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satela [25.4K]
3 years ago
15

PLEASE ANSWER Which is/are true?

Chemistry
1 answer:
Alona [7]3 years ago
3 0

You have to check each statement, so this is equivalent to 5 different questions.

<u>Answers:</u>

The true statements are:

  • b. Si has valence electrons in the n = 3 energy level.

  • d. Xe has valence electrons in the n = 5 energy level.

<u>Explanations:</u>

<u>a. Li has valence electrons in the n = 1 energy level.</u>

  • <u>Answer: False.</u>

<em>Valence electrons</em> are the electrons in the outermost main energy level (shell of electrons).

To determine where the valence electrons are, you build the electron configuration, using Aufbau rules to predict the orbital filling: in increasing order of energy.

The atomic number of lithium (Li) is 3. Hence, you have to distribute 3 electrons, and so its electron confiuration is:

  • 1s² 2s¹

The only valence electron is in the 2s orbital, i.e. in the n = 2 energy level.

<u>b. Si has valence electrons in the n = 3 energy level.</u>

  • <u>Answer: True</u>

Silicon (Si) has atomic number 14, so you have to distribute 14 electrons in increasing order of energy:

  • 1s² 2s² 2p⁶ 3s² 3p²

Thus, Si has five valence electrons, and they are in the n = 3 energy level.

<u>c. Ga has valence electrons in the n = 3 energy level.</u>

  • <u>Answer: False</u>

Gallium has atomic number 31, so you have to distribute 31 electrons, filling the orbitals in increasing order of enery.

  • 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p¹

The highest energy level is 4. This is where the valence electrons are. So, Ga has the valence electrons in the n = 4 level (not n = 3 as the statement describes).

<u>d. Xe has valence electrons in the n = 5 energy level.</u>

  • <u>Answer: True</u>

The atomic number of Xe is 54.

Using the short notation (noble gas notation), and filling the orbitals in increasing order of energy, you get the configuration:

  • [Kr] 5s² 4d¹⁰ 5p⁶.

Hence, the valence electrons are in the n ) 5 level, such as the statement describes.

<u>e. P has valence electrons in the n = 2 energy level.</u>

  • <u>Answer: False</u>

Phosphorus (P) has atomic number 15, hence there are 15 electrons.

The electron configuration following the increasing order of energy, which you can remember using Aufbau rules, is:

  • 1s² 2s² 3s² 3p³

Then, the valence electrons are in the n = 3 energy level; not in the n = 2 energy level.

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6 0
3 years ago
What volume (in liters) of a solution contains 0.14 mol of KCl?
oksano4ka [1.4K]

Answer:

\boxed {\boxed {\sf 0.078 \ L }}

Explanation:

We are asked to find the volume of a solution given the moles of solute and molarity.

Molarity is a measure of concentration in moles per liter. It is calculated using the following formula:

molarity= \frac{moles \ of \ solute}{liters \ of \ solution}

We know there are 0.14 moles of potassium chloride (KCl), which is the solute. The molarity of the solution is 1.8 molar or 1.8 moles of potassium chloride per liter.

  • moles of solute = 0.14 mol KCl
  • molarity= 1.8 mol KCl/ L
  • liters of solution=x

Substitute these values/variables into the formula.

1.8 \ mol \ KCl/ L = \frac { 0.14 \ mol \ KCl}{x}

We are solving for x, so we must isolate the variable. First, cross multiply. Multiply the first numerator and second denominator, then the first denominator and second numerator.

\frac {1.8 \ mol \ KCl/L}{1} = \frac{0.14 \ mol \ KCl}{x}

1.8 \ mol \ KCl/ L *x = 1*0.14 \ mol \ KCl

1.8 \ mol \ KCl/ L *x = 0.14 \ mol \ KCl

Now x is being multiplied by 1.8 moles of potassium chloride per liter. The inverse operation of multiplication is division, so we divide both sides by 1.8 mol KCl/L.

\frac {1.8 \ mol \ KCl/ L *x}{1.8 \ mol \ KCl/L} = \frac{0.14 \ mol \ KCl}{1.8 \ mol \ KCl/L}

x= \frac{0.14 \ mol \ KCl}{1.8 \ mol \ KCl/L}

The units of moles of potassium chloride cancel.

x= \frac{0.14 }{1.8 L}

x=0.07777777778 \ L

The original measurements of moles and molarity have 2 significant figures, so our answer must have the same. For the number we found, that is the thousandth place. The 7 in the ten-thousandth place tells us to round the 7 up to a 8.

x \approx 0.078 \ L

There are approximately <u>0.078 liters of solution.</u>

5 0
3 years ago
Please help I’m marking a branliest answer ☹️☹️☹️☹️☹️☹️
Doss [256]
The answer would be C
7 0
2 years ago
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