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Each element is distinguished by the __. The number of neutrons is what? What are isotopes?
- number of protons in the nucleus
- usually similar to the number of protons, but can vary.
- atms with the same number of protons but different numbers of neurons
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__ form bonds and determine the structure of hte resulting molecules. Because they are both small and light, they show properties of __ and __. Those that are bound to nuclei are found in __.
- electrons
- waves
- particles
- orbitals
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Heisenberg Uncertainty principle
we can bever really know exactly where the electron is; but we can determine the electron density (the probability of finding an electron ina particular part of the orbital)
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Atomic orbitals are goruped into different __ at different distances from the nucleus. Each shell is identified by a __, with __ for the lowest energy one closest to the nucleus.
- WHat happens as n increases?
- shells
- principal quantum number
- n=1
- the shells are farther from the nucleus, higher in energy, and can hold more electrons
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What is a nodal plane?
Orbitals with identical energies are __.
What is the Pauli Exclusion principle?
- flat (planar) region of space, including the nucleus, with zero electron density
- degenerate orbitals
- each orbital can hold a max of two electrons, provided their spins are paired
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What are valence electrons?
Carbon has __, N: __, O: _
- those in the outermost shell
- carbon=4
- nitrogen=5
- oxygen= 6
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Hund's rule
when there are two or more orbitals of the same energy, electrons will go into different orbitals rather than pair up in the same orbital
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Explain the two ways atoms can interact to attain noble gas config, thus fulfilling hte octet rule?
ionic bonding: transfer of electrons, resulting in large crystal lattice
covalent bonding: shared electrons not transferred
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What are nonbonding electrons?
A pair of nonbonding electrons is called a __
valence-shell electrons that are not shared between two atoms
lone pair
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What do we use electronegativities as? What is the trend in EN?
as a guide in predicting whether a given bond will be polar and the direction of its dipole moment
increases from left to right and from bottom to top
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How to calculate formal charge?
FC= [group number]- [nonbonding e]-[number of bonds (or 1/2 the number of shared electrons)]
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Some organic compounds contain __. For example, the structure of CH3NH3Cl cannot be drawn using just __ becuase it would require nitrogen to have five bonds, implying ten valence electrons. Therefore, what is the correct structure?
- ionic bonds
- covalent bonds
- having a chloride ion bonded, not a covalent bond to chloride
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Explain resonance in terms of stability?
Type of arrows that are used for resonance? equilibrium?
In terms of resonance, what don't hte electrons do?
- charge delocalization (the positive on the less EN and hte negative on the more EN)
- a single double-headed arrow
- two single headed arrows in opposite directions
- oscillate back and forth; they are delocalized over all the resonance forms at the same time
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True or False:
Individual resonance forms do not exist.
True
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Are resonance structures equal in energy? Explain?
no; there are major and minor contributors, depending on the most stable
the major is the one with the lowest energy, generally having all octets satisfied, as many bonds as possible, and as little charge separation as possible; negative charges are on the more EN, like O, N, and S
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Two types of structural formulas. What are they?
What is the other way to draw formulas?
- lewis structures
- condensed structural formulas
line angle formula
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What is the molecular formula?
How can you determine molecular formulas?
the number of atoms of each element (ex: C2H2)
- two step process:
- - first, determine the empirical formula, simply the relative ratios of the elements present
- - divide the MW of the sample by the empirical weight
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How to convert to an empirical formula?
- 1) assume the sample contains 100g so the percent value gives the number of grams. Divide that number of grams by the atomic weight to get the number of moles.
- 2) Divie each of the number of moles by the smallest one.
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Arrhenius acids and bases
What does this give us?
- acid: substances htat dissociate in water to give hydronium ions
- bases: substances that dissociate in water to give hydroxide ions
the pH and hte acidity in logarithms (neutral is 7)
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BL acids and bases
- acid: any species that can donate a proton
- base: any species that can accept a proton
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Difference between Arrhenius and BL?
- BL bases do not have to have hydroxides
- Arrhenius bases must have OH
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Conjugate acids and bases?
conjugate acid= when a base accepts a proton, it becoems an acid capable of returning that proton
conjugate base= when an acid donates a proton, it becomes a base capable of accepting that proton
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What is Ka?
the acid-dissociation constant and its value indicates the relative strength of the acid; the stronger the acid, the more it dissociates, giving a larger value of Ka
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Explain the pKa of of strong and weak acids?
strong acids: around 0 or negative
weak acids: around four
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The strength of an acid is what?
For an acid to be strong, what must happen?
inversely related to the strength of its conjugate base
its conjugate base must be stable in its anionic form; otherwise, HA would not easily lose its proton. Therefore, the conjugate base of a strong acid must be a weak base. On the other hand, if an acid is weak, its conjugate base is a strong base
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What are the first seven strong acids from strongest to weakening?
- HCl
- H3O+
- HF
- H-COOH
- CH3COOH
- HCN
- NH4
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What are the first five strong bases from strongest to weakening?
- -CH3 (methyl anion)
- NH2- (amide ion)
- CH3CH2O-
- HO-
- NH3
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In the rxn of an acid with a base, the equilibrium generally favors what?
the weaker acid and base
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Generalize acids and bases and their conjugates.
- The stronger an acid, the weaker its conjugate base
- the weaker an acid, the stronger its conjugate base
- acid-base reactions favor the weaker acid and the weaker base
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Electronegativity trend
a more electronegative element bears a negative charge more easily, giving a more stable conjugate base and a stronger acid; increases from left to right
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Size
the negative charge of an anion is more stable if spread over a larger region of space; acidity increases down the colum as the size of the element increases
- Acidity: HF < HCl <HBr < HI
- Stability F- < Cl- < Br- < I-
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__ is the dominant effect helping stabilize an anion. __ is the strongest base because it has the negativ charge localized on one oxygen atom. Why?
- the dominant
- ethoxide
- because acids are stronger if theey lose a proton give resonance-stabilized conjugate bases. Therefore, if there is no resonance possible, the base will be strong and the acid will be weak
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Electron-withdrawing atoms and groups can also stabilize a conjugate base through the __ of hte molecule Stabilization of the conjgate bases results in a stronger acid. The magintude of this __ depends on what?
- sigma bond
- inductive effect
the number of bonds between the EN element and the site of hte negative charge
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Explain the inductive effect in terms of the example of the book with the chlorine?
Explain it in terms of general electron-withdrawing groups?
the acidity increases by adding a chlorine, and the effect is larger if the chlorine atom is closer to the acidic group
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Lewis Acids and bases
- acids: species that can accept these electron pairs to form new bonds (accepts a pair of electrons; electrophile)
- base: species with available electrons that can be donated to form new bonds (donates a pair of electrons (nucleophile))
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