Question

activity b (continued from previous page)

1. count: review the lewis diagrams you drew on the previous page. note that each element tends to form a certain number of chemical bonds. this value is the valence of the element.

for each element in the table below, use the gizmo to find the number of valence electrons and the list the valence based on the lewis diagram. then find the sum of these numbers.

element	symbol	# of valence electrons	valence	sum
hydrogen	h
oxygen	o
nitrogen	n
chlorine	cl
carbon	c

1. make a rule: if you knew the number of valence electrons in a nonmetal atom, how would you determine the valence of the element? (hint: ignore hydrogen for now.)

1. analyze: the first shell can hold a maximum of two electrons. how does this explain the valence of hydrogen?

1. apply: selenium has six valence electrons. what is the valence of selenium?

1. think and discuss: the last column of the periodic table contains the noble gases, elements that do not easily form chemical bonds.

why dont these gases tend to form chemical bonds?

Explanation:

Step1: Determine valence - electrons and valence for each element

• Fluorine (F): Has 7 valence electrons. Its valence is 1 (as it needs 1 electron to achieve a stable octet).
• Hydrogen (H): Has 1 valence electron. Its valence is 1 (as it needs 1 electron to achieve a stable duet).
• Oxygen (O): Has 6 valence electrons. Its valence is 2 (as it needs 2 electrons to achieve a stable octet).
• Nitrogen (N): Has 5 valence electrons. Its valence is 3 (as it needs 3 electrons to achieve a stable octet).
• Chlorine (Cl): Has 7 valence electrons. Its valence is 1 (as it needs 1 electron to achieve a stable octet).
• Carbon (C): Has 4 valence electrons. Its valence is 4 (as it needs 4 electrons to achieve a stable octet).

Step2: Calculate the sum of valence - electrons

Sum = 7 + 1+6 + 5+7 + 4=30

Step3: Rule for non - metal valence (excluding hydrogen)

For non - metal elements (excluding hydrogen), the valence is 8 minus the number of valence electrons. This is because non - metals tend to gain electrons to achieve a stable octet configuration.

Step4: Explain hydrogen's valence

Hydrogen has 1 valence electron. The first shell can hold a maximum of 2 electrons. So, hydrogen needs 1 more electron to fill its outer shell, giving it a valence of 1.

Step5: Determine selenium's valence

Selenium has 6 valence electrons. Using the rule for non - metals (8 minus the number of valence electrons), its valence is 8 - 6=2.

Step6: Explain noble gases' lack of bonding

Noble gases have a full outer shell of electrons. Helium has 2 electrons in its outer shell, and the other noble gases have 8 electrons in their outer shell. Since they have a stable electron configuration, they do not need to gain, lose, or share electrons to become stable, so they do not easily form chemical bonds.

Answer:

Element	Symbol	# of valence electrons	Valence	Sum
Hydrogen	H	1	1
Oxygen	O	6	2
Nitrogen	N	5	3
Chlorine	Cl	7	1
Carbon	C	4	4

Rule for non - metal valence (excluding hydrogen): Valence = 8 - number of valence electrons.
Hydrogen's valence is 1 because it needs 1 electron to fill its first (and only) shell.
Selenium's valence is 2.
Noble gases do not form chemical bonds easily because they have a full outer shell of electrons and are already in a stable configuration.