Question

element symbol # of valence electrons valence sum
fluorine f 7 1 30
hydrogen h 1 1
oxygen o 6 2
nitrogen n 5 3
chlorine cl 7 1
carbon c 4 4

1. make a rule: if you knew the number of valence electrons in a non - metal atom, how would you determine the valence of the element? (hint: ignore hydrogen for now.)
2. analyze: the first shell can hold a maximum of two electrons. how does this explain the valence of hydrogen?
3. apply: selenium has six valence electrons. what is the valence of selenium?
4. think and discuss: the last column of the periodic table contains the noble gases, elements that do not easily form chemical bonds. why don’t these gases tend to form chemical bonds?

Explanation:

Step1: Analyze non - metal valence rule

For non - metals (excluding hydrogen), the valence is 8 minus the number of valence electrons.

Step2: Explain hydrogen valence

Hydrogen has 1 valence electron. The first shell can hold a maximum of 2 electrons. Hydrogen wants to gain 1 electron to fill its shell, so its valence is 1.

Step3: Determine selenium valence

Selenium has 6 valence electrons. Using the rule (8 - number of valence electrons), 8 - 6 = 2, so the valence of selenium is 2.

Step4: Explain noble gas non - reactivity

Noble gases have a full outer shell of electrons. They do not need to gain, lose, or share electrons to achieve a stable electron configuration, so they do not easily form chemical bonds.

Answer:

1. For non - metals (excluding hydrogen), valence = 8 - number of valence electrons.
2. Hydrogen has 1 valence electron and the first shell can hold 2. It wants to gain 1 electron, so valence is 1.
3. 2
4. Noble gases have a full outer shell of electrons and are already in a stable state, so they do not easily form chemical bonds.