NEX Basic Chemistry: Atomic Structure and Chemical Reactions 2 — Questions and Answers

Question 1: How many electrons can the second energy level (shell) of an atom hold?

2
6
8 (Correct answer)
18

Correct answer: 8

The second electron shell can hold a maximum of 8 electrons, following the formula 2n² where n is the shell number (2 x 2² = 8).

Electron shells (energy levels) surround the nucleus and hold electrons in specific capacities determined by the formula 2n². The first shell (n=1) holds 2 electrons, the second (n=2) holds 8, the third (n=3) holds 18, and the fourth (n=4) holds 32. Understanding electron configuration is essential in nursing for comprehending how atoms bond to form molecules important in pharmacology and biochemistry. For example, the electron configuration of sodium (Na) determines its tendency to lose one electron and form Na⁺ ions critical for fluid balance.

Question 2: Which type of chemical bond involves the sharing of electron pairs between atoms?

Ionic bond
Covalent bond (Correct answer)
Hydrogen bond
Metallic bond

Correct answer: Covalent bond

Covalent bonds form when two atoms share one or more pairs of electrons to achieve stable electron configurations.

Covalent bonds occur when atoms share electrons rather than transferring them. Each shared pair of electrons constitutes one covalent bond. Single bonds share one pair, double bonds share two pairs, and triple bonds share three pairs. Covalent bonds are fundamental to organic chemistry and biological molecules. Water (H₂O) has covalent bonds between oxygen and hydrogen atoms. In nursing, understanding covalent bonding helps explain drug molecular structures, enzyme-substrate interactions, and the behavior of biological molecules like proteins, carbohydrates, and nucleic acids.

Question 3: What is the pH of a neutral solution at 25°C?

0
5
7 (Correct answer)
14

Correct answer: 7

A neutral solution has a pH of 7, where the concentration of hydrogen ions equals the concentration of hydroxide ions.

The pH scale measures the acidity or alkalinity of a solution, ranging from 0 (most acidic) to 14 (most alkaline). At pH 7, the concentration of H⁺ ions equals the concentration of OH⁻ ions (both at 10⁻⁷ mol/L at 25°C). Pure water is the classic example of a neutral solution. In nursing, pH is critical for understanding blood gas analysis (normal blood pH is 7.35-7.45), medication stability, and body fluid balance. A blood pH below 7.35 indicates acidosis, while above 7.45 indicates alkalosis, both of which can be life-threatening.

Question 4: In a chemical equation, what does a catalyst do?

Increases the products formed
Speeds up the reaction without being consumed (Correct answer)
Changes the equilibrium position
Adds energy to the reaction

Correct answer: Speeds up the reaction without being consumed

A catalyst increases the rate of a chemical reaction by lowering the activation energy without being consumed or permanently altered in the process.

Catalysts work by providing an alternative reaction pathway with a lower activation energy, allowing more reactant molecules to successfully convert to products at a given temperature. The catalyst participates in the reaction mechanism but is regenerated, so its amount remains unchanged. In biological systems, enzymes serve as catalysts for virtually all biochemical reactions. For nursing students, understanding catalysts is crucial for grasping how enzymes like amylase, lipase, and various liver enzymes function, and why enzyme levels in blood tests indicate organ damage.

Question 5: Which of the following is an example of a decomposition reaction?

2H₂ + O₂ → 2H₂O
2H₂O → 2H₂ + O₂ (Correct answer)
NaCl + AgNO₃ → AgCl + NaNO₃
CH₄ + 2O₂ → CO₂ + 2H₂O

Correct answer: 2H₂O → 2H₂ + O₂

The breakdown of water into hydrogen and oxygen is a decomposition reaction because a single compound breaks down into two or more simpler substances.

Decomposition reactions follow the pattern AB → A + B, where a single compound breaks down into two or more simpler substances. The electrolysis of water (2H₂O → 2H₂ + O₂) is a classic example. Option A is a synthesis (combination) reaction, option C is a double replacement reaction, and option D is a combustion reaction. In the human body, decomposition reactions are essential in metabolism: catabolism breaks down complex molecules like glycogen into glucose, proteins into amino acids, and triglycerides into fatty acids and glycerol. Understanding these reaction types helps nurses comprehend metabolic pathways and drug metabolism.

Question 6: What is the atomic number of an element determined by?

Number of neutrons
Number of protons (Correct answer)
Number of electrons
Total mass of the nucleus

Correct answer: Number of protons

The atomic number is determined by the number of protons in the nucleus of an atom, which defines the element's identity.

The atomic number (Z) equals the number of protons in an atom's nucleus and uniquely identifies each element. For example, hydrogen always has 1 proton (Z=1), carbon has 6 (Z=6), and oxygen has 8 (Z=8). In a neutral atom, the number of electrons equals the number of protons. Neutrons contribute to atomic mass but not atomic number; atoms with the same number of protons but different numbers of neutrons are called isotopes. In nuclear medicine and nursing, understanding atomic structure explains how radioactive isotopes like Iodine-131 and Technetium-99m work in diagnostic imaging and cancer treatment.

NEX Basic Chemistry: Atomic Structure and Chemical Reactions 2

How many electrons can the second energy level (shell) of an atom hold?