atomic mass of an element divided
by its density.
atomic weight See relative
atomic mass.
atom-probe Üeld-ion microscopy A technique for identifying individual atoms on surfaces. In the
atom-probe *Üeld-ionization microscope (FIM) there is a hole in the
Ûuorescent screen, with which the
FIM image of an adsorbed atom is
brought into coincidence. The gas
causing the imaging is removed. The
49
atom-probe Üeld-ion microscopy
a
ATOMIC THEORY
c.430 BC
Greek natural philosopher Empedocles (d. c. 430 BC) proposes that all
matter consists of four elements: earth, air, fire, and water.
c.400 BC
Greek natural philosopher Democritus of Abdera (c. 460–370 BC)
proposes that all matter consists of atoms.
c.306 BC
Greek philosopher Epicurus (c. 342–270 BC) champions Democritus’
atomic theory.
1649
French philosopher Pierre Gassendi (1592–1655) proposes an atomic
theory (having read Epicurus).
1803
John Dalton proposes Dalton’s atomic theory.
1897
J. J. Thomson discovers the electron.
1904
J. J. Thomson proposes his ‘plum pudding’ model of the atom, with
electrons embedded in a nucleus of positive charges.
Japanese physicist Hantaro Nagaoka (1865–1950) proposes a ‘Saturn’
model of the atom with a central nucleus having a ring of many
electrons.
1911
New Zealand-born physicist Ernest Rutherford (1871–1937) discovers the
atomic nucleus.
1913
Niels Bohr proposes model of the atom with a central nucleus
surrounded by orbiting electrons.
British physicist Henry Moseley (1887–1915) equates the positive charge
on the nucleus with its atomic number.
Frederick Soddy discovers isotopes.
1916
German physicist Arnold Sommerfield (1868–1951) modifies Bohr’s
model of the atom specifying elliptical orbits for the electrons.
1919
Ernest Rutherford discovers the proton.
1920
Ernest Rutherford postulates the existence of the neutron.
1926
Erwin Schrödinger proposes a wave-mechanical model of the atom (with
electrons represented as wave trains).
1932
British physicist James Chadwick (1891–1974) discovers the neutron.
Werner Heisenberg proposes a model of the atomic nucleus in which
protons and neutrons exchange electrons to achieve stability.
1939
Niels Bohr proposes a ‘liquid drop’ model of the atomic nucleus.
1948
German-born US physicist Marie Goeppert-Meyer (1906–72) and
German physicist Hans Jensen (1907–73) independently propose the
‘shell’ structure of the nucleus.
1950
US physicist Leo Rainwater (1917–86) combines the ‘liquid-drop’ and
‘shell’ models of the nucleus into a single theory.
www.AzShimi.ir www.AzShimi.com
by its density.
atomic weight See relative
atomic mass.
atom-probe Üeld-ion microscopy A technique for identifying individual atoms on surfaces. In the
atom-probe *Üeld-ionization microscope (FIM) there is a hole in the
Ûuorescent screen, with which the
FIM image of an adsorbed atom is
brought into coincidence. The gas
causing the imaging is removed. The
49
atom-probe Üeld-ion microscopy
a
ATOMIC THEORY
c.430 BC
Greek natural philosopher Empedocles (d. c. 430 BC) proposes that all
matter consists of four elements: earth, air, fire, and water.
c.400 BC
Greek natural philosopher Democritus of Abdera (c. 460–370 BC)
proposes that all matter consists of atoms.
c.306 BC
Greek philosopher Epicurus (c. 342–270 BC) champions Democritus’
atomic theory.
1649
French philosopher Pierre Gassendi (1592–1655) proposes an atomic
theory (having read Epicurus).
1803
John Dalton proposes Dalton’s atomic theory.
1897
J. J. Thomson discovers the electron.
1904
J. J. Thomson proposes his ‘plum pudding’ model of the atom, with
electrons embedded in a nucleus of positive charges.
Japanese physicist Hantaro Nagaoka (1865–1950) proposes a ‘Saturn’
model of the atom with a central nucleus having a ring of many
electrons.
1911
New Zealand-born physicist Ernest Rutherford (1871–1937) discovers the
atomic nucleus.
1913
Niels Bohr proposes model of the atom with a central nucleus
surrounded by orbiting electrons.
British physicist Henry Moseley (1887–1915) equates the positive charge
on the nucleus with its atomic number.
Frederick Soddy discovers isotopes.
1916
German physicist Arnold Sommerfield (1868–1951) modifies Bohr’s
model of the atom specifying elliptical orbits for the electrons.
1919
Ernest Rutherford discovers the proton.
1920
Ernest Rutherford postulates the existence of the neutron.
1926
Erwin Schrödinger proposes a wave-mechanical model of the atom (with
electrons represented as wave trains).
1932
British physicist James Chadwick (1891–1974) discovers the neutron.
Werner Heisenberg proposes a model of the atomic nucleus in which
protons and neutrons exchange electrons to achieve stability.
1939
Niels Bohr proposes a ‘liquid drop’ model of the atomic nucleus.
1948
German-born US physicist Marie Goeppert-Meyer (1906–72) and
German physicist Hans Jensen (1907–73) independently propose the
‘shell’ structure of the nucleus.
1950
US physicist Leo Rainwater (1917–86) combines the ‘liquid-drop’ and
‘shell’ models of the nucleus into a single theory.
www.AzShimi.ir www.AzShimi.com