Chem Exam 2 PQ

Calculate the lattice energy of potassium chloride given the following data: K(s) ⟶K(g) +89 kJ mol-1 K(g) ⟶K+(g) + e- +418 kJ mol-1 1/2Cl2(g)⟶Cl(g) +122 kJ mol-1 Cl(g) + e- ⟶Cl-(g) -349 kJ mol-1 K(s) + 1/2Cl2(g) ⟶KCl(s) -437 kJ mol-1

-717 kJ mol-1

A dipole moment describes charges separated by a distance. Polar covalent bonds have negative and positive ends. The shape of a molecule determines whether or not the dipoles cancel.

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Elements in a single group (same column) of the periodic table have similar chemistry. The valence electrons for elements in each column of the periodic table are essentially the same . The properties of the valence electrons are related to the strength of their interaction with the nucleus . The nuclear charge is of course the same for all of the electrons in an atom. However, we can understand some complex interactions in atoms based on some simple ideas that assumes that the valence electrons experience a different nuclear charge than the core electrons. We refer to this reduced nuclear charge as the effective nuclear charge.

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Ionic radii trends loosely follow the standard atomic radii trends. From top to bottom of the periodic table, ions will increase in radii. However, as you move across the periodic table, the radius is more of a function of the number of electrons. In general, cations are all smaller than their neutral analogs while anions are the exact opposite.

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Valence Bond theory describes the bonds in molecules as arising from the overlap of atomic orbitals centered on the atoms in the molecule. To achieve the correct geometries it must often use new "hybrid" orbitals that result from the mixing of some number of pure atomic orbitals.

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A central atom that is sp2 hybridized can form up to _____ pi bond(s) with a neighboring atom that has a p orbital?

1

How many non-bonding electron pairs are on the central atom in SF5-?

1

Draw the Lewis structure for NO2-. How many single bonds, double bonds, triple bonds, and unshared pairs of electrons are on the central atom, in that order?

1,1,0,1

In PCl3, the total number of nonbonded pairs of electrons is

10

The P2- anion has how many total electrons and how many valence electrons respectively?

17, 7

The carbonate ion (CO32-) has how many resonance configurations?

3

A central atom that is sp3 hybridized could bind up to how many other atoms?

4

Which of the following would be expected to have the highest first ionization energy? Ar, Cl, Na, Xe, Si

Ar

Arrange the following ions in order of increasing radius:K+, Li+, Be2+, Na+

Be2+ < Li+ < Na+ < K+

Which of the following atoms has the largest radius? Br, Ne, F, Cl

Br

For which of these elements would the electron affinity process shown be more favorable (i.e., largest negative value)?

C + e- > C-

Which of the following contains only covalent bonding and no ionic bonding?

CCl4

Rank the following compounds by lattice energy, from least to greatest: KI, CaSe, BeO, CsAt.

CsAt < KI < CaSe < BeO

An element E has the electronic configuration [Ne] 3s2 3p1. Write the formula of its compound with sulfate.

E2(SO4)3

Why is it harder to remove an electron from fluorine than from carbon? To put it another way, why are the valence electrons of fluorine more strongly bonded than those of carbon?

The valence electrons of both fluorine and carbon are found at about the same distance from their respective nuclei but the greater positive charge of the fluorine nucleus attracts its valence electrons more strongly.

An element E has the electronic configuration 1s22s22p4. What is the formula of its compound with lithium?

Li2 E

Rank the following species from smallest to largest atomic radius: K, Mg, Rb, Ca.

Mg, Ca, K, Rb

Using what you know about periodic trends, arrange the following atoms in order of decreasing atomic radius. F, Mg, N, O, Na

Na, Mg, N, O, F

Which of the following compounds are exceptions to the octet rule? Select all of the correct answers.

PCl5, XeF2

Which of the following compounds contains exactly one unshared pair of valence electrons? An unshared pair of valence electrons is another name for a lone pair or non-bonding pair.

PH3

Which has a stronger carbon-oxygen bond. carbon monoxide or carbon dioxide?

The C-O bond in carbon monoxide (CO) is stronger as it is a carbon/oxygen triple bond. In carbon dioxide (CO2), the carbon/oxygen bond is a double bond. You would know this by drawing the Lewis structures of these two molecules.

True or False: All non-polar molecules have non-polar bonds.

This statement is false. It is possible to have a nonpolar molecule with polar bonds! The geometry of the molecule matters because the net dipole moments of the bonds can sometimes cancel. CO2 is a molecule with polar bonds (C-O) but with a net dipole moment of zero due to the symmetric geometry of the molecule.

A double bond in a compound like C2H4 consists of

a sigma and a pi bond

Which of the following best describes where the highest electron density is for a π bond between two atoms in a molecule?

above and below the axis but not on the bond axis.

When two H atoms are brought together from large distances they can make H2. As the bond beings to form, the force between the atoms becomes more (attractive/repulsive) and the potential energy (increases/stays the same/decreases).

attractive/decreases

When dealing with electrons in atoms and molecules, the electrons that are not considered as valence electrons (can/cannot) effectively shield the nucleus and thereby (decrease/increase) the effective nuclear charge.

can; decrease

The basic fact that determines molecular shapes is that

electron pairs repel each other

These hybridized atomic orbitals occupy the correct regions in space that allow for the given __________ geometry around the atom.

electronic

You have been asked to draw a molecule that exhibits resonance, in which there are single and double bonds in different locations in the drawings. If you could do an experiment to measure the bond strength of these single and double bonds, you would find that

every time the measurement would give the same bond strength close to the average of a single and double bond.

In line drawings, hydrogen atoms and lone pairs are ______, which means they are not shown in the drawing.

implicit

As an atom's radius decreases...

its ionization energy increases

The concept of "polarity" is due to

one atom of a bonded pair of atoms exerting a greater attractive force on the shared electrons.

To make sp2 hybrid orbitals, what orbitals are mixed?

one s and two p

You would expect a phosphorous-chlorine bond to be...

polar, with the chlorine end having a partial negative charge

Electrons with great electron affinities (large negative values) often have

small sizes and high ionization energies

Identify the hybrid orbitals used by the bolded atom in acetone (CH3COCH3).

sp3

Which of the following combinations of hybridization and molecular geometry is possible?

sp3, trigonal pyramidal

Usually, the shorter the bond, the ______ the bond.

stronger

The electronic geometry of NH3 (ammonia) is

tetrahedral

The bond angle of the molecule H2O is less than the tetrahedral bond angle of 109.5˚ because

the repulsion between lone pairs of electrons is greater than the repulsion between bonding pairs.

The electronic arrangement is the same as the molecular shape when

there are no lone pairs of electrons on the central atom

The molecular geometry of ammonia (NH3) is

trigonal pyramidal

Covalent compounds are generally made up of elements found in which part of the periodic table? upper right, lower left, upper left, lower right

upper right

Resonance is a concept that describes the bonding in molecules...

where there is more than one choice of location for a double or triple bond as deduced from Lewis dot structures. The true bonding is the average over all possible multiple bond locations.