Chemical Bonds and Their Properties: A Comprehensive Study
**Chemical Bonds: Types and Characteristics**
**Main Types of Bonds**
- Ionic or Electrovalent Bond (transfer of electrons)
- Covalent Bond (sharing a pair of electrons between two atoms)
- Coordinate Covalent Bond (one of the two atoms provides the pair of electrons to share)
**Other Types of Bonds**
- Metallic Bond
- Hydrogen Bond
- Van der Waals Forces
**Ionic Substances**
Ionic substances result from electrostatic forces holding ions in a rigid, well-defined, three-dimensional structure. They are usually solid with a high melting point, not liquid or gaseous with a low melting point.
**Covalent Bond**
In this model, a pair of electrons is shared between atoms that are attracted by the two nuclei of the atoms. It is also formed from a pair of electrons, also called an electron pair bond.
When considering covalent bonds, take into account:
- The orbital occupied by the pair of electrons
- How this pair of electrons is arranged
- If there are multiple bonds (2 or 3)
- If there are nonbonding electron pairs or lone pairs
- If the bond formed is polar or nonpolar
**Coordinate Covalent Bond**
In many compounds, each atom provides one electron for bond formation. There are some cases in which one atom supplies both electrons. This bond consists of sharing a pair of electrons between two atoms, where the pair is provided by one of the bound atoms.
**Polarity of Bonds**
Polarity describes the proportion in which electrons are shared. When joining two atoms of different electronegativity, the electrons are attracted toward the more electronegative atom. Therefore, the electronic cloud will not be equally distributed in the atoms. This creates a negative charge and a positive charge in the molecule, giving rise to a polar bond. The greater the difference in electronegativities, the greater the bond polarity. An extreme case of this is the ionic bond.
- In a nonpolar covalent bond, electrons are shared equally.
- In a polar bond, one of the atoms has a higher attraction to the electron cloud.
- An extreme case is an ionic bond, where an electron is permanently transferred to one atom and accepted by another, generating the corresponding ions.
To differentiate between a polar, nonpolar, and ionic bond, you should know the difference in electronegativities between the two bound atoms:
- If it is 0 to 0.4, it will be nonpolar.
- If it is 0.4 to 1.7, it will be polar.
- If it is greater than 1.7, it will be ionic.
**Strength of Covalent Bonds**
The strength of the covalent bond between two atoms is determined by the energy required to break the bond.
**Metallic Bond**
Metallic bonds are the association of metal atoms to unite, based on their periodic character. The nuclei of atoms come together, forming a network. The free electrons are located around the positive network, forming what is called a “sea of electrons.”
**Dissolution**
A solution is a homogeneous mixture formed when a substance is dispersed in another.
Forces involved:
- Van der Waals Forces: Dipole-dipole / London dispersion forces
- Hydrogen Bond
- Ion-dipole solutions
Note:
- Forming a bond releases energy.
- Breaking a bond requires energy.
**Intermolecular Forces**
- London Forces: Intermolecular forces between nonpolar covalent molecules.
- Dipole-Dipole Forces: Intermolecular attractions between polar covalent molecules.
- Ion-Dipole Forces: These are interactions that occur between charged species. Like charges repel, while opposites attract.
**Effects of Pressure on Solubility**
The solubility of a gas in any solvent increases as the pressure of the gas on the solvent increases. In contrast, the solubilities of solids and liquids are not significantly affected by pressure.
**Colligative Properties**
Freezing point depression and boiling point elevation are examples of physical properties of solutions that depend on the concentration, but not the kind of solute particles. Such properties are called colligative properties (colligative means “dependent on the collection”; colligative properties depend on the collective effect of the solute particles).
- Freezing Point Depression
- Boiling Point Elevation
- Reduction of Vapor Pressure
- Osmotic Pressure
**Vapor Pressure Reduction**
The vapor pressure of a liquid is the result of a dynamic equilibrium. The rate at which molecules leave the liquid surface and pass into the gas phase equals the rate at which molecules from the gas phase return to the liquid phase.
**Boiling Point Elevation**
The boiling point of a volatile solute is greater than the boiling point of the pure solvent because volatile solutes depress the vapor pressure of the solution. A higher temperature will be required to make the solution boil.
**Freezing Point Depression**
The freezing point corresponds to the temperature at which the vapor pressures of the liquid and solid phases are equal. The freezing point decreases in a solution because usually the solute is not soluble in the solid phase of the solvent.
**Osmotic Pressure**
When a solution and a solvent are separated by a semipermeable membrane that allows the passage of solvent molecules, osmotic pressure develops in the solution. Osmosis is the net movement of solvent from a pure solvent or a solution with a low concentration of solute to a solution with a high concentration of solute.
**Electronegativity**
- Ionic compounds: > 2
- Polar compounds: > 0 and < 2
- Nonpolar compounds: = 0
**Bond Types and Compounds**
- Electrovalent = Ionic compounds
- Polar = Polar covalent compound
- Nonpolar = Nonpolar covalent compound
**Formulas**
- Molarity (M) = mol / Liters
- Molality (m) = mol / Kg
- Weight % = (solute / solution) * 100
- ppm = (solute / solution) * 106
- FM = solute mass / moles of solution