Dalton’s Atomic Theory in 1808 All matter is composed of extremely small particles called atoms. Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties. Atoms cannot be subdivided, created, or destroyed.
Dalton’s Atomic Theory, continuedAtoms of different elements combine in simple whole-number ratios to form chemical compounds.In chemical reactions, atoms are combined, separated, or rearranged.
Modern Atomic Theory Not all aspects of Dalton’s atomic theory have proven to be correct. We now know that: • Atoms are divisible into even smaller particles. • A given element can have atoms with different masses. Some important concepts remain unchanged. • Atoms of any one element differ in properties from atoms of another element. • All matter is composed of atoms.
Discovery of the Subatomic Particles For the better part of 70 years Dalton’s ideas remained unchanged. In 1897, using Cathode ray tubes, J.J. Thomson reported that cathode rays were made up of negatively charged particles in motion.
Discovery of the Atomic Nucleus More detail of the atom’s structure was provided in 1911 by Ernest Rutherford and his associates Hans Geiger and Ernest Marsden. The results of their gold foil experiment led to the discovery of a very densely packed bundle of matter with a positive electric charge. Rutherford called this positive bundle of matter the nucleus.
Discovery of the Proton 1919 Ernest Rutherford
Discovery of the neutron 1932 James Chadwick
The Structure of the AtomAn atom is the smallest particle of an element that retains the chemical properties of that element.The nucleus is a very small region located at the center of an atom.The nucleus is made up of at least one positively charged particle called a proton and usually one or more neutral particles called neutrons.
The matter component of the StandardModel is comprised of twelve particles.
These particles all have an intrinsic spinvalue of ½, making them conform to thePauli Exclusion Principle.
All matter particles of the Standard Model alsohave corresponding antimatter particles. Theseparticles breakdown into groups of quarks (up,down, strange, charm, top, and bottom) andleptons (electron, muon, tau, andcorresponding neutrinos).Quarks and leptons are further grouped intosets known as generations.
Quarks carry color charges (red, blue, orgreen) so they participate in stronginteractions.
The up, charm, and top quarks carry theelectric charge (+2/3).The down, strange, and bottom quarkscarry the electric charge (-1/3).This allows the quarks to participate inelectromagnetic interaction.
Leptons are color neutral and do notparticipate in strong interaction.
The electron, muon, and tau particlescarry the electric charge (-1) andparticipate electromagnetic interaction.
Neutrinos have no electric charge and donot participate in electromagneticinteractions.
Quarks and leptons carry flavor chargesand participate in weak nuclearinteractions.
Force-mediating particles of theStandard Model group into threecategories that correspond with three ofthe four fundamental interactions.All three mediating particles are bosonsand have intrinsic spins of (1).
This allows these particles to not conformto the Pauli Exclusion Principle.
Photons are electromagnetic forcemediators involving charge particles.Photons are considered masslessparticles.
W+, W-, and Zo gauge bosons are weaknuclear mediators involving particles ofdifferent flavors (quarks and leptons).W+, W-, and Z0 bosons are massiveparticles.
Gluons are strong nuclear force-mediators involving color chargedparticles (quarks).Gluons are considered massless particles.
The Standard Model predicts theexistence of one more particle known asthe “Higgs boson.”The Large Hadron Collider (LHC) atCERN is hoped to confirm the existenceof the Higgs boson in the near future.
Quarks• Protons and neutrons are composed of quarks.• There are six different types of quarks. u up (+2/3) d down (-1/3) t top (truth) b bottom (beauty) c charm s strange