Unit 3: Chemical Bonding — Short Questions

Metals are the elements which prefer to lose their valence electrons and form cation (positively charged ion), So, they are electropositive in nature.

Non-metals are the elements which prefer to gain electrons from others and form anion (negatively charged ion). So, they are electronegative in nature.

Low molecular mass covalent compounds exist as gases or have low boiling liquids because of their weak intermolecular forces make it easier for the molecule to separate and move apart.

Diamond is an example of an element that exists as a crystalline solid and has covalent bonds in its atoms.

Metals are malleable and ductile because of their ability to undergo plastic deformation without breaking. This property is due to the metallic bonding present in metals which allows the layers of metal atoms to slide over each other when a force is applied.

Coordinate covalent bonds are strong bonds but not stronger than covalent bond. In a coordinate covalent bond, the shared electron pair donated by one atom. This results in a strong bond because both electrons are held together tightly between the two atoms creating a stable molecular structure. This type of one sided sharing of electrons provides the strength which makes it a strong type of covalent bond.

Dot-cross formula of nitric acid is shown with oxygen, nitrogen and hydrogen atoms arranged with dots and crosses indicating electron pairing.

An ionic bond is formed between metals and non-metals. Metals are electropositive prefer to lose electrons and non-metals are electro-negative prefer to gain electrons.

There should be large electronegativity difference between two atoms, allow them to transfer electrons, from one atom to another.
i. One atom should be metal (electro-positive) and other atom should be non-metal (electro negative) in nature.
ii. There should be strong electrostatic force of attraction between atoms to hold them together.

The non-metals elements show tendency of sharing electrons between them and form covalent bond.

In a covalent bond, atoms share electrons while in an ionic bond, one atom gives up electrons to another. Covalent bonds form between non-metals whereas, ionic bond form between metal'& non-metal.

An ionic compound is not able to form a coordinate covalent bond.

Metallic bonds consist of sea of mobile electrons with positive metal ions. They are present in elements which have loosely bound electrons that do not remain in the valence shell and leave the atom to form a sea of electrons. Such a structure is observed usually in atoms e.g., sodium and iron.

Property comparison table Definition: Metallic Bond - A bond which has positively charged ions, bound together by the mobile electrons. Ionic Bond - A bond formed by the transfer of electrons from one atom (metal) to another (non-metal), resulting in ions.
Nature: Metallic Bond - Non-directional; electrons are delocalized and shared across all atoms. Ionic Bond - Non-directional; electrostatic attraction occurs between specific positively and negatively charged ions.
Formation: Metallic Bond - Found in pure metals and alloys. Ionic Bond - Found in compounds between metals and non-metals.
Electron Behavior: Metallic Bond - Electrons form a "sea of electrons" that move freely within the metal lattice. Ionic Bond - Electrons are transferred from the metal (which becomes a cation) to the non-metal (which becomes an anion).
Bond Strength: Metallic Bond - Strong due to the attraction between the positive metal ions and the sea of delocalized electrons. Ionic Bond - Strong due to the electrostatic forces between oppositely charged ions.
Electrical Conductivity: Metallic Bond - High delocalized electrons allow metals to conduct electricity efficiently. Ionic Bond - Low in solid form; high when dissolved in water or molten, as ions become free to move.
Thermal Conductivity: Metallic Bond - Free electrons transfer energy efficiently. Ionic Bond - Low; thermal conduction depends on ionic vibrations rather than free electrons.
Malleability/Ductility: Metallic Bond - High the delocalized electron cloud allows layers of atoms to slide over each other without breaking the bond. Ionic Bond - Low; ionic bonds are brittle and shifting the lattice causes repulsion between like charges, leading to fracture.
Examples: Metallic Bond - Found in metals like copper, gold, aluminum, and alloys like brass. Ionic Bond - Found in compounds like sodium chloride (NaCl) and magnesium oxide (MgO).

Atoms react to form a chemical bond and achieve stability by acquiring inert gas electronic configuration.

The attaining of two electrons in the outermost shell by sharing, by losing or by gaining electrons is called duplet rule. e.g. helium.

The attaining of eight electrons in the outermost shell by sharing, by losing or by gaining electrons is called octet rule. e.g. neon.

Types of Bonds
We shall consider here three types of bonds.
i. Ionic bond
ii. Covalent bond
iii. Coordinate covalent bond

Because they would like to lower their energy by completing their duplet or octet. For example, for sodium atom it is easy to lose one electron and stabilize itself than to gain seven electrons while completing its octet.

Electropositive Elements i. Electropositive means tendency to lose electron to form cation.
ii. All metals are electropositive in nature.
iii. They have low ionization energy and low electronegativity.

Electronegative Elements i. Electronegative means tendency to accept electron to form anion.
ii. All non-metals are electronegative in nature.
iii. They have high ionization energy and high electronegativity.

Atoms have a tendency to decrease their energy. They can do this by combining with other atoms. It is a natural phenomenon because it increases the stability of atoms.

Atoms can lower their energy by forming chemical bonds with other atoms and to achieve more stable configuration with lower energy.

The atoms having less than 2 or 8 electrons in their valence shells are unstable.

The arrangement of electrons around the nucleus of an atom in shells and sub-shells is called electronic configuration.

A force of attraction between atoms that holds them together in a molecule is called a chemical bond. e.g. H – H (hydrogen molecule)

If attractive forces become dominant, the decrease in the energy of the system takes place, due to which chemical bond is formed. While, if repulsive forces become dominant, the increase in the energy of the system takes place, due to which no chemical bond is formed.

Conduction of ionic compounds in molten state and in form of an aqueous solution has been utilized to prepare many important elements and compounds.
For example, electrolysis of molten sodium chloride gives us sodium metal and chlorine gas. Similarly electrolysis of aqueous sodium chloride gives sodium hydroxide and chlorine gas.

The bond formed by the complete transfer of electrons from one atom (electropositive) to another (electronegative) is called ionic bond. e.g. Formation of bond between sodium and chloride ions.

Compounds that consist of ions joined by electrostatic forces are called ionic compounds. The total positive charge of the cations must be equal to the total negative charge of the anions. This is because ionic compounds are electrically neutral as a whole.

As ionic compounds are made up of positive and negative ions, there exist strong electrostatic forces of attraction between oppositely charged ions. So, a great amount of energy is required to break these forces.

Ions are spherical and oppositely charged they can surround each other from all the sides, ionic bonds are non-directional. This arrangement of ions is called crystal lattice.

Ionic compounds in solid state are bad conductor of electricity because ions are tightly packed and unable to move, whereas in solution or molten form ions can move freely which make them good conductor of electricity.

Ionic compounds have strong electrostatic forces of attraction between positively and negatively charged ions which holds them together in a three dimensional crystalline or solid form. e.g. sodium chloride (NaCl) is crystalline solid.

Water has high dielectric constant that weakens the attraction between the ions of ionic compounds due to which they are easily soluble in water.

This is because ionic compounds involve breaking the ionic bond. Breaking the electrostatic forces between ions requires large amounts of energy. Thus, ionic compounds have high melting points and boiling points. Melting of covalent solids involves the breaking of intermolecular forces, which are much weaker than electrostatic forces. Thus, less energy is required to break the intermolecular forces between covalent molecule.

The valence electrons, which are involved in the chemical bonding, are termed as bonding electrons. e.g. H• ×H

The bond formed by the mutual sharing of electrons between non-metals is called covalent bond. Covalent bond is classified into three types.
• Single covalent bond
• Double covalent bond
• Triple covalent bond

When one electron is contributed by each bonded atom, one bond pair is formed and it forms a single covalent bond. It is represented by (—). Examples: Molecules with single covalent bonds are hydrogen, (H—H), hydrochloric acid, (H—Cl).

When each bonded atom contributes two electrons, two bond pairs are shared and a double covalent bond is formed. It is represented by (=).
e.g. A molecule with double covalent bond is oxygen, (O = O) ; or O₂.

When each bonded atom contributes three electrons, three bond pairs are shared and a triple covalent bond is formed. It is indicated by (≡).
Example: molecules with triple covalent bonds are nitrogen (N₂) and ethyne (C₂H₂).
₂N + ₂N ⟶ ₂N≡N: or N≡N or N₂

i. CH₄ has 4 Single covalent bond
ii. C₂H₄ has 1 Double covalent bond and 4 Single covalent bond.
iii. N₂ has triple covalent bond N ≡ N
iv. O₂ has double covalent bond. O = O

The electronic configuration of nitrogen is N₇: 1s², 2s², 2p³. The valence shell of nitrogen is deficient of three electrons. Thus two nitrogen atoms share their three valence electrons each to form a triple covalent bond with three pairs of electrons and six electrons as a total are shared, i.e. :N:N:

A water molecule is formed when two hydrogen atoms share their electrons separately with the electrons of one oxygen atom.

A carbon dioxide molecule is formed when an atom of carbon shares its four electrons with two oxygen atoms. Each oxygen atom also shares two electrons.

A type of covalent bond in which the bond pair of electrons is donated by one of the bonded atoms only is called coordinate covalent or dative bond. Example: [H₃O]⁺

Nitrogen from ammonia molecule donates its lone pair of electrons to H⁺ in order to form a coordinate covalent bond.

Donor atom During the formation of coordinate covalent bond the atom which donate a lone pair of electron is called donor. Example: In formation of NH₄⁺, N is donor.

Acceptor atom During the formation of coordinate covalent bond the atom which accept an electron pair is called acceptor. Example: In formation of NH₄⁺ · H⁺ is acceptor.

Boron has the electronic configuration as 1s² 2s² 2p¹. This means that it needs five more electrons to be stabilized. In BF₃ it shares three electrons with three fluorine atoms and attains six electrons in its valence shell and still two electrons are required to complete octet. It still retains the tendency to gain two more electrons and therefore remains electron deficient.

Lewis dot and cross structure of ammonia with nitrogen at center bonded to three hydrogen atoms in trigonal pyramidal arrangement.

Lewis dot and cross structure of nitrogen molecule showing N≡N triple covalent bond.

Nitrogen from ammonia donates its lone pair to boron in BF₃, forming a coordinate covalent bond between them.

Lewis dot and cross structure of methane with carbon at center bonded to four hydrogen atoms in tetrahedral arrangement.

Lewis dot and cross structure of ethyne showing H-C≡C-H with triple bond between carbons.

The atom which attract the bond pair of electrons more strongly than the other one in polar covalent bond formation will be called as more electronegative atom as compared to the other bonded atom. For example, in HCl molecule, Cl is more electronegative atom as compared to H atom .

Acids provide protons (H⁺) when dissolved in water. This proton has an empty outer shell and can accept a pair of electrons present on the oxygen atom in water molecule. As a result of this, a hydronium on (H₃O⁺) is formed.

A bond formed between metal atoms (positively charged ions) due to mobile or free electrons is called metallic bond.

i. Metals have high melting and boiling points.
ii. They are good conductor of heat and electricity.
iii. They are mostly solids, possess metallic luster and can be polished.
iv. They are hard, malleable and ductile.

Electricity is produced as a result of movement of free electrons. Metals are good conductor of electricity as they have free or mobile electrons which move freely in the spaces between atoms of a metal.

Malleable means a material that can be hammered into sheets and ductile means a material that can be drawn into wires.

Metals are extensively used in many industries. They are used in machinery, automobiles, railways, air crafts, rockset, construction industry, electronics industry, jewellery, electric wires and many more.

Electropositivity is the property of a metal element to readily lose its valence electrons and gain a positive charge. Metals are highly electropositive elements. e.g. Sodium atom can lose 1 electron to from a positive ion.

Non-metals have an affinity towards y electrons. They tend to gain electrons and become negatively charged ions called anions. They are therefore, named as electronegative elements. Non-metals readil react with metals forming ionic bonds.

Ionic i. In ionic compounds oppositely charged ions are properly arranged to give a crystalline structure. As a whole the compound is neutral. There exists a strong electrostatic force between their ions.

ii. Ionic compounds are usually solids having high melting and boiling points. The melting point of sodium chloride is 801°C because it is difficult to break the strong electrostatic forces of attraction between the oppositely charged ions.

Covalent i. Covalent compounds mostly exist as discrete neutral molecules. There exists a strong electrostatic attraction between the nuclei and the shared electrons.

ii. Covalent compounds are made of two or more non-metals. Lower molecular mass covalent compounds are gases or low boiling liquids. High molecular mass covalent compounds exist as solids. Generally, they have lower melting and boiling points.

A weak force of attraction formed between two molecules is called intermolecular force.
e.g: i) Dipole-Dipole forceattraction
ii) Hydrogen Bonding

In HCl chlorine being more electronegative atom attracts the shared pair of electron and partial negative charge is created on chlorine and in turn partial positive charge on hydrogen.
When partial positive and partial negative charges exist at different poles in a molecule, the adjacent molecules will arrange themselves in such a way that negative end of that molecule comes near to positive end of other molecule. It results a net force of attraction called dipole-dipole interaction.

Halogen molecules form a non-polar covalent bond between them. In order to make non-polar bonds, no electronegativity difference of elements is required, due to which dipole forces do not develop in halogen molecules.

Weak intermolecular forces exist between HCl molecules, i.e. Dipole - Dipole forces between HCl molecule.

A bond formed between partially positive charge hydrogen atom of one molecule and partially negative charge atom (F, O or N) of the other molecule is called hydrogen bonding. e.g. HF, H₂O,NH₃ etc.

Structure showing water molecules with hydrogen bonding between the δ+ hydrogen of one molecule and δ- oxygen of another molecule.

Coal is the amorphous form of carbon whereas diamond and graphite are crystalline forms. Coal is used as a fuel in electricity generating plants.

Diamond is an allotrope of carbon in which the carbon atoms are arranged in a diamond cubic crystal lattice. Due to the presence of strong covalent bonds and a rigid tetrahedral structure, diamond is the hardest material ever discovered.

In graphite, each carbon atom is linked with 3 other carbon atoms by a single covalent bond resulting hexagonal ring arranged in a layer. It has a 2-dimensional layers structure. The 4 valency of the carbon atom is satisfied by weak van der waal's forces between 2 layers.

(i) Due to its stability in high temperatures and chemical inertness, graphite is used in many refractory items such as carbon refractory bricks.
(ii) The electrodes of graphite are used in electrical metallurgical furnaces. It is used as an anode in electrolytic processes.

Diamonds, due to their exceptional hardness, are highly valued in industries.
i. Diamond tipped glass cutters are used to make clean cuts in glass.
ii. Diamond-tipped drill bits are used to drill through hard rocks in mining operation.

Hydrofluoric acid (HF) is a liquid at room temperature, while hydrochloric acid (HCl) is a gas. The primary reason for this difference lies in the nature of the intermolecular forces present in each substance.

Intermolecular Forces HF molecules can form strong hydrogen bonds due to the highly electronegative fluorine atom. These hydrogen bonds lead to stronger attractions between HF molecules, resulting in a higher boiling point and allowing it to exist as a liquid at room and temperature.

Molecular Structure HCl is a polar molecule but does not form hydrogen bonds as strong as those in HF. The intermolecular forces in HCl are primarily dipole-dipole interactions and London dispersion forces, which are weaker than hydrogen bonds. As a result, HCl has a lower boiling point and exists as a gas at room temperature.

Covalent compounds are generally not soluble in water because they do not dissociate into ions when they are dissolved in water. Water is a polar molecule; it has partial positive charge on one end and a partial negative charge on the other. Ionic compounds dissolve in water because water molecules surround and separate the ions due to their charges. However, covalent compounds do not have ions to interact with water molecules. So, they do not dissolve easily in water.

Metals conduct heat because of their free moving electrons. These electrons can move throughout the metal structure carrying heat energy from one part of the metal to another. This ability of electrons to move freely in metals allows them to transfer heat efficiently making metals good conductors of heat.

Nitrogen forms several oxides including:
• Nitrogen monoxide (NO)
• Nitrogen dioxide (NO₂)
• Dinitrogen trioxide (N₂O₃)
• Nitrous oxide (N₂O)
• Dinitrogen pentaoxide (N₂O₅)

When sodium bromide is treated with silver nitrate in water, a chemical reaction will occur. The silver nitrate will react with the sodium bromide to form silver bromide which is insoluble in water and will precipitate out of the solution as a white solid. The other product of the reaction will be sodium nitrate which will remain dissolved in water.
NaBr + AgNO₃→AgBr + NaNO₃

Iodine exists as a solid while chlorine (Cl₂) exists as a gas due to differences in their molecular structures and intermolecular forces.
Iodine (I₂) is a larger molecule than chlorine. The larger size of iodine molecule leads to stronger vander Waals forces (dispersion forces) between them. These stronger intermolecular forces require more energy to overcome that's why, iodine is a solid at room temperature.
Chlorine (Cl₂) consists of smaller molecules with weaker vander Waals forces. This allows chlorine to remain in a gaseous state at room temperature because the energy is sufficient for the molecules to move freely and not be held together as a solid.