chp 3 test Flashcards
atom
the smallest particle of an element that retains the chemical identity of the element
atomic theory:
dalton vs modern pt 1
dalton- atoms of a given element are identical in size, mass, and other properties
modern- atoms of the same element have the same chemical properties
why?- isotopes have the same chemical properties but differ in mass and size
atomic theory:
dalton vs modern pt 2
dalton- atoms are not subdivided, created, or destroyed in chemical reactions
modern- atoms cannot be subdivided, created or destroyed
why?- nuclear reactions change the composition of an atom’s nucleus
cathode ray tube experiment:
how did the cathode ray tube experiment prove that electrons have a negative charge?
J.J. Thomson observed that the cathode way is repelled by a negative charge
cathode ray tube experiment:
how did the cathode ray tube experiment prove that electron are particles?
J.J. Thomson observed that a paddle wheel placed in the middle of the tube spins which meant the cathode ray is made of particles, the cathode ray is also repelled by a negative charge which showed him the cathode ray has a negative charge
oil drop experiment:
how was the charge of an electron determined?
Millikan used the oil drop experiment and adjusted the voltage so the (charged) drop was suspended in mid-air (between two plates)
he used the formula: upward force~(charge on drop)(voltage between plates), where he knows the upward force and voltage between plates and can find the charge on drop
oil drop experiment:
how was the mass of an electron determined?
Millikan used the charge and Thomson’s ratio
he used: m = 9.1 x 10-31 kg
atoms were known to be neutral yet the cathode ray tube experiment showed that electrons are negative. what conclusion did scientists draw from this?
there must be something positive in the atom, because atoms are neutral
atoms were known to have a much larger mass than the mass of an electron. what conclusion did the scientists draw from this?
there is something else that has to be positive
plum pudding model:
what is happening to all the alpha particles?
they are passing by the positive charge and electrons
gold foil experiment:
how does the behavior of the alpha particles differ from their behavior in the plum pudding model? how did rutherford explain this behavior?
as the alpha particles pass by, they avoid/are being pushed away from the nuclei when they get too close, and spread in different directions. he explained this behavior by saying the nucleus is the positively charged, dense central portion of the atom that contains nearly all the atom’s mass but takes up only a fraction of its volume
gold foil experiment:
the alpha particles are being blank by something at the center so the center must be blank because like charges repel
bounced
positive
repel
gold foil experiment: rutherford could not see the alpha particles. how did he observe their behavior?
a burst of light was produced when the alpha particles hit the screen
gold foil experiment:
compare the behavior of low energy alpha particles to the behavior of high energy particles. explain any diffeeence
low energy- they move slower when passing by and do not get as close to the nucleus when they are headed toward them
high energy- they move faster when passing by and don’t get closer to the nucleus when they head toward them
gold foil experiment:
change the number of protons and neutrons to 20. observe
when the number of neutrons is higher alpha particles are being rebounded back to the direction they came from, when the number of neutrons are lower alpha particles almost go around the nucleus and typically do not go back in the direction they came from
