Which of the following statements is not true of using electron dot diagrams?

A. The element's group number provides a clue about the number of valence electrons. B. An element with eight valence electrons is chemically unstable.
C. Dots should be placed one at a time on each side of the chemical symbol.
D. An atom is chemically stable if all dots are paired.

To determine which statement is not true of using electron dot diagrams, let's examine each statement and assess its accuracy.

A. The statement "The element's group number provides a clue about the number of valence electrons" is generally correct. In most cases, the group number on the periodic table indicates the number of valence electrons for elements in that group. For example, elements in Group 1 (such as hydrogen and lithium) have one valence electron, while elements in Group 17 (such as fluorine and chlorine) have seven valence electrons. Therefore, Statement A is true.

B. The statement "An element with eight valence electrons is chemically unstable" is not true. In fact, elements with eight valence electrons are considered to be chemically stable, and this is known as the octet rule. Octet rule states that atoms tend to gain, lose, or share electrons in order to attain a stable electron configuration similar to the noble gases. These noble gases have a full valence shell of eight electrons, which makes them stable and unreactive. Elements such as oxygen and neon have eight valence electrons, and they are stable. Therefore, Statement B is false.

C. The statement "Dots should be placed one at a time on each side of the chemical symbol" is accurate. When drawing an electron dot diagram, each dot represents one valence electron. For example, if an element has three valence electrons, you would place three dots around the chemical symbol, preferably one dot on each side before doubling up. So, Statement C is true.

D. The statement "An atom is chemically stable if all dots are paired" is not true. Chemical stability is achieved when an element has a full valence shell, typically containing eight electrons or two electrons for hydrogen and helium. However, in electron dot diagrams, electrons are represented as unpaired dots. In fact, it is the unpaired electrons that are available for bonding and chemical reactions. Therefore, Statement D is false.

In conclusion, the statement that is not true of using electron dot diagrams is:
B. An element with eight valence electrons is chemically unstable.

The correct answer is B. An element with eight valence electrons is chemically unstable.

B. An element with eight valence electrons is chemically unstable.

It would be unstable only with one to seven valence electrons, not eight.