Page 15 - Chemistry_Form_2

Chemistry
for Secondary Schools

FOR ONLINE READING ONLY
Neon (2: 8)

Potassium (2: 8: 8: 1) Sulfur (2: 8: 6)

Figure 1.6: Electronic configurations of some atoms

Note that the hydrogen atom has no neutron in its nucleus. Helium and neon
atoms have their outermost shells completely filled with electrons, and so they
are stable atoms. The electrons are not fixed at particular positions within the
shell. Instead, they move extremely fast and can be at any point within the shell.

Bohr’s findings provided more information about elements that are summarised
in a table called the periodic table (Appendix 1). The electronic arrangements of
the first 20 elements are shown in Table 1.2.

Exercise 1.1

1. How did the discovery of the nucleus refine earlier atomic models?

2. Why are atoms considered electrically neutral under normal conditions?

3. Compare the Rutherford atomic model with the Bohr atomic model.

4. The atomic number is unique for each element in the periodic table. Explain.

8 Student’s Book Form Two

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