[CHEM] Chapter 2.3 - 2.6 - Chemical Bonding

1 DARRELL ER (COPYRIGHTED) TOPIC 2.3 - 2.6: CHEMICAL BONDING DARRELL ER (COPYRIGHTED) ©

2 CHAPTER ANALYSIS THE ABOUT TIME EXAM WEIGHTAGE • Important chapter, will always be tested • 3 key concepts • 1 advanced concept • Commonly tested, especially for Section A • Tested as together with other chapters  Atomic Structure, Chemical Equations • Medium overall weightage • Constitute to 4.5% of marks for past 5 year papers DARRELL ER (COPYRIGHTED) ©

3 ELEMENTS, COMPOUNDS, MIXTURE Elements Compound Mixture Formation Naturally found Combined using chemical methods Combined using physical methods Separation technique Cannot be separated further Separation by chemical methods (Decomposition, electrolysis, reduction with carbon) Separation by physical methods (separation techniques) Composition Exist by itself or in diatomic molecule form for gases such as H2 or O2. Fixed ratio Any ratio Melting Point / Boiling Point Fixed MP & BP Fixed MP & BP Melts and boils over a range of temperature *A compound is a subset of a molecule, but a molecule does not need to be a compound. Definition of a molecule is when 2 or more atoms chemically combined. An element can also exist as a diatomic molecule. (N2, O2, H2) A compound is defined as 2 or more elements chemically combined, hence a compound must be a molecule. Understanding the term ‘molecule’

*A compound is a subset of a molecule, but a molecule does not need to be a compound. Definition of a molecule is when 2 or more atoms chemically combined. An element can also exist as a diatomic molecule. (N2, O2, H2) A compound is defined as 2 or more elements chemically combined, hence a compound must be a molecule. 4 ELEMENTS, COMPOUNDS, MIXTURE Understanding the term ‘molecule’

5 3 types of bonds IONIC COVALENT METALLIC Understanding all 3 types of bonds is needed to master this chapter while paying special attention to keywords you must include in your answers. For each type of bond, you must be able to explain: - How the bond is formed - The dot-&-cross diagram - The structure - Physical properties (with explanations) DARRELL ER (COPYRIGHTED) ©

Why are chemical bonds formed? Atoms of elements strive for stability by achieving a stable electronic configuration (2,8,8). This is by forming chemical bonds with other atoms. The formation of chemical bonds can be done by transferring electrons, sharing electrons or forming a metal lattice. Non-metal atoms, such as the Group VII halogens, would form ionic bonds with metal atoms. They can also form covalent bonds with other non-metal atoms. Metal atoms can also form metallic bonds with other metal atoms. 6 BASICS MUST KNOW DARRELL ER (COPYRIGHTED) ©

7 IONIC BONDS METAL ION + NON-METAL ION GIANT IONIC LATTICE STRUCTURE KEY CONCEPT DARRELL ER (COPYRIGHTED) ©

Recall: Cation: positively charged ion  t = ‘+’ sign, positive Anion: negatively charged ion  n = negative Ionic bonds are formed between metals and non-metals. The transfer of electron from the metal to the non-metal would allow both atoms to have complete valence shells and to attain a stable electronic configuration. The metal would become a cation while the non-metal would become the anion. Ionic bond formed is the forces of attraction between oppositely charged ions. 8 IONIC BONDS KEY CONCEPT DARRELL ER (COPYRIGHTED) ©

9 GIANT IONIC LATTICE STRUCTURE GIANT IONIC LATTICE STRUCTURE Ionic compounds have a giant ionic lattice structure that is held together by strong electrostatic forces of attraction between oppositely charged ions. Naming convention: (Cation)(Anion) eg: Sodium Chloride DARRELL ER (COPYRIGHTED) ©

10 giant ionic lattice Physical properties - High MP & BP - Soluble in water - Able to conduct electricity in molten & aqueous state - Poor conductor of heat - Not volatile (does not evaporate easily) - Strong High melting and boiling points Ionic compounds usually have high melting and boiling points. (<1000 Degree Celsius) These ions are held together by strong ionic bonds which require a huge amount of energy to overcome. Solubility Ionic compounds are soluble in water because the partially charged (polar) water molecules can attract the ions, causing disruption to the ionic lattice structure. This results in the ions separating and dissolving in the solution. To conduct electricity, there needs to be the presence of mobile charge carriers. In its solid state, as the ions are all held tightly in place, ionic compounds in solid state do not have the ability to conduct electricity. However, when in molten or aqueous state, the ions are able to move freely, able to act as mobile charge carriers to conduct electricity. ADVANCED DARRELL ER (COPYRIGHTED) © Electrical conductivity