CH 4 FINAL EXAM GUIDE Flashcards
Summarize Millikan’s oil drop experiment
In 1909, Robert Millikan and Harvey Fletcher conducted the oil drop experiment to determine the charge of an electron. They suspended tiny charged droplets of oil between two metal electrodes by balancing downward gravitational force with upward drag and electric forces.
what did millikan’s oil drop experiment tell us about atoms?
Robert Millikan was able to determine the mass of an electron by using charged oil drops. Electrons have such a small mass, they were believed to be massless. Millikan’s experiment determined that the electrons did, indeed, have mass.
summarize Rutherford’s gold foil experiment
Physicist Ernest Rutherford established the nuclear theory of the atom with his gold-foil experiment. When he shot a beam of alpha particles at a sheet of gold foil, a few of the particles were deflected. He concluded that a tiny, dense nucleus was causing the deflections.
what did Rutherford’s gold foil experiment explain about an atom?
Showed that the atom is mostly empty space with a tiny, dense, positively-charged nucleus. Rutherford proposed the nuclear model of the atom.
Who discovered the proton
James Chadwick detected neutrons and measured their mass in an invisible game of billiards. He fired the neutrons at a block of paraffin wax, Some of the neutrons collided with protons in the wax and knocked them out. Chadwick could then detect these protons and measure their energy.
who discovered the electron
J.J. Thomson’s experiments with cathode ray tubes showed that all atoms contain tiny negatively charged subatomic particles or electrons.
who discovered the neutron
Ernest Rutherford’s gold foil experiment showed that the atom is mostly empty space with a tiny, dense, positively-charged nucleus.
what is the charge of a proton
positive
what is the charge of a neutron
uncharged
what is the charge of a electron
negative
what is an Ion?
Ion is an atom that has gained or lost one or more electrons, thus becoming positively or negatively charged.
what is the charge of an atom
Atoms have an equal number of protons and electrons; therefore, they have a no net charge.
summarize 4 parts of Dalton’s atomic theory
Dalton’s atomic theory describes all matter in terms of atoms and their properties.
- all matter is made of atoms, which are indivisible.
- says all atoms of a given element are identical in mass and properties.
- compounds are combinations of two or more different types of atoms.
- a chemical reaction is a rearrangement of atoms.
Waht is the modern model of the atom and how does it describe the atom?
The current model of the atom shows an atom that is mostly empty space. In the center is a tiny nucleus made of protons and neutrons. The nucleus contains nearly all the mass of an atom. Surrounding the nucleus is a cloud-like region with electrons moving too fast and too unpredictably for us to know their location.
How did the Bohr model describe the atom?
Bohr proposed that the electrons could only orbit the nucleus in certain special orbits at different energy levels around the nucleus.
Who put forth the plum pudding model of the atom?
J.J. Thomson. The atomic nucleus had not been discovered yet and so the “plum pudding model” was put forward in 1904. In this model, the atom is made up of negative electrons that float in a “soup” of positive charge, much like plums in a pudding or raisins in a fruit cake
what are atoms comprised of?
An atom itself is made up of three tiny kinds of particles called subatomic particles: protons, neutrons, and electrons.
how do you determine how many protons are in an atom of an element?
The atomic number is located above the element symbol, in the upper left-hand corner of the square. The atomic number will tell you how many protons in an atom of that element.
how do you determine how many electrons are in an atom of an element?
an element in a neutral state will have the same number of protons and electrons.
For example, boron (B) has an atomic number of 5, therefore it has 5 protons and 5 electrons.
However, if the element includes a negative or positive ion, then the protons and electrons will not be the same. You will have to calculate them. The ion number will appear as a small superscript after the element.
how do you determine how many neutrons are in an atom of an element?
The atomic mass can be found underneath the symbol and round to a whole number.
THEN: Subtract the atomic number (upper left) from the atomic mass.
For our boron example, 11 (atomic mass) – 5 (atomic number) = 6 neutrons
Determine the composition of an atom of the following element:
sodium
Symbol: Na Atomic Mass: 22.98977 amu , rounded to 23 subtract the atomic number: 11 equals 12 neutrons Number of Protons/Electrons: 11 Number of Neutrons: 12
Determine the composition of an atom of the following element:
magnesium
Symbol Mg Atomic Mass 24.305 atomic mass units, rounded to 24 subtract Atomic Number 12 equals neutrons: Number of Neutrons 12 Number of Protons 12 Number of Electrons 12
Determine the composition of an atom of the following element:
uranium
Symbol: U Atomic Mass: 238.0289 amu or 238 rounded subtract Atomic Number: 92 equals 146 neutrons Number of Protons/Electrons: 92 Number of Neutrons: 146
Determine the composition of an atom of the following element:
fluorine
Name Fluorine Atomic Mass 18.998 atomic mass units or 19 subtract atomica number: 9 equals 10 neutrons Number of Protons 9 Number of Neutrons 10 Number of Electrons 9
