Chemistry Exam 3: Scientists and Atomic Theory Contributions

Democritus

First proposed that matter is made of tiny, indivisible particles called atomos: The point at which matter can no longer be subdivided.

Aristotle

All matter is composed of 4 elements (earth, water, air, and fire) and all matter is continuous, not atomistic.

Lavoisier

Law of Conservation of Mass: During a chemical change matter is neither created nor destroyed. Discovered Oxygen.

Proust

Law of Definite Proportions: A compound always contains the same elements in certain definite proportions.

Dalton

The 'Father of modern chemistry' who developed the atomic theory. He proposed that elements are made of small particles called atoms, which are identical within an element but different across elements, and are neither created, nor destroyed in chemical reactions.

Avogadro

Postulated that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules; established that 1 mole of any gas occupies 22.4 L at standard temperature and pressure (STP), containing 6.022×10²³ particles.

Thomson

Discovered the charge/mass ratio of electrons to be 1.76X108 C/g.

Mullikan

Determined the exact charge of a single electron 1.602x10-19 using his famous Oil Drop Experiment.

Becquerel

Known as the 'Grandfather of Radiation' Discovered Radioactivity.

Rutherford

Discovered alpha particles, beta particles, and gamma rays, and used unexpected particle deflections in his Gold Foil Experiment to uncover the atomic nucleus, proving that an atom is mostly empty space with its mass concentrated in a tiny central core.

Plank

Is the founder of quantum theory who proposed that energy is emitted or absorbed in discrete packets called quanta, establishing Planck's constant h = 6.626x10-34 JxS.

Einstein

Provided the explanation of the photoelectric effect, proposing that light travels in discrete packets of energy called photons that eject electrons from metal surfaces.

Balmer

Studied the emission line spectra of hydrogen and developed a mathematical equation to calculate the wavelengths of its visible light lines.

Rydberg

Expanded on Balmer's work by developing a general equation to predict all hydrogen line spectra including non-visible regions using the Rydberg constant RH=1.097x107m-1.

Bohr

Developed the planetary model of the atom, proposing that electrons travel around the nucleus in fixed, circular orbits (energy levels) and emit or absorb light when jumping between levels.

De Broglie

Proposed that all moving particles and forms of matter exhibit wave-like properties (wave-particle duality), establishing the wavelength equation.

Heisenberg

Formulated the Uncertainty Principle, stating that it is impossible to simultaneously know the exact position and momentum of an electron.

Schrödinger

Developed the quantum mechanical model of the atom by treating electrons as waves, using a mathematical wave equation to define atomic orbitals (regions of high probability for finding an electron).

Born

Proposed that squaring the wavefunction determines the probability of finding an electron in a specific region of space, giving physical meaning to Schrödinger's wave equation.

Maxwell

Developed the theory of electromagnetism, demonstrating that light consists of oscillating electric and magnetic fields traveling as a wave at a constant speed c=3.00x108 m/s.