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Topic 4 Bonding
4.1 The octet rule
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Understandings:
The “octet rule” refers to the tendency of atoms to gain a valence shell with a total of 8 electrons. Some atoms, like Be and B, might form stable compounds with incomplete octets of electrons. |
4.1 Electronegativity and bonding
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This video covers the relationship between the difference in electronegativity between atoms and the type of bonding.
Understandings: Bond polarity results from the difference in electronegativities of the bonded atoms. |
4.1 Ions and ion formation
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Understandings:
Positive ions (cations) form by metals losing valence electrons. Negative ions (anions) form by non-metals gaining electrons. The number of electrons lost or gained is determined by the electron configuration of the atom. |
4.1 Ionic bonding
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Understandings:
The ionic bond is due to electrostatic attraction between oppositely charged ions. Under normal conditions, ionic compounds are usually solids with lattice structures. |
| topic_4_ionic_bonding.pdf |
4.1 Structure and properties of ionic compounds
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Applications and skills:
Explanation of the physical properties of ionic compounds (volatility, electrical conductivity and solubility) in terms of their structure. |
4.1 Writing formulae of ionic compounds
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This video covers how to write formulae for ionic compounds.
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4.1 Polyatomic ions
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Applications and skills:
Deduction of the formula and name of an ionic compound from its component ions, including polyatomic ions. Guidance: Students should be familiar with the following polyatomic ions: NH4+ OH- HCO3- CO32- SO42- PO43- NO3- |
4.2 Covalent bonding
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Understandings:
A covalent bond is formed by the electrostatic attraction between a shared pair of electrons and the positively charged nuclei. Bond polarity results from the difference in electronegativities of the bonded atoms. Single, double and triple covalent bonds involve one, two and three shared pairs of electrons respectively. Bond length decreases and bond strength increases as the number of shared electrons increases. Applications and skills: Deduction of the polar nature of a covalent bond from electronegativity values. |
| topic_4_covalent_bonding.pdf |
| topic_4_bond_polarity.pdf |
4.2 Polar and non-polar covalent bonds
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Understandings:
Bond polarity results from the difference in electronegativities of the bonded atoms. Applications and skills: Applications and skills: Deduction of the polar nature of a covalent bond from electronegativity values. |
4.2 Coordinate covalent bonds
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Guidance:
Coordinate covalent bonds should be covered |
4.2 Polar and non-polar molecules
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Applications and skills:
Prediction of molecular polarity from bond polarity and molecular geometry. |
| topic_4_polar_and_non-polar_molecules.pdf |
4.3 Lewis structures
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Understandings:
Lewis (electron dot) structures show all the valence electrons in a covalently bonded species. The “octet rule” refers to the tendency of atoms to gain a valence shell with a total of 8 electrons. Some atoms, like Be and B, might form stable compounds with incomplete octets of electrons. Applications and skills: Deduction of Lewis (electron dot) structure of molecules and ions showing all valence electrons for up to four electron pairs on each atom. |
| topic_4_lewis_structures.pdf |
4.3 VSEPR theory (molecular geometry)
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Understandings:
Shapes of species are determined by the repulsion of electron pairs according to VSEPR theory. Applications and skills: Deduction of Lewis (electron dot) structure of molecules and ions showing all valence electrons for up to four electron pairs on each atom. The use of VSEPR theory to predict the electron domain geometry and the molecular geometry for species with two, three and four electron domains. Prediction of bond angles from molecular geometry and presence of non- bonding pairs of electrons. |
4.3 Structure and properties of covalent compounds
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Understandings:
Carbon and silicon form giant covalent/network covalent structures. Application and skills: Explanation of the properties of giant covalent compounds in terms of their structures. Explanation of the physical properties of covalent compounds (volatility, electrical conductivity and solubility) in terms of their structure and intermolecular forces. |
| topic_4_structure_and_properties_of_covalent_compounds.pdf |
4.3 Allotropes of carbon
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Guidance:
Allotropes of carbon (diamond, graphite, graphene, C60 buckminsterfullerene) should be covered. |
4.3 Resonance structures
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Understandings:
Resonance structures occur when there is more than one possible position for a double bond in a molecule. Guidance: Deduction of resonance structures, examples include but are not limited to C6H6 , CO2- and O3. |
4.4 Intermolecular forces
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Understandings:
Intermolecular forces include London (dispersion) forces, dipole-dipole forces and hydrogen bonding. The relative strengths of these interactions are London (dispersion) forces < dipole-dipole forces < hydrogen bonds. Applications and skills: Deduction of the types of intermolecular force present in substances, based on their structure and chemical formula. |
Note: The term van der Waals forces includes London dispersion forces (instantaneous and induced dipoles) and dipole-dipole forces.
| topic_4_intermolecular_forces.pdf |
4.4 Solubility and intermolecular forces
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This video covers polar and non-polar solvents and the different types of intermolecular forces that exist in solutions.
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Bonding and electrcial conductivity
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This video covers the electrical conductivity of substances with different bonding (covalent, ionic and metallic).
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4.4 Group 16 hydrides
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This video covers the bonding and properties of the group 16 hydrides.
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4.5 Metallic bonding
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Understandings:
A metallic bond is the electrostatic attraction between a lattice of positive ions and delocalized electrons. The strength of a metallic bond depends on the charge of the ions and the radius of the metal ion. Applications and skills: Explanation of electrical conductivity and malleability in metals. Explanation of trends in melting points of metals. |
4.5 Alloys
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Understandings:
Alloys usually contain more than one metal and have enhanced properties. Applications and skills: Explanation of the properties of alloys in terms of non-directional bonding. Guidance: Examples of various alloys should be covered. |
