The diameter of an atom is 0.1 to 0.5 nm. This is 1 to 5 ten billionths of a meter. ... the way to an understanding of the subatomic structure of the atom. ...
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5.1 Early Thoughts
5.6 Subatomic Parts of the Atom
5.7 The Nuclear Atom
5.2 Dalton's Model of the Atom
5.8 General Arrangement ofSubatomic Particles
5.3 Composition of Compounds
5.9 Atomic Numbers of theElements
5.4 The Nature of Electric Charge
5.5 Discovery of Ions
5.10 Isotopes of the Elements
5.11 Atomic Mass
Atoms under special circumstances can be decomposed.Dalton’s Atomic Theory
Atoms of each element are alike in mass and size.
Atoms of different elements are not alike in mass and size.
Properties of Electric Charge
NaCl → Na+ + Cl-Discovery of Ions
NaCl → Na+ + Cl-
In 1897 Sir Joseph Thompson demonstrated that cathode rays:
Rutherford’s alpha particle scattering experiment.
Deflection and scattering of alpha particles by positive gold nuclei.
1 proton in the nucleus
Every atom with an atomic number of 1 is a hydrogen atom.
6 protons in the nucleus
Every atom with an atomic number of 6 is a carbon atom.
92 protons in the nucleus
Every atom with an atomic number of 92 is a uranium atom.
Isotopes of the Same Element Have
Equal numbers of protons
Different numbers of neutrons
6 protons + 6 neutrons
6 protons + 8 neutrons
8 protons + 8 neutrons
8 protons + 9 neutrons
8 protons + 10 neutrons
Hydrogen 1 1 0
Hydrogen 1 1 1
Hydrogen 1 1 2
Uranium 92 92 143
Uranium 92 92 146
Chlorine 17 17 18
Chlorine 17 17 20
Electrical field at slits accelerates positive ions.
Deflection of positive ions occurs at magnetic field.
A Modern Mass Spectrometer
From the intensity and positions of the lines on the mass spectrogram, the different isotopes and their relative amounts can be determined.
A mass spectrogram is recorded.
Using a mass spectrometer, the mass of one hydrogen atom was determined to be 1.673 x 10-24 g.
To overcome this problem of such a small mass relative atomic masses using “atomic mass units” was devised to express the masses of elements using simple numbers.
The standard to which the masses of all other atoms are compared to was chosen to be the most abundant isotope of carbon – carbon 12.
A mass of exactly 12 atomic mass units (amu) was assigned to carbon 12.
1 amu is defined as exactly equal to the mass of a carbon-12 atom
1 amu = 1.6606 x 10-24 g
Average atomic mass 1.00797 amu.
Average atomic mass 39.098 amu.
Average atomic mass 248.029 amu.
Dalton’s Atomic Mode;
Law of Definite Composition
Law of Multiple Proportions
Three principle subatomic particles
Thomson Model of the Atom
Rutherford alpha-scattering experiment
Atomic Number, Mass number, number of neutrons, number of Protons, Number of Electrons
Three Isotopes of Hydrogen
Average Atomic Mass of an Element