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Matter
Anything that occupies space and has mass.
Atoms
The basic building blocks that compose matter.
Atoms
The smallest identifiable unit of an element.
Leucippus and Democritus
Theorized that matter is composed of small, indivisible particles.
Democritus
Coined the term “atomos.”
Antoine Lavoisier
Established the “Law of Conservation of Mass.”
Law of Conservation of Mass
Matter cannot be created or destroyed, only rearranged in a chemical reaction.
Joseph Proust
Proposed the “Law of Definite Proportions.”
Law of Definite Proportions
Different samples of the same element contain its constituent elements in the same proportion by mass.
John Dalton
Formalized the Atomic Theory.
Wilhelm Rontgen
Discovered X-rays while studying vacuum tubes and cathode rays.
Henri Becquerel
Discovered spontaneous emission of radiation from Uranium ores.
Marie Curie
Coined the term “radioactivity” for observed spontaneous radiation.
Joseph John Thomson
Discovered electrons as the first subatomic particle.
Ernest Rutherford
Demonstrated at least two distinct types of radiation.
Alpha and beta radiation
Two distinct types of radiation.
Hans Geiger
Proved that α particles are He 2+ ions with Rutherford.
1927 Solvay Conference
Marked the birth of Quantum Mechanics.
Max Planck
Proposed quantization of energy of light to explain Blackbody radiation.
Albert Einstein
Provided theoretical background for the Photoelectric Effect.
Photoelectric Effect
Electrons are emitted from a plate when exposed to light.
Robert Millikan
Precisely determined the magnitude of the electron’s charge.
Ernest Rutherford, Hans Geiger, and Ernest Marsden
Discovered protons by bombarding gold foils with α particles.
James Chadwick
Discovered neutrons.
Protons
Positively charged particles in an atom.
Electrons
Negatively charged particles in an atom.
Neutrons
Particles with no charge in an atom.
Unified atomic mass
Defined as 1/12 of the mass of a carbon atom with 6 protons and 6 neutrons.
Nucleus
The dense core of the atom containing protons and neutrons.
Electron cloud
The region where electrons are located, comprising most of the atom’s volume.
Element
A pure substance that cannot be broken down by chemical reactions.
Atomic number
Indicates the number of protons in an element.
Z
Symbol for atomic number.
Julius Lothar Meyer
Created a Periodic Table of Elements similar to Mendeleev’s work.
Clemens Winkler
Discovered eka-silicon, now known as Germanium.
Alkali metals
Soft, shiny metals with low melting points.
Alkaline earth metals
Good conductors of heat and electricity, react with water to form basic solutions.
Halogens
Very reactive elements that exist as diatomic molecules.
Noble gases
Stable elements that rarely combine with others.
Isotopes
Atoms with the same number of protons but different numbers of neutrons.
Werner Heisenberg
Formulated the Quantum Theory.
Schrodinger equation
A wave equation describing the electronic structure of atoms.
Quantum Numbers
Numerical labels for the probable location of electrons in an atom.
s-orbital
Has a spherical shape.
p-orbital
Has a dumbbell shape.
Electron configuration
Arrangement of electrons in an atom’s orbitals.
Ground state
The lowest energy arrangement of electrons.
Aufbau Principle
As protons are added one by one to the nucleus to build up the elements, electrons are similarly added to the atomic orbitals.
Pauli Exclusion Principle
No two electrons can have the same set of four quantum numbers.
Hund's Rule
The most stable arrangement of electrons has the greatest number of parallel spins.
Valence electrons
Electrons in the outermost shell of an atom.
Valence shell
The outermost shell of an atom.
Periodic trends
Patterns in the periodic table illustrating different aspects of elements.
Atomic radius
Half the distance between the nuclei of two adjacent atoms.
Ionic radius
The radius of a cation or anion.
Ionization energy
Energy required to remove the most loosely held electron from an atom.
Electron affinity
Energy change when an electron is accepted by an atom.
