6

Scientists at that time thought that all matter
was composed of four substances:

four basic essences

_ substances/elements have been identified

_ naturally occuring

additional _ have been artificially produced in high enegy particle accelerators

particles that are smaller than atom

an English school teacher, published a book summarizing his experiments,
which showed that the elements could be classified
according to integral values of atomic mass. (hook-and-eye)

showed that if the elements were
arranged in order of increasing atomic mass, a periodic
repetition of similar chemical properties occurred

He described the atom as looking something like
a plum pudding, in which the plums represented negative electric charges (electrons) and the pudding was a
shapeless mass of uniform positive electrification

disproved Thomson’s model of
the atom. he introduced the nuclear model,
which described the atom as containing a small, dense,
positively charged center surrounded by a negative
cloud of electrons. He called the center of the atom
the nucleus

improved Rutherford’s description
of the atom. model was a miniature solar system
in which the electrons revolved about the nucleus in
prescribed orbits or energy levels.

fundamental particles

are very small particles that carry one unit
of negative electric charge.

mass of electron

They can be pictured as revolving about the
nucleus in precisely fixed orbits, just as the planets in
our solar system revolve around the sun.

number of protons

proton + neutron

amu of electron

The atomic mass number of an
electron is