MCAT General Chemistry Flashcards

Comprehensive review flashcards covering General Chemistry concepts for the MCAT based on lecture notes.

What does the mass number ($A$) equal?

Protons + neutrons.

What does the atomic number ($Z$) equal?

The number of protons.

What determines an element's identity?

Its number of protons (atomic number).

What is atomic weight?

The abundance-weighted average mass of an element's naturally occurring isotopes.

What are isotopes?

Atoms of the same element with the same number of protons but different numbers of neutrons.

How do you calculate the number of neutrons in an isotope?

Mass number - atomic number ($A - Z$).

What did Rutherford's nuclear model establish?

Atoms contain a small, dense, positively charged nucleus surrounded mostly by empty space and electrons.

What key idea did the Bohr model add?

Electrons occupy discrete energy levels, or orbits.

In the Bohr model, what happens to electron energy farther from the nucleus?

It increases.

What happens when an electron drops to a lower energy level?

A photon is emitted.

What happens when an electron rises to a higher energy level?

A photon is absorbed.

State the Heisenberg uncertainty principle.

The exact position and momentum of a particle cannot both be known simultaneously.

State Hund's rule.

Degenerate orbitals are filled singly with parallel spins before electrons pair.

State the Pauli exclusion principle.

No two electrons in an atom can have the same four quantum numbers; two electrons in one orbital must have opposite spins.

What is Avogadro's number?

$6.022 \times 10^{23}$ particles per mole.

What is Planck's constant ($h$)?

$6.626 \times 10^{-34}\,\text{J}\cdot\text{s}$.

What is the speed of light ($c$)?

$3.00 \times 10^8\,\text{m/s}$ in vacuum.

What equation relates photon energy and frequency?

$E = hf$.

What equation relates the speed of light, wavelength, and frequency?

$c = \lambda f$.

What equation relates photon energy and wavelength?

$E = \frac{hc}{\lambda}$.

How are photon energy and frequency related?

Directly: higher frequency means higher energy.

How are photon energy and wavelength related?

Inversely: shorter wavelength means higher energy.

What does the principal quantum number $n$ describe?

The electron's principal energy level or shell and its average distance from the nucleus.

What values can the principal quantum number $n$ take?

Positive integers: $1$, $2$, $3$, …

What does the azimuthal quantum number $l$ describe?

The subshell and orbital shape.

What values can $l$ take for a given $n$?

Integers from $0$ to $n - 1$.

Which $l$ values correspond to s, p, d, and f subshells?

s = $0$, p = $1$, d = $2$, f = $3$.

What does the magnetic quantum number $m_l$ describe?

The orientation/specific orbital within a subshell.

What values can $m_l$ take?

Integers from $-l$ through $+l$, including $0$.

What does the spin quantum number $m_s$ describe?

Electron spin.

What values can $m_s$ take?

$+\frac{1}{2}$ or $-\frac{1}{2}$.

What is the maximum number of electrons in shell $n$?

$2n^2$.

What is the maximum number of electrons in a subshell with quantum number $l$?

$4l + 2$.

How many orbitals are in an s subshell, and how many electrons can it hold?

$1$ orbital; $2$ electrons.

How many orbitals are in a p subshell, and how many electrons can it hold?

$3$ orbitals; $6$ electrons.

How many orbitals are in a d subshell, and how many electrons can it hold?

$5$ orbitals; $10$ electrons.

How many orbitals are in an f subshell, and how many electrons can it hold?

$7$ orbitals; $14$ electrons.

What is a free radical?

An atom or molecule with one or more unpaired electrons.

What makes a species paramagnetic?

It has at least one unpaired electron and is attracted to an external magnetic field.

What makes a species diamagnetic?

All electrons are paired, so it is weakly repelled by an external magnetic field.

Is helium, $1s^2$, paramagnetic or diamagnetic?

Diamagnetic; both electrons are paired.

Is carbon, $1s^2 2s^2 2p^2$, paramagnetic or diamagnetic?

Paramagnetic; it has two unpaired 2p electrons in the ground state.

State the Aufbau principle.

Electrons fill the lowest-energy orbitals available before higher-energy orbitals.

How many orbitals are present in a subshell with quantum number $l$?

$2l + 1$.

What are the horizontal rows of the periodic table called?

Periods.

What are the vertical columns of the periodic table called?

Groups or families.

Why do elements in the same main-group column have similar chemical properties?

They have the same number of valence electrons and similar outer-electron configurations.

What are the two detached rows at the bottom of the periodic table?

The lanthanide and actinide series (the f-block).

Where are metals primarily located on the periodic table?

On the left and center.

What physical properties generally characterize metals?

They are lustrous, malleable/ductile, and good conductors of heat and electricity.

What electron behavior generally characterizes metals?

They tend to lose electrons and form cations.

Where are nonmetals primarily located on the periodic table?

On the upper right, plus hydrogen.

What physical properties generally characterize nonmetals?

They are often dull or gaseous and are poor conductors.

What electron behavior generally characterizes nonmetals?

They tend to gain electrons or share electrons in covalent bonds.

Where are metalloids located?

Along the staircase boundary between metals and nonmetals.

What characterizes metalloids?

They show mixed metal/nonmetal properties and often act as semiconductors.

What are Group 1 elements, excluding hydrogen, called?

Alkali metals.

How many valence electrons do alkali metals have, and what ion do they usually form?

$1$ valence electron; $+1$ cations.

How does alkali-metal reactivity change down Group 1?

It increases because the valence electron is farther from the nucleus and easier to remove.

What are Group 2 elements called?

Alkaline earth metals.

How many valence electrons do alkaline earth metals have, and what ion do they usually form?

$2$ valence electrons; $+2$ cations.

What are Groups 3-12 called?

Transition metals.

Why can transition metals have multiple oxidation states?

Their ns and (n-1)d electrons can be similar in energy and participate in bonding/ion formation.

What family is Group 13?

The boron family.

How many valence electrons does Group 13 have, and what oxidation state is common?

$3$ valence electrons; $+3$ is common.

What family is Group 14?

The carbon family.

How many valence electrons does Group 14 have?

$4$.

What bonding behavior is common for Group 14?

Sharing electrons in covalent bonds; oxidation states from $-4$ to $+4$ can occur.

What family is Group 15?

The nitrogen family, or pnictogens.

How many valence electrons does Group 15 have?

$5$.

What ion is commonly associated with Group 15 nonmetals?

A $-3$ anion, although covalent bonding and multiple oxidation states are common.

What family is Group 16?

The chalcogens.

How many valence electrons does Group 16 have, and what ion is common?

$6$ valence electrons; $-2$ anions are common.

What family is Group 17?

The halogens.

How many valence electrons do halogens have, and what ion do they usually form?

$7$ valence electrons; $-1$ anions.

Why are halogens highly reactive?

They need only one electron to complete their valence shell.

What family is Group 18?

The noble or inert gases.

Why are noble gases largely unreactive?

They have filled valence shells (He has $2$ electrons; the others generally have $8$).

What is effective nuclear charge ($Z_{\text{eff}}$)?

The net attractive charge experienced by a valence electron after accounting for shielding.

Give the common approximation for effective nuclear charge.

$Z_{\text{eff}} \approx Z - S$, where $Z$ is nuclear charge and $S$ is shielding.

How does effective nuclear charge change from left to right across a period?

It increases.

Why does $Z_{\text{eff}}$ increase across a period?

Proton number increases while added electrons enter the same principal shell, so shielding changes relatively little.

Why is the nucleus's pull on valence electrons weaker down a group?

Additional shells increase distance and electron shielding.

What is electron shielding?

Reduction of the nucleus's attraction for valence electrons by inner-shell electrons.

How does atomic radius change from left to right across a period?

It decreases.

Why does atomic radius decrease across a period?

Increasing $Z_{\text{eff}}$ pulls electrons closer to the nucleus.

How does atomic radius change down a group?

It increases.

Why does atomic radius increase down a group?

Additional principal shells and increased shielding place valence electrons farther from the nucleus.

For the same element, rank cation, neutral atom, and anion size.

Cation < neutral atom < anion.

Why is a cation smaller than its neutral atom?

Electron removal decreases electron-electron repulsion and may remove the outer shell, allowing the remaining electrons to be pulled closer.

Why is an anion larger than its neutral atom?

Added electrons increase electron-electron repulsion within the valence shell.

What is ionization energy?

The energy required to remove an electron from a gaseous atom or ion.

How does first ionization energy generally change across a period?

It increases from left to right.

How does first ionization energy generally change down a group?

It decreases.

Why is each successive ionization energy greater than the previous one?

After each electron is removed, the remaining electrons experience a stronger attraction and less electron-electron repulsion.

What causes a very large jump in successive ionization energies?

The next electron would have to be removed from a stable inner/core shell.

Why is sodium's second ionization energy much higher than its first?

The first removal gives $\text{Na}^+$ a noble-gas configuration; the second would remove a core electron.

What is electron affinity?

The energy change associated with adding an electron to a gaseous atom.

How does electron affinity generally change across a period?

Electron gain generally becomes more favorable toward the right, with important exceptions.

Why are noble-gas electron affinities unfavorable?

An added electron must enter a new, higher-energy shell because the valence shell is full.