Download chapter 7 – cyu

CHAPTER 7 – CYU
7.1
1. Work by scientist Humphry Davy using air as an electricity conductor helped Heinrich
Geissler develop the gas discharge tube. This tube, when it has all the air pumped out of
it, initially glowed blue then green at one end when under very low pressure. The green
glow at the anode end was the result of the electrons being released from the cathode at
the opposite end of the tube. The electron is negative, near weightless, and is located in
shells outside of the nucleus of an atom.
2. A gas discharge tube is a device originally designed by Davy and refined by Geissler
to remove the particles of air within the tube, therefore only allowing the electrons to
show up.
3. Crookes put an iron cross in the middle. The cross blocked the rays coming from the
cathode end. The shadow on the one end (anode) allowed him to see where the electrons
were coming from. Crookes also had another experiment using a pinwheel in which
electric currents, when switched on, would cause the wheel to spin. This allowed them to
conclude that they had mass as well as motion.
4. German physicist Eugen Goldstein detected rays coming from the anode. Since an
atom is electrically neutral, there must be an opposite charge to the electron that existed.
This positive charge came from the proton. A proton is positive and has a large mass in
comparison to an electron.
7.2
1. Uranium, Polonium, Radium
2. Searching for other radioactive elements, exploring the composition of the rays, using
the rays to probe atomic structure.
3. The spectrum of hydrogen atoms is not continuous. Bohr concluded that if an electron
had more energy, then it circled the nucleus at a greater distance.
7.3
1. Mendeleev constructed his periodic table using chemical properties and atomic mass
as his guiding principles. Moseley rearranged the periodic table in order of increasing
atomic number, called periodicity. When he did this, there are instances where the
atomic mass of an element is heavier then the following element. This is called a
reversal.
2. Modern atomic mass units are ratios of the mass of a 12 6C atom. A proton is = a.m.u.
An electron is = 1/1837 a.m.u. A neutron is = 1 a.m.u.
3. An isotope is any of 2 or more forms of an element that have the same number of
protons but a different number or neutrons. If an element has a high percentage of
“heavy” isotopes then its mass will be slightly heavier. The same applies to the other
scenario.
4.a) Chlorine, p = 17, e = 17, n = 18
4.c) Iron, p = 26, e = 26, n = 30
4.b) Uranium, p = 92, e = 92, n = 146