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Atomic Theory and the Periodic Table
Answers
Worksheet 1 Establishing order among the elements
Time to Think (p. 9)
1.
Different elements are composed of different kinds of atom.
2.
He noticed that elements with different atomic weights showed similar
chemical properties.
3.
He predicted that the missing elements in his periodic table would have
chemical properties similar to those in the same column.
4.
Over the next 15 years, three new elements were discovered and they showed
the properties predicted by Mendeleev.
5.
Elements in the same column of the periodic table have the same number of
electrons in their outermost electron shell, which is an important factor in
determining the chemical properties of an element.
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Atomic Theory and the Periodic Table
Answers
Worksheet 2 Discovery of electrons
Time to Think (p. 14)
1.
Cathode rays contain energy which is absorbed by the phosphorescent
substance. The phosphorescent substance emits the absorbed energy in forms
of light.
2.
Cathode rays can travel in vacuum (vacuum tube), which is a distinctive
property of electromagnetic wave.
3.
The rays were deflected away from the negative plate and towards the positive
plate in the vacuum tube, indicating that they are negatively charged particles.
4.
It can be concluded that the mass of a cathode ray particle is much smaller than
that of a hydrogen ion.
5.
It shows that atoms are made up of smaller subatomic particles such as
electrons. Thus atoms are not indivisible.
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Atomic Theory and the Periodic Table
Answers
Worksheet 3 Rutherford – father of nuclear physics
Time to Think (p. 17)
1.
The electrons in beta rays move much faster than those in cathode rays.
2.
Gamma rays have more energy than X-rays.
3.
Thomson showed that cathode rays are made up of particles that are negatively
charged and have a mass of 1/1 000 of a hydrogen ion. He called these particles
electrons. Since electrons are much smaller than hydrogen, the smallest atom,
they should be a component of atoms.
Time to Think (p. 20)
4.
(a) Most space of an atom is occupied by a cloud of electrons, which has a very
low density.
(b) When positively charged alpha particles pass near the nucleus of an atom,
they are deflected because the nucleus is also positively charged.
(c) When the alpha particles hit straight on a nucleus, they bounce directly
back because the nucleus is very dense.
5.
A metal of greater atomic weight has a larger nucleus. So there is a higher
chance for the alpha particles to hit directly onto the nucleus and bounced back.
6.
An atom of large atomic mass has a very large nucleus, which is unstable and
easily breaks down. When this occurs, the atom releases various kinds of
radiations spontaneously.
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