Bonding and Structure | Ionic Bonding | Metallic Bonding | Covalent Bonding

Bonding and Structure:

Lesson Objectives

• Ionic Bonding
  • Definition
  • Metal and Non-Metal Ionic Bond Formation
  • Ionic Lattice
  • Properties of Ionic Substances
  • Formulae of Ionic Compounds
• Metallic Bonding
  • Definition
  • Properties of Metals
  • Malleability of Metals
  • Conductivity of Metals
• Covalent Bonding
  • Definition
  • Dot and Cross Diagrams
  • Types of Covalent Bonds
  • Properties of Covalent Compounds
  • Types of Covalent Compounds
    • Simple molecular structures
    • Macromolecular structures
  • Allotropes

Ionic Bonding:

Definition:

• The bond that is formed by the transfer of electrons between metal and non-metal atoms is known as an ionic bond.
• Ions are atoms with charge.
• Ionic bond is formed by atoms to gain stability since every atom wants to achieve a complete octet valence shell (discussed earlier).
• The bonding is called Ionic bonding since the bonds are formed when the atoms turn into ions and attract each other due to charge.

Metal and Non-Metal Ionic Bond Formation:

• Ionic Bonding occurs between metal and non-metal atoms.
  • Metals are in the first groups of the periodic table and non-metals in the last groups.
• The metal atom has a valence shell that has a fewer number of valence electrons and the non-metal atom has a deficiency of a few electrons.
• All atoms want to complete their octet to gain stability (discussed earlier). Hence, the metal atom gives its valence electron to the non-metal atoms and so its last shell is removed. The valence shell is now the previous shell which has a complete octet.
• When the atom loses its electrons, the number of protons become more than the number of electrons and hence, the overall atom gets a positive charge and becomes a positive ion.
• The non-metal atoms gain the electron lost by the metal atom and this completes their valence octet. Since now the non-metal atom has more electron than protons, the overall charge on the atom becomes negative and hence, the atom becomes a negative ion.
• The positive and negative ions attract each other and form ionic bonds.

Example: Sodium Chloride:

We know that sodium is a metal and chlorine is a non-metal. Sodium chloride is a salt that is known as the table salt. Consider the diagram.

• Sodium (Na) loses 1 electron and gets a positive charge. It turns into Na¹⁺
• Chlorine (Cl) gains that electron and gets a negative charge. It turns into Cl^1-
• Both now have a complete valence shell with 8 electrons.
• The form an ionic bond and become NaCl = Sodium Chloride.

Example: Magnesium Chloride:

We know that magnesium is a metal and it has 2 valence electrons, and chlorine is a non-metal which requires one valence electron to complete its octet. Consider the diagram.

• Magnesium (Na) loses 2 electrons and gets a positive charge. It turns into Mg²⁺
• Two chlorine (Cl) atoms gain those electrons and get a negative charge. They turn into Cl^1-
• All three have a complete valence shell with 8 electrons.
• The form an ionic bond and become MgCl₂ = Magnesium Chloride.

Ionic Lattice:

• The ions that are formed by the loss or gain of electron are regularly arranged in the form of a giant crystal lattice.
• These lattices are very stable due to the strong electrostatic forces between the ions.
• Ionic compounds are mostly solids and have a high melting and boiling point.
• Another property of crystal lattice is that they are non-conductor of electricity since the ions are fixed in positions and are unable to move.

The diagram below shows the crystal lattice for Sodium Chloride.

Properties of Ionic Substances

• All ionic compounds exist as solids
• Ionic substances are conductor of electricity only in the solution form and molten forms,
• They have a very high melting and boiling point due to the strong electrostatic forces between the ions,
• The ions in the ionic compounds exist in a giant crystal lattice,
• There are strong bonds between ions.

Formulae of Ionic Compounds:

The simplest way to write formula for ionic atoms is to interchange the valency of metal and non-metal atoms as the number of atoms required to form the bond. Detailed discussion will require the knowledge of periodic table but for reference, let us consider, Calcium Chloride.

• Calcium has valency of +2 as it is in Group two of the periodic table. Chlorine on the other hand is in group 7 and hence has a valency of -1 (8-valence electrons for non-metals). This means, one chlorine atom can almost gain 1 electron to complete octet and one calcium atom has to lose 2 electrons to complete octet.
• Hence, we interchange the valency and get the formula for their ionic compound. (Do not include sign or 1 charge)
• Detailed discussion after periodic table will be discussed.

Metallic Bonding:

Definition:

Metallic Bonding involves the delocalization of valence electron resulting in the metal ion being surrounded in a sea of electrons. The diagram shows the metallic bonding in sodium metal.

Properties of Metals:

• Metals are hard and shiny.
• They have high melting and boiling points,
• They are good conductors of heat and electricity,
• Some metals are soluble in water,
• Metals form giant stable lattices,
• They are ductile: can be pulled into wires.
• They are malleable: they can be hammered to change their shape or turn into sheets.

Malleability of Metals:

In metals, atoms are arranged in the form of rows. When we apply pressure, these rows slide over each other so we get different shapes.

Conductivity of Metals:

• Metals are good conductors of electricity since the metal ions are surrounded by a sea of electrons where the electrons can move freely around the positive metal ions. Due to this free movement of electrons, metals can conduct electricity easily.
• Metals are god conductors of heat since:
  • There are moving electrons which allow transfer of heat,
  • The ions in metals are close together, so when they vibrate, heat can be transferred easily.

Covalent Bonding:

Definition:

A bond formed by the sharing of electron between non-metal atoms.

Dot and Cross Diagrams:

• Dot and cross diagrams are used to show covalent bonding.
• Similar to ionic bonding, the goal of the atoms is to complete their octet and hence, they share their electron so that all atoms have a complete valence shell.
• To draw dot and cross diagrams, we only consider valence shells and place the shared electrons in the intersection of the valence shells as shown in the diagrams.
• We assign dot to one type of atom and cross to the other type of atom similar to the way ionic bonding was depicted.

Types of Covalent Bonds:

Single Covalent bond:

• A bond formed by the sharing of a pair of electrons between two non-metal atoms.
• It is represented by a single line e.g. H₂ (H-H), H₂O(H-O-H)

Double Covalent Bond:

• A bond formed by the sharing of two pair of electrons between two non-metal atoms.
• This happens when both sides are deficient with two electrons to complete octet.
• It is represented by a double line e.g. O₂ (O=O), CO₂(O=C=O),

Triple Covalent Bond:

• A bond formed by the sharing of three pair of electrons between two non-metal atoms.
• It is represented by three line e.g. N₂ (N≡N)

Properties of Covalent Compounds:

• Covalent compounds can exist in all three states of matter,
• They have low melting and boiling points,
• They do not conduct electricity,
• Covalent compounds are insoluble in solvents like water,

Types of Covalent Compounds:

The covalent compounds are divided into two types:

• The compounds that form simple molecules,
• The compounds that form macromolecules.

Simple molecular structures:

• These are the compounds which are formed from simple(small) independent molecules.
• These molecules are held together by weak attractive forces called Van der Waal’s forces e.g. H₂O, Cl₂, NH₃, CH₄

Macromolecular structures:

• These compounds are formed by giant macromolecules with extremely large molecular lattice.
• They are very stable as all the atoms are joined together by strong covalent bonds to give a giant three-dimensional lattice.
• These lattices are tetrahedral in shape as each atom joins covalently to 4 other atoms.
• For example, Diamond, graphite and sand.

Allotropes:

Allotropes are different forms of the same element which have different physical properties and similar chemical properties.

Allotropy:

The property of an element to have different forms or allotropes.

Carbon Allotropes:

The two commonly discussed allotropes of carbon are diamond and graphite. They are both macromolecules with tetrahedral shape.  

• High melting points:
  • Diamond and graphite both have high melting points as they are macromolecules and have strong forces between them. As a result, more heat energy is required to melt the lattice.
• Graphite as lubricant:
  • Graphite has atoms arranged in layer-like structure. When force is applied, the layers slide over each other and hence reduce friction.
• Graphite conduction:
  • Graphite is a non-metal, but it is a conductor of electricity. This is because the atoms in graphite are arranged in layers which have free moving electrons between them. As a result of these electrons, graphite is able to conduct electricity

Lesson Tags

Bonding | Ionic Bonding | Metallic Bonding | Covalent Bonding | Detailed Notes For Preparation & Revision | O Level Chemistry 5070 and IGCSE Chemistry 0620

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