Chemical bond: A chemical bond is defined as a force of attraction between atoms that holds them together in a substance (molecule).
Types of chemical bond: Depending upon the involvement of valence electrons in bond formation, there are four types of chemical bond.
- Ionic bond.
- Covalent bond.
- Dative bond or coordinate covalent bond.
- Metallic bond.
Question) What is an ionic bond? How is it formed? Discuss the formation of ionic bond between sodium and chlorine atoms?
ANSWER: Ionic bond or Electrovalent bond: The type of chemical bond which is formed by complete transfer of electrons from one atom to other atom is called ionic bond. “OR” The electrostatic forces of attraction between positive (cation) and negative (anion) ion is called ionic bond.
Formation of ionic bond: An ionic bond is formed when a high elecctronegative atom approaches a high electropositive atom. The electronegative atom take electrons from the electropositive atom and ions formation occurs. This type of bond is called ionic bond because of formation of ions.
FORMATION OF IONIC BOND BETWEEN Na & Cl: Electronic Configuration of Na is K = 2 , L = 8, M = 1
Due to low ionization potential value, Na-atom loses its valance electron
Electronic configuration after losing an electron is K = 2, L = 8 , M = 0
Na è Na+ + e–
Due to loss of one electron Na becomes Na+ -ion.
Electronic configuration of Cl is K = 2, L = 8, M = 7
Electron lost by Na atom picks up by Cl atom.
Electronic configuration after acquiring an electron: K = 2, L = 8, M = 8
Cl + e– → Cl–
Chlorine atom is now converted into Cl– ion
We know that positive and negative ions attract each other, therefore an electrostatic force of attraction is set up between Na+ & Cl- ions. This force unites these ions in a unit. In this way ionic bond is formed between Na and Cl atoms which results the formation of sodium chloride.
Other examples: ionic bond is mostly present in salts. Following are the basic examples of compounds having ionic bonds: MgCl2, CaCl2, KBr, MgSO4, etc.
Question) What is a covalent bond? How it is formed? What type of chemical bonds are formed between hydrogen, oxygen and nitrogen molecules? Explain their bonding with dot and cross formulas? Explain the type of covalent bonds with examples? Also explain that how a covalent bond develops ionic character in it? How can you justify that bond strength in polar covalent compounds is comparable to that of ionic compounds?
Answer: The type of chemical bond which is formed by mutual sharing of electrons is called covalent bond.
Formation of covalent bond: a covalent bond establishes when the two approaching atoms have same electronegativity or less electronegativity difference. In such case the bonded pair of electrons feel approximately equal forces of attraction from both the atoms and so the bond formed is due to the sharing of electrons, and are called covalent bond.
Types of covalent bond based on the number of bond pair of electrons : There are three main types of covalent bond based on the number of shared or bond pair of electrons:
- Single covalent bond : A covalent bond formed by the mutual sharing of one electron pair between two atoms is called a “Single Covalent bond.”
It is denoted by single short line(-). In single bond formation each atom provide one electron.
BOND IN HYDROGEN MOLECULE: In hydrogen molecule each of hydrogen atom share only one electron, so a single covalent bond establishes between hydrogen atoms in H2O molecule.
DOUBLE COVALENT BOND: A covalent bond formed between two atoms by the mutual sharing of two electron pairs is called a “double covalent bond”. It is denoted by double short line (). Examples: The molecules like oxygen (O2) gas and ethene (C2H4) show such type of double covalent bonds.
Bond in Oxygen molecule: In oxygen molecule, each of the oxygen atom share two electron with other oxygen atom, so two bonded pairs are formed and so called double covalent bond.
Triple Covalent Bond:
When each bonded atom contributes three electrons, three bond pairs are involved in bond formation. This type is called triple covalent bond. Three small lines are used to indicate these three pairs of electrons between those atoms in the molecules of such compounds. The examples of molecules having triple covalent bonds are nitrogen (N2 ) and ethyne (C2 H 2).
Bond in Nitrogen molecule: In nitrogen molecule each of nitrogen atom share three electrons, so three bonded pairs are formed in nitrogen molecule(N2) and that’s why bond is triple covalent bond.
Things to Remember
The electronic configuration of the valence shells of
atoms is shown in small ‘dots’ or ‘crosses’ around the
symbol of the element. Each dot or cross represents
an electron. This is a standard method of Lewis to
describe the electronic configuration of valence shell
of an atom. It is called Lewis Structure Diagram.
Types of covalent bond on the basis of polarity: On the basis of polarity there are two types of covalent bond.
Polar covalent bond.
Non-polar covalent bond.
A) Polar covalent bond: A covalent bond formed between two different atoms is known as Polar covalent bond. In a polar covalent bond the electrons are unequally shared.
For example when a Covalent bond is formed between H and Cl , it is polar in nature because Cl (3.2) is more electronegative than H(2.2) atom . Therefore, electron cloud is shifted towards Cl atom. Due to this reason a partial -ve charge appeared on Cl atom and an equal +ve charge on H atom.
Other examples are H2O AND HF.
- B) NON-POLAR BOND: Acovalent bond formed between two like atoms is known as Non-polar bond. Since difference of
electro negativity is zero therefore, both atoms attract electron pair equally and no charge appears on any atom and the whole molecule becomes neutral. Examples: H – H→ H2
Cl – Cl→ Cl2
F – F→ F2
Br – Br → Br2
Bond strength in polar covalent compound is comparable to that of ionic “OR Comparison between bond strength of ionic and polar covalent compounds:
The polar covalent bond is formed between two or more atoms by unequal sharing of electrons while ionic bond is formed by the complete transfer of electrons. The ionic bond is stronger than the polar covalent bond. Both the bonds are compareable due to the following reasons.
- Both type of bonds forms between different electronegative atoms. In which one is more electronegative than the other. The more electronegative attract the electrons more towards itself.
- In pure ionic bond the bonded atoms attains positive and negative charges while in polar covalent bond partial positive and partial negative chaeges appears on the bonded atoms.
- Both the bonds are stronger type of bonds.
Question) How can you predict that the bond is covalent or ionic?
Answer: By using electronegativity values, it is possible to predict whether a chemical bond will be ionic or covalent in nature.
- A bond formed between elements of high electronegativity (halogen group) and elements of low electronegativity (alkali metals) are ionic in nature.
- The bond between elements of comparable electronegativities will be covalent in nature as the bond between carbon and hydrogen in methane, or nitrogen and hydrogen in ammonia.
- If the difference of electronegativities between two elements is more than 1.7 the bond between them will be predominantly ionic bond and if it is less than 1.7, the bond between two atoms will be predominantly covalent.
Question) What is a coordinate covalent bond? How a coordinate covalent bond is formed? Explain with examples?
Answer: Coordinate covalent bond OR Dative bond: The type of chemical bond in which shared pair of electrons is donated(provided) by only one of the bonded atoms is called coordinate covalent bond or dative bond.
Formation of coordinate covalent bond: In the formation of coordinate bond other atom does not provide electron for sharing. It is one sided sharing.
Formation of coordinate covalent bond is the property of atoms that have lone pair of electrons.
Explanation: A small arrow is usually used to indicate the atom and pair of electron being donated. The head of arrow is towards the acceptor atom. The atom which donates the electron pair is called donor and the atom which accepts the electron pair is called acceptor.
Example: Ammonium ion (NH4+), Hydronium ion (H3O+). NH3 has one lone pair of electrons. It donates its lone pair to H+ and a coordinate covalent bond is formed between NH3 and H+ ion.
Question) What is metallic bond? Explain the metallic bonding with the help of a diagram?
Answer: Metallic Bond
The metallic bond is defined as a bond formed between metal atoms (positively charged ions) due to mobile or free electrons.
Explanation: In case of metals, the hold of nucleus over the outermost electrons is weak because of :
- large sized atoms.
- Greater number of shells in between nucleus and valence electrons.
- Because of low ionization potentials, metals have the tendency to lose their outermost electrons easily. Resultantly, these loose or free electrons of all metal atoms move freely in the spaces between atoms of a metal. None of these electrons is attached to any particular atom. Either they belong to a common pool, or belong to all the atoms of that metal. Nuclei of metal atoms appear submerged in sea of these free mobile electrons. These mobile electrons are responsible for holding the atoms of metals together forming a metallic bond.
|EXAMPLES; All metals, like Zn , Na, etc.|