Unit 3
Chapter Overview
During this unit, students investigate differences in properties between covalent and ionic compounds, while also considering metals. They learn how to represent bonding with Lewis dot structures. In addition, students apply valence shell electron pair repulsion (VSEPR) theory to identify covalent molecular shapes and predict polarity.
Main Ideas
Scientists use a variety of ways to model electron arrangement depending on the properties expressed and used.
How can the arrangement of electrons in atoms be expressed?
Atoms form systems of ionic, covalent and metallic bonds through the interactions of their valence electrons.
How are electron dot formulas used to model bonds?
How does the nature of metallic bonding apply to metallic properties?
How is Valence Shell Electron Pair Repulsion (VSEPR) theory used to predict molecular structure for molecules?
Misconceptions
Students may think atoms “want” to gain, share, or lose electrons, rather than understanding that chemical bonds result in more stable (less reactive) products.
Vocabulary
Covalent Bond – bond in which electrons are shared, equally or unequally
Ionic Bond – bond in which one or more electrons are given by one atom to another
Metallic Bond – bond in which the valence electrons are shared among all the atoms in the metal, atoms move freely among atoms
Valence Shell Electron Pair Repulsion (VSEPR) Theory – unshared electron pairs of atoms in covalent molecules repel each other; thus the shape of the molecule will tend to minimize the net repulsions
Electron Orbitals (SPDF) – the different energy levels filled by electrons within an atom
Electron Affinity – energy released when an electron is added to an atom to form an ion
Ion – negatively or positively charged atom (monatomic) or group of atoms (polyatomic)
Ionization Energy – energy required to remove an electron from a gaseous atom or ion
Lewis Dot Structure – atomic symbol with dots showing valence electrons
Electron Dot Formula – diagrams that show the bonding between atoms of a molecule and the lone pairs of electrons that may exist in the molecule
Molecular Geometry – the 3D shape of a covalent molecule as determined by shared and unshared electrons
Bent – geometric shape of a molecule that, non-collinear
Linear – geometric shape where the atoms of a molecule are in a line
Tetrahedral – geometric shape of a molecule with one central atom located at the center with four substituents that are located at the corners of a tetrahedron
Trigonal Planar – geometric shape of a molecule with one central atom and three atoms at the corners of an equilateral triangle, all in one plane
Lattice – arrangement of atoms in a pattern that results in a crystal
Oxidation Number – for atoms of pure elements the oxidation number is zero; for monatomic ions it is the charge on the ion; in polyatomic ions the oxidation numbers of the component atoms add up to the charge on the ion; in a neutral molecule the oxidation numbers add up to zero
Polar and Non-Polar Molecules – because of differences in electronegativity, different types of atoms in covalent molecules do not share electrons equally; in a 3D symmetrical molecule the unequal sharing cancels out and the molecule is non-polar; in a 3D non-symmetrical molecule, the unequal sharing does NOT cancel out, so that there is a partial positive area and a partial negative area
Conductivity – ability or power to conduct or transmit heat, electricity, or sound
Ductility – physical property of a material associated with the ability to be drawn into a wire
Luster – how shiny something is; the manner in which the surface of a mineral reflects light
Malleability – physical property of a material associated with the ability to be hammered thin into a sheet
Electronegativity – measure of the tendency of an atom to attract a bonding pair of electrons
Repulsion - electrons tend to orient themselves as far apart as possible; they don’t want to be around each other
Notes
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