02 Atomic Structure and Interatomic Bonding Flashcards Preview

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Flashcards in 02 Atomic Structure and Interatomic Bonding Deck (17)
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1. Name the two atomic models cited, and note the differences between them.

1. Bohr model and 2. wave-mechanical model: the Bohr model assumes e- to be particles orbiting the nucleus in discrete paths and e- energy is quantized in shells. In wave mechanics we consider them to be wavelike and treat e- position in terms of probability distribution (=orbital). e- energy is quantized in both shells and sub-shells.

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2. Describe the important quantum-mechanical principle that relates to electron energies.

QM-principle: energies of e- are quantized i.e. e- are permitted to have only specific values of energy. It just can make a quantum jump either to an allowed higher energy or to a lower energy (refer to energy states/levels). 

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3. (a) Name the four electron quantum numbers.

  1. n principal quantum number
  2. l azimuthal quantum number
  3. ml magnetic quantum number
  4. ms spin moment

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3. (b) For a specific electron, note what each of its quantum numbers determines.

n electron orbital size or its average distance from the nucleus, describes e- shell

l orbital shape (designates the subshell s,p,d,...)

ml # of e- orbitals for each subshell (s=1 orbital(s), p=3, d=5,…) e.g. for p-subshell ml can be -1, 0, or 1, for the d-subshell -2, -1, 0, 1, 2.

ms spin moment (+1/2 spin up or -1/2 spin down)

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4. Write a definition of the Pauli exclusion principle.

Each electron state can accommodate no mor than two e-, which must have opposite spin (QM-principle/concept)

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5.Cite the distinctive electron configuration characteristic for each group of elements in the periodic table.

  • Group 0 (inert gases): filled e- shells and stable e- configuration
  • Group VIIA (halogens): one e- deficient from having stable structures
  • Group VIA (chalcogens): two e- deficient from having stable structure
  • Group IA (alkali-metals): one e- in excess of stable structure
  • Group IIA (alkaline earth metals): two e- in excess of stable structure
  • Group IIIB to IIB (transition metals): partially filled d states
  • Group IIIA, IVA, and VA: intermediate characteristics between metals and nonmetals e.g. B, Si, Ge, As 

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6. Write the equation that relates energy and force.

the energy-force relation is described by the two equivalent equations on top

the equation below describes the relation for the atomic system with EN = net energy, EA = attractive energy, and ER = repulsive energy for two isolated and adjacent atoms.

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7. (a) Schematically plot attractive, repulsive, and net energies versus interatomic separation for two atoms or ions.

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7. (b) Now note on "energy-interatomic separation plot" the equilibrium separation and the bonding energy.

the equilibrium separation corresponds to the energy value at the minimum of the curve

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8.  (a)  Briefly describe ionic, covalent, and metallic bonds - the primary interatomic bonds

  • ionic bonds: electrically charged ions are formed by the transference of valence electrons from one atom type to another
    always found in metallic-nonmetallic compounds (elements situated at the horizontal extremities) large EN-difference
  • covalent bonds: sharing of valence e- between adjacent atoms 
    found in materials whose atoms have small differences in electronegativity -> small EN-difference
  • metallic bonds: valence e- form a "sea of e-" that is uniformly dispersed  around the metal ion cores and acts as a form of glue for them
    found in metals and their alloys

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8.  (a) cont.: Briefly describe hydrogen and van der Waal's bonds - the secondary bonds OR van der Waals bonds

  • hydrogen: highly polar molecules form when hydrogen covalently bonds to a nonmetallic element s.a. fluorine
  • van der Waals: this relatively weak bond results from attractive forces between electric dipoles, which may be induced or permanent.

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8. (b)  Note which materials exhibit each of these bonding types.

  • polymers - covalent
  • metals - metallic
  • ceramics - ionic and mixed ionic-covalent
  • molecular solids - van der Waals
  • semi-metals - mixed covalent-metallic
  • intermetallics - mixed metallic-ionic

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9.  Given the chemical formula for a material, be able to cite what bonding type(s) is (are) possible.

look at EN-difference: if large -> ionic, if small -> covalent
additionally, you can use ionic character formula

what kind of atoms are in the compound: metals and alloys -> metallic
metal and nonmetal->ionic

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10.  Given the electronegativities of two elements, compute the percent ionic character of the bond that forms between them.

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11.  Briefly explain why water expands when it freezes.

strong tendency in water to form a network of hydrogen bonds, where each hydrogen atom is in a line between two oxygen atoms. This hydrogen bonding tendency gets stronger as the temperature gets lower (because there is less thermal energy to shake the hydrogen bonds out of position). The ice structure is completely hydrogen bonded, and these bonds force the crystalline structure to be very "open" i.e. decreasing density. In a liquid state the water molecules can get closer to each other, hence making it denser (max. density at 4°C).

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Which properties (related to the bonding and phys. properties) are related to bonding?

bond length r (interatomic separation)

bond energy E0

Melting temperature Tm: the larger E0 the larger Tm

Coefficient of thermal expansion: the smaller E0 the higher the therm. expansion

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Describe the properties of ceramics, metals, and polymers in terms of their type of bonding?

ceramics (ionic and covalent bonding): high Tm, large E0, small αl

metals (metallic bonding): variable bond energy, moderate Tm, moderate E, moderate αl

polymers (covalent and Secondary): weak bond energy between chains -> secondary bonds responsible for most phys. properties
low Tm, small E0, large αl