1

SPM Form 4 Chemistry - Chemical Bonds

http://spmchemistry.onlinetuition.com.my/2013/10/chemical-bond.html1. Stability of Noble Gases2. Chemical Bond3. Formation of Iona. Formation of Positive Ionb. Formation of Negative Ionc. Difference Between an Atom and an Ion That Have Same Electrons Arrangement

4. Ionic Bonding5. Predicting the Formula of Ionic Compounds (Video)6. Covalent Bondingo Number of Bond

o Predicting the Formula of Covalent Compounds

7. Physical Properties of Ionic and Covalent Compounda. Ionic Compound b. Covalent Compounds

i. Simple Moleculeii. Macromolecular compounds8. Mind Map

Stability 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

2

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.

3

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:

a. throw away the excess electron(s)

b. receiving electron(s) from other atom if they are lack of electron(s)

c. sharing electron

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

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

4

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

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

The 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.

5

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 Positive Ion

1. 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 ChargeThere are two types of atomic bonds - ionic bonds and covalent bonds. They differ in their structure and properties. Covalent bonds consist of pairs of electrons shared by two atoms, and bind the atoms in a fixed orientation. Relatively high energies are required to break them (50 - 200 kcal/mol). Whether two atoms can form a covalent bond depends upon their electronegativity i.e. the power of an atom in a molecule to attract electrons to itself. If two atoms differ considerably in their electronegativity - as sodium and chloride do - then one of the atoms will lose its electron to the other atom. This results in a positively charged ion (cation) and negatively charged ion (anion). The bond between these two ions is called an ionic bond.

6

Comparison chart</> Embed this chart

Covalent Bonds Ionic Bonds

Polarity Low High

Formation

A covalent bond is formed between two non-metals that have similar electronegativities. Neither atom is "strong" enough to attract electrons from the other. For stabilization, they share their electrons from outer molecular orbit with others.

An ionic bond is formed between a metal and a non-metal. Non-metals(-ve ion) are "stronger" than the metal(+ve ion) and can get electrons very easily from the metal. These two opposite ions attract each other and form the ionic bond.

Shape Definite shape No definite shape

What is it?

Covalent bonding is a form of chemical bonding between two non metallic atoms which is characterized by the sharing of pairs of electrons between atoms and other covalent bonds.

Ionic bond, also known as electrovalent bond is a type of bond formed from the electrostatic attraction between oppositely charged ions in a chemical compound. These kinds of bonds occur mainly between a metallic and a non metallic atom.

Melting point low High

ExamplesMethane (CH4), Hydro Chloric acid (HCl) Sodium chloride (NaCl), Sulphuric Acid

(H2SO4 )

Occurs between

Two non-metals One metal and one non-metal

Boiling point Low High

State at room temperature

Liquid or gaseous Solid

Contents 1 About Covalent and Ionic Bonds

7

2 Formation and examples o 2.1 Examples (video)

3 Characteristics of the bonds 4 Video comparing types of atomic bonds 5 Further Reading 6 References

About Covalent and Ionic Bonds

The covalent bond is formed when two atoms are able to share electrons whereas the ionic bond is formed when the "sharing" is so unequal that an electron from atom A is completely lost to atom B, resulting in a pair of ions.

Each atom consists of protons, neutrons and electrons. At the centre of the atom, neutrons and protons stay together. But electrons revolve in orbit around the centre. Each of these molecular orbits can have a certain number of electrons to form a stable atom. But apart from Inert gas, this configuration is not present with most of the atoms. So to stabilize the atom, each atom shares half of its electrons.

Covalent bonding is a form of chemical bonding between two non metallic atoms which is characterized by the sharing of pairs of electrons between atoms and other covalent bonds. Ionic bond, also known as electrovalent bond is a type of bond formed from the electrostatic attraction between oppositely charged ions in a chemical compound. This kind of bonds occurs mainly between a metallic and a non metallic atom.

Formation and examples

Covalent bonds are formed as a result of the sharing of one or more pairs of bonding electrons. The electro negativities (electron attracting ability) of the two bonded atoms are either equal or the difference is no greater than 1.7. As long as the electro-negativity difference is no greater than 1.7, the atoms can only share the bonding electrons.

8

A model of the double and single covalent bonds ofcarbon within a benzene ring.

For example, let us consider a Methane molecule i.e.CH4.Carbon has 6 electrons and its electronic configuration is 1s22s22p2, i.e. it has 4 electrons in its outer orbit. According to the Octate rule ( It states that atoms tend to gain, lose, or share electrons so that each atom has full outermost energylevel which is typically 8 electrons.), to be in a stable state, it needs 4 more electrons. So it forms covalent bond with Hydrogen (1s1), and by sharing electrons with hydrogen it forms Methane or CH4.

If the electro-negativity difference is greater than 1.7 then the higher electronegative atom has an electron attracting ability which is large enough to force the transfer of electrons from the lesser electronegative atom. This causes the formation of ionic bonds.

Sodium and chlorine bonding ionically to form sodium chloride.

For example, in common table salt (NaCl) the individual atoms are sodium and chlorine. Chlorine has seven valence electrons in its outer orbit but to be in a stable condition, it needs eight electrons in outer orbit. On the other hand, Sodium has one valence electron and it also needs eight electrons. Since chlorine has a high electro-negativity, 3.16 compared to sodium’s 0.9, (so the difference between their electro-negativity is more than 1.7) chlorine can easily attract sodium's one

9

valence electron. In this manner they form an Ionic bond, and share each other’s electrons and both will have 8 electrons in their outer shell.

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

Example: Formation of Ion with +2 Charge

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

Example: Formation of Ion with +3 Charge

10

(A sodium atom release one electron to form a sodium ion with +3 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 charge whereas neon atom is neutral.

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

11

Ionic BondingIonic 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

12

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.

13

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.

Chemistry Form 4: Chapter 5 - Ionic Bond Ionic bonds are formed when valence electrons are transferred from a metal atom to a non-metal atom.

Metal atom releases valence electron to form positive ion in order to achieve stable noble gas octet electron arrangement.

14

Non-metal atom gains valence electron to form negative ion in order to achieve stable noble gas octet electron arrangement.

Positive ions and negative ions are held strongly by electrostatic force.

Chemistry Form 4: Chapter 5 - Covalent BondCovalent bonds are formed when one or more electron pairs are shared between non-metallic atoms to form a molecule in order to achieve a stable duplet or octet electron arrangements of noble gas.

 How covalent bond is formed in carbon dioxide:

Atom oxygen has 6 valence electrons and 2.6 electron arrangement.

15

Each atom oxygen needs 2 more electrons to fill the valence shell in order to achieve a stable octet electron arrangement. Hence, each atom oxygen contributes 2 electrons for sharing. Atom carbon has 4 valence electrons and 2.4 electron arrangement. Each atom carbon needs 4 more electrons to fill the valence shell in order to achieve a stable octet electron arrangement. Hence, each atom carbon contributes 4 electrons for sharing. One atom carbon shares 4 electrons with two atom oxygen to achieve a stable octet electron arrangement. 

Some examples of covalent bond:

16

Types of covalent bond:

Covalent BondingCovalent 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 Compound

Formula Covalent Compound

Formula

Chlorine Cl2 Phosphorus P4

Hydrogen H2 Sulfur dioxide SO2

Oxygen O2 Carbon dioxide CO2

NitrogenN2 Tetrachloro-

methaneCCl4

17

Examples of Formation of Covalent CompoundsFormation of Fluorine Molecule

1. The electrons arrangement of a fluorine atom is 2.7

2. To achieve octet electrons arrangement, 2 fluorine atoms share 1 pair of electrons

between each other.

3. As a result, a covalent bond formed between the 2 atoms.

Number of BondNumber of Bond1. There are 3 types of covalent bond:a. Single covalent bond – sharing of one pair of electronsb. Double covalent bond – sharing of two pairs of electronsc. Triple covalent bond – sharing of three pairs of electrons

Example

Number of electron Example and type of covalent bond

1 pair type of covalent bond: Single Bond

2 pair type of covalent bond: Double Bond

18

3 pair type of covalent bond: Triple Bond

Formation of Single Bond (Hydrogen Molecule)

Formation of Double Bond (Oxygen Molecule)

19

Formation of Triple Bond (Nitrogen Molecule)

20

Predicting the Molecular Formula of Covalent Compounds

1. 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 combine Formula of the ionic compound

Element X from Valency Element Y from Valency

Group 15 3 Group 15 3  XY

Group 15 3 Group 16 2  X2Y3

Group 15 3 Group 17 1  XY3

Group 16 2 Group 16 2  XY

Group 16 2 Group 17 1  XY2

Group 17 1 Group 17 1  XY

21

Formation of Oxygen Molecule

1. The electrons arrangement of an oxygen atom is 2.6

2. To achieve octet electrons 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 octet electrons arrangement, the oxygen atom share 2 pair of electrons with 2 hydrogen atoms.

22

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.

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 structure with 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.

23

(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

24

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.

Physical Properties of Covalent Compounds - Macromolecular compoundsMacromolecular Compounds

1. The macromolecular compounds have giant, covalent molecules with extremely large molecular lattices.

2. They have very high melting and boiling points.

25

3. They don't conduct electricity — not even when molten (except for graphite).

4. They're usually insoluble in water.

5. Examples of such macromolecules are diamond, silica and graphite.

Diamond and Silica(Sand)

(3 dimensional structure macromolecular compound - Diamond)

1. A diamond crystal or a grain of sand is just one giant molecule. Such molecules, because they

are so rigid and strong, have very high melting points.

2. Each carbon atom forms four covalent bonds in a very rigid giant covalent structure, which

makes diamond the hardest natural substance. This makes diamonds ideal as cutting tools.

3. All those strong covalent bonds give diamond a very high melting point.

4. It doesn't conduct electricity because it has no free electrons.

5. Diamond is an allotrope of carbon. Allotropes are different forms of the same element in the

same physical state

26

Graphite

(3 dimensional layer structure: graphite)

1. Carbon also occurs in the form of graphite. The carbon atoms form joined hexagonal

rings forming layers 1 atom thick.

2. Graphite is black and opaque.

3. Each carbon atom only forms three covalent bonds, creating sheets of carbon atoms

which are free to slide over each other. This makes graphite slippery, so it's useful as a

lubricant.

4. The layers are held together so loosely that they can be rubbed off onto paper to leave

a black mark — that's how pencils work.

5. Graphite has a high melting point — the covalent bonds need lots of energy before

they break.

6. Only three out of each carbon's four outer electrons are used in bonds, so there are lots

of spare electrons. This means graphite conducts electricity — it's used for electrodes.

Physical Properties of Covalent Compounds - Macromolecular compoundsMacromolecular Compounds

1. The macromolecular compounds have giant, covalent molecules with extremely large molecular lattices.

27

2. They have very high melting and boiling points.3. They don't conduct electricity — not even when molten (except for graphite).4. They're usually insoluble in water.5. Examples of such macromolecules are diamond, silica and graphite.

Diamond and Silica(Sand)

(3 dimensional structure macromolecular compound - Diamond)

1. A diamond crystal or a grain of sand is just one giant molecule. Such molecules, because they are so rigid and strong, have very high melting points.2. Each carbon atom forms four covalent bonds in a very rigid giant covalent structure, which makes diamond the hardest natural substance. This makes diamonds ideal as cutting tools.3. All those strong covalent bonds give diamond a very high melting point.4. It doesn't conduct electricity because it has no free electrons.5. Diamond is an allotrope of carbon. Allotropes are different forms of the same element in the same physical state

28

Graphite

(3 dimensional layer structure: graphite)

1. Carbon also occurs in the form of graphite. The carbon atoms form joined hexagonal rings forming layers 1 atom thick.2. Graphite is black and opaque.3. Each carbon atom only forms three covalent bonds, creating sheets of carbon atoms which are free to slide over each other. This makes graphite slippery, so it's useful as a lubricant.4. The layers are held together so loosely that they can be rubbed off onto paper to leave a black mark — that's how pencils work.5. Graphite has a high melting point — the covalent bonds need lots of energy before they break.6. Only three out of each carbon's four outer electrons are used in bonds, so there are lots of spare electrons. This means graphite conducts electricity — it's used for electrodes.