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Chemistry > Lecture 2: Bonding, Reactions And Decay > Flashcards

Lecture 2: Bonding, Reactions And Decay Flashcards

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1
Q

What force governs bonding

A
  1. Electrostatic forces (F=kq1q2/r^2)
    1a. Like charges repel, opposites attract
  2. Lowest energy level=bond length
    2a. Bond dissociation energy: energy necessary to break bond apart
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2
Q

Intramolecular bonds: covalent

A
  1. When 2 electrons are shared by a nuclei: explained by Coulomb’s law
    1a. Bond length is inversely related to bond order: longest/weakest have 1 bond
    1b. Stronger bonds are shortest
  2. Types of covalent bonds: non metal x nonmetal
    2a. Nonpolar: (EN<0.5) ex: H2, N2, O2, F2, CL2, BR2, I2
    2b. Polar: (0.5<EN<1.7): unequal sharing = dipole moments (u=qd)
    2c. Coordinate covalent: both electrons are donated from one molecule (ex: Lewis acids and bases)
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3
Q

Intramolecular bonds: metallic

A
  1. Cations tightly packed surrounded by many electrons
  2. Electrons are nonlocalized
  3. Metal x metal
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4
Q

Intramolecular bonds: ionic

A
  1. EN>1.7 ; usually occurs between metal and nonmetal
  2. When two ions with opposite charges attract each other with F=kq1q2/r^2
  3. Stronger than covalent bonds
  4. Ionic bonds are solid at room temp, have very high freezing point, conduct electricity
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5
Q

Intermolecular attractions:

A
  1. Van der Waals: Weak intermolecular forces between 2 neutral molecules
    1a. Dipole-dipole: both have polar moment
    1b. London dispersion: induced dipoles
  2. Hydrogen bonds: H-O,N,F
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6
Q

Lewis dot structure instructions

A
  1. Count all valence electrons (add electron for negative charge, and subtract one for a positive charge)
  2. Arrange and connect atoms
  3. Complete outlets and conform to valences by adding bonds/lone pairs (must be lowest state of formal charge)
    3a. Formal charge=valence electrons-dots-sticks
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7
Q

Exceptions to the octet rule

A
  1. Expanded octet: for atoms from 3rd period or more
  2. Electron deficient octets: for second row (period?) elements
  3. Odd number of valence electrons
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8
Q

VSEPR Theory

A
  1. A: Central atom , X=any attached atom, E=lone pair of electrons
    1a. AX2: Linear: 180
    1b. AX3: Trigonal planar: 120
    1c. AX2E: Bent: <120
    1d. AX4: tetrahedral: 109.5
    1e. AX3E: Trigonal pyramidal: <109.5
    1f. AX5: trigonal bipyramidal: 120, 90
    1g. AX6: Octahedral: 90
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9
Q

Valence bond theory (VBT)

A
  1. A bond is a combination of 2 half filled atomic orbitals and the bond is made when 2 atoms share 2 electrons
    1a. Atomic orbitals with similar sizes and energy levels overlap to form a bond…more overlap=stronger bond
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10
Q

VBT: Electron arrangements according to sp notation

A
  1. Electron arrangement: number of atomic orbitals: hybridization: number of hybrid orbitals
    1a. Linear: 2: sp: 2
    1b. Trigonal planar: 3: sp2: 3
    1c. Tetrahedral: 4: sp3: 4
    1d. Trigonal bipyamidal: 5: sp3d: 5
    1e. Octahedral: 6: sp3d2: 6
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11
Q

VBT: pi and sigma bonds

A
  1. Single covalent bond (sigma bonds) is an overlap of atomic orbitals
  2. Pi bonds: overlap of 2 p orbitals
  3. The bigger the bond order=the smaller the bond length=the bigger the bond dissociation energy
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12
Q

Molecular orbital (MO) theory

A
  1. Says orbitals are formed from linear combinations of atomic orbitals (LCAO) from different atoms
  2. Says valence electrons are depolarized
  3. Says there are 3 types of orbitals
    3a. Bonding orbitals: when LCAO-MO has lower energy than atomic orbitals it made (constructive interference)
    3b. Antibonding orbitals: pull nuclei away from each other (destructive interference)
    3c. Non bonding orbitals: wave functions don’t interact
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13
Q

Bond order in MO theory

A
  1. Bond order=(# bonding electrons-#nonbonding electrons)/2
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14
Q

Types of formulas

A
  1. Empirical formula: ratio of whole numbers/simple form
  2. Molecular formula: exact number of atoms
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15
Q

Percent composition by mass

A
  1. Molecular weight (g/mol) of atom being measured/ empirical formula x 100%
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16
Q

Physical and chemical reactions

A
  1. Physical reaction: when compound undergoes a reaction but maintains its molecular structure (Ex: melting, boiling, evaporation, rotation of polarized light)
  2. Chemical reaction: when compound undergoes a reaction and changes its molecular structure to form a new compound (ex: combustion, metathesis, redox)
17
Q

Reactions running to completion

A
  1. Means it moves to the right until the supply of at least one reactants is depleted
    1a. Limiting reagent is used up first (moles is used up first(
18
Q

Chemical yield

A
  1. Percent yield=actual yield /theoretical yield x 100%
    1a. Actual yield: real experiment
    1b. Theoretical: value of reaction if it were to run to completion
19
Q

Reaction types

A
  1. Combination: A+B->C
  2. Decomposition: C->A+B
  3. Single displacement/replacement: A+BC->B+AC
  4. Double displacement/replacement or metathesis: AB+CD->AD+CB
20
Q

Nuclear reactions (delete)

A
  1. Nuclides that undergo radioactive decay spontaneously break apart which releases energy
  2. Radioactive isotopes are unstable
21
Q

Half life

A
  1. Length of time necessary for one half of an amount of a substance to decay (only for unstable isotopes)
  2. N(t)=No(1/2)^(t/t(1/2))
    2a. N(t): final amount , No: initial amount, t(1/2): half life , t=total time
  3. Examples
    3a. If given only final amount in percent and want to find # of half lives…start at 100% and count until you reach that number
    3b. Given initial, final and half life period…find total time: start from initial and count to final…take that number and multiply by half life period
22
Q

Types of radioactive decay

A
  1. Alpha: (mass #-2) & (atomic # -2)
  2. Beta
    2a. Electron emission/beta decay: neutron turns into a proton which adds 1 to the atomic # (1 up on the periodic table)
    2b. Positron emission: proton turns into neutron which takes away one from teh atomic number (1 down on periodic table)
    2c. Electron capture: proton->neutron which releases energy in the form of the x ray (1 down on the periodic table)
  3. Gamma: emits gamma rays
23
Q

Mass defect

A
  1. Rest mass energy of any mass: E=mc^2
    1a. If mass is created or destroyed, that equation gives the energy to create/replace the energy (c=3x10^8m/s)
  2. Missing mass=mass defect and rest of the energy of mass defect is nuclear binding energy

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