Q: A sample of chlorine contains two isotopes: $$\displaystyle \frac{35}{17}\text{Cl} (75.76$$%) and $$\displaystyle \frac{37}{17}\text{Cl} (24.24$$%). Calculate the atomic mass of chlorine using the weighted average formula.

$$\displaystyle (0.7576 \times 35) + (0.2424 \times 37) = 35.48$$

Q: Which isotope of lithium is more abundant if the atomic mass of lithium is 6.941 amu?

$$\displaystyle \frac{7}{3}\text{Li}$$

Q: If an atom has 17 protons, 20 neutrons, and 17 electrons, what is its atomic symbol?

$$\displaystyle \frac{37}{17}\text{Cl}$$

Question 1

Which statement best describes isotopes of an element?

Accepted Answer

Isotopes have the same number of protons and electrons, but different numbers of neutrons.

Question 2

Given the atomic symbol $$\displaystyle \frac{24}{12}	ext{Mg}$$, how many neutrons are present in this isotope?

Accepted Answer

12

Question 3

A sample of chlorine contains two isotopes: $$\displaystyle \frac{35}{17}	ext{Cl} (75.76$$%) and $$\displaystyle \frac{37}{17}	ext{Cl} (24.24$$%). Calculate the atomic mass of chlorine using the weighted average formula.

Accepted Answer

$$\displaystyle (0.7576 	imes 35) + (0.2424 	imes 37) = 35.48$$

Question 4

Which isotope of lithium is more abundant if the atomic mass of lithium is 6.941 amu?

Accepted Answer

$$\displaystyle \frac{7}{3}	ext{Li}$$

Question 5

Which form of electromagnetic radiation has the shortest wavelength and highest energy?

Accepted Answer

X-rays

Question 6

What happens when an electron moves from $$n=3 to$$ $$n=1 in an $$atom?

Accepted Answer

Energy is emitted.

Question 7

Write the electron arrangement for sodium (Na), atomic number 11.

Accepted Answer

$$2,8,1$$

Question 8

Which element in Period 2 has the highest ionization energy?

Accepted Answer

Neon (Ne)

Question 9

Which element has the most metallic character in Group 1A?

Accepted Answer

Potassium (K)

Question 10

Which element has the largest atomic size among the following: potassium (K), lithium (Li), and sodium (Na)?

Accepted Answer

Potassium (K)

Question 11

How many valence electrons does silicon (Si) have?

Accepted Answer

4

Question 12

Which element is most likely to lose electrons easily, based on its position in the periodic table?

Accepted Answer

Sodium (Na)

Question 13

What is the atomic mass of magnesium as listed on the periodic table?

Accepted Answer

24.31 amu

Question 14

Which element has a Lewis symbol with three dots around it?

Accepted Answer

Aluminum (Al)

Question 15

If an atom has 17 protons, 20 neutrons, and 17 electrons, what is its atomic symbol?

Accepted Answer

$$\displaystyle \frac{37}{17}	ext{Cl}$$

Question 16

Which element in Group 8A (18) is stable with only two valence electrons?

Accepted Answer

Helium (He)

Question 17

Which element has the highest ionization energy among the following: calcium (Ca), bromine (Br), and potassium (K)?

Accepted Answer

Bromine (Br)

Question 18

Which element is most likely to be used in light therapy for seasonal affective disorder (SAD) due to its emission of visible light?

Accepted Answer

A lamp emitting visible light

Question 19

Which element belongs to Group 5A (15) and has an electron arrangement of $$2,5$$?

Accepted Answer

Nitrogen (N)

Question 20

Which periodic property increases as you move from left to right across a period?

Accepted Answer

Ionization energy

Atoms and Elements: Isotopes, Atomic Mass, Electron Energy Levels, and Periodic Trends

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