Gen Chem 1: Fundamentals

Question 1

in SI units, density is expressed in _______

whereas in chemistry, density is usually expressed as ________

Answer 1

SI units: kg/m³

chemistry: g/cm³

to convert,

multiply g/cm³ by 1000 → kg/m³

divide kg/m³ by 1000 → g/cm³

Question 2

density of water

Answer 2

1 g/cm3

1000kg/m³

Question 3

density = ?/?

Answer 3

mass/volume

Question 4

nano-

Answer 4

10^-9

Question 5

micro-

Answer 5

10^{<span>-6</span>}

Question 6

milli-

Answer 6

10^-3

Question 7

centi-

Answer 7

10^-2

Question 8

kilo-

Answer 8

10³

Question 9

mega-

Answer 9

10⁶

Question 10

1L=_______cm³

Answer 10

1000cm³

Question 11

1 mL = ? cc

Answer 11

1 mL = 1 cc (cubic cm)

cc aka cm³

Question 12

1 Å = ? m

Answer 12

1 Å = 10^-10

Question 13

what does the formula weight refer to?

Answer 13

the sum of the atomic weights of all the atoms in the molecule

we use the term molecular weight MW when the compound exists as discrete molecules

we use the term formula weight when the compound exists as an ionic compound.

Question 14

how do you find moles of a substance in a molecule?

Answer 14

moles = mass in grams / MW

MW= total mass of molecule

Question 15

what does percentage composition by mass (aka percent mass composition) refer to? how is it calculated?

Answer 15

the percentage of the compound’s mass that is made up of a given molecule

• tip: use the empirical formula, which will give you the same answer as molecular formula but is shorter*
  e. g. C₂H₂N

find the percent mass of carbon from ^

given: atomic mass of C is 12 g/mol and molecular weight of ^ is 40

%Composition=mass of element in formula/molar mass x100

%Composition = (2x12)/40 x 100

Question 16

how many oxygen atoms in 5H²O?

Answer 16

5

the 5 in front denotes that there is 5 of each component

Question 17

How do you find the empirical formula from the percentage composition by mass?

Answer 17

1. assume there is 100g of the substance so that the percentages you are given in the problem can equal that number in grams
2. find the moles of the components using moles=mass in grams (assumed to equal the percentage)/ MW.
3. divide the ratios found for each component. the resulting ratio is the ratio of the component that the first ratio belong to / component that the second ratio belonged to.
4. plug that ratio into your emprical formula

Question 18

nuclear binding energy

Answer 18

the energy relealsed by the protons and neutrons (called nucleon) when they came together to form a nucleus.

equal to the force required to break the nucleus into its respective nucleons

not all nuclei contain protons and neutrons

Question 19

the mass of a combined nucleus is less than the sum of the mass of all the nucleons taken individually. why?

Answer 19

because then a nucleus comes together, some mass is converted to energy

the difference is called the mass defect, Δm

Question 20

Δm

Answer 20

mass defect

the difference between total mass of separate nucleons and mass of nucleus

its mass-energy equivalent (found by Einstein’s formula) is the nuclear binding energy

Question 21

how can you find the nuclear binding energy, E_B from the mass defect?

Answer 21

through Einstein’s equation for mass-energy equivalence: E_B=(Δm)c²

c=speed of light

Question 22

amu

Answer 22

atomic mass unit: weight of an atom

e.g. C is 12 and 1 amu is 1/12 of carbon’s amu (by convention)

Question 23

divide the _________formula by the greatest common factor to get the _________formula

Answer 23

molecular

empirical

Question 24

polyatomic ions

Answer 24

ions with more than one atom

e.g. NH₄⁺

Question 25

T/F : molecular weight is grams per mole

Answer 25

true

Question 26

What effect does vaccuum distillation have on boiling point?

Answer 26

Lowers Boiling Point

boiling occurs when the P_vapor of the substance in question equals the P_atm. Typically, we boil substances by increasing the temperature, thereby increasing P_vap. Alternatively, however, we can lower boiling point by reducing P_atm, which can be accomplished through the introduction of a vacuum. Vacuum distillation is often used when components have very high boiling points and would otherwise be difficult to distill.

Question 27

What’s the difference between Bohr model and Quantum model of electron density?

Answer 27

Bohr: electrons in an atom orbit the nucleus in circular paths where distance from nucleus corresponds to energy of electrons. Only certain orbitals at certain distances are allowed. If an electron absorbs energy that is exactly equal to the difference in energy between it’s current state and that of the next, then it moves up into the next higher energy orbital and visa cersa. The name of the unit of energy released or absorbed is called a photon. Only specific energies (as seen by wavelengths) occur.

Quantum: accounts for the interactions seen in atoms with many electrons. It organizes “quantizes” the electrons by shell, subshell, orbital, and spin (these all fall into the category of “quantum numbers” which help add specificity to the locations of electrons.

Question 28

what are the components of the quantum model of the atom?

Answer 28

1. Energy Shell

• denotes energy level: high the energy level, higher the energy
• analogous to circular orbits of Bohr model
• denoted by 1n, 2n, 3n

2. Subshell:

• describes the probability of finding an electron within the given subshell.
• composed of more than one orbital of the same energy
• denoted by letters s, p, d, or f

3. Orbital

• each orbital has different orientation in space and the orientation increased by 2 in each successive subshell.
  
  • denoted by 1s, 2s, 3s for S subshell; p_x, p_y, p_z for p orbitals.

4. Electron Spin

• each electron can be either spin up or spin down
• there can be 2 electrons per orbital, one spin up and one spin down
• when there are 2 electrons, the spin states must be opposed as it is a measure of magnetism

Question 29

what are the 3 rules for how electons can occupy an orbital?

Answer 29

1. Aufbau principle: electrons occupy the lowest energy orbitals available (meaning, that 2 will be filled before S is filled) since the numbers indicate energy levels. It also means that S will be filled before P
2. Hund’s Rule: electrons in the same subshell occupy available orbitals singly, before pairing up
3. Pauli Exclusion Principle: there can be no more than two electrons in any given orbital.

Question 30

An s subshell has only one possible orbital orientations. Since only 2 electrons can fill any given orbital, an s subshell can hold no more than __#__ electrons.

Answer 30

1 orbital x 2 electrons = 2 electrons

Question 31

a d subshell has __#__ possible orbital orientations. a d shell can contain ___#___ electrons

Answer 31

5 (2 more than the p subshell)

10 electrons

Question 32

an f subshell has ___#__ possible orbital orientations and can have ___#__ total electrons

Answer 32

7 orientations

14 electrons

Question 33

“diamagnetic” means

Answer 33

an atom has all its electrons spin-paired

A diamagnetic atoms must contain an even number of electrons and ahve all its occupied subshells filled.

Question 34

T/F diamagnetic atoms are repelled by an externally produced magnetic field

Answer 34

true, because they have no net magnetic field

(all canceled out)

Question 35

T/F an atom with an odd number of electrons is paramagnetic

Answer 35

true, but not every even numbered atom is diamagnetic because you can have a 2p⁴ orbital

so it is attracted to externaly produced magentic fields

Question 36

atoms with the same electron configuration are called

Answer 36

isoelectric

Question 37

when electrons are removed from an atom its called _________ and they only leave from the _________shell

Answer 37

ionization

valence

Question 38

T/F: only after all s electrons are lost do d electrons get ionized (ie lost)

Answer 38

True

Question 39

the d block corresponds to what type of atom?

Answer 39

transition metals (for the most part)

Question 40

If Ti is 4s²3d² then Ti⁺ is

Answer 40

4s¹3d²

because electrons leave in order of highest configuration (n=4) to lowest (n=3)

Question 41

Chromium has an irregular electron configuration. Why?

Answer 41

because a d subshell can hold a max of 10 electrons, when d⁵ is reached, it actually becomes more stable. This means that what would be a configuration of [Ar] 4s²3d⁴ is actually [Ar] 4s¹3d⁴.

essentially an “s” electron is promoted to d orbital

Question 42

T/F: atoms in an excited state have additional electrons

Answer 42

FALSE. They have absorbed energy but not addition of electrons.

Question 43

what pattern is associated with each family/group/column of the periodic table

Answer 43

valence electrons: each element in that group have the same number of valence electrons

Question 44

halogens are powerful _________ing agents

Answer 44

oxidizing because they share electrons, which results in gain of electrons for the oxidized molecule

Question 45

Z_eff stands for _____

Answer 45

effective nuclear charge: the amount of force felt by the electron after shielding effect is accounted for

Z_eff = Z - core electrons

core electrons = Atomic number (Z) - # valence electrons

(represented by group (column number)

https://www.youtube.com/watch?v=hwM4mCj8Oh8

Question 46

T/F: gravitational forces between electrons and nucleons of an atom are negligible

Answer 46

true

Question 47

what is the periodic trend for atomic radius

Answer 47

• atomic radius decreases as you move from left to right on the table
• increases as you move down a group

because the number of protons is increasing from left to right but new shells are not being made, so the electrons feel a greater effective nuclear charge, which means that the radius is decreasing.

It increases as you go down a group because new shells are added each period, which increases the atomic radii

Question 48

equation for coulumb’s law as it applies to atomic theory

Answer 48

F_e ∝​ (Z_eff + C)/r²

Where F_e is effective nuclear force

and Z_eff is effective nuclear charge

r = size of valence shell

**r does NOT equal the atomic radius, in fact the atomic radius can get smaller while valence shell remains unchanged

Question 49

Which is accurate in terms of atomic radius?

1. cation radius < neutral atom radius < anion radius
2. neutral atom radius < anion radius < cation radius
3. anion radius <neutral></neutral>

</neutral>

Answer 49

cation radius < neutral atom radius < anion radius

because as you remove electrons, the radius gets smaller because the electrons are held more tightly to the nucleus

Question 50

Moving top to bottom within a group core electrons are added at the same rate as protons. What happens to Z_eff , C, and r

^the variables in Coulumbs equation

Answer 50

Z_eff and C both remain constant

(C, charge, is determined by number of valence electrons, which remains constant as you move down)

r increases because new shells are added, which increases shielding

Question 51

T/F: F_e increases as you move down a group

Answer 51

True

because Z_eff and C remain constant but r increases (refer to Coulumb equation)

Question 52

Moving left to right across the periodic table, what happens to Z_eff , C and r? What happens to F_e ?

Answer 52

Z_{<strong>eff</strong>} increases because protons are added while core electrons remain the same

C valence electrons are added at the same rate as protons, so charge remains zero

r (size of valence shell) is unchanged since there is no change to core electrons and therefore no increase in shielding

This means that according to the equation (Fe=Zeff + C/r2), F_e increases

Question 53

what happens to the variables in coulumbs law when you move from positive to negative?

Answer 53

Question 54

T/F: atomic radius increases with increasing electron charge

Answer 54

true

this means that an anion has a greater atomic radius than a neutral molecule or cation

Question 55

ionization energy increases/decreases with higher F_e

Answer 55

increases

ionization energy is the force required to remove the outermost electron, so the greater the F_e pulling the electron toward the nucleus, the greater the force required to overcome F_e

Question 56

IE₂ represents ?

Answer 56

the energy required to remove the least tightly bound electron from the cation X⁺

energy required to remove the least tightly bound electron = “ionization energy”

Question 57

T/F: Elements with a closed subshell/shell have a greater ionization energy

Answer 57

true

Question 58

How do you solve this problem?

Answer 58

Notice there’s a huge jump in ionization energy between the second and the third ionization energies.

That means it’s much harder to remove a third electron than the second.

So look for the one that will be in noble gas configuration (very stable) after removing 2 electrons.

Answer is Calcium

Question 59

in groups where the valence shell is filled, the electron affinity (EA) is a ___pos/neg_____ value

Answer 59

positive value

because energy is required to make it happen, which is less favorable

this is because moving it into an electron configuration that is not completely filled is less stable

examples of these groups are alkaline earth metals and noble gases

Question 60

electron affinity def

Answer 60

energy change that occurs when one electron is added to an atom in gas phase

aka EA

Question 61

what are the 9 most electronegative atoms in order from most electronegative to least?

Answer 61

FONCLBrISCH

F>O>N_~Cl>Br>I>S>C_~H

Question 62

an alpha particle consists of

Answer 62

2 protons and 2 neutrons

Question 63

when calculating ground state configurations for atoms, you must do what first?

Answer 63

check to see if it’s a transition metal! if it is, then the electrons that are lost first are from the S orbitals not d orbitals

Question 64

what is the number for the orbital class associated with the first row of d orbitals

Answer 64

3 (not 4, as is the case for the S orbitals)

Question 65

what determines the energy level of a given subshell compared to the other subshells

Answer 65

the quantum number

meaning, the number associated with each row of subshells

e.g. 4p² is higher in energy than 3p²

Question 66

which of the following has the smallest atomic or ionic radius?

1. Cl^-
2. Ar
3. K⁺
4. Ca²⁺

Answer 66

4. Ca²⁺

even though Ca is to the far left on the periodic table, if it’s 2+ then it’s moved 2 spaces to the left which corresponds to the same configuration as a noble gas, making Ca2+ the farthest ion to the right

Question 67

What are the nuclear numbers and their symbols?

Answer 67

Question 68

How do you name polyatomic Ions with multiple oxyanions - Most oxidized

Answer 68

prefix = per-

suffix = -ate

Examples: perchlorate (ClO₄^-)

Question 69

How do you name polyatomic Ions with multiple oxyanions - second most oxidized

Answer 69

no prefix

suffix = -ate

Examples:

1. Bicarbonate (HCO₃^-)
2. Carbonate (CO₃²)
3. Sulfate (SO₃^2-)
4. Phosphate (PO₄^3-) and biphosphate (HPO₄³⁻ )
5. Acetate (CH₃COO^-)
6. Nitrate (NO₃^-)

Question 70

How do you name Polyatomic Ions with multiple Oxyanions - Second least oxidized

Answer 70

no prefix

suffix = -ite

Examples:

1. Nitrite (NO₂^-)
2. Sulfite (SO₃^-2)

Question 71

How do you name Polyatomic Ions with multiple Oxyanions - Least oxidized

Answer 71

prefix = hypo-

suffix = -ite

Example: hypochlorite (ClO⁻)

Question 72

Polyatomic Ions w/o multiple oxygens

Answer 72

NH₄⁺

H₃O⁺

CN^-

OH^-

Question 73

Oxidation number of Hydrogen

Answer 73

0 when bonded to carbon

+1 when bonded to element more electronegative than carbon

-1 when bonded to less electronegative element than carbont

how to know what’s less electronegative:

FONClBrISCH (most electronegative to least in order) so anything not on this list gives hydrogen a -1 oxidation state

Question 74

Oxidation number of oxygen

Answer 74

-2 unless bonded to perchloride (in which case it is usually -1)

*other exception: when paired with other more electronegative elements

Question 75

Oxidation number of Group 1A Elements in Compounds

Answer 75

+1

Question 76

oxidation number of Group 2A Elements in Compounds

Answer 76

+2

Question 77

oxidation numbers of halogens

Answer 77

-1

Question 78

how to determine how much product will be produced in a given reaction equation (ie the theoretical yield)

Answer 78

Question 79

Consider two electron transitions. In the first case, an electron falls from n=4 to n=2 giving off a photon of light with wavelength of 488nm. In the second transition, an electron moves from n=3 to n=4, for the second transition we would expect that:

1. energy is absorbed/emitted _{pick one}
2. the wavelength of the corresponding photon release will be longer/shorter _{pick one} than the first transition

Answer 79

energy (a photon) is absorbed

wavelength of the corresponding photon will be longer

explanation: since the electron transitions between energy levels that are closer together, the ΔE between levels is smaller. By the ΔE=hc/λ equation, ΔE and λ are inversely proportional.

Question 80

descibe the direction of the periodic trend of mettalic character

Answer 80

increases from top to bottom and from right to left (“towards california”)

mnemonic: california is the golden state and gold is a metal