrons with the O atom, thereby making O atom stable, by forming a double covalent bond with it. Since C atom needs two more electrons to attain stability, it forms a double covalent bond with another O atom as well, thereby making itself stable as well, and the CO₂ molecule is formed. A triple covalent bond is the covalent bond formed after sharing of three pairs of electrons. Triple covalent bonds are weaker than double and single bonds. The most common example of a triple covalent bond is that between two nitrogen atoms. One N atom contains 5 electrons in its valence shell, and requires three more electrons to achieve noble gas configuration. When two N atoms come together, they share three electrons each, thereby attaining stability. Thus, N₂ diatomic molecule is formed. The triple bond in a nitrogen molecule is the strongest of all triple bonds. Covalent bonds can again be divided into polar and non-polar covalent bonds, based on the electro negativity of the atoms coming in contact. These bonds are exhibited between two H atoms, two Fl atoms, two O atoms, and other diatomic molecules, wherein, the shared electron pair is shared equally by both atoms. The shared electron pair will be in the middle of the two atoms. Thus, electrical symmetry is seen in the molecule formed. Thus, non-polar covalent bonds are seen to occur between two atoms of the same element. As in the case of fluorine atoms, one fluorine atom has seven electrons, and requires one more electron to attain stability. When two fluorine atoms come in contact, they share one electron each and attain stability. However, because the two atoms are of the same element, there is no electro negativity difference, which is why the shared pair remains equidistant from both atoms. When atoms of different elements have some amount of electro-negativity difference, they form polar covalent bonds. In these bonds, an electron pair is shared, however, the electron pair will be more closer to the atom with the higher electron affinity (or more electro-negative). Thus, the atom with the higher affinity will develop a partial negative charge, while the atom further away from the electron pair, gets a partial positive charge. HCl is a good example of polar covalent bonds. When one H atom comes in contact with one Cl atom, both share an electron each to attain stability. However, because Cl atom is more electronegative, it pulls the electron pair towards itself. Thus, even though the electron pair is shared, it remains more closer to the Cl atom. A partial negative charge develops of Cl atom, while a slight partial charge develops on H atom. ● An ionic bond is a type of chemical bond, in which one atom gives away/transfers its valence electron to another electron, to gain stability according to the octet rule, thus, forming oppositely charged ions. ● When an ionic bond is formed, a negative ion and positive ion is formed, which are attracted to each other, thereby maintaining the bond. ● The attractive force between the negative and positive ions increases as the distance between the atoms decreases. ● Ionic bonds are formed between metals and nonmetals, with significantly large electro-negativity difference. ● Ionic bonds are weaker than covalent bonds. Example The most common and popular example of an ionic bond is that of sodium chloride or table salt. Since sodium (Na) possesses 11 electrons (2, 8, 1), with one electron in the outermost valence shell. Thus, Na is able to give off one electron easily to form Na⁺ ion, whereby it becomes more stable as per the octet rule. As far as Chlorine is concerned, it belongs to the halogen group, possesses 17 electrons (2,8,7), with seven electrons in its outermost shell. Thus, chlorine can easily gain an electron to form Cl ^- ion, whereby it becomes more stable as per the octet rule. When one Na atom comes in contact with one Cl atom, the Na atom will readily give up its electron to become a more stable Na⁺ ion, while the Cl atom will readily accept the electron to form a more stable, Cl^- ion. The resultant ions are oppositely charged, which is why they get attracted to each other, until they touch each other, forming Na⁺Cl^- molecule. The electric attraction between Na⁺ and Cl^- ions, is nothing but the ionic bond. Ionic bonds are not as strong as covalent bonds, which is why we are able to break salt into smaller pieces. ● As the name indicates, metallic bonds are chemical bonds formed between metal atoms, with low electro-negativity and those that do not hold their valence electrons tightly. ● Metallic bonds can be formed between two metal atoms of the same element, such as two Al atoms, or between two metal atoms of different elements, such as Cu and kkkk, to form an alloy. ● The valence electrons are shared among all metal atoms of the substance, thereby, forming a negative electron cloud, and positive ions of the metal. ● The electron sea is considered common to all positive ions of the metal, and move freely throughout the sea. Thus, unlike covalent or ionic bonds, metallic bonds are not held by the atoms. ● This electron sea is why we metals are able to conduct electricity and heat. Example Aluminum has atomic number 13 (2,8,3), with three electrons in the outermost shell. These three electrons are loosely held by the nucleus, as compared to those in the inner two shells. These atoms in the valence shell de-localize and form a sea of electrons, along with the other de-localized electrons of other aluminum atoms, and move freely throughout this electron sea. The delocalization forms aluminum ions. ● We've already seen what covalent bonds are, and now, we move ahead to hydrogen bonds. ● Hydrogen bonds occur in molecules with polar covalent bonds. ● Hydrogen bonds are the weakest of all bonds, formed between two atoms. ● A hydrogen bond is formed between hydrogen and an electronegative atom, which is part of another molecule. Example The most common example of hydrogen bond is that of water, H₂O. Water is formed by the formation of a polar covalent bond between two H atoms and one O atom. Because O atom is more electro-negative, it pulls the shared electron pair towards itself, thereby attaining a partial negative charge, while H atom gains a partial positive charge. This water molecule is perfect for the formation of hydrogen bonds. One H atom (partial 'δ' +ve charge) from one water molecule, gets attracted to the O atom (partial 'δ' -ve charge) of another water molecule, to form a hydrogen bond between two water molecules. When these water molecules meet other water molecules, the same bonding takes place and weak hydrogen bonds are formed. Thus, water stays together due to hydrogen bonding.