Chemistry Chapter 4: Chemical Bonding

 CHEMISTRY KEYWORDS:

Anion: Negatively charged ion

Cation: Positively charged ion

Lattice: Regularly repeating arrangement of atoms, molecules or ions in 3D throughout the crystal structure.

Van der Waals’ forces: Weak forces of attraction between molecules involving either instantaneous dipole-induced dipole (id-id) or permanent dipole-permanent dipole (pd-pd) forces (including hydrogen bonding). The expression covers all types of intermolecular forces.

Intermolecular forces: Weak forces between molecules.

Electrovalent bond: Another name for an ionic bond.

Dot-and-cross diagram: Diagram showing the arrangement of the outer shell electrons in an ionic or covalent element or compound. The electrons are shown as dots or crosses to show their origin.

Double Covalent Bond: 2 shared pairs of electrons bonding 2 atoms together.

Triple Covalent Bond: 3 shared pairs of electrons bonding 2 atoms together.

Co-ordinate bond: Sharing of pair of electrons between 2 atoms where both the electrons in the bond come from the same atom. Also called a dative covalent bond.

Electron Deficient: Atom or molecule with less than its usual share of electrons.

Delocalised Electrons: Electrons that are not associated with any particular atom. In metals, the delocalised electrons move throughout the metallic structure between the metal ions when a voltage is applied. (In the molecule benzene, the delocalised electrons have a more limited movement).

Metallic Bonding: Electrostatic attraction between positive ions and delocalised electrons.

Polar Bonds: The electron pair in the bond is drawn towards the atom with the larger electronegativity, making one end of the molecule slightly positive compared with the other.

Bond Polarity: Partial separation of charge when 2 different atoms are joined by a covalent bond. This results in an unequal attraction for the bonding pair of electrons.

Instantaneous dipole-induce dipole forces (id-id forces): Weakest intermolecular attractive force. It results from temporary instantaneous dipole induced in both polar and non-polar molecules. These forces are also called London dispersion forces. The dipoles are not permanent. In this context, ‘induced’ means that one molecule has an attractive or repulsive effect on another.

Permanent dipole-permanent dipole forces (pd-pd forces): Attractive intermolecular forces result from permanent molecule dipoles.

Hydrogen bond: Strongest type of intermolecular force but weaker than covalent bonds. It is a strong type of pd-pd force.

Hydrolysis: Breakdown of a compound by water. Hydrolysis is also used to describe the breakdown of a substance by dilute acids or alkali.

 

CHEMISTRY DEFINITIONS:

Ionic bonding: Electrostatic attraction between oppositely charged ions.

Covalent bonding: Electrostatic attraction between the nuclei of 2 atoms and a shared pair of electrons.

Lone pairs (of electrons): Pairs of electrons in the outer shell of an atom that are not involved in bonding.

Bond Energy: Energy required to break 1 mole of a particular covalent bond in the gaseous state. The units of bond energy are kilojoules per mole.

Bond Length: Distance between the nuclei of 2 covalently bonded atoms.

Electronegativity: The power of a particular atom covalently bonded to another atom to attract the bonding pair of electrons towards itself.

 

CHEMISTRY IMPORTANT NOTES:

Ionic Bond is also known as Electrovalent Bond.

Instantaneous dipole–induced dipole forces are also known as London Dispersion forces, and they are sometimes called Temporary dipole–induced dipole forces.

A shared pair of electrons is called a Single Covalent Bond or a Bond Pair.

A Co-ordinate Bond is also called a Dative Covalent Bond. The coordinate bond is represented by an arrow.

The mixing of atomic orbitals is called hybridization.

The strength of metallic bonding increases with:

•   Increasing positive charge on the ions in the metal lattice.
•  Decreasing the size of metal ions in the lattice.
• Increasing the number of mobile electrons per atom.

The electronegativity depends on:

·       Nuclear Charge

·       Atomic Radius

·       Shielding

Nitrogen is a non-polar molecule and is fairly unreactive.

Compound	Bond Angle	Structure
Methane	109.5o	Tetrahedral
Ammonia	107o	Pyramidal
Water	104.5o	Non-linear V shape
Boron Trifluoride	120o	Trigonal Planar
Carbon Dioxide	180o	Linear
Phosphorus Pentafluoride	120o and 90o	Trigonal Bipyramidal
Sulfur Hexafluoride	90o	Octahedral

 

SUMMARY:

Ionic bonding is the electrostatic attraction between oppositely charged ions. Covalent bonding is the electrostatic attraction between the nuclei of 2 atoms and a shared pair of electrons.

Electronegativity is the power of a particular atom covalently bonded to another atom to attract the bonding pair of electrons towards itself.

Bond energy is the energy required to break 1 mole of a particular covalent bond in gaseous state. The units of bond energy are kilojoules per mole.

Bond angles within molecules and the shapes of molecules can be predicted by VSEPR theory (lone pairs of electrons repel each other more than bonding pairs of electrons).

Bonding can be described in terms of hybridization of atomic orbitals and sigma bonds and pi bonds.

Van der Waals’ forces can be classified as instantaneous dipole-induced dipole forces (very weak), permanent dipole-permanent dipole forces (slightly stronger) and hydrogen bonding (strongest). Van der Waals’ forces are weaker than covalent, ionic or metallic bonding.

Metallic bonding is the electrostatic attraction between positive ions and delocalised electrons.

Some of the physical properties of ionic, simple covalent molecules and metals can be related to the type of bonding present.