Types of Bonds

Firstly, a covalent bond results when two atoms "share" valence electrons between them.
• Covalent compounds consist of molecules and not ions. The molecules do not have any electric charge on them. The molecules are held together by weak forces called Van der Waal's forces.
• Covalent compounds are either gases, volatile liquids or soft solids. As there are weak, Van der Waal's forces between the molecules, they are not held in rigid position. The state depends on the bond energy. If the bond energy is very low, they stay as gases, if it is appreciable they are volatile liquids. If very high, they exist as soft solids.
• Covalent compounds generally have low melting and boiling points. As Van der Waal's forces are weak, a very small amount of energy is required to break the bond between the molecules corresponding to low melting point and boiling point.
• Covalent compounds dissolve in organic solvents. As they do not contain ions, solvation does not take place when water is added to the compound. Hence they do not dissolve in water.
• Covalent compounds are bad conductors of electricity. They do not contain ions in the fused state, nor do ions migrate on application of an electric potential. Hence, there is no conduction of current.
• Covalent compounds are less dense when compared to water. Very weak Van der Waal's forces hold the molecules together, hence there are large inter molecular spaces. Consequently less number of molecules per unit volume, which means mass per unit volume is also less. Hence they have a low density.
A good example of a covalent bond is that which occurs between two hydrogen atoms. Atoms of hydrogen (H) have one valence electron in their first electron shell. Since the capacity of this shell is two electrons, each hydrogen atom will "want" to pick up a second electron. In an effort to pick up a second electron, hydrogen atoms will react with nearby hydrogen (H) atoms to form the compound H2. Because the hydrogen compound is a combination of equally matched atoms, the atoms will share each other's single electron, forming one covalent bond.

Exceptions:
Diamond and graphite, the allotropes of carbon have high melting point.
Hydrogen chloride in the aqueous state conducts electricity.
Glucose, sugar and urea are soluble in water. Ammonia and hydrogen chloride also dissolve in water.

Secondly, ionic bonding is nothing but a type of chemical bond formation. Ionic bonding is the process of formation of a chemical bond by complete transfer of electrons from one atom to another. When the atoms lose or gain electrons, they become differentially charged ions or oppositely charged ions. The charged ions are then attracted towards each other due to the resulting electrostatic force. The electrostatic force gives rise to the formation of an ionic bond. The most common example of ionic bonding is the formation of sodium chloride in which the sodium atom donates its outer electron to the chlorine atom, which required only one electron to fill its outer shell. The sodium ion becomes positively charged due to the loss of electron whereas the chloride ion becomes negatively charged due to the addition of the electron. The oppositely charged ions thus are attracted to each other and result in the formation of an ionic bond.
• Owing to the fact that metals tend to lose electrons and non-metals tend to gain electrons, ionic bonding is seen between metals and non-metals. Hence unlike covalent bonds, ionic bonds can be formed between metals and non-metals.
• While naming the ionic compounds the name of the metal always comes first and the name of the non-metal comes second. For instance in case of common salt that is chemically named sodium chloride. Sodium is the metal whereas chlorine is the non-metal.
• Compounds which contain ionic bonds dissolve quickly in water as well as several other polar solvents. Ionic bonds thus tend to have an effect on the solubility of the resultant compounds.
• When ionic compounds are dissolved into a solvent to form a homogeneous solution, the solutions tends to conduct electricity.
• Ionic bonding has an effect on the melting point of the compounds as well. Ionic compounds have higher melting temperature, which means that ionic bonds remain stable for a greater temperature range.

Ionic bonds normally form crystalline atoms and have higher melting points and boiling points compared to covalent compounds. These conduct electricity in molten or solution state and they are extremely polar bonds. Most of them are soluble in water but insoluble in non-polar solvents. They require much more energy than covalent bond to break the bond between them.


There is a third type of bonding, called metallic bonding. As the name implies, metallic bonding usually occurs in metals.

According to Electron sea model or Electron gas theory, a metallic bond can be defined as a force of attraction that holds firmly a definite geometrical arrangement of metal ions and sea of freely moving electrons. The force of attraction between a group of electrons and a group of positive ions should be stronger when compared to the force of attraction between one electron and one nucleus. The metallic bond is non-directional. Metallic bond is weaker than a covalent bond.

• The metal atoms lose their valence electrons readily. They can form a group of positively charged ions called Kernel.
• The positively charged metal ions are arranged in a definite geometric shape. This array or kernel of metal ions is submerged in the sea of freely moving electrons.
• Due to smaller ionization energy, the valence electrons of metal are not held by the nucleus firmly and the electrons can move freely using vacant orbitals.
• The mobile electrons move around the group of metal ions freely similar to the free movement of sea water or any gas. Hence, it is called electron sea model for metallic bond formation or electron gas theory.
• Metallic bond is formed by mutual attraction between mobile electrons and positive metal ion layers.
• Metallic bond is weaker because valence electrons are mobile and weakly attracted by metal ions.
• Bond is present around identical metal ions.
• Metallic bond is weaker because mobile electrons are weakly attracted by metal ions.
The strength of metallic bond formation depends on:
• Number of valence electrons.
• Charge on the metal ions.
• Size of the metal ions.
Metallic bond is weaker in alkali metals because of:
• Only one valence electron on each metal atom.
• One positive charge on the metal ion.
• Larger size of the metal ion.
Transition metals have a strong metallic bond because:
• The number of valence electrons are more
• Metal ions have higher positive charges.
• Smaller size of these metal ions.
Any metal you hold in your hand is held together with flexible metallic bonds. These bonds are what enable metal to be both malleable and ductile.
Essential to understanding all types of chemical bonding is realizing that all bonds use electron "glue." Every substance is made up of atoms, and all atoms are surrounded by the charged particles called electrons.