Q: Given the isotopic abundances and masses for chlorine: $$^{35}Cl (75.78$$%, 34.969 amu) and $$^{37}Cl (24.22$$%, 36.966 amu), calculate the atomic weight of chlorine.

$$(0.7578 \times 34.969) + (0.2422 \times 36.966) = 35.45$$ amu

Q: What is the maximum number of electrons that can occupy the third principal energy level ($$n=3) of an $$atom?

$$2n^2 = 2$$ \times $$3^2 = 18$ electrons

Question 1

Which subatomic particle is responsible for the identity of an element, and how is this reflected in the periodic table?

Accepted Answer

The proton; it determines the atomic number, which is used to arrange elements in the periodic table.

Question 2

An atom of chlorine has an atomic number of 17 and a mass number of 35. How many neutrons does it contain?

Accepted Answer

$$35 - 17 = 18$$ neutrons

Question 3

Which of the following statements about isotopes is correct?

Accepted Answer

Isotopes of an element have the same number of protons but different numbers of neutrons.

Question 4

Given the isotopic abundances and masses for chlorine: $$^{35}Cl (75.78$$%, 34.969 amu) and $$^{37}Cl (24.22$$%, 36.966 amu), calculate the atomic weight of chlorine.

Accepted Answer

$$(0.7578 	imes 34.969) + (0.2422 	imes 36.966) = 35.45$$ amu

Question 5

Which of the following elements is a diatomic molecule in its natural state?

Accepted Answer

Oxygen

Question 6

What is the maximum number of electrons that can occupy the third principal energy level ($$n=3) of an $$atom?

Accepted Answer

$$2n^2 = 2$$ 	imes $$3^2 = 18$ electrons

Question 7

Which orbital has a spherical shape and can hold a maximum of two electrons?

Accepted Answer

s orbital

Question 8

What is the electron configuration in noble-gas notation for phosphorus ($$Z=15$$)?

Accepted Answer

$$[Ne] 3s^2$ 3p^3$

Question 9

Which of the following elements has 6 valence electrons in its outermost shell?

Accepted Answer

Sulfur

Question 10

Arrange the following atoms in order of increasing atomic radius: F, K, Br, Cu, Rb.

Accepted Answer

F \u003c K \u003c Cu \u003c Br \u003c Rb

Question 11

Which of the following elements has the highest first ionization energy?

Accepted Answer

Fluorine

Question 12

What is the electron configuration for a $$Cl^-$$ ion?

Accepted Answer

$$[Ne] 3s^2$ 3p^6$

Question 13

Which principle states that no two electrons in an atom can have the same set of quantum numbers?

Accepted Answer

Pauli exclusion principle

Question 14

A neutral atom of $$^{13}C$$ has how many protons, neutrons, and electrons?

Accepted Answer

6 protons, 7 neutrons, 6 electrons

Question 15

Which of the following elements has 2 unpaired electrons in its valence shell?

Accepted Answer

Carbon

Question 16

Which of the following best explains why atomic radius increases down a group in the periodic table?

Accepted Answer

Electrons are added to higher principal energy levels, increasing the distance from the nucleus.

Question 17

Which element has the electron configuration $$[Ar] 4s^2$ 3d$$^{10}$$ 4p^5$?

Accepted Answer

Bromine

Question 18

What is the main reason ionization energy increases across a period?

Accepted Answer

The number of protons increases, increasing the nuclear charge and pulling electrons closer.

Question 19

Which of the following ions has the same electron configuration as argon?

Accepted Answer

$$Cl^-$$

Question 20

Which of the following statements about valence electrons is correct for main group elements?

Accepted Answer

The group number (1A-8A) equals the number of valence electrons.

Atoms and Elements: Structure, Properties, and Periodic Trends

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