Chemical Bonding and Structure

Question 1

Bonding

Answer 1

It refers to the way in which atoms are joined together and combine with one another.

Question 2

Aim of Bonding

Answer 2

To achieve fully-filled valence electron shells which is very stable just like those of noble gases.

Question 3

Atom

Answer 3

Smallest particle of an element that has the chemical properties of that element.

Question 4

Molecule

Answer 4

Two or more atoms covalently bonded together.

Question 5

Element

Answer 5

Pure substance that cannot be split into two or more simpler substances by physical or chemical processes.

Question 6

Compound

Answer 6

Substance which contains two or more elements chemically combined in a fixed composition.

Question 7

Mixture

Answer 7

Two or more substances physically mixed in any proportion.

Question 8

Differences between compounds and mixtures

• How are they made?
• How are they separated/broken down?
• Are their properties the same as that of their components?

Answer 8

• C: Two or more elements chemically combined in a fixed composition.
• M: Two or more substances physically mixed together in any proportion.
• C: Can only be broken down into its elements or into simpler compounds by chemical processes.
• M: Components of a mixture can be separated by physical means.
• C: Physical and chemical properties of a compound are different from its constituent elements.
• M: The chemical properties of a mixture are the same as those of its components.

Question 9

Ion

Answer 9

A charged particle either formed by either the gain or loss of electrons.

Question 10

Anion & Cation

Answer 10

Anion
- Gain es, negative ion
- No. of p < e
- Normally metals
Cation
- Lose es, positive ion
- No. of p > e
- Normally non-metals

Question 11

Ionic Bonding

• How are these atoms joined together?
• What holds the charged particles together?
• Summarize ionic bonding.

Answer 11

• Atoms are joined together by electron transfer.
• These charged particles are held together by strong electrostatic attraction between oppositely charged ions.
• Essentially complete electron transfer from an element that has high tendency to give away es to an element that has high tendency to take in es.

Question 12

Electron Transfer

Answer 12

The gain or loss of electrons resulting in the formation of ions.

Question 13

Ionic Bonds

Answer 13

Strong electrostatic forces of attraction between oppositely charged ions

Question 14

Ionic Compounds

Answer 14

• Giant ionic (lattice) structure, not just with one cation and one anion
• https://docbrown.info/page04/4_72bond/Image546.gif

Question 15

Properties of Giant Ionic Structure

Answer 15

MOST UNIQUE PROPERTY: Unable to conduct electricity in solid state, but able to conduct electricity in molten and aqueous state.
- It has giant ionic structure. In solid state, the oppositely charged ions can only vibrate about their fixed positions. Hence, there are no free-moving/mobile ions to conduct electricity.
- In the aqueous/molten state, there are free moving/mobile ions to conduct electricity.

High melting & boiling point. Generally exist as solids at r.t.p. Ionic compounds are hard.
- It has a giant ionic structure. Large amount of energy needed to overcome strong electrostatic forces of attraction/strong ionic bonds between the oppositely-charged ions.

Most ionic compounds are soluble in water. Usually insoluble in organic solvents (eg. ethanol, hexane).

E.g. NaCl / Sodium Chloride

Question 16

Covalent Bonding

How is it formed?

Answer 16

Covalent bond is formed by the sharing of electrons

Question 17

Covalent Bonds

Answer 17

Strong electrostatic forces of attraction between the positively-charged nuclei and shared pair of electrons (bonding electrons).
No charged particles formed; only groups of atoms called molecules.

Question 18

Simple Covalent Structure

Answer 18

• Strong covalent bonds between atoms
• Weak intermolecular (i.e. between molecules) forces of attraction

• Melting/boiling point is low if intermolecular forces of attraction are weak, high if strong
• If intermolecular forces of attraction are broken, the molecules will break apart and move randomly at high speeds.

Question 19

Properties of Simple Covalent Structure

Answer 19

MOST UNIQUE PROPERTY: Low melting & boiling point. Many substances with simple covalent structures are liquids and gases at r.t.p.
- It consists of small, discrete molecules with a
simple covalent structure. Only a small amount of energy needed to overcome the weak intermolecular forces of attraction
- Note: Strong covalent bonds between atoms are not broken (eg. water does not change chemically when boiled) during changes of state.

Generally unable to conduct electricity in any state.
- It consists of small, discrete molecules with a
simple covalent structure. There are no mobile/free-moving ions or delocalised electrons to conduct electricity.

Most molecules with simple covalent structures are insoluble in water.
- Some exceptions: ammonia, hydrogen chloride, sulfur dioxide (refer to Experimental Chemistry notes)
- Usually soluble in organic solvents (eg. ethanol, hexane).

E.g. CO2 / Carbon dioxide, H2 / Hydrogen molecule, N2 Nitrogen molecule, CH4 / Methane etc.

Question 20

Giant Covalent Structure

ONLY COVERING DIAMOND AND GRAPHITE.

Answer 20

• Diamond and graphite are allotropes of carbon, which are different forms of an element
• Diamond and graphite are examples of substances having giant covalent structures

Question 21

Giant Covalent Structure
(Diamond)

Answer 21

Each carbon atom is covalently bonded to 4 other carbon atoms in a repeated tetrahedral arrangement.

Question 22

Giant Covalent Structure
(Graphite)

Answer 22

• Each carbon atom is covalently bonded to 3 other carbon atoms in a repeated hexagonal arrangement. They form parallel layers of carbon atoms, which are held by weak intermolecular forces of attraction.
• Since only 3 out of 4 valence electrons of each carbon atom are involved in covalent bonding, the fourth valence electron is not used in bonding, and is delocalised and able to conduct electricity.

Question 23

Properties of Giant Covalent Structure

Answer 23

MOST UNIQUE PROPERTY: Very high melting and boiling point.
- It has a giant covalent structure. Large amount of energy needed to overcome strong covalent bonds between carbon atoms.

Diamond is unable to conduct electricity. Graphite is able to conduct electricity.
- Diamond has a giant covalent structure. Each carbon atom uses up all four of its valence electrons to form covalent bonds with four other carbon atoms.
- It does not have any delocalised electrons to conduct electricity.
- Graphite has a giant covalent structure. Each carbon atom uses 3 out of 4 of its valence electrons to form covalent bonds with 3 other carbon atoms.
- Each carbon atom has one valence electron not used in bonding; it is delocalised and is able to conduct electricity.

Diamond is very hard. Used as a cutting tool or drill bit to cut hard objects like glass and rocks. Graphite is soft and slippery. Used as a lubricant and in pencil lead.
- Diamond has a giant covalent structure, large amount of energy needed to overcome strong covalent bonds between carbon atoms.
- Graphite has a giant covalent structure, is soft and slippery because the layers of carbon atoms are held by weak intermolecular forces and can slide over each other easily.

Insoluble in water and organic solvents.

Question 24

Metallic Bonds

Answer 24

Strong electrostatic forces of attraction between metallic cations and ‘sea’ of delocalised electrons.

Question 25

Giant Metallic Structure

Answer 25

In metals, each metal atom contributes its valence electrons to a ‘sea’ of delocalised electrons which are free-moving and can move throughout the metallic structure.
- Note: metals are electrically neutral (overall charge = 0)

Question 26

Properties of Giant Metallic Structure