If you don’t understand something , watch a yt video on the entire chap or topic, or
small portion of the vid of the entire chap. (Najam’s academy). Exams ask only
byhearting stuff (definitions,laws, examples… and textbook qs )
Chapter- CHEMICAL BONDING -- EXPLAIN TO URSELF
- Molecules are obtained by the combination of two or more than two
atoms of the same or different elements
VALENCE ELECTRONS
-The outer most shell of any atom is called its valence shell
-The electrons in the outermost shell are called valence electrons.they
decide valency of atom
- a chemical bond is a bond that happens when two atoms have combined
or a bond is formed between the two. Chemical bond is caused by a
decrease of energy. (Lower energy = more stable.) the properties of
atoms change after they have been formed into molecule.
Why do atoms bond? - Atoms bond because they want a full outer shell
like noble gases that makes them stable. (all noble gases have stable
electronic configuration, valency is 0 always)
- Kossel’s theory says Atoms can get a stable electronic configuration like
noble gases by losing, gaining, or sharing electrons. There are dif types of
chemical bonds: 1. Ionic or electrovalent bond , 2. Covalent bond , 3. Co-
ordinate covalent bond, theres also special bond called hydrogen bond.
IONIC OR ELECTOVALENT BOND
- Formation of ionic compound NaCl: for Na (sodium) - Its atomic
number is 11. Electronic configuration: 2,8,1. Being highly
electropositive, it loses one electron to achieve the noble gas
configuration of neon (2,8) and becomes a positively charged ion
(Na⁺) (cause it lost 1 negative electron, and now has more protons,
11 protons, 10 electrons)
- Now for Cl , 2nd part of nacl : Its atomic number is 17. Electronic
configuration: 2,8,7. It gains one electron to achieve the noble gas
configuration of argon (2,8,8) and becomes a negatively charged ion
(Cl⁻).
- Bonds are held together by electrostatic attraction. Ionic bonds/
electrovalent are the electrostatic force of attraction that holds the
cation and anion together. The compounds formed by ionic bonds
are termed as ionic or electrovalent compounds.
-
- Energetics of Ionic Compound Formation:
, Sodium needs more energy to lose an electron than chlorine releases when gaining an
electron, yet the formation of NaCl still lowers the overall energy. Let’s look at this more
closely
Born Harber Cycle
Steps to form nacl, not ways to form nacl.
1. Sublimation of solid sodium directly to gaseous sodium atoms.
Equation -> Na(s) ⎯⎯→ Na(g) ; ΔH = 108.7 kJ mol–1
2. Ionization of gaseous sodium atom to give sodium ion.
Na(g) ⎯⎯→ Na+ (g) + e– ΔH = 493.8 kJ mol–1
(js to know, not imp: The process in which an atom or molecule loses an
electron and becomes a positively charged ion (cation), so before
ionisation ,it was neutral, now it has a charge and it is +)
3. Dissociation of gaseous chlorine molecule into chlorine atoms
Js to know: The process in which a molecule splits into two or more
atoms/ ions.
4. electron gain: Conversion of gaseous chlorine atom to chloride ion
(addition of electron) :
Cl(g) + e– ⎯⎯→ Cl– (g); ΔH = –379.5 kJ mol–1
(js to know : electron gain is opposite of ionization- → atom gains an
electron → forms anion (–) 5. Formation of NaCl from sodium and chloride
ions.(Crystal or lattice formation).
Na+ (g) + Cl– (g) ⎯⎯→ Na+ Cl– (s). The energy released in this step is lattice
energy.
ΔH = –754.8 kJ mol–1
so throughout entire process, there has been increase in energy but more
than that there’s larger decrease in energy. This entire process is based
on law of conservation of energy and is the BornHaber cycle.
Born Haber Cycle: A stepwise method to calculate the energy changes
occured in forming an ionic compound from its elements.
, Imp - The formation of an ionic compound is favoured / determined by 1. .
Low ionisation energy of the metal, 2. High electron affinity of the other
element (non-metal), and 3. High lattice energy..
Characteristic Properties of Ionic Compounds:
Ionic compounds exist as crystalline solids, in which the ions are arranged in a regular
three-dimensional structure. They are generally hard and brittle.
They have high melting and boiling points due to the strong
electrostatic forces between the ions.
They are generally soluble in water but less soluble in non-polar
solvents like ether or alcohol.
They conduct electricity when in the molten state or in aqueous
solution.
Limitations / problems of Kossel’s Theory: -- solved by Lewis theory
of covalent bonding.
It explains bonding only for solids made of electropositive elements (from group 1 and 2)
and electronegative elements.
It cannot explain the formation of molecules like SO₂ or O₂.
COVALENT BOND
Like Kossel, Lewis proposed another method atoms can achieve a noble gas electronic
configuration by atoms sharing a pair of electrons instead of kossel's method - gain/lose
electrons.
Here, atoms share 1 electron to form the shared pair. Electrons are shows as dots.
- they share 1 electron each, form a
shared pair of 2.
This shared pair of electrons makes both atoms stable and creates a bond between them,
this is called covalent bond.
covalent bonds- A bond formed when two atoms share a pair of electrons to achieve a
stable noble gas configuration.
Covalent compounds: Compounds that are formed due to covalent bonds between
atoms.
Lewis Structure
- Lewis gave a simple way to represent bonding in molecules, called
Lewis electron-dot structures or Lewis structures.
small portion of the vid of the entire chap. (Najam’s academy). Exams ask only
byhearting stuff (definitions,laws, examples… and textbook qs )
Chapter- CHEMICAL BONDING -- EXPLAIN TO URSELF
- Molecules are obtained by the combination of two or more than two
atoms of the same or different elements
VALENCE ELECTRONS
-The outer most shell of any atom is called its valence shell
-The electrons in the outermost shell are called valence electrons.they
decide valency of atom
- a chemical bond is a bond that happens when two atoms have combined
or a bond is formed between the two. Chemical bond is caused by a
decrease of energy. (Lower energy = more stable.) the properties of
atoms change after they have been formed into molecule.
Why do atoms bond? - Atoms bond because they want a full outer shell
like noble gases that makes them stable. (all noble gases have stable
electronic configuration, valency is 0 always)
- Kossel’s theory says Atoms can get a stable electronic configuration like
noble gases by losing, gaining, or sharing electrons. There are dif types of
chemical bonds: 1. Ionic or electrovalent bond , 2. Covalent bond , 3. Co-
ordinate covalent bond, theres also special bond called hydrogen bond.
IONIC OR ELECTOVALENT BOND
- Formation of ionic compound NaCl: for Na (sodium) - Its atomic
number is 11. Electronic configuration: 2,8,1. Being highly
electropositive, it loses one electron to achieve the noble gas
configuration of neon (2,8) and becomes a positively charged ion
(Na⁺) (cause it lost 1 negative electron, and now has more protons,
11 protons, 10 electrons)
- Now for Cl , 2nd part of nacl : Its atomic number is 17. Electronic
configuration: 2,8,7. It gains one electron to achieve the noble gas
configuration of argon (2,8,8) and becomes a negatively charged ion
(Cl⁻).
- Bonds are held together by electrostatic attraction. Ionic bonds/
electrovalent are the electrostatic force of attraction that holds the
cation and anion together. The compounds formed by ionic bonds
are termed as ionic or electrovalent compounds.
-
- Energetics of Ionic Compound Formation:
, Sodium needs more energy to lose an electron than chlorine releases when gaining an
electron, yet the formation of NaCl still lowers the overall energy. Let’s look at this more
closely
Born Harber Cycle
Steps to form nacl, not ways to form nacl.
1. Sublimation of solid sodium directly to gaseous sodium atoms.
Equation -> Na(s) ⎯⎯→ Na(g) ; ΔH = 108.7 kJ mol–1
2. Ionization of gaseous sodium atom to give sodium ion.
Na(g) ⎯⎯→ Na+ (g) + e– ΔH = 493.8 kJ mol–1
(js to know, not imp: The process in which an atom or molecule loses an
electron and becomes a positively charged ion (cation), so before
ionisation ,it was neutral, now it has a charge and it is +)
3. Dissociation of gaseous chlorine molecule into chlorine atoms
Js to know: The process in which a molecule splits into two or more
atoms/ ions.
4. electron gain: Conversion of gaseous chlorine atom to chloride ion
(addition of electron) :
Cl(g) + e– ⎯⎯→ Cl– (g); ΔH = –379.5 kJ mol–1
(js to know : electron gain is opposite of ionization- → atom gains an
electron → forms anion (–) 5. Formation of NaCl from sodium and chloride
ions.(Crystal or lattice formation).
Na+ (g) + Cl– (g) ⎯⎯→ Na+ Cl– (s). The energy released in this step is lattice
energy.
ΔH = –754.8 kJ mol–1
so throughout entire process, there has been increase in energy but more
than that there’s larger decrease in energy. This entire process is based
on law of conservation of energy and is the BornHaber cycle.
Born Haber Cycle: A stepwise method to calculate the energy changes
occured in forming an ionic compound from its elements.
, Imp - The formation of an ionic compound is favoured / determined by 1. .
Low ionisation energy of the metal, 2. High electron affinity of the other
element (non-metal), and 3. High lattice energy..
Characteristic Properties of Ionic Compounds:
Ionic compounds exist as crystalline solids, in which the ions are arranged in a regular
three-dimensional structure. They are generally hard and brittle.
They have high melting and boiling points due to the strong
electrostatic forces between the ions.
They are generally soluble in water but less soluble in non-polar
solvents like ether or alcohol.
They conduct electricity when in the molten state or in aqueous
solution.
Limitations / problems of Kossel’s Theory: -- solved by Lewis theory
of covalent bonding.
It explains bonding only for solids made of electropositive elements (from group 1 and 2)
and electronegative elements.
It cannot explain the formation of molecules like SO₂ or O₂.
COVALENT BOND
Like Kossel, Lewis proposed another method atoms can achieve a noble gas electronic
configuration by atoms sharing a pair of electrons instead of kossel's method - gain/lose
electrons.
Here, atoms share 1 electron to form the shared pair. Electrons are shows as dots.
- they share 1 electron each, form a
shared pair of 2.
This shared pair of electrons makes both atoms stable and creates a bond between them,
this is called covalent bond.
covalent bonds- A bond formed when two atoms share a pair of electrons to achieve a
stable noble gas configuration.
Covalent compounds: Compounds that are formed due to covalent bonds between
atoms.
Lewis Structure
- Lewis gave a simple way to represent bonding in molecules, called
Lewis electron-dot structures or Lewis structures.
