A Comprehensive Guide to Ionic, Covalent, Metallic Bonds and Intermolecular Forces
Chemical bonds are the attractive forces that hold atoms together in compounds. Atoms form bonds to achieve greater stability, typically by attaining the electron configuration of noble gases.
Octet Rule: Atoms tend to gain, lose, or share electrons to achieve a full outer shell of 8 electrons (or 2 for hydrogen and helium). This configuration provides maximum stability.
The formation of chemical bonds always results in a decrease in the potential energy of the system, making the bonded atoms more stable than their isolated forms.
Definition: A chemical bond formed by the complete transfer of electrons from one atom to another, resulting in the formation of oppositely charged ions.
NaCl: Sodium transfers one electron to chlorine
CaCl₂: Calcium transfers two electrons (one to each chlorine)
MgO: Magnesium transfers two electrons to oxygen
Definition: A chemical bond formed by the mutual sharing of electron pairs between atoms.
H₂: Two hydrogen atoms share one electron pair
H₂O: Oxygen shares electrons with two hydrogen atoms
CH₄: Carbon shares electrons with four hydrogen atoms
Definition: A chemical bond formed by the attraction between positively charged metal ions and a “sea” of delocalized electrons.
Sodium (Na): Each atom contributes one electron
Magnesium (Mg): Each atom contributes two electrons
Iron (Fe): Forms strong metallic bonds
Definition: A covalent bond formed by the sharing of one pair of electrons (2 electrons) between two atoms.
Represented by a single line (-) between atoms in structural formulas.
H-H
Hydrogen (H₂)
H-Cl
Hydrogen Chloride
H₃C-CH₃
Ethane
Definition: A covalent bond formed by the sharing of two pairs of electrons (4 electrons) between two atoms.
Represented by a double line (=) between atoms in structural formulas. Double bonds are shorter and stronger than single bonds.
O=O
Oxygen (O₂)
H₂C=CH₂
Ethene
O=C=O
Carbon Dioxide
Definition: A covalent bond formed by the sharing of three pairs of electrons (6 electrons) between two atoms.
Represented by a triple line (≡) between atoms in structural formulas. Triple bonds are the shortest and strongest covalent bonds.
N≡N
Nitrogen (N₂)
HC≡CH
Acetylene
HC≡N
Hydrogen Cyanide
Definition: A covalent bond in which both electrons of the shared pair come from the same atom.
Also known as a dative bond. Once formed, it is identical to a regular covalent bond.
Ammonium Ion (NH₄⁺): Nitrogen in ammonia donates a pair of electrons to a hydrogen ion (H⁺)
Hydronium Ion (H₃O⁺): Oxygen in water donates a pair of electrons to a hydrogen ion (H⁺)
Boron Trifluoride-Ammonia Complex (BF₃·NH₃): Nitrogen in ammonia donates a pair of electrons to boron
Intermolecular forces are attractive forces that exist between molecules. They are weaker than chemical bonds but significantly influence physical properties like boiling points, melting points, and solubility.
Definition: Attractive forces between the positive end of one polar molecule and the negative end of another polar molecule.
HCl-HCl: Interaction between hydrogen chloride molecules
CH₃Cl-CH₃Cl: Interaction between chloromethane molecules
SO₂-SO₂: Interaction between sulfur dioxide molecules
Definition: A special type of dipole-dipole interaction that occurs when hydrogen is bonded to highly electronegative atoms (N, O, F).
Water (H₂O): Extensive hydrogen bonding explains its high boiling point
Ammonia (NH₃): Hydrogen bonding between ammonia molecules
Hydrogen Fluoride (HF): Strong hydrogen bonding makes it a liquid at room temperature
DNA: Hydrogen bonds between base pairs hold the double helix together
| Property | Ionic Bonds | Covalent Bonds | Metallic Bonds |
|---|---|---|---|
| Formation | Transfer of electrons | Sharing of electrons | Sea of delocalized electrons |
| Bond Strength | Strong | Strong (varies with bond type) | Variable (depends on metal) |
| Melting/Boiling Points | High | Low to moderate | Moderate to high |
| Electrical Conductivity | Only when molten/dissolved | Poor | Good |
| Solubility in Water | Generally high | Generally low | Insoluble |
| Examples | NaCl, CaCO₃ | H₂O, CH₄, CO₂ | Fe, Cu, Na |
i. When molten copper and molten zinc are mixed together, they give rise to a new substance called brass. Predict what type of bond is formed between copper and zinc.
Answer: (c) Metallic bond
Explanation: Brass is an alloy of copper and zinc, and alloys typically have metallic bonding where metal atoms share a “sea” of delocalized electrons.
ii. Which element is capable of forming all the three types of bonds; covalent, coordinate covalent and ionic?
Answer: (b) Oxygen
Explanation: Oxygen can form covalent bonds (as in H₂O), coordinate covalent bonds (as in H₃O⁺), and ionic bonds (as in metal oxides like MgO).
iii. Why is H₂O a liquid while H₂S is a gas?
Answer: (b) Because water is a polar compound and there exists strong forces of attraction between its molecules
Explanation: Water molecules form strong hydrogen bonds due to high electronegativity of oxygen, resulting in higher boiling point. H₂S has weaker intermolecular forces.
iv. Which of the following bonds is expected to be the weakest?
Answer: (d) F – F
Explanation: The F-F bond is unusually weak due to strong repulsion between the lone pairs of electrons on the small fluorine atoms.
v. Which form of carbon is used as a lubricant?
Answer: (c) Graphite
Explanation: Graphite has a layered structure where layers can slide over each other easily, making it an excellent lubricant.
vi. Keeping in view the intermolecular forces of attraction, indicate which compound has the highest boiling point:
Answer: (a) H₂O
Explanation: Water has the highest boiling point due to extensive hydrogen bonding between its molecules.
vii. Which metal has the lowest melting point?
Answer: (d) Rb
Explanation: Rubidium has the lowest melting point among these alkali metals due to its larger atomic size and weaker metallic bonding.
viii. Which ionic compound has the highest melting point?
Answer: (c) LiCl
Explanation: LiCl has the highest melting point due to the small size of Li⁺ ion, which results in stronger electrostatic forces in the crystal lattice.
i. What type of elements lose their outer electron easily and what type of elements gain electron easily?
Answer: Metals (especially alkali and alkaline earth metals) lose their outer electrons easily. Non-metals (especially halogens) gain electrons easily.
iii. Give one example of an element which exists as a crystalline solid and it has covalent bonds between its atoms.
Answer: Diamond is an example of an element that exists as a crystalline solid with covalent bonds between its carbon atoms.
v. Is coordinate covalent bond a strong bond?
Answer: Yes, once formed, a coordinate covalent bond is as strong as a regular covalent bond. The difference lies only in how the bond is formed.
vi. Write down dot and cross formula of HNO₃.
Answer: The dot and cross formula for HNO₃ (nitric acid) shows:
– A covalent bond between H and O
– A double bond between N and one O atom
– A coordinate covalent bond between N and another O atom
– A single covalent bond between N and the third O atom (which is bonded to H)
i. Why HF is a liquid while HCl is a gas?
Answer: HF is a liquid at room temperature due to strong hydrogen bonding between its molecules, which requires more energy to break. HCl has weaker dipole-dipole interactions, so it exists as a gas.
ii. Why covalent compounds are generally not soluble in water?
Answer: Most covalent compounds are non-polar or have low polarity, while water is a highly polar solvent. According to the principle “like dissolves like,” non-polar covalent compounds do not dissolve well in polar water.
iii. How do metals conduct heat?
Answer: Metals conduct heat through their “sea” of delocalized electrons. When heat is applied, these electrons gain kinetic energy and transfer it rapidly throughout the metal structure.
iv. How many oxides does nitrogen form. Write down the formulae of oxides?
Answer: Nitrogen forms several oxides, including:
– Nitrous oxide (N₂O)
– Nitric oxide (NO)
– Nitrogen dioxide (NO₂)
– Dinitrogen trioxide (N₂O₃)
– Dinitrogen tetroxide (N₂O₄)
– Dinitrogen pentoxide (N₂O₅)
i. Explain the formation of an ionic bond and a covalent bond.
Answer:
Ionic Bond: Formed by complete transfer of electrons from a metal atom to a non-metal atom. The metal becomes a positively charged cation, and the non-metal becomes a negatively charged anion. These oppositely charged ions are held together by strong electrostatic forces. Example: NaCl formation.
Covalent Bond: Formed by mutual sharing of electron pairs between atoms. Each atom contributes one electron to the shared pair. This sharing allows both atoms to achieve stable electron configurations. Example: H₂O formation.
iii. Explain the properties of metals keeping in view the nature of metallic bond.
Answer: Metallic bonding explains several properties of metals:
– Electrical conductivity: Delocalized electrons can move freely and carry electric current.
– Thermal conductivity: Mobile electrons transfer heat energy efficiently.
– Malleability and ductility: Atoms can slide past each other without breaking bonds due to the electron sea.
– Luster: Electrons absorb and re-emit light energy.
– High melting and boiling points: Strong metallic bonds require significant energy to break.
vi. Why are metals usually hard and heavy?
Answer: Metals are usually hard and heavy because:
– Hardness: Strong metallic bonds hold atoms firmly in place in a closely packed arrangement.
– Heaviness: Metal atoms are typically dense with high atomic masses, and the close packing of atoms in metallic structures results in high density.
Bond Strength Order: Triple bond > Double bond > Single bond > Hydrogen bonding > Dipole-dipole