atomic theory and structure of the atom. first to suggest the existence of atoms believed atoms were...
DESCRIPTION
B. Dalton Atomic theory composed of 4 postulates – Elements are composed of atoms – Atoms of the same element are identical, each element is unique – Compounds are composed of atoms of more than 1 element, atoms combine in fixed ratios to form compounds – Chemical rxn involves separation, combination, or rearrangement of atoms Name of theory Billard Ball ModelTRANSCRIPT
Atomic Theory and Structure of the Atom
• first to suggest the existence of atoms
• believed atoms were small indivisible particles
• Atom: smallest particle of an element that retains all properties of the element.
A. Democritus (460 B.C. – 370 B.C)
B. Dalton• Atomic theory composed of 4
postulates– Elements are composed of atoms– Atoms of the same element are
identical, each element is unique– Compounds are composed of atoms
of more than 1 element, atoms combine in fixed ratios to form compounds
– Chemical rxn involves separation, combination, or rearrangement of atoms
Name of theoryBillard Ball
Model
C. Electron1. Symbol: e−
– Charge −1
**after Dalton, there was a big hiatus in the theory of the atom. Everyone accepted Daltons theory and went on to study radiation for a while, and this is when the electron was discovered
D. J.J. Thomson• An atom is thought of as a uniform positive
sphere with electrons evenly distributed through out (like plum pudding or a chocolate chip cookie)
Name of theoryPlum Pudding
Model
Cathode Ray Tube
Battery
Evacuated tube
CathodeAnode
− +
E. MillikanMillikan Oil Drop
• Found the mass of an
electron to be 9.10×10−28 g
F. Rutherford• Conducted gold foil experiment
What did Rutherford expect?
Gold Foil Experiment Animation and Discussion
Click here for video!
What did Rutherford actually see?
F. Rutherford
• Concluded all positive charge and mass is concentrated in small region called nucleus and the electrons are outside the nucleus
• Proposed atom is mostly empty space
Name of theoryNuclear Model
Proton– p+
– Charge: +1– Mass:1.673×10−24 g
G. Bohr• Expanded on the nuclear atom• Electrons travel in circular orbits around
the nucleus
Name of theoryPlanetary Model
H. Schrödinger• model allowed the electron to occupy
three-dimensional space like an electron “cloud”
Name of theoryQuantum Mechanical
Model or Electron Cloud Model
I. ChadwickThe NeutronSymbol: n0
Charge: noneMass:1.675×10−24 g
**The neutron was found by comparing the mass of hydrogen to helium, since He increased by 1proton, the mass should be double, but it was four times, leading to a subatomic particle that had mass but no charge.
Fun Facts
• The volume of a hydrogen nucleus is a trillion times smaller than the volume of a hydrogen atom, yet the nucleus contains most of the mass.
• If the nucleus (proton) of a hydrogen atom were as large as the width of a human thumb, the electron would be on the average about one kilometer away in a great expanse of empty space.