S2. Models of bonding and structure

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2.1 The ionic model

2.2 The covalent model

2.2 The covalent model (AHL)

2.3 The metallic model

2.4 From models to materials

2.4 From models to materials (AHL)

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Understanding points

Transfer of electron(s) from a metal to a non-metal and the resulting electrostatic attraction between oppositely charged ions

Metals lose valence electrons to form positive ions (cations)

Non-metals gain electrons to form negative ions (anions)

Charge of cation and anion

Polyatomic ions - charged covalent compound

2.1 The ionic model

Understanding points

Sharing of electron pair(s) between two atoms and resulting electrostatic attraction between (-ve) shared electron pair(s) and (+ve) two bonding nuclei

Comparison of bond length and strength

Bond length: distance between 2 bonded nuclei

Bond Strength/Enthalpy: energy required to break the bond

∵ greater attractive force between the nuclei as bond order increases

3 steps to identify carbon-carbon bond type

Identify no. of H for each C

2.2 The covalent model

Understanding points

Resonance structures

Occurs when there is more than one position possible for double/triple bonds in a molecule

Individual structures are called resonance forms

Actual electronic structure of species is called resonance hybrid: hybrid of the two resonance forms with delocalized e-s

Structure: cyclic, planar, delocalised 𝛑 electron cloud

Evidence to explain structure of benzene:

2.2 The covalent model (AHL)

2.3 The metallic model

2.4 From models to materials

2.4 From models to materials (AHL)