History of the atom Flashcards
what was discovered in the 1800s and by who
in 1897 J.J. Thomson created the plum pudding model. and discovered the electron
what was discovered in the early 1900s done by two people
in 1911 Ernest Rutherford and Hans Geiger created the golden foil experiment and proved that the atom is mostly empty space with the mass concentrated in the nucleus
what was the discovery in the early 1900s done by one person
in 1913 Henry Moseley proved that each element had a unique number of protons and that sequential elements increased atomic number by 1
what new theory was made in the early 1900s
in 1913 Niels Bohr created a new model of the atom where electrons orbited in fixed energy levels with a quantifiable kinetic and potential energy. to change orbits electrons must absorb or emit a fixed amount of energy.
what was discovered in the late 1910s
in 1917 Ernest Rutherford created the first nuclear reaction and discovered the proton
what was discovered in the early to mid-1900s
in 1932 James Chadwick proved the existence of the neutron using radiation
how did Thomson discover the electron
he used cathode ray tubes. a high voltage is applied across two electrodes in a vacuum creating a beam of particles. phosphors sparked when hit with the beam. he tested its charge by using electrically charged plates. he changed the electrodes and got the same results. he concluded that it was negatively charged particles that exist in every element
how does the gold foil experiment work
alpha radiation is directed toward thin gold foil. the radiation was expected the slightly deflect. it actually had large deflections/reflections. they concluded this was due to concentrated positive charge. its was suggested this was in a small compact nucleus
what was Moseley’s experiment
he fired electrons at atoms causing them to emit X-rays. he measured their wavelength and frequency. he noticed when the square root of the frequency was plotted against atomic number it was a linear relationship proving each element has a unique atomic number and it increases by one across periods
how did the proton get proved
Rutherford directed alpha particles at nitrogen nuclei. these nitrogen nuclei then emitted one positive particle he called the hydrogen nucleus (later named proton)
how did the neutron get proved
James Chadwick directed alpha particles at beryllium using polonium’s natural radiative decay. the resulting radiation penetrated lead shielding. Chadwick could explain this assuming a neutral particle of equal mass to a proton existed
who explained how electrons affect atoms
Neils Bohr. he showed that each shell can only hold a fixed number of electrons. chemical properties are determined by the number of electrons in the outer shell. atoms with a full outer shell are chemically inert
