6. 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.)
7. analyze: the first shell can hold a maximum of two electrons. how does this explain the valence of hydrogen?
8. apply: selenium has six valence electrons. what is the valence of selenium?
9. 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?

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Accepted Answer

### Question 8:
# Explanation:
## Step1: Recall valence concept
Valence relates to electron gain/loss/share to achieve octet (or duet for H). For nonmetals, valence = 8 - valence electrons (if valence e⁻ < 4) or valence e⁻ (if forming bonds by sharing). Selenium (Se) is a nonmetal, group 16, has 6 valence e⁻.
## Step2: Calculate selenium's valence
To achieve octet (8 electrons), Se needs $ 8 - 6 = 2 $ more electrons (or can share 2 pairs). Alternatively, since it has 6 valence e⁻, it can form bonds by sharing 2 (or accept 2). So valence is 2 (or 6, but common valence for group 16 nonmetals like O, S, Se is 2 or 6; here, with 6 valence e⁻, to fill octet, it needs 2, so valence is 2 (or 6, but typical for bonding, 2 or 6; but since it has 6, and needs 2 to complete octet, valence is 2 (or 6, but more accurately, for nonmetals, valence = 8 - valence e⁻ when valence e⁻ < 4, but Se has 6, so valence can be 2 (gaining 2) or 6 (sharing 6). But in most cases, for group 16, common valence is 2 (like O: valence 2). So selenium's valence is 2 (or 6, but primary is 2).
# Answer: The valence of selenium is 2 (or 6, but commonly 2).

### Question 9:
# Brief Explanations:
Noble gases (group 18) have full valence shells (octet, except He with duet: 2 electrons). A full valence shell means they have low energy and high stability. Chemical bonds form to achieve stable electron configurations (like octet/duet). Since noble gases already have stable configurations, they don’t need to gain/lose/share electrons, so they rarely form chemical bonds.
# Answer: Noble gases have full valence shells (stable electron configuration), so they don’t need to form bonds to achieve stability, hence rarely form chemical bonds.

### Question 7:
# Brief Explanations:
Hydrogen (H) has 1 electron in its only (first) shell. The first shell can hold max 2 electrons. To achieve stability (duet), H can gain 1 electron (forming $ H^- $) or share 1 electron (in covalent bonds, e.g., $ H_2 $ or $ H_2O $). So its valence is 1 (since it needs 1 more electron to fill the first shell, or shares 1, so it can form 1 bond, valence = 1). The first shell’s max of 2 electrons explains H’s valence: it needs 1 more to reach 2 (stable), so valence is 1.
# Answer: Hydrogen’s valence is 1. The first shell holds max 2 electrons; H has 1, so it needs 1 more (or shares 1) to stabilize, giving valence 1.

### Question 6:
# Brief Explanations:
For a nonmetal atom, valence is determined by the number of electrons needed to achieve a stable octet (8 valence electrons, except H/He). If the nonmetal has $ V $ valence electrons ($ V < 4 $), valence = $ 8 - V $ (needs to gain electrons). If $ V \geq 4 $, valence can be $ V $ (shares electrons) or $ 8 - V $ (gains electrons). For example, O has 6 valence e⁻: $ 8 - 6 = 2 $, so valence 2. S has 6: valence 2 or 6. So rule: For a nonmetal, valence = $ 8 - \text{number of valence electrons} $ (if valence e⁻ < 8, and to achieve octet) or equal to valence electrons (if sharing to form bonds).
# Answer: For a nonmetal atom with $ n $ valence electrons, valence = $ 8 - n $ (to achieve octet by gaining electrons) or $ n $ (by sharing electrons). E.g., O (6 valence e⁻): $ 8 - 6 = 2 $, valence 2.

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QUESTION IMAGE

Question

Explanation:

Question 8:

Step1: Recall valence concept

Step2: Calculate selenium's valence

Answer:

Question 9: