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Unit 4

Chapter Overview
During this unit, students further their understanding of periodic trends in chemical families, relate these trends to electron configurations within and between
atoms, and 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
The arrangement of the elements in the modern Periodic Table system is based on their physical and chemical properties. Analysis of this arrangement reveals similarities  among the elements in a chemical family and trends that allow for powerful predictions.
    *How is the Periodic Table used to identify and explain periodic patterns (trends) among elements?
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.
***Students may have difficulty understanding how and why ionization energy and electronegativity vary on the Periodic Table.

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 Electrons – electron that is associated with an atom and that can participate in the formation of a chemical bond
Aufbau Principle – the configuration (order of filling) of the s, p, d, and f orbitals; electrons fill the lowest energy levels first
Hund’s Rule – electrons fill empty orbitals before they pair up
Octet Rule – elements other than transition metals tend to react so that each atom has eight electrons in its outer (valence) shell, orbitals are full
Pauli Exclusion Principle – electrons in the same orbital and value must have opposite spins
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
Excited State – state in which an atom or molecule picks up energy, causing an electron to move into a higher-energy orbital
Ground State – the lowest allowed energy state of an atom, molecule, 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
Electron Configuration – the distribution of electrons of an atom or molecule in atomic or molecular orbitals
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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