Chapter 5 : Chemical BondStability of Noble Gases1. Group 18 elements (Noble Gases) exist as monoatom in nature.2. They are inert in nature and do not react with any other elements (or themselves) to form any chemical compounds.3. In other words, they are chemically very stable (or chemically very non-reactive).

Duplet and Octet Electron Arrangement

1. The charge on the nucleus and the number of electrons in the valence shell determine the chemical properties of an atom.2. The stability of noble gas is due to their electrons arrangement.3. The diagram above shows the first four elements of Noble Gas. We can see that the outer most shell (valence shell) of Helium has 2 electrons. We call this duplet electron arrangement.4. The maximum number of electrons can be filled in the first shell is 2 electrons, which means 2 electrons in the first shell is considered FULL.5. The valence shell all other Group 18 elements (including Xenon and Radon which is not shown in the diagram) has 8 electrons, and we call this octet electron arrangement.6. When the electron arrangement of an atom is duplet or octet, the energy of the electrons is very low, and it is very difficult (even though it is not impossible) to add or remove electrons from the atom.7. This explains why noble gases are reluctant to react with all other elements.

The Octet Rule1. Atoms of other main group elements which are not octet tend to react with other atoms in various ways to achieve the octet.2. The tendency of an atom to achieve an octet arrangement of electrons in the outermost shell is called the octet rule.3. If the outermost shell is the first shell, then the maximum number of electrons is two, and the most stable electron arrangement will be duplet.4. A configuration of two electrons in the first shell, with no other shells occupied by electrons, is as stable as the octet electron arrangement and therefore is also said to obey the octet rule.How Atoms Achieve Duplet or Octet Electron Arrangement?1. Atoms can achieve duplet or octet electron arrangement in 3 ways:1. throw away the excess electron(s)1. receiving electron(s) from other atom if they are lack of electron(s)1. sharing electron

(A sodium atom throws away an electron to achieve octet electron arrangement)

(A fluorine atom receives one electronto achieve octet electron arrangement)

(Two fluorine atoms share one pair of electronsto achieve octet electron arrangement)

Chemical Bond1. 2 types of chemical bonds are commonly formed between atoms, namely1. Ionic Bond1. Covalent BondThe Ionic Bond

(Ionic Bond)

1. By releasing or receiving electron(s), the atoms will become ions and consequently form ionic bond between the ions.2. Ionic bonds are always formed between metal and non-metal. For example, sodium (metal) react with chlorine (non-metal) will form an ionic bond between sodium ion and chloride ion.3. The compounds formed are called the ionic compounds.4. Some time, an ionic bond is also called electrovalent bond.

The Covalent Bond

(Covalent Bond)

1. By sharing electron(s), the atoms will form covalent bond between the atom and the molecule formed is called the covalent molecule.2. Covalent bond is always formed between non-metal with another non-metal.

Formation Of Ion1. An ion is an atom or group of atoms carrying positive or negative charge. Example Ca2+, O2-, SO42-etc.2. If a particle has equal numbers of protons (+) and electrons (-), the particle charge is zero, and the particle is said to be neutral.3. In a chemical reaction, electron(s) can be transferred from atom to another atom.4. If electron(s) is removed from an atom, the number of protons will be more than number of electrons. In this case, the atom will has excess positive charge and hence form a positive ion (cation).

(An atom losses electron to form positive ion)

5. If an atom gains electrons, there is an excess negative charge in the atom, so a negative ion is formed.6. In other words,6. The atom losing electrons forms a positive ion (cation) and is usually a metal.6. The atom gaining electrons forms a negative ion (anion) and is usually a non-metallic element.

(An atom gain electron to form negative ion)

Formation Of Positive Ion1. Usually, the atom of metals consist of 1, 2 or 3 valence electrons.2. In order to achieve octet electrons arrangement, the atoms will release the valence electrons.3. After releasing the valence electrons, the protons in the nucleus will out number the electrons. As a result, positive ions formed.

Example: Formation of Ion with+1 Charge

(A sodium atom release one electron to form a sodium ion with +1charge)

Example: Formation of Ion with+2 Charge

(A magnesium atom release one electron to form a sodium ion with+2charge)

Example: Formation of Ion with+3 Charge

(An aluminium atom release one electron to form a sodium ion with+3charge)

Formation Of Negative Ion1. Negative ions are formed among atoms of non-metal elements except group-18 elements.2. Non-metal elements usually located in group 15, 16 and 17 in the periodic table and have 5, 6 or 7 valence electrons.3. To achieve octet arrangement of electrons, their atoms will receive 3, 2 or 1 electron.4. As a result, the electrons will out number the protons and hence negative ions formed.Formation of Negative Ions of -1 Charge

(A fluorine atom receives one electron to form a fluoride ion with -1 charge)

Formation of Negative Ions of -2 Charge

(An oxygen atom receives two electrons to form a oxide ion with -2 charge)

Difference Between An Atom And An Ion That Have Same Electrons ArrangementDifference Between Fluoride Ion and Neon Atom

1. After forming an ion, the electron arrangement of the ion is similar to the noble gases.2. For example, the electron arrangement of fluoride ion is 2.8 which is similar to a Neon atom, 2.8.3. Fluoride ion and the neon atom have similar electron arrangement.4. Fluoride ion carries chargewhereasneon atom is neutral.

(The electrons arrangement of a fluoride ion is the same as a neon atom. However, they are so much different chemically)

Ionic Bonding

1. Ionic bonds are formed by one atom transferring electrons to another atom to form ions.2. Ions are atoms, or groups of atoms, which have lost or gained electrons.3. The atom losing electrons forms a positive ion (a cation) and is usually a metal.4. The atom gaining electrons forms a negative ion (an anion) and is usually a non-metallic element.5. Ions of opposite charge will attract one another by strong electrostatic force, thus creating an ionic bond.6. Ionic bond is also known as electrovalence bond.Example: Ionic Bonding between Group 1 Metals and Group 17 Elements

1. Figure above shows the illustration of the formation of ionic bond between a sodium atom (group 1 metal) and a chlorine atom (group 17 element).2. The electron arrangement of sodium atom is 2.8.1, which is not octet and hence not stable.3. To achieve octet electrons arrangement, the sodium atom donate/release one electron and form sodium ion.4. The electron arrangement of chlorine atom is 2.8.7, which is also not octet and hence not stable, too.5. To achieve octet electrons arrangement, the chlorine atom receives one electron from sodium atom and form a chloride ion.6. The sodium ion and the chloride ion carry opposite charge, hence they attract each other and form an ionic bond between each other.

Example: Ionic Bonding between Group 2 Metals and Group 17 Elements

1. Figure above shows the illustration of the formation of ionic bond between two potassium atoms (group 1 metal) and an oxygen atom (group 16 element).2. The electron arrangement of potassium atom is 2.8.8.1, which is not octet and hence not stable.3. To achieve octet electrons arrangement, the potassium atom donate/release one electron and form potassium ion.4. The electron arrangement of oxygen atom is 2.6, which is also not octet and hence not stable, too.5. To achieve octet electrons arrangement, the oxygen atom receives two electrons from potassium atoms and form an oxide ion.6. The potassium ions and the oxide ion carry opposite charge, hence they attract each other and form two ionic bond between the ions.

Example: Ionic Bonding between Group 2 Metals and Group 16 Elements

1. Figure above shows the illustration of the formation of ionic bond between a calcium atom (group 2 metal) and an oxygen atom (group 16 element).2. The electron arrangement of calcium atom is 2.8.8.2, which is not octet and hence not stable.3. To achieve octet electrons arrangement, the potassium atom donate/release two electrons and form calcium ion.4. The electron arrangement of oxygen atom is 2.6, which is also not octet and hence not stable, too.5. To achieve octet electrons arrangement, the oxygen atom receives two electrons from the calcium atom and form an oxide ion.6. The calcium ion and the oxide ion carry opposite charge, hence they attract each other and form an ionic bond between each other.

Predicting The Formula Of Ionic Compound

1. We can predict the charge of the ions formed from an element base on the group of the element.2. From the charge, we can then write the formula of the ionic compound formed.3. In short, we can predict the formula of an ionic compound if we know the group (in periodic table) of the elements in the compound.4. Table below shows the formula of the ionic compounds formed by the elements from different group in a periodic table.

ElementsFormula of Ionic CompoundExamples

Atoms of Metal, MAtoms of Non-Metal, N

Group 1Group 15M3NNa3N

Group 1Group 16M2NK2O

Group 1Group 17MNLiCl

Group 2Group 15M3N2Ca3N2

Group 2Group 16MNMgO

Group 2Group 17MN2BaBr2

Group 13Group 15MNAlN

Group 13Group 16M2N3Al2O3

Group 13Group 17MN3AlI3

Covalent Bonding1. Covalent bonds are formed by atoms sharing electrons to form molecules. This type of bond usually formed between two non-metallic elements.2. In the formation of covalent bonds, atoms of non-metals will combine with each other to donate one, two or three electrons for sharing.3. The compound formed through the formation of covalent bonds is called the covalent compounds.

Examples of Covalent CompoundCovalent CompoundFormulaCovalent CompoundFormula

ChlorineCl2PhosphorusP4

HydrogenH2Sulfur dioxideSO2

OxygenO2Carbon dioxideCO2

NitrogenN2Tetrachloro-methaneCCl4

Examples of Formation of Covalent CompoundsFormation of Fluorine Molecule

1. The electrons arrangement of a fluorine atom is 2.72. To achieve octetelectrons arrangement, 2 fluorine atoms share 1 pair of electrons between each other.3. As a result, a covalent bond formed between the 2 atoms.Formation of Oxygen Molecule

1. The electrons arrangement of an oxygen atom is 2.62. To achieve octetelectrons arrangement, 2 fluorine atoms share 2 pair of electrons between each other.3. As a result, 2 covalent bonds formed between the 2 atoms.

Formation of Carbon Dioxide Molecule

1. The electrons arrangement of an oxygen atom is 2.6 and the electrons arrangement of a hydrogen atom is 1.2. To achieve octetelectrons arrangement, the oxygen atom share 2 pair of electrons with 2 hydrogen atoms.3. The hydrogen atoms achieve duplet electrons arrangement after sharing electron with the oxygen atom.4. As a result, covalent bonds formed between the oxygen atom and the hydrogen atoms.

Number of Bond1. There are 3 types of covalent bond:1. Single covalent bond sharing of one pair of electrons1. Double covalent bond sharing of two pairs of electrons1. Triple covalent bond sharing of three pairs of electrons

ExampleNumber of electronExample and type of covalent bond

1 pairtype of covalent bond: Single Bond

2 pairtype of covalent bond: Double Bond

3 pairtype of covalent bond: Triple Bond

Formation of Single Bond (Hydrogen Molecule)

Formation of Double Bond (Oxygen Molecule)

Formation of Triple Bond (Nitrogen Molecule)

Predicting The Molecular Formula Of Covalent Compounds1. Like the formula of ionic compounds, the formula of most covalent compounds can be predicted by referring to the group in periodic table of the elements in the compound.2. We can predict the formula of a covalent compound by referring to the valency of the elements in the compound, if we know which group in periodic table the element is located.3. The valency of an atom is the number of electrons receive of release to achieve octet electrons arrangement.4. For example, the electron arrangement of an oxygen atom is 2.6. To achieve octet electrons arrangement, the oxygen atom need to receive 2 electrons. Therefore, the valency of oxygen is 2.5. Table below shows the group of the elements, the valency of the elements and the predicted formula of covalent compounds formed among the elements.

Element that combineFormula of the covalent compound

Element X fromValencyElement Y fromValency

Group 153Group 153XY

Group 153Group 162X2Y3

Group 153Group 171XY3

Group 162Group 162XY

Group 162Group 171XY2

Group 171Group 171XY

Physical Properties - Ionic CompoundsStructure Ionic Compound

1. In an ionic compound, the alternate positive and negative ions in an ionic solid are arranged in an orderly way as shown in the image to the right.2. The ions can form a giant ionic lattice structurewith ionic bond between the ions.3. The ionic bond is the strong electrical attraction (electrostatic force) between the positive and negative ions next to each other in the lattice.

(Giant Lattice Structure)

(Strong Electrostatic Force formed between the positive and negative ions)

Properties of Ionic Compounds

1. The strong bonding force makes ionic compounds has high melting and boiling points.2. All ionic compounds are crystalline solids at room temperature.3. They are hard but brittle, when stressed the bonds are broken along planes of ions which shear away.4. Many, ionic compounds (but not all) are soluble in water.5. The solid crystals DO NOT conduct electricity because the ions are not free to move to carry an electric current.6. However, if the ionic compound is melted or dissolved in water, the liquid will now conduct electricity, as the ion particles are now free.

Physical Properties Of Covalent Compounds - Simple MoleculeCovalent compounds can be divided into 2 types:

1. Simple molecular compound2. Macromolecular compound

Simple Molecules

1. Most covalent compounds are made up of independent molecular units, as shown in figure above.2. The attraction force between molecules is the weak Van der Waals force.

Properties of Simple Covalent Molecular Substances - Small Molecules!

1. The intermolecular force between the simple covalent molecules is very weak. Therefore, covalent compounds have low melting and boiling point.2. They are also poor conductors of electricity because there are no free electrons or ions in any state to carry electric charge.3. Most small molecules will dissolve in a solvent to form a solution.