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Unit 2 Molecular and Ionic Compound Structure and Properties

Unit 2 Molecular and Ionic Compound Structure and Properties. Topic 2.3 Structure of Ionic Solids Text Reference Ch 12, section 12.5 TPWB page 252-254. Understanding: Atoms or ions bond due to interactions between them, forming molecules.

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Unit 2 Molecular and Ionic Compound Structure and Properties

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  1. Unit 2Molecular and Ionic Compound Structure and Properties Topic 2.3 Structure of Ionic Solids Text Reference Ch 12, section 12.5 TPWB page 252-254

  2. Understanding:Atoms or ions bond due to interactions between them, forming molecules. Learning Objective: Represent an ionic solid with a particulate model that is consistent with Coulomb’s law and the properties of the constituent ions. Essential Knowledge: The cations and anions in an ionic crystal are arranged in a systematic, periodic 3-D array that maximizes the attractive forces among cations and anions while minimizing the repulsive forces.

  3. 12.5 Ionic Solids • They are held together by electrostatic attractions between cations and anions. • Ionic solids have very high melting and boiling points and are quintessential crystals. • Because the valence electrons are confined to the anions, rather than being delocalized, ionic compounds are electronic insulators. • However, when melted, the ions are free to move and conduct electricity. • Aqueous solutions of ionic compounds also conduct electricity because the dissolving process breaks down the lattice and frees ions to move throughout the solution. • The strength of ionic bonds depends on the charges and sizes of the ions. Recall Coulomb’s law: F = kQ1Q2/d2 Small ions with large charges produce very strong forces of attraction. Larger ions with smaller charges are less tightly bound.

  4. The interactions between cations and anions also increase as the ions get smaller

  5. Properties of Ionic Substances • Ions maintained in rigid, well-defined, 3-D structures • Usually crystalline • Ionic crystals can be cleaved along smooth, flat surfaces • Brittle with high melting points

  6. When stress is applied to an ionic crystal, planes of atoms can shift allowing to separation of layers.

  7. Topic 2.4 Structure of Metals and Alloys Text Reference Ch 12, section 12.3 TPWB pg 250 - 251 See pages 33 – 36 in Topic 2.1 notes

  8. Understanding:Atoms or ions bond due to interactions between them, forming molecules. Learning Objective: Represent a metallic solid and/or alloy using a model to show essential characteristics of the structure and interactions present in the substance. Essential Knowledge: Metallic bonding can be represented as an array of positive metal ions surrounded by delocalized valence electrons (i.e., “a sea of electrons”). Interstitial alloys form between atoms of different radii, where the smaller atoms fill the interstitial spaces between the larger atoms (e.g., with steel in which carbon occupies the interstices in iron). Substitutional alloys form between atoms of comparable radius, where one atom substitutes for the other in the lattice. (In certain brass alloys, other elements, usually zinc, substitute for copper.)

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