Question

21 fill in the blank 1 point
909 atoms of silver has what mass?
type your answer... x 10 type your answer... grams

22 numeric 1 point
how many shielding electrons does sodium have?
answer

Explanation:

Convert atoms to moles

Using the Avogadros Number knowledge point

$$ n = \frac{909 \text{ atoms}}{6.022 \times 10^{23} \text{ atoms/mol}} \approx 1.5095 \times 10^{-21} \text{ mol} $$

Calculate mass of silver

Using the Molar Mass Calculations knowledge point

$$ \text{Molar mass of Ag} = 107.87 \text{ g/mol} $$

$$ m = 1.5095 \times 10^{-21} \text{ mol} \times 107.87 \text{ g/mol} \approx 1.628 \times 10^{-19} \text{ grams} $$

Rounding to three significant figures gives \(1.63 \times 10^{-19}\) grams.

Determine shielding electrons of sodium

Using the Shielding Electrons knowledge point

$$ \text{Na (Z = 11): } 1s^2 2s^2 2p^6 3s^1 $$

The valence electron is in the \(3s\) subshell. The remaining 10 inner-shell electrons act as shielding electrons:

$$ \text{Shielding electrons} = 11 - 1 = 10 $$

Answer:

Question 21

909 atoms of silver has what mass?
<blank>\(1.63\)</blank> \(\times 10\) <blank>\(-19\)</blank> grams

Question 22

How many shielding electrons does sodium have?
Answer: <blank>10</blank>