Page 334 - ABCTE Study Guide_Neat

C 64

D 94

Answer

The correct choice is B. The number of neutrons is the mass number, 64, minus the atomic number, 30.

The Periodic Table

There are a variety of chemical and physical properties of the elements, but they have patterns of
similarity for different elements. The periodic table is a method for organizing the elements based on
these similarities.

The periodic table is an important tool for all scientific endeavors. Understanding the significance of
Groups IA through VIIIA is the key to the rest of the periodic table. The increasing Group A number
corresponds to the increasing number of valence (outer) electrons. Group VIIIA elements all (except He)
have 8 valence electrons, hence the rule of octet. Helium (He) is such a small atom that only two
electrons have room to fit so near the nucleus and fill the outer shell. The elements in Groups IA and IIA
easily lose electrons to become positive ions. The tendency to lose electrons easily identifies elements
that are commonly called metals. Group IIIA elements tend to lose electrons but not as readily as the
Group IA and IIA elements. They often combine with other atoms by sharing electrons. The elements in
Group VIA and VIIA easily gain electrons to become negative ions. The tendency to gain electrons easily
identifies elements that are commonly called non-metals. The Group V elements tend to gain electrons,
but not as readily as Groups VIA and VIIA. They too often combine with other atoms by sharing electrons.
The Group IVA elements invariably combine with other atoms by sharing electrons, they do not readily
transfer electrons. The Group B elements have more complicated electron structures and will be
discussed shortly.

Elements in each column of the periodic table exhibit similar properties and are said to be in the same
elementalgroup or family. For example, sodium and potassium, both in the first column of the table, have
very similar chemical and physical properties because they share the same number of electrons in their
outermost energy level. They are in Group IA which means they each have one electron in their valence
shell.

The periodic table is also arranged by increasing atomic number (number of protons) from left to right in
each row. Many elements can be classified by their position on the periodic table. Some of the regions of
interest are:

Metals are the elements on the left and center of the table and the lower section of the right side of the
table. Metals tend to be hard, shiny elements that conduct heat and electricity well.

Nonmetals are the elements on the right side of the table. Nonmetals form soft, brittle solids. Many of
them are gases at room temperature. Nonmetallic elements do not conduct heat or electricity well.

Metalloids are the elements in a zigzag line that separates metals and nonmetals. These elements share
some properties of both metals and nonmetals.