Q: What is the maximum number of electrons that can occupy the second electron shell of an atom?

$$2n^2 = 2$$ \times $$2^2 = 8$ electrons

Question 1

Which of the following best describes the difference between an element and a compound?

Accepted Answer

An element is a substance that cannot be broken down into other substances by chemical means, while a compound is a substance consisting of two or more elements combined in a fixed ratio.

Question 2

A sodium atom (Na) has an atomic number of 11 and a mass number of 23. How many neutrons does it have?

Accepted Answer

$$23 - 11 = 12$$ 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

Which of the following best explains why water is a polar molecule?

Accepted Answer

Water has a bent shape and the oxygen atom is more electronegative than hydrogen, creating a partial negative charge near the oxygen and a partial positive charge near the hydrogens.

Question 5

Which type of chemical bond involves the transfer of electrons from one atom to another?

Accepted Answer

Ionic bond

Question 6

What is the maximum number of electrons that can occupy the second electron shell of an atom?

Accepted Answer

$$2n^2 = 2$$ 	imes $$2^2 = 8$ electrons

Question 7

A radioactive isotope of carbon, carbon-14, is used in radiometric dating. If the half-life of carbon-14 is 5,730 years, how much of a 10 g sample will remain after 11,460 years?

Accepted Answer

$$10 \div 2 \div 2 = 2.5 g$$

Question 8

Which of the following best describes a hydrogen bond?

Accepted Answer

A weak interaction between a hydrogen atom covalently bonded to a highly electronegative atom and another electronegative atom.

Question 9

Which of the following molecules is nonpolar?

Accepted Answer

Methane ($$CH_4)$$

Question 10

Which of the following statements about Van der Waals interactions is correct?

Accepted Answer

They are weak, distance-dependent interactions that arise from fluctuations in electron clouds.

Question 11

If an atom has 17 protons, 18 neutrons, and 17 electrons, what is its atomic number and mass number?

Accepted Answer

Atomic number = 17, Mass number = 35

Question 12

Which of the following best explains why sodium (Na) and chlorine (Cl) form an ionic bond to make table salt (NaCl)?

Accepted Answer

Sodium donates an electron to chlorine, resulting in oppositely charged ions that attract each other.

Question 13

Which of the following is a real-world application of radioactive isotopes?

Accepted Answer

Determining the age of ancient fossils using carbon-14 dating.

Question 14

Which of the following elements is the most abundant in the human body by mass?

Accepted Answer

Oxygen

Question 15

Which of the following best describes the trend of electronegativity in the periodic table?

Accepted Answer

Electronegativity increases from left to right across a period and decreases down a group.

Question 16

A molecule of hydrochloric acid ($$HCl) $$has an electronegativity difference ($$\Delta EN) of 0.9. $$What type of bond is present between hydrogen and chlorine?

Accepted Answer

Polar covalent bond

Question 17

Which of the following is true about the valence shell of an atom?

Accepted Answer

It is the outermost electron shell and determines the chemical behavior of the atom.

Question 18

Which of the following best explains why methane ($$CH_4) is a $$nonpolar molecule?

Accepted Answer

Methane has a symmetrical tetrahedral shape, causing the dipole moments to cancel out.

Question 19

Which of the following is a property of weak chemical interactions such as hydrogen bonds and Van der Waals interactions?

Accepted Answer

They are easily broken and play a key role in the structure and function of biological molecules.

Chapter 2: The Chemical Context of Life – Study Notes

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