General Chemistry

Question 1

Which subatomic particle is the most important for determining each of the following properties of an atom? charge, atomic number, isotope

Answer 1

Charge = electrons
atomic number = protons
isotope = neutrons

Question 2

Determine the number of protons, neutrons, and electrons in each of these species? 18O, 18F

Answer 2

18O: 8 protons, 10 neutrons, 8 electrons

18F: 9 protons, 9 neutrons, 9 electrons

Question 3

What are the definitions of atomic mass and atomic weight?

Answer 3

atomic mass: protons plus neutrons
atomic weight: the weighted average of the naturally occurring isotopes of an element

isotopes = same proton diff neutron

Question 4

While mass is usually written g/mol, is the ratio mol/g also acceptable?

Answer 4

Yes but you just have to adjust in your math to where units cancel out

Question 5

Calculate and compare subatomic particles that make up: 19O, 16O, 17O, 19F, 16F, 238U, 240U

Answer 5

19O = 8p, 11n, 8e
16O = 8p,8n,8e
17O = 8p, 9n, 8e
19F = 9p, 10n, 9e
16F = 9p, 7n, 9e

Question 6

The valence electron in a lithium atom jumps from energy level n = 2 to n = 4. What is the energy of this transition in joules? in eV?

Answer 6

E = Rh [1/ni2 - 1/nf2] = 2.18 x 10^-18 [1/2^2 - 1/4^2] = 2x10^-18[3/16] = 3.75x19^-19J

E = Rh [1/ni2 - 1/nf2] = 13.6 [1/2^2 - 1/4^2] = 14(3/16) = 2.5eV

Question 7

If an electron emits 3eV of energy, what is the corresponding wavelength of the emitted photon?

Answer 7

400nm (check p. 36 of book)

Question 8

Calculate the energy of a photon of wavelength 662nm

Answer 8

3.00 x 10^-19J (check p. 36 of book)

Question 9

Planck’s constant? and what did he propose?

Answer 9

He developed first quantum theory proposing that energy emitted as electromagnetic radiation from matter comes in discrete bundles called quanta. the energy of a quantum is given by his relationship E = hf where h is known as planck’s constant 6.626 x 10^-34 Js

• f is frequency of radiation

Question 10

what is speed of light

Answer 10

3.00 x 10^8 m/s

Question 11

Hund’s rule?

Answer 11

within a given subshell, orbitals are filled such that there are a maximum umber of half-filled orbitals with parallel spins

Question 12

paramagnetic and diamegnetic

Answer 12

paramagnetic = magnetic field will cause PARAllel spins in unpaired electrons and cause an attraction

diamagnetic = atoms that have only paired electron and will be slightly repelled by a magnetic field

Question 13

If given the following quantum numbers, which element do they likely refer to? 
n = 2, l =1
n = 3, l = 0
n = 5, l = 3
n = 4, l = 2

Answer 13

1. B, C, N, O, F, Ne
2. Na, Mg
3. actinide series
4. Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd

Question 14

Write out and compare an orbital diagram for a neutral oxygen atom and an O2- atom

Answer 14

write it out

Question 15

MRA is a technique that can resolve defects like stenotic (narrowed) arteries. A contrast agent like gadolinium or manganese injected into the blood stream interacts with the strong magnetic fields of the MRI device to produce such images. Based on their orbital configurations, are these contrast agents paramagnetic or diamagnetic?

Answer 15

Both of these molecules have an unfilled valence electron shell with relatively less paired electrons THEREFORE they are paramagnetic

Question 16

What is the modern periodic table arranged by?

Answer 16

atomic number

Question 17

Based on their locations on the periodic table, identify a few elements that likely possess: luster, poor conductivity of heat and electricity, good conductivity but brittle

Answer 17

luster: metals
poor conductivity of heat and electricity: nonmetals
conductivity but brittle: metalloids

Question 18

Which elements are metalloids?

Answer 18

B, Si, Ge, As, Sb, Te, Po, At

Question 19

Which has a larger radius?
F or F-
K or K+

Answer 19

Anions are bigger

F- and K

Question 20

Rank the following elements by DECREASING first ionization energy: Ca, C, Ge, K
(most to least)

Answer 20

C > Ge > Ca > K

Question 21

Rank the following by increasing electron affinity: Ba, Cu, S, Y

Answer 21

Ba < Y < Cu < S

Question 22

rank by decreasing electronegativity: Sb, Ne, O, Tl

Answer 22

O > Sb > Tl > Ne

Question 23

increasing atomic radius: Nb, Pr, Ta, Xe

Answer 23

Xe < Nb < Ta < Pr

Question 24

Write down the groups of the periodic table that exhibit:

1. high reactivity to water
2. six valence electrons
3. contain at least 1 metal
4. multiple oxidation states
5. negative oxidation states
6. possess a full octet in the neutral state

Answer 24

1. high reactivity to water = groups 1 and 2
2. six valence electrons = group 6 and 16
3. contain at least 1 metal = groups 1 through 15
4. multiple oxidation states = all groups; most notably groups 3-12 transition metals
5. negative oxidation states = almost all groups; most notably 14-17 nonmetals
6. possess a full octet in the neutral state = noble gasses

Question 25

Describe the atomic differences between ionic and covalent compounds:

Answer 25

ionic = involve gain or loss of electrons 
covalent = electrons shared between 2 atoms

Question 26

List 3 elements that violate octet rule and why

Answer 26

H - only has 1 electron
He - only has 2
Li, Be, or B
period 3 or greater

Question 27

which periodic trend determines whether a covalent bond is polar or nonpolar?

Answer 27

electronegativity

Question 28

Why do ionic bonds tend to form between nonmetals and metals?

Answer 28

Metals lose electrons bc they have LOW ionization energies while nonmetals gain electrons because they have HIGH electron affinities.

Question 29

describe 5 characteristics of ionic compounds

Answer 29

1. high melting and boiling points due to electrostatic attractions
2. solubility of ions in water due to interactions with polar solvents
3. good conductors of heat and electricity
4. crystal lattice arrangement to minimize repulsive forces
5. large electronegativity differences between ions

Question 30

Describe the relationship between bond strength, bond length, and bond energy

Answer 30

bond strength: electrostatic attraction between nuclei and electrons; multiple bonds (higher bond order) increases strength

bond length: consequence of the attractions of bond strength; the STRONGER the bond, the SHORTER it is

bond energy: minimum amount of energy required to break a bond; the stronger the bond, the higher the bond energy

Question 31

For what values of ΔEN will a nonpolar covalent bond form? polar covalent? ionic?

Answer 31

nonpolar covalent = 0 to 0.5
polar covalent = 0.5 to 1.7
ionic = 1.7 or higher

Question 32

Predict the molecular geometry of:
PCl5
MgF2
AlF3
UBr6
SiH4

Answer 32

PCl5 = trigonal bypyramidal
MgF2 = linear
AlF3 = trigonal planar
UBr6 = octahedral
SiH4 = tetrahedral

Question 33

Rank the major IMFs strongest to weakest:

Answer 33

hydrogen bond > dipole-dipole > van der Waal/dispersion

Question 34

Describe what occurs during dipole-dipole interactions

Answer 34

A dipole consists of a segment of a molecule with partial positive and partial negative regions. The + end of one molecule is attracted to the - end of another

Question 35

In order to exhibit hydrogen bonding, what must be true of a given molecule?

Answer 35

it must have Nitrogen, Oxygen, or Fluorine