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Discrete MCAT Questions > General chemistry > Flashcards

General chemistry Flashcards

1
Q

What is the principle quantum number?

A

is n
Is the number in front of each orbital. For example 1S or 2S

When electrons are removed from an element, forming a cation, they will be removed from the sub shell with the highest n value first. For example 4s will be empty before 3d because it has a higher quantum number even though 3D is after 4s in the electron configuration.

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2
Q

What is the azimuthal quantum number?

A

Represented by L, cannot be higher than n-1

Orbital L=

s. 0
p. 1
d. 2
f. 3

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3
Q

What does the ml number stand for?

A

Described the chemicals magnetic properties. Can only be an integer Vaud between +L and -L. It cannot be equal to 1 if L=0, this would imply that the s orbital has these subshells when we know it only has one

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4
Q

What does ms describe?

A

The electron spin (magnetic moment) -1/2 is down and +1/2 is up

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5
Q

What is the maximum number of electrons allowed in a single atomic energy level in terms of the principal quantum number n?

A

2n^2

Two per orbital.

There are only two elements (H and He) that have valence electrons in the n=1 shell

Eight elements (Li to Ne) have valence electrons in the n=2 shell. This is the only equation that matches this pattern

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6
Q

What is the equation that describes the maximum number of electrons that can fill a sub shell?

A

4L+2

Sub shell      L.       Electrons
S.                 0.          2
P.                  1.          6
D.                  2.         10
F.                   3.         14
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7
Q

What is the equation for photon energy?

A

E=hc/wavelength

h=6.62x10^-34 J•s. (Plancks constant)
c=3x10^8 m/s (speed of light)
Wavelength is normally given in nm and needs to be m

E is in J

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8
Q

What is Avogadro’s number?

A

NA=6.02x20^23 mol^-1

Gives moles

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9
Q

What is the Heisenberg uncertainty principle?

A

Limitations inherent in the measuring process. Measuring things simultaneously creates a larger error

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10
Q

How does an electron gain energy?

A

Must absorb energy from photons to jump up to a higher energy level. For example moving from n=2 to n=6

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11
Q

What is Hunds rule?

A

Electrons fill empty orbitals first before doubling up electrons in the same orbital

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12
Q

Heisenberg uncertainty principle?

A

Refers to inability to know the momentum and position of a single electron simultaneously

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13
Q

What is the Bohr model?

A

An early attempt to describe the behavior of the single electron in a hydrogen atom.

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14
Q

What is the Rutherford model?

A

Described a dense, positively charged nucleus.

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15
Q

How is the periodic table organized?

A

Periods (rows) and groups (columns)

Groups represent elements with same valence electron configurations which helps determine chemical properties

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16
Q

How do electron shells change in periodic table?

A

From top to bottom in a group (column) extra electron shells accumulate.
These extra shells provide shielding between the positive nucleus and the outer electrons which decreases the electrostatic attraction which increases the atomic radius.

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17
Q

What determines the length of an elements atomic radius?

A

Number of valence electrons and number of electron shells

As one moves across a period (row) protons and valence electrons are added and the electrons are more strongly attracted to the central protons which shrinks the atomic radius.

More electron shells (increases down column) the larger atomic radius is

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18
Q

Ionization energy

A

Amount of energy it takes to remove an electron from an atom.

Increases from left to right. Second ionization energy is ALWAYS LARGER than the first ionization energy.
First ionization energy increases up and to the right

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19
Q

What properties of the periodic table increase to the right and up

A

Electronegativity and first ionization energy

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20
Q

Why are metals good conductors?

A

They have valence electrons that can move freely

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21
Q

What is important about group 2 of the periodic table?

A

They form divalent cations

These are also the alkaline earth metals.

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22
Q

Why are transition metals such as iron special?

A

Can form more than one ion which allows them to form hydration complexes with water because of the various oxidation states.

When a transition metal can form a complex its solubility within the related solvent will increase

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23
Q

What is the effective nuclear charge?

A

Strength at which the protons in the nucleus can pull on electrons. Increases same way as electronegativity left and up.

24
Q

Why do halogens often form ionic bonds with alkaline earth metals?

A

Ionic bonds form from UNEQUAL sharing of electrons. These bonds typically occur because the electron affinities of the two bonded atoms differ greatly.

The halogens have High electron affinities because they only need one electron to fill valence shell while alkaline metals are the opposite and would have to lose two electrons to have a full valence shell so they are more likely electron donors and have a low electron affinity

25
Q

What is the highest energy orbital of elements with electrons in the n=3 shell?

A

D orbital

When n=3, L=0,1, or 2

The highest value for L in this case is 2 which corresponds to the d sub shell.

26
Q

Ionic bond

A

Complete transfer of valence electrons between atoms. Generates two oppositely charged ions. The metal loses electrons to become positively charged and non metal accepts electrons to become negatively charged

27
Q

Polar covalent bond

A

Pair of electrons is unequally shared between two atoms

28
Q

Nonpolar covalent bond

A

Type of bond that occurs when two atoms shares a pair of electrons with each other such as between two hydrogens

29
Q

Coordinate covalent bond

A

The two electrons derive from the same atom. The binding of metal ions to ligands involves this.

30
Q

Formal charge

A

FC=valence electrons- (Bonds+dots)

Bond is a stick
Count individual dots not lone pairs.

31
Q

Valence electrons periodic table

A

Each group 1A-8A ignoring the transition metals in the center corresponds to valence electrons

So H has 1
Be has 2
B has 3
C has 4 etc…

32
Q

What is the order of increasing strength of intermolecular forces?

A

London dispersion—-> dipole-dipole——>hydrogen bonds——> ionic bonds

33
Q

What effects bond lengths?

A

Bond lengths decrease as the bond order increases and they also decrease with larger differences in electronegativity. Bond length decreases when moving to the right along the periodic table

34
Q

Why can some atoms exceed the octet rule?

A

Atoms that exceed the octet can do so because they have d orbitals in which extra electrons can reside. All atoms in the third period or greater have d orbitals which can hold an additional 10 electrons.

35
Q

What type of intermolecular force provides the most accurate explanation for why noble gases can liquefy?

A

Dispersion forces. Noble gases are entirely uncharged and do not have polar covalent bonds, ionic bonds or dipole moments.

36
Q

Ionic compound

A

Ionic compounds are three dimensional arrays or charged particles.
Composed of atoms held together by ionic bonds.
Ionic bonds associate charged particles with large differences in electronegativity.
Measured with formula weights
Electrons are not really shared but donated from less electronegative atoms to the more

37
Q

Covalent compounds are measured in

A

Molecular weights not formula weights.

38
Q

Acetone

A

C3H6O

39
Q

Ethanol

A

Ethyl alcohol

C2H5OH

40
Q

Propane

A

C3H8

41
Q

Methanol

A

CH3OH

42
Q

Neutralization

A

Acid and a base react to form water and a new aqueous compound

43
Q

Double displacement

A

Exchange of positive ions between two compounds

AY+BX——> BY+AX

44
Q

Single replacement

A

A single element replaces a second element in a compound

Br2+2KI—-> 2KBr+I2

45
Q

How to find how much excess reagent is left over once a reaction has gone to completion

A

Given both of the masses to start the reaction.
First determine which species is the limiting reagent.

Find formula weights for both reagents (ignore mols in the equation for now) just trying to find out how many grams per mole

Then divide what you are given by the formula weight you just found. This will tell you how many mols you were given of each reagent

Now pay attention to how many moles are needed of each molecule in the reaction. If you need more moles of one molecule that is the limiting reagent.
What is left over will be the other reagent

46
Q

Combination reaction

A

Also known as a synthesis reaction. Where two or more elements or compounds combine to form a single product

47
Q

Combustion

A

A reaction that utilizes oxygen and hydrocarbons as reactants and that produced carbon dioxide and water

48
Q

Metathesis

A

Exchange of positive ions between two compounds that generally take place between two ionic compound in an aqueous solution. Wants to decrease the number of ions from the reactants to the products. Make more stable products

A double replacement reaction

49
Q

Theoretical yield

A

Amount of product synthesized is the limiting reagent is completely used up

  1. Balance equation
  2. Take grams of limiting reagent given
  3. Convert to mols using molar mass
  4. Multiply by moles of target product/ moles of limiting reagent
  5. Multiply by molar mass of target product/1mol

Gives you grams of product produced

50
Q

What makes the strongest electrolytic solution?

A

Dissociate rapidly (have a high dissociation constant) and are ionic compounds with large amounts of cations and anions.

51
Q

Nonspontaneous reactions are

A

Endergonic

Products are higher than reactions on energy diagram

52
Q

Zero order reaction

A

Unaffected by concentrations of any reactants in the reaction

53
Q

What experimental method never should affect the rate of a reaction?

A

Removing the product of an irreversible reaction

54
Q

If the sum of the exponents (orders) of the concentrations is two then the rate law is

A

2, second order

The exponents of the rate law are unrelated to stoichiometric coefficients

55
Q

Exergonic

A

Is energy is released by the reaction. Net energy change is negative so free energy of products is lower than the free energy of the reactants.

56
Q

Intermediated exist where on a reaction diagram?

A

The valleys

Transition states are the tops of the hills of these valleys

57
Q

How to find rate law for a second order reaction with a slow step and fast step?

A

Rate law is related to the concentrations of the reactants of the SLOW step not the overall reaction

Discrete MCAT Questions (6 decks)

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