Understanding Atomic Structure for the MCAT

Atom

Fundamental unit of matter in chemistry.

Subatomic Particles

Particles making up an atom: protons, neutrons, electrons.

Neutron

Neutral particle in an atom's nucleus.

Electron

Negatively charged particle surrounding the nucleus.

Atomic Number (Z)

Number of protons in an atom's nucleus.

Mass Number (A)

Total number of protons and neutrons in nucleus.

Charge of Proton

Fundamental unit of charge: +1 e (1.6 × 10^-19 C).

Charge of Electron

Equal in magnitude to proton, but negative: -1 e.

Bohr Model

Early model of atom, electrons in fixed orbits.

Quantum Mechanical Model

Modern model, electrons in probabilistic orbitals.

Valence Electrons

Electrons in outermost shell, important for bonding.

Hydrogen Isotopes

Protium, deuterium, and tritium are hydrogen isotopes.

Electrostatic Force

Attraction between oppositely charged particles.

Gravitational Force

Weak attraction based on mass of particles.

Quarks

Fundamental particles making up protons and neutrons.

Leptons

Elementary particles, includes electrons.

Gluons

Particles that mediate strong force between quarks.

Nucleus

Central part of an atom containing protons and neutrons.

Electrons

Negatively charged subatomic particles in orbitals.

Cation

Positively charged atom due to electron loss.

Anion

Negatively charged atom due to electron gain.

Atomic Mass Unit (amu)

Unit defined as 1/12 the mass of carbon-12. and Unit for measuring mass of atomic particles.

Proton

Positively charged subatomic particle in the nucleus.

Neutron

Neutral subatomic particle in the nucleus.

Electron Mass

Approximately 1/1836 of a proton's mass.

Binding Energy

Energy required to hold protons and neutrons together.

Reactivity

Tendency of an atom to engage in chemical reactions.

Electrostatic Pull

Attractive force between charged particles.

Atomic Weight

Weighted average mass of an element's isotopes.

Electrons in Neutral Atom

Equal to the number of protons.

Atomic Mass Calculation

Mass number approximates atomic mass in amu.

Isotopes

Atoms of the same element with different neutrons.

Protium

Hydrogen isotope with one proton, atomic mass 1 amu.

Deuterium

Hydrogen isotope with one proton, one neutron, 2 amu.

Tritium

Hydrogen isotope with one proton, two neutrons, 3 amu.

Half-Life

Time for half of a radioactive sample to decay.

Stability

Longer half-lives indicate greater isotope stability.

Avogadro's Number

6.02 × 10²³, number of particles in a mole.

Mole

Quantity equal to Avogadro's number of entities.

Atomic Mass

Mass of an average atom in atomic mass units.

Planck's Constant

6.626 x 10⁻³⁴ J•s, relates energy and frequency.

Quantum Theory

Energy emitted in discrete packets called quanta.

Centripetal Force

Force keeping electron in circular orbit around nucleus.

Energy Transition

Energy change when an electron jumps energy levels.

Photon Wavelength

Distance between successive peaks of emitted light.

Energy of a Photon

Energy calculated from its wavelength.

Chemical Properties

Similar characteristics exhibited by isotopes due to identical protons.

Angular Momentum

Defined as L = mvr, quantized in Bohr's model.

Kinetic Energy

Calculated as K = ½ mv² for moving objects.

Bohr's Model

Describes electron orbits with quantized energy levels.

Principal Quantum Number (n)

Positive integer indicating electron energy levels.

Rydberg Unit of Energy (Ry)

Value equal to 2.18 × 10⁻¹⁸ J.

Speed of Light (c)

Constant value of 3 x 10⁸ m/s.

Energy Equation 1

E = -Ry/n², relates energy to quantum number.

Ground State

Lowest energy state of an atom, stable configuration.

Quantized Energy

Energy changes occur in discrete amounts.

Negative Energy Values

Indicates attractive force between electron and nucleus.

Discreteness of Energy Levels

Energy levels are not continuous, but quantized.

Electron Orbit

Defined pathway around the nucleus in Bohr's model.

Attractive Force

Force between electron and proton, represented negatively.

Energy Increase

Electron energy becomes less negative as n increases.

Quantization Concept

Similar to discrete steps on a staircase.

Equation for Angular Momentum

L = nh, where n is a quantum number.

Temperature Effect

Atoms exist in ground state unless heated or irradiated.

Force Representation

Negative sign indicates attraction in energy equations.

Conceptual Understanding

Focus on ratios and relationships for problem-solving.

Energy Transfer

Movement of energy between electron orbits.

Electron Jump

Transition of electron to higher energy orbit.

Ground State

Lowest energy state of an atom (n=1).

Excited State

State when electrons occupy higher energy levels.

Atomic Emission Spectrum

Light emitted when electrons return to ground state.

Photon Emission

Release of energy as photons during transitions.

Speed of Light (c)

Velocity of light in vacuum, 3.00 × 10⁸ m/s.

Wavelength (λ)

Distance between successive peaks of a wave.

Quantized Energy Levels

Discrete energy states electrons can occupy.

Line Spectrum

Spectrum showing distinct lines for specific transitions.

Fluorescence

Emission of light from excited electrons returning to ground state.

Emission Spectrum

Spectrum of light emitted by excited atoms.

Energy Equation 2

E = hf; relates energy to frequency.

Frequency Equation

c = fλ; relates speed of light to frequency and wavelength.

Atomic Fingerprint

Unique emission spectrum identifying elements.

Hydrogen Emission Spectrum

Simplest emission spectrum, used for analysis.

Energy Transition

Movement between quantized energy levels.

Subshell

Energy level within an atom's electron configuration.

Electromagnetic Energy

Energy carried by photons in electromagnetic waves.

Excitation Sources

Heat or energy forms causing electron transitions.

Discrete Energy Amounts

Specific energy values emitted during transitions.

Lyman series

Hydrogen emission lines from n≥2 to n=1.

Balmer series

Hydrogen emission lines from n≥3 to n=2.

Paschen series

Hydrogen emission lines from n≥4 to n=3.

Energy transitions

Changes between quantum energy levels in atoms.

Photon wavelength

Distance between successive peaks of light waves.

Energy and wavelength relationship

Energy is inversely proportional to wavelength.

Planck's quantum theory

Energy quantization based on photon emission.

Bohr's model

Atomic structure model describing electron orbits.

Atomic absorption spectrum

Unique wavelengths absorbed by an element's electrons.

Atomic emission spectrum

Unique wavelengths emitted by an element's electrons.

Energy absorption

Electrons gain energy to move to higher levels.

Energy emission

Electrons lose energy moving to lower levels.

Conservation of energy

Energy remains constant in transitions between levels.