Chp 3 of Chem

Leucippus of Miletus

First proposed that matter consists of tiny, discrete, indivisible particles called atoms.

Democritus of Abdera

Student of Leucippus who further developed the atomistic theory, arguing atoms are the building blocks of all matter.

Atom

The smallest unit of matter that retains the properties of an element.

John Dalton

Developed the first atomic theory that proposed atoms as fundamental building blocks of matter.

Law of Constant Composition

Also known as the law of definite proportions; states that the elemental composition of a pure substance never varies.

Law of Multiple Proportions

When two elements form more than one compound, the weights of one element that combine with a fixed weight of the other are in ratios of small whole numbers.

Law of Conservation of Mass

The total mass of substances present at the end of a chemical process is the same as the mass of substances present before the process.

Sir Humphrey Davy

Used electrolysis to isolate potassium and sodium, contributing to understanding chemical reactivity.

Cathode Ray Tube

An experimental device that helped discover the electron by observing the behavior of cathode rays.

Sir J.J. Thomson

Credited for measuring the mass-to-charge ratio of an electron and proposed the plum-pudding model of the atom.

Plum-Pudding Model

Thomson's model of the atom depicting it as a positively charged sphere with embedded negative electrons.

Robert Milikan's Oil Drop Experiment

Used droplets of oil to measure the charge of an electron accurately, confirming the quantization of charge.

Ernest Rutherford

Conducted the gold foil experiment demonstrating that atoms are mostly empty space with a dense nucleus.

Nucleus

The small, dense center of an atom containing protons and neutrons, discovered by Rutherford.

Isotope

Atoms of the same element with different masses due to varying numbers of neutrons.

Cation

A positively charged ion, formed by the loss of one or more electrons.

Anion

A negatively charged ion, formed by the gain of one or more electrons.

Mass-Spectrometry

Technique for measuring the mass-to-charge ratio of ions, aiding in the identification of isotopes.

Weighted Average

Calculated by using the total abundance and mass for each isotope to accurately represent isotopic composition.