Lecture 2: Bonding, Reactions And Decay Flashcards
1
Q
What force governs bonding
A
- Electrostatic forces (F=kq1q2/r^2)
1a. Like charges repel, opposites attract - Lowest energy level=bond length
2a. Bond dissociation energy: energy necessary to break bond apart
2
Q
Intramolecular bonds: covalent
A
- 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 - 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)
3
Q
Intramolecular bonds: metallic
A
- Cations tightly packed surrounded by many electrons
- Electrons are nonlocalized
- Metal x metal
4
Q
Intramolecular bonds: ionic
A
- EN>1.7 ; usually occurs between metal and nonmetal
- When two ions with opposite charges attract each other with F=kq1q2/r^2
- Stronger than covalent bonds
- Ionic bonds are solid at room temp, have very high freezing point, conduct electricity
5
Q
Intermolecular attractions:
A
- Van der Waals: Weak intermolecular forces between 2 neutral molecules
1a. Dipole-dipole: both have polar moment
1b. London dispersion: induced dipoles - Hydrogen bonds: H-O,N,F
6
Q
Lewis dot structure instructions
A
- Count all valence electrons (add electron for negative charge, and subtract one for a positive charge)
- Arrange and connect atoms
- 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
7
Q
Exceptions to the octet rule
A
- Expanded octet: for atoms from 3rd period or more
- Electron deficient octets: for second row (period?) elements
- Odd number of valence electrons
8
Q
VSEPR Theory
A
- 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
9
Q
Valence bond theory (VBT)
A
- 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
10
Q
VBT: Electron arrangements according to sp notation
A
- 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
11
Q
VBT: pi and sigma bonds
A
- Single covalent bond (sigma bonds) is an overlap of atomic orbitals
- Pi bonds: overlap of 2 p orbitals
- The bigger the bond order=the smaller the bond length=the bigger the bond dissociation energy
12
Q
Molecular orbital (MO) theory
A
- Says orbitals are formed from linear combinations of atomic orbitals (LCAO) from different atoms
- Says valence electrons are depolarized
- 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
13
Q
Bond order in MO theory
A
- Bond order=(# bonding electrons-#nonbonding electrons)/2
14
Q
Types of formulas
A
- Empirical formula: ratio of whole numbers/simple form
- Molecular formula: exact number of atoms
15
Q
Percent composition by mass
A
- Molecular weight (g/mol) of atom being measured/ empirical formula x 100%
16
Q
Physical and chemical reactions
A
- Physical reaction: when compound undergoes a reaction but maintains its molecular structure (Ex: melting, boiling, evaporation, rotation of polarized light)
- 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
- 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
- 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
- Combination: A+B->C
- Decomposition: C->A+B
- Single displacement/replacement: A+BC->B+AC
- Double displacement/replacement or metathesis: AB+CD->AD+CB
20
Q
Nuclear reactions (delete)
A
- Nuclides that undergo radioactive decay spontaneously break apart which releases energy
- Radioactive isotopes are unstable
21
Q
Half life
A
- Length of time necessary for one half of an amount of a substance to decay (only for unstable isotopes)
- 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 - 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
- Alpha: (mass #-2) & (atomic # -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) - Gamma: emits gamma rays
23
Q
Mass defect
A
- 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) - Missing mass=mass defect and rest of the energy of mass defect is nuclear binding energy
