Why are the elements of Group $8$ called the noble or inert gas elements?

What is the general formula for an ionic compound formed by elements in the following groups? Explain your reasoning and provide an example for each (name and formula).
c. Group 1 with group 6

Are most of the chemical elements found in nature in the elemental form or combined in compounds? Explain.

Use the tables on the inside back cover of the book to give the chemical symbol, atomic number, and group number of each of the following elements and to specify whether each element is a metal, a metalloid, or a nonmetal.

a. rubidium
b. germanium
c. magnesium
d. titanium
e. iodine

Which elements exist naturally as diatomic molecules? Write their formulas.

Give the symbol for each of the given elements. a. Aluminum b. Sodium c. Mercury d. Helium e. Oxygen f. Potassium

What does the term noble mean when referring to noble metals and noble gases?

What evidence do we have that convinces us that sodium chloride is an ionic compound?

In 2006,115 elements were known. How many of these elements occur naturally, and how many are synthesized artificially? What are the most common elements present on earth?

Which of the following represents a pair of isotopes?

A. ${ }^{23} \mathrm{Na}$ and ${ }^{23} \mathrm{Na}^{+}$
B. ${ }^{14} \mathrm{C}$ and ${ }^{14} \mathrm{~N}$
C. ${ }^{14} \mathrm{C}$ and ${ }^{12} \mathrm{C}$
D. ${ }^{16} \mathrm{O}$ and ${ }^{16} \mathrm{O}^{2-}$

Did Dalton's model of the atom include protons, neutrons, and electrons inside the atoms? Explain.

Solve the following exercise which is about operations on complex numbers.

Locate these points on the complex plane. Simplify them if necessary:

(a) $2+i$

(b) $(2+i)^2$

(c) $\frac{1}{2+i}$

(d) $|2+i|$

Give some applications for
(a) flash welding,
(b) stud welding, and
(c) percussion welding.

Discuss the need for, and the role of, work-holding devices in the welding operations described in this chapter.