MCAT Study - General and Organic Chemistry

What do the X, A, and Z represent on this figure?

X is the element (Na, H, etc)

A is the mass number (protons + neutrons)

Z is the atomic number (# of protons)

What is the Rutherford Model and the year it was described?

• concept that the electrons surround a compact nucleus in an atom

• 1911

What is the Bohr Model and the year it was described?

• concept that described orbits in more detail (farther orbits require more energy, photons emitted vs absorbed)

• AHED (Absorb light, Higher potential, Excited, Distant from nucleus)

• 1913

A photon is ______ when n decreases (when electron moves closer to nucleus) and a photon is _____ when n increases.

A photon is emitted when n decreases (when electron moves closer to nucleus) and a photon is absorbed when n increases.

What does the AHED mnemonic describe?

• Absorb light or energy

• moves to a Higher potential

• enters an Excited state

• travels a path Distant from the nucleus

this describes what happens when an electron jumps from a lower energy level to a higher one

What is the Heisenberg Uncertainty?

the fundamental rule that you cannot know both the exact position and exact momentum of a subatomic particle at the same time

What is Hund’s Rule?

electrons can only double up in orbitals if all orbitals already have 1 electron each

What is Pauli Exclusion Principle?

paired electrons must have a +½ and a -½

What is Avogadro’s Number?

• 6.022 × 10²³

• equals 1 mol

• often represented by Nₐ

What is Planck’s constant?

• 6.626 × 10^-34 J•s

• often represented by h

What is the speed of light?

• 3.0 × 10⁸ m/s

• often represented by c

What is the equation for light energy that uses wavelength?

E = (h • c) / λ

E = light energy

h = Planck’s constant

c = speed of light

λ = wavelength

What is the equation for light energy that uses frequency?

E = h • f

E = light energy

h = Planck’s constant

f = frequency

Planck’s constant (h) multiplied by the speed of light (c) is what?

around 2.0 × 10^-25 J•m

What does quantum number n represent?

electron energy levels or the shell number

What does quantum number l represent?

the 3D shape of the orbital (s, p, d, f)

What are the possible values for quantum number n?

1, 2, 3, …

What are the possible values for quantum number l?

0, 1, 2, … (aka n-1)

How does the # value of l correlate to the orbital shape?

0 = s orbital

1 = p orbital

2 = d orbital

3 = f orbital

4 = g orbital

What does quantum number m_l represent?

• magnetic

• orbital subtype

What values can quantum number m_l be?

+ or - l values (…, -2, -1, 0, 1, 2, …)

What does quantum number m_s represent?

• electron spin (direction)

What values can quantum number m_s be?

+½ or -½

Describe the shapes of the orbitals.

What is the Aufbau Principle?

Electrons fill orbitals in order of increasing energy, generally following this sequence:
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s...

What does the term diamagnetic mean and when does it apply?

• paired electrons are repelled by an external magnetic field

• occurs when all electrons are paired

• used to describe an atom

What does the term paramagnetic mean and when does it apply?

• electrons are pulled into an external magnetic field

• occurs when there is one or more unpaired electrons

• used to describe an atom

What is the Z_eff and what is its periodic trend?

• effective nuclear charge is the net positive charge experienced by an electron in a multi-electron atom

• inner electrons block outer electrons from the full pull of the nucleus

• Z_eff = Z (atomic number) - S (shielding constant typically 2)

• increases to the right