Chemistry Unit 1: Atomic Theory, Isotopes, Ions, and Electron Configuration

Vocabulary flashcards covering key terms from the lecture notes on atomic theory, isotopes, ions, and electron configuration.

Dalton's postulates

Four principles: (1) matter is made of atoms; (2) atoms cannot be created or destroyed; (3) atoms of the same element have the same mass; (4) compounds are formed by fixed, simple ratios of atoms.

Cathode ray

A glowing beam produced between electrodes in a tube; Thomson used it to deduce the existence of electrons and proposed the electron theory.

Electron

Negatively charged subatomic particle; located in the electron cloud; very small mass.

Plum Pudding Model

Thomson's model of the atom with a spread-out positive charge and embedded electrons.

Rutherford's Gold Foil Experiment

Most alpha particles passed through; some deflected; revealed a dense, positively charged nucleus.

Nucleus

Dense center of the atom containing protons and neutrons; positively charged.

Proton

Positively charged subatomic particle in the nucleus; defines atomic number.

Neutron

Electrically neutral subatomic particle in the nucleus; contributes to mass.

Bohr energy levels

Electrons occupy fixed energy levels; energy determines distance from the nucleus; electrons can jump to higher levels when excited.

Electron configuration

Arrangement of electrons in atomic orbitals written as 1s^2 2s^2 2p^6 3s^2 3p^6, etc.

Aufbau principle

Electrons fill orbitals in order of increasing energy, from lowest to highest.

Hund's rule (bus-seat rule)

Within a subshell, electrons occupy empty orbitals singly before pairing.

Shorthand electron configuration

Use [noble gas] core to represent inner electrons, then add remaining electrons (e.g., [Ar] 4s^2 3d^7).

Noble gas notation

Electron configuration written starting from the nearest preceding noble gas.

Ion

Atom with unequal numbers of protons and electrons, giving a net electrical charge.

Cation

Positively charged ion formed by losing electrons.

Anion

Negatively charged ion formed by gaining electrons.

Isotope

Atoms of the same element with different numbers of neutrons and thus different mass numbers.

Mass number

Total number of protons and neutrons in the nucleus (A); used in isotope notation.

Hyphen notation

Isotope notation using mass number after a dash (e.g., Uranium-235).

Atomic weight

Weighted average mass of an element's isotopes; usually shown as the atomic mass.

Ion notation (example: Cl^-)

Shows gained electrons yielding a net negative charge; ions can be positive or negative.

Wavelength (λ)

Distance between successive crests of a wave; measured in meters; 1 nm = 1×10^-9 m.

c = λ f

Speed of light equals wavelength times frequency; relates wavelength and frequency.

E = h f

Energy of a photon equals Planck's constant times frequency (h ≈ 6.626×10^-34 J·s).

Planck's constant

h ≈ 6.626×10^-34 J·s; relates energy and frequency (E = h f).

Energy-wavelength relationship

Larger wavelength means lower frequency and lower energy; shorter wavelength means higher frequency and higher energy.

Energy levels (quantized)

Distinct energy levels around the nucleus where electrons reside; transitions correspond to emitted/absorbed photons.

Atomic number

Number of protons in the nucleus; identifies the element.

Blocks of the periodic table

s-block, p-block, d-block, f-block correspond to orbital types in electron configuration.

Noble gas core

Using a noble gas configuration to simplify electron notation by replacing inner electrons with [NobleGas].