Chemical Bond and structure
N.G Nyirenda
Checkpoint Science form 3
1
LESSON OBJECTIVES
• Know and understand what a bond is.
• Know different the different types of bonds
• Know and understand to explain how different types of bonds are
formed.
• Know and understand the process of molecule formation.
• Know and understand the chemical structure due to bond formation
Checkpoint Science form 3
2
MOLECULE FORMATION
• When two or more elements combine.
• Create a new structure.
• Structure known as a molecule.
• Molecules can be simple or compound.
• The formation is dependent upon a connection that is referred to as a
bond.
• Bonds can form between different atoms in some cases molecules.
• Mostly make use of the valence electrons in the outer most shell.
Checkpoint Science form 3
3
VALENCE ELECTRONS
• Electrons in the outermost shell
of an atom.
• Outer shell should not be filled.
• Responsible and involved in the
bond formation process.
• When the outer shell is filled it is
sometimes referred to as a
valence shell.
Checkpoint Science form 3
4
VALENCE ELECTRONS PER GROUP
Periodic Table Group
Valence Electrons
Alkali metals – Group 1 (I)
1
Alkaline earth metals – Group 2 (II)
2
Boron group – Group 13 (III)
3
Carbon group – Group 14 (IV)
4
Nitrogen group – Group 15 (V)
5
Oxygen group – Group 16 (VI)
6
Halogens – Group 17 (VII)
7
Noble gases – Group 18 (VIII or 0)
8
Checkpoint Science form 3
5
CHEMICAL BONDS
• Bonds is a general term.
• In the science we use the term chemical bond.
• This is to be specific.
• We will look at two types of chemical bonds, namely:
• Covalent chemical bonds
• Ionic chemical bonds
• Each of these still depends on the use of valence electrons to form
the bonds
Checkpoint Science form 3
6
IONIC BONDS
• Formed when an electron is lost or gained by an atom.
• Causes a change in the overall charge of an atom.
• The charge can be positive or negative.
• Electrostatic charges responsible for keeping the bond stable
• Protons and neutron numbers remain the same.
• Mostly form between metals and non-metals.
• Ionic bonds have strong electrostatic forces between oppositely
charged ions
• Forms the basis upon which electricity generation and transmission is
possible
Checkpoint Science form 3
7
IONIC BOND FORMATION ILLUSTRATION
BEFORE BOND FORMATION
AFTER BOND FORMATION
Checkpoint Science form 3
8
IONS AND THEIR TYPES
• Atoms that lose an electron are
called Ions
• Ions with overall positive charge
are called Cations.
• Ions with overall negative charge
are called Anions.
Checkpoint Science form 3
9
DIFFERENCES IN TYPES OF IONS
CATIONS
ANIONS
• Positive-charged ion
• Number of protons is greater than
the number of electrons
• Metals, in general, produce
cations.
• Cations are smaller than anions.
• E.G. Na+, mg+2
• Negative-charged ion
• Number of electrons greater than
number of protons.
• Non–metals, in general, produce
anions.
• Anions often bigger than cations.
• E.G. Cl–, br–
Checkpoint Science form 3
10
IONIC LATTICE
2D
3D
Checkpoint Science form 3
11
COVALENT BONDS
• Forms when two atoms share a pair of electron.
• Neither of the two atoms has full control of the electron
• No change in atomic charge
• The shared electron leads to a valence shell for each respective atom.
• Form extremely strong bonds needing a lot of energy to break them.
• Forms between non-metals and non-metals
• An atom can form multiple covalent bonds with other atoms
depending on the valence needs.
• The number of covalent bonds is equal to eight minus the group
number. (Key Fact)
Checkpoint Science form 3
12
COVALENT BOND ILLUSTRATION
BEFORE BOND FORMATION
AFTER BOND FORMATION
Checkpoint Science form 3
13
COVALENT BONDS CONT…
Checkpoint Science form 3
14
DOUBLE COVALENT BOND
BEFORE BOND FORMATION
AFTER BOND FORMATION
Checkpoint Science form 3
15
DIFFERENCE BETWEEN IONIC AND COVALENT BOND
COVALENT BONDS
IONIC BONDS
• Between non-metals
• Definite shape
• Low melting and boiling points
• Low polarity (+/- charge)
• More flammable
• Liquid or gaseous state at room
temperature
• Between a metal and non-metal
• No definite shape
• High melting and boiling points
• High polarity (+/- charge)
• Less flammable
• Solid state at room temperature
Checkpoint Science form 3
16
CHEMICAL STRUCTURES
• The spatial arrangement of atoms in a molecule.
• Spatial = relating to the position, area, and size of things
• Determines the molecular geometry of the molecule.
• Molecules are not random clusters of atoms.
• Functional groups but are arranged in a concrete pattern.
Checkpoint Science form 3
17
TYPES OF CHEMICAL STRUCTURE
• Kekule or Lewis Structure
• Condensed Structure
• Skeletal or Line Structure
Checkpoint Science form 3
18
KEKULE OR LEWIS STRUCTURE
• Focuses on the valence shell electrons in the
molecule.
• depicts how atoms are bonded within a molecule.
• electrons are shown as Dots.
• dashes indicates the bond between the atoms.
• A single dash indicates a single bond.
• A double dash indicates a double bond.
• A triple dash indicates a triple bond.
• All atoms and lone pairs are shown in the structure.
Checkpoint Science form 3
19
CONDENSED STRUCTURE
• A condensed structure represents molecular entities in which atoms
of the molecule are shown without a bond.
Checkpoint Science form 3
20
SKELETAL OR LINE STRUCTURE
• A skeletal or line structure represents molecular entities in which
bonds between atoms are shown without actual atoms.
Checkpoint Science form 3
21
CHEMICAL STRUCTURES
COVALENT STRUCTURES
IONIC STRUCTURES
Checkpoint Science form 3
22
Questions and PREP
• Topic self paced revision
• Student text book pages 70-80
• Form test next week
• The revision is your prep effective 02/11/2023 up to 06/11/2023
• Presentation available on portal at HTTPS://SCHOOL.KA.AC.MW
Checkpoint Science form 3
23
END OF TOPIC.
Checkpoint Science form 3
24