Atomic Models & History
This ancient Greek philosopher proposed the first idea of the atom as indivisible particles called atomos.
Democritus
This process uses electrical current to decompose a compound, such as splitting water into hydrogen and oxygen gas.
Electrolysis
Holding atomic number 1, this element sits at the top of Group 1 but is classified as a nonmetal rather than an alkali metal.
Hydrogen
When an excited electron transitions back to this state, it releases stored potential energy in the form of light.
Ground state
Robert Boyle defined pure particles that cannot be broken down by chemical means in his landmark 1661 text titled this.
The Sceptical Chymist
He proposed the "Plum Pudding Model" after discovering the electron in 1897.
J.J. Thomson
This law states that compounds are always composed of two or more elements combined chemically in fixed proportions by mass.
Law of Definite Proportion/s
With atomic number 2, this p-block gas is the lightest noble gas and possesses a completely full outer electron shell.
Helium
This metal ion produces a characteristic green color in a flame test, a phenomenon explained by quantized electronic transitions.
Copper
Paracelsus advocated for this Latin term referring to the "three primes": mercury, sulfur, and salt.
Tria prima
Niels Bohr refined Rutherford's nuclear model by introducing these fixed circular paths where electrons travel.
Orbits
Located along a staircase pattern between metals and nonmetals, these elements display intermediate physical and chemical properties.
Metalloids/Semimetals
This alkali metal with atomic number 3 sits in Period 2 and forms the first triad with Sodium and Potassium.
Lithium
Bohr’s orbital energy levels ($n$) are described as this, meaning they hold specific, fixed amounts of energy rather than a continuous gradient.
Quantized
Antoine Lavoisier published a list of 33 substances and disproved this obsolete theory by showing oxygen is essential for combustion.
Phlogiston theory
This scientist formulated the Uncertainty Principle, stating an electron's position and momentum cannot be simultaneously measured with exact precision.
Werner Heisenberg
An electron reaches this condition when it absorbs energy and jumps to a higher energy level.
Excited state
Holding atomic number 9, this Group 17 halogen has the highest electronegativity value on the entire periodic table.
Flourine
Louis de Broglie revolutionized atomic physics by proposing this theory, treating electrons as both particles and waves.
Wave-particle duality
Group 15 elements are systematically known by this collective name, derived from the Greek word for "stifle" or "choke".
Pnictogens
Erwin Schrödinger developed a wave equation that treats electrons as 3D wave functions, defining these regions of probability where electrons are most likely found.
Orbitals
These international governing bodies officially maintain and oversee the 118 elements on the periodic table.
IUPAC & IUPAP
Marking the end of Period 4's s-block at atomic number 20, this Group 2 alkaline earth metal produces distinct flame test colors and forms essential structural alloys.
Calcium
Bohr's atomic model specifically explained the line emission spectrum of this simplest chemical element.
Hydrogen
Leopold Gmelin published this major work that helped systematically organize chemical substances before Mendeleev's table.
Handbook of Chemistry