Chemical Bonding - Grade 10


Chemical bonding is the attraction between atoms that allows the formation of chemical substances. There are several types of chemical bonds, including:

• Ionic bonds: Formed when one atom transfers electrons to another, resulting in the attraction between positively and negatively charged ions.

• Covalent bonds: Involve the sharing of electron pairs between atoms, leading to the formation of molecules.

• Metallic bonds: Occur in metals, where electrons are pooled and shared among a lattice of positive ions, resulting in conductivity and malleability.

1.IONIC BONDING

• Ionic Bond is the electrostatic force of attraction formed when there is complete transfer of electrons between atoms to attain stability resulting into 2 oppositely charged ions

• Generally ionic bonds are formed between a metal and a non-metal except in Aluminium and Chlorine

• All ionic compounds form Giant Ionic Structures

PYSICAL PROPERTIES OF IONIC COMPOUNDS

1. SOLUBILITY: Most ionic compounds dissolves in water because they are made of oppositely charged ions that are attracted by the polar water molecules.

2. MELTING AND BOILING POINT: Ionic compounds have a high melting and boiling point because they have a giant ionic structure with strong ionic bonds.

3. ELECRRICAL CONDUCTIVITY: Ionic compounds conduct electricity in molten or aqueous state due to presence of mobile ions

FACTORS THAT CONTRIBUTE TO STRENGTH OF IONIC BOND

1. ATOMIC SIZE: The smaller the atomic size the stronger the ionic bond

2. CHARGE OF ION :The higher the charge the stronger the ionic bond


2.COVALENT BOND

• A covalent bond is a bond formed when atoms mutually share valence electrons to attain stability. Meaning, each of the 2 bonded atoms contribute one electron to form the shared pair electrons (mutual sharing)

• A covalent bond is mostly formed between non-metals, except in Aluminium and Chlorine where a metal and a non-metal form a covalent bond

• In a diagram representing the covalent bond, a pair of shared electrons is represented by a dash (-) and is called single covalent bond. It can also be a double or triple covalent bond .

• However, non-metals can also bond to form a dative covalent bond or also known as a coordinate bond

• A dative covalent bond is a type of covalent bond where both of the electrons in the shared pair are from the donor atom

• In a diagram representing the dative covalent bond, it can be shown as an arrow .The arrow points at the acceptor atom

• Covalent bonding are associated with 2 structures:

• 1.Simple molecular structures

• 2.Giant covalent structures

1.Simple molecular structures

Most molecular structures are either gasses or liquids at room temperatures

Molecules associated with simple molecular structures are held intermolecular forces of attraction:

a .Van der Waal's forces -It is present in all molecules .They occur due to opposite charges developing between atoms or molecules. They generally have a low melting and boiling point. The strength of the van der Waal force increase as size of the molecular increases.

b. Hydrogen bonding- It's an intermolecular force where electro-positive hydrogen atom is attracted to an electro-negative atom of a neighbouring molecule

Physical Properties of Substances with Simple Molecular Structures

• Electrical Conductivity: They are a poor conductor of both heat and electricity in both solid and molten state. In solid state, it's because it lacks mobile ions and in molten state it's because it lacks delocalized electrons.

• Melting and boiling point: They have a low melting and boiling point_because their molecules are held by weak van der Waal forces of attraction

• Solubility: They are mostly insoluble in water except with the molecules with hydrogen bonding due to the polar nature of water

2.Giant Covalent Structures

• Giant covalent structures occur in group vi elements and some of there compounds

• Examples of substances with giant covalent structures include: Diamonds, Silicon, Graphite, Silicon iv oxide

• Diamond and graphite are allotropes of carbon. Allotropes are different forms of an element that exists in the same physical state

• In a diamond structure all four valence electrons in each carbon atom are used in bonding leaving no delocalized electrons .This makes diamond a poor conductor of electricity

• Diamond is the hardest known substance due to the uniformity of strong covalent bonds between atoms through out the giant covalent structure .

• Properties of diamond include:

1.It's a colorless, transparent and shiny crystalline solid

2.Its has a high density due to its continuous close packaging of carbon atoms that are held by strong covalent bond between atoms throughout the giant covalent structure

3.Has a very high melting point because it has a giant covalent structure with strong covalent bond

4.It is the hardest known substance due to its uniformity of strong covalent bond between atoms throughout the giant covalent structure

• Diamond is mainly used for making jewelry (due to its shiny appearance after polishing) and to make drill bits (due to its hardness)

• In Graphite, each carbon atom is bonded to 3 other carbon atom

• In the graphite structure, hexagonal layers in which the carbon atoms are held by strong covalent bond while the hexagonal layers are held by weak van der Waals forces. Each carbon atom uses two 3 valence electrons in bonding hence leaving 1 delocalized electrons. This explains why graphite is a good conductor of heat and electricity

• Graphite can be used as:

1.A lubricant ( because it's soft and slippery and has a high melting point)

2. An electrode (because it's a good conductor of electricity)

3.Making pencil lead (because the hexagonal layers held by weak van der Waals forces hence slide over each other when pressed)

• In Silicon, each silicon atom is covalently bonded to form other silicon atoms, forming a giant covalent structure

• Silicon has a high melting and boiling point because it has a strong covalent structure with strong covalent bonds

• In Silicon iv Oxide, each silicon atom is covalently bonded to 4 oxygen atoms, forming a giant covalent structure

• Silicon vi oxide is insoluble in water

• It's also doesn't conduct electricity because it lacks delocalized electrons in its structure

• Silicon iv oxide has a high boiling and melting point because it has a giant covalent structure with strong covalent bonds

Properties of Giant Atomic Structures

• They have a high melting and boiling point because they have giant covalent structure with strong covalent bond

• They are poor conductors of electricity because they lack delocalized electrons except silicon and graphite which are metaloids

• They are insoluble in water

3.METALLIC BONDING

• Metallic Bonding is an electrostatic force of attraction between positive ions and delocalized electrons

• Metallic atoms lose valence electrons which results in delocalized electrons

• These delocalizes electrons are mutually attracted by the main nuclei

• A metallic bond is a very strong bond hence needs a lot of energy to break

• Metallic bonds form metallic structures

• For example, a group i element known as alkali metals form metallic bonds with giant metallic structures and each positive nucleus as one delocalized electrons

• it goes the same in group ii and iii elements except the fact that there is increase in delocalized electrons and has different family

Physical Properties of Metals

1. Electrical Conductivity- Metals are good conductors electricity due to presence of delocalized electrons. Electrical conductivity increases in increase in delocalized electrons. An increase in temperature reduces the electrical conductivity of metals because increase in temperature increases the vibrational energy and resistance which interferes with flow of electrons

2. Melting and Boiling Point- Metals have a high melting and boiling point because it has a metallic structure with strong metallic bond that requires a lot of energy to break

Factors Affecting Strength of metallic Bond

1. Number of Delocalized Electrons- The more the number of delocalized electrons, the stronger the metallic structure

2. Atomic Size- The smaller the atomic size the stronger, the stronger the metallic bond

Properties of substances with Giant Metallic Structures

  1. Are good conductors of heat and electricity

  2. Are insoluble in water

  3. They have a high melting and boiling point