MCAT Chemistry

Atomic Structure

MCAT Chemistry > Atomic Structure


MCAT Atomic Structure - Atom


see Atoms


See Protons

Protons (H) form part of the nucleus

Atomic Number

See Atomic Number

Atomic Number = number of protons.


See Neutrons

Neutrons (n) form part of the nucleus; amount may vary (isotopes)

Atomic Mass

See Atomic Mass

Atomic Mass = number of protons + neutrons in an atom


See Electrons

Electrons (e-) move in discrete pathways around the nucleus called orbitals. Electrons closest to nucleus have lower energy and electrons furthest away have the highest energy

Atomic Weight

See Atomic Weight

Atomic Weight (Molar Mass) (g/mol) is the mass of one mole of atoms

1 mole = Avogadro's number = 6.022 x 1023 particles = 22.4 L


See Isotopes

Bohr's Atomic Model

See Bohr's Atomic Model

Bohr's Atomic Model states that there is a dense core nucleus of one proton around which, a single electron travels in a discrete circular orbital. The electrons energy increases as it moves further away from nucleus into surrounding orbitals.

Atomic Structure - Bohr's Model of the Atom

Transferring an amount of energy equal to the difference between pathways results in "jumping" between pathways and moving from the ground to an excited state or vice versa. Electrons are only affected by radiation and high temperature

E = hf

Angular Momentum = L = (nh)/2π

Energy of the electron = E = -RH/n2

Atomic Emission & Absorption Spectra

Atoms at room temperature are in the ground state (n = 1), however electrons can become excited by absorbing heat and energy (+ΔE/endothermic) to jump to higher orbital levels. The excitation of electrons results in energy absorption at a specific λ. As the electrons rapidly return to the ground state from this excited state, energy emission in the form of discrete amounts of photons (light) occurs at a specific frequency on the visible light spectrum (−ΔE/exothermic). We see color not absorbed by the compound. Each element possesses unique characteristic absorption spectra. The λ of absorption corresponds to λ of emission (energy level difference unchanged).

E = (hc)/λ

Balmer Series

Balmer Series represents a pattern of photon emission from hydrogen electrons falling from n > 2 to n = 2 energy level (4 wavelengths)

Lyman Series

Lyman Series represents a pattern of transitions from n > 1 to n = 1. This causes larger energy transitions and a shorter photon wavelength. Molecules usually appear in the UV region.

E = -RH(1/nf2) – (1/ni2)

Heisenberg's Uncertainty Principle

Heisenberg's Uncertainty Principle states that we can only determine either momentum or location of an electron but not both at a given time

Quantum Numbers

See Quantum Numbers

Electron Configuration

See Electron Configuration

Click here to move onto periodic table trends.

Atomic Structure

Atomic Structure Topics

MCAT Chemistry

Chemistry Topics