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Titel
3
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Topic 3 Bonding
Structure 2.1.1—When metal atoms lose electrons, they form positive ions called cations.
When non-metal atoms gain electrons, they form negative ions called anions.
Predict the charge of an ion from the electron configuration of the atom.'
Structure 2.1.2—The ionic bond is formed by electrostatic attractions between oppositely charged ions. Deduce the formula and name of an ionic compound from its component ions, including polyatomic ions. Binary ionic compounds are named with the cation first, followed by the anion. The anion adopts the suffix “ide”.
Interconvert names and formulas of binary ionic compounds.
Structure 2.1.3—Ionic compounds exist as three-dimensional lattice structures, represented by empirical formulas.
Explain the physical properties of ionic compounds to include volatility, electrical conductivity and solubility.
Structure 2.2.1—A covalent bond is formed by the electrostatic attraction between a shared pair of electrons and the positively charged nuclei.The octet rule refers to the tendency of atoms to gain a valence shell with a total of 8 electrons.
Deduce the Lewis formula of molecules and ions for up to four electron pairs on each atom.
Structure 2.2.2—Single, double and triple bonds involve one, two and three shared pairs of
electrons respectively.
Explain the relationship between the number of bonds, bond length and bond strength.
Structure 2.2.3—A coordination bond is a covalent bond in which both the electrons of the shared pair originate from the same atom.
Identify coordination bonds in compounds.
Structure 2.2.4—The valence shell electron pair repulsion (VSEPR) model enables the shapes of molecules to be predicted from the repulsion of electron domains around a central atom.
Predict the electron domain geometry and the molecular geometry for species with up to four electron domains.
Structure 2.2.5—Bond polarity results from the difference in electronegativities of the bonded atoms.
Deduce the polar nature of a covalent bond from electronegativity values.
Structure 2.2.6—Molecular polarity depends on both bond polarity and molecular geometry.
Deduce the net dipole moment of a molecule or ion by considering bond polarity and molecular geometry.
Structure 2.2.7—Carbon and silicon form covalent network structures.
Describe the structures and explain the properties of silicon, silicon dioxide and carbon’s allotropes: diamond, graphite, fullerenes and graphene.
Structure 2.2.8—The nature of the force that exists between molecules is determined by the size and polarity of the molecules. Intermolecular forces include London (dispersion), dipole-induced dipole, dipole–dipole and hydrogen bonding.
Deduce the types of intermolecular force present from the structural features of covalent molecules.
Structure 2.2.9—Given comparable molar mass, the relative strengths of intermolecular forces are generally: London (dispersion) forces < dipole–dipole forces < hydrogen bonding.
Explain the physical properties of covalent substances to include volatility, electrical conductivity and solubility in terms of their structure.
Structure 2.2.10—Chromatography is a technique used to separate the components of a mixture based on their relative attractions involving intermolecular forces to mobile and stationary phases.
Explain, calculate and interpret the retardation factor values, RF.
Structure 2.3.1—A metallic bond is the electrostatic attraction between a lattice of cations and delocalized electrons.
Explain the electrical conductivity, thermal conductivity and malleability of metals.
Structure 2.3.2—The strength of a metallic bond depends on the charge of the ions and the radius of the metal ion.
Explain trends in melting points of s and p block metals.
Structure 2.4.1—Bonding is best described as a continuum between the ionic, covalent and metallic models, and can be represented by a bonding triangle.
Use bonding models to explain the properties of a material
Structure 2.4.2—The position of a compound in the bonding triangle is determined by the relative contributions of the three bonding types to the overall bond.
Determine the position of a compound in the bonding triangle from electronegativity data.
Predict the properties of a compound based on its position in the bonding triangle.
Structure 2.4.3—Alloys are mixtures of a metal and other metals or non-metals. They have
enhanced properties.
Explain the properties of alloys in terms of non-directional bonding.
Structure 2.4.4—Polymers are large molecules, or macromolecules, made from repeating subunits called monomers.
Describe the common properties of plastics in terms of their structure.
Structure 2.4.5—Addition polymers form by the breaking of a double bond in each monomer.
Represent the repeating unit of an addition polymer from given monomer structures.
HL only:
Structure 2.2.11—Resonance structures occur when there is more than one possible position for a double bond in a molecule.
Deduce resonance structures of molecules and ions.
Include the term “delocalization”.
Structure 2.2.12—Benzene, C6H6, is an important example of a molecule that has resonance.
Discuss the structure of benzene from physical and chemical evidence.
Structure 2.2.13—Some atoms can form molecules in which they have an expanded octet of
electrons. Visually represent Lewis formulas for species with five and six electron domains around the central atom.
Deduce the electron domain geometry and the molecular geometry for these species using the VSEPR model.
Structure 2.2.14—Formal charge values can be calculated for each atom in a species and used to determine which of several possible Lewis formulas is preferred.
Apply formal charge to determine a preferred Lewis formula from different Lewis formulas for a species.
Structure 2.2.15—Sigma bonds σ form by the head-on combination of atomic orbitals where the electron density is concentrated along the bond axis.
Pi bonds π form by the lateral combination of p-orbitals where the electron density is
concentrated on opposite sides of the bond axis.
Deduce the presence of sigma bonds and pi bonds in molecules and ions.
Structure 2.2.16—Hybridization is the concept of mixing atomic orbitals to form new hybrid
orbitals for bonding.
Analyse the hybridization and bond formation in molecules and ions.
Identify the relationships between Lewis formulas, electron domains, molecular geometry and type of hybridization.
Predict the geometry around an atom from its hybridization, and vice versa.
Structure 2.3.3—Transition elements have delocalized d-electrons.
Explain the high melting point and electrical conductivity of transition elements
Structure 2.4.6—Condensation polymers form by the reaction between functional groups in each monomer with the release of a small molecule.
Represent the repeating unit of polyamides and polyesters from given monomer structures.
Practicals:
- Solubility of ionic compounds
- Making bioplastics
Project: The plastic problem, group presentations.
TOK/NOS:
- To what extent does collaboration and competition help or hinder production of knowledge? Use idea of large plastic molecules as example.
- The bonding triangle is a tool with predictive power about propertives of substances
(NOS)
- Electron orbitals and hybridization does not exast as physical entities, but provides a convinient model for explaining electron properties and bonding. To what extent does language and imagery enhance or mask understanding of what is represented?
ATL:
Collaboration: Working collaboratively to achieve a common goal
• Assigning and accepting specific roles during group activities
• Appreciating the diverse talents and needs of others
Communication: Clearly communicating complex ideas in response to open-ended
questions
• Using digital media for communicating information
Thinking skills:
Experimenting with new strategies for learning
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