Question 1

Which of the following statements best explains why the 4s sublevel is filled before the 3d sublevel when writing electron configurations?

Accepted Answer

Because the 4s sublevel has a lower energy than the 3d sublevel, as shown in the filling diagram.

Question 2

How many electrons can the third energy level ($$n=3) $$hold in total?

Accepted Answer

$$18$$

Question 3

Which of the following electron configurations correctly represents the sodium ion ($$\mathrm{Na^+}$$)?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ $$2p^6$$

Question 4

A neutral atom of chlorine ($$\mathrm{Cl}) $$has the electron configuration $$1s^2$$\ $$2s^2$$\ $$2p^6$$\ $$3s^2$$\ $$3p^5. $$How many valence electrons does it have?

Accepted Answer

$$7$$

Question 5

Which of the following elements is most likely to form a $$2^+$$ ion based on its position in the periodic table?

Accepted Answer

Magnesium ($$\mathrm{Mg})$$

Question 6

Given the electron configuration $$1s^2$$\ $$2s^2$$\ $$2p^6$$\ $$3s^2$$\ $$3p^6$$\ $$4s^2$$\ $$3d^{10}$$\ $$4p^5$$, which element does this represent?

Accepted Answer

Bromine ($$\mathrm{Br})$$

Question 7

Which of the following sublevels can hold a maximum of $$14$$ electrons?

Accepted Answer

$$f$$ sublevel

Question 8

If an atom has the electron configuration $$1s^2$$\ $$2s^2$$\ $$2p^6$$\ $$3s^2$$\ $$3p^6$$\ $$4s^2$$, what is the atomic number of this element?

Accepted Answer

$$20$$

Question 9

Which of the following best describes the trend in atomic radius across a period from left to right?

Accepted Answer

Atomic radius decreases because the increased nuclear charge pulls electrons closer.

Question 10

How many sublevels are present in the $$n=4$$ energy level?

Accepted Answer

$$4$$

Question 11

Which of the following ions has the same electron configuration as neon ($$\mathrm{Ne}$$)?

Accepted Answer

$$\mathrm{Na^+}$$

Question 12

What is the maximum number of electrons that can occupy the $$3d$$ sublevel?

Accepted Answer

$$10$$

Question 13

Which element has the electron configuration $$[Ar]\ 4s^2$\ 3d^6$?

Accepted Answer

Iron ($$\mathrm{Fe})$$

Question 14

A student claims that the $$2p$$ sublevel can hold $$8$$ electrons. Which concept from electron configuration disproves this claim?

Accepted Answer

Each $$p$$ sublevel can hold a maximum of $$6$$ electrons.

Question 15

Which of the following elements has the smallest atomic radius?

Accepted Answer

Fluorine ($$\mathrm{F})$$

Question 16

Which block of the periodic table contains elements whose valence electrons are being added to $$d$$ sublevels?

Accepted Answer

$$d$$ block

Question 17

Which of the following ions is formed when an atom loses two electrons from its outermost shell?

Accepted Answer

$$\mathrm{Mg$$^{2+}$$}$$

Question 18

If an atom has the electron configuration $$1s^2$$\ $$2s^2$$\ $$2p^6$$\ $$3s^2$$\ $$3p^6$$\ $$4s^1$$, what is the element?

Accepted Answer

Potassium ($$\mathrm{K})$$

Question 19

Which of the following is the correct order for filling sublevels according to the diagram shown in the study materials?

Accepted Answer

$$1s \rightarrow 2s \rightarrow 2p \rightarrow 3s \rightarrow 3p \rightarrow 4s \rightarrow 3d \rightarrow 4p$$

Question 20

Which of the following elements has two valence electrons?

Accepted Answer

Calcium ($$\mathrm{Ca})$$

Electron Configurations and Periodic Trends: Study Notes

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