Chpt. 4, Old Models of the Atom Flashcards Preview

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Atomic Theory of Matter

Devised by Leucippus and recorded by Democritus, it assumed that matter was made of atoms that were infinitely small and indestructible, and that they traveled through empty space. Atoms could also combine in various ways, and changes in these combinations led to changes in the type of matter that they made.


Essence of Matter

Devised by Aristotle, it proposed that all matter had a fundamental essence that gave it properties. By this thinking, gold was not made of gold atoms, but instead was composed of materials that had a gold essence. Because this model didn't require belief in something that was invisible (as opposed to the Atomic Theory of Matter), this is the one that people believed.


Dalton's Laws

Atoms are small and indestructible.

Atoms of the same element have the same properties.

Atoms of different elements have different properties.

Atoms obey the law of conservation of mass.

Atoms obey the law of multiple proportions.


What was J.J. Thompson's experiment?

J.J. Thompson made a great discovery while experimenting on a cathode ray tube. Basically, a cathode ray tube consists of a big, empty glass tube with an electrode on each end. Each electrode is hooked up to one side of a battery; the cathode is the negative electrode and the anode is the positive electrode. When the electricity is turned on, a beam of particles can be seen moving from the cathode to the anode. This beam is called the cathode ray.When a magnetic field was applied to the tube, the cathode ray bent toward the positive area of the field. As a result, people were able to figure out that these cathode rays consisted of negative particles.


plum pudding model

The model of the atom that J.J. Thompson established in order to explain the phenomenon that occurred in the cathode ray tube. It theorizes that an atoms consists of a big blob of positive charge with negatively charged electrons embedded.


Describe the experiments of Rutherford.

In 1911, Rutherford took time out of his usual schedule of wresting tigers and making out with hot chicks to do some more experimenting with nuclear stuff. In this experiment, he shot a beam of positively- charged alpha particles10 at a really thin piece of gold foil to see what would happen. He surrounded the whole thing with a phosphorescent detector screen so he could see where his alpha particles ended up.

When he had run this experiment, he was totally like “WTF.” Though most of the particles travelled right through the foil, others went bouncing off at crazy angles. This didn’t make a lot of sense to him, but being the badass he was, he tried to come up with a good explanation for this phenomenon.

The way he explained the deflection of these particles was that the atom has all of its positive charge stuck in a central nucleus. When the positively charged alpha particles didn’t go near the nucleus, they passed straight through the gold foil. However, when the particles came near the positively charged nucleus, they were deflected away at odd angles.


atomic number

the number of protons an atom has; it is equivalent to roughly 1/2 of the atomic mass, except for certain isotopes



versions of an atom with numbers of neutrons that differ from other atoms (though the same number of neutrons)


atomic mass

protons + neutrons; this value indicates the mass of the atom (excluding the electrons, which have so little mass as to barely even matter)


average atomic mass

(abundance of isotope)(mass of isotope)



the emission of particles by unstable nuclei


alpha radiation

when a nucleus gives off a helium-4 nucleus (aka an alpha particle)


beta radiation

when a nucleus emits an electron (a beta partile)


gamma radiation

occurs when a nucleus gives off gamma rays, which are basically just extremely energetic light; they are given off during others types of radioactive decay