which element would you expect to be least reactive

HESI A2

Chemistry HESI A2 Practice Test

1. Which element would you expect to be least reactive?

A. Li
B. Cr
C. Nd
D. Xe

Correct answer: D

Rationale: Xenon (Xe) is a noble gas located in Group 18 of the periodic table. Noble gases are known for their stable and unreactive nature due to having a full outer shell of electrons. Therefore, xenon would be expected to be the least reactive among the given elements. Choice A (Li) is a metal in Group 1 of the periodic table, which tends to be reactive, especially with water. Choice B (Cr) is a transition metal known for its reactivity in some forms. Choice C (Nd) is a rare earth element, which can exhibit varying reactivity depending on the compound or environment.

2. What is the chemical reaction that involves breaking down a compound into component parts?

A. Decomposition
B. Synthesis
C. Combustion
D. Single replacement

Correct answer: A

Rationale: Decomposition is the correct answer because in a decomposition reaction, a compound is broken down into simpler substances. This type of reaction involves the splitting of a compound into its component parts, often through the use of heat, light, or electricity. Synthesis (choice B) is the opposite process where simpler substances are combined to form a more complex compound. Combustion (choice C) is a reaction involving rapid oxidation often accompanied by heat and light. Single replacement (choice D) is a reaction where one element replaces another in a compound.

3. What are positively charged ions called?

A. Neutrons
B. Protons
C. Cations
D. Electrons

Correct answer: C

Rationale: Positively charged ions are called cations. When an atom loses electrons, it becomes positively charged and is referred to as a cation. Neutrons are neutral particles found in the nucleus of an atom, not charged. Protons are positively charged particles in the nucleus. Electrons are negatively charged particles orbiting the nucleus, not positively charged ions.

4. What type of bond is an electrostatic attraction between two oppositely charged ions?

A. Covalent
B. Metallic
C. Ionic
D. Hydrogen

Correct answer: C

Rationale: An ionic bond forms when one atom transfers electrons to another, resulting in the formation of positively and negatively charged ions. The attraction between these oppositely charged ions creates an electrostatic bond, known as an ionic bond. Choice A, covalent bonds, involve the sharing of electrons, not the transfer. Choice B, metallic bonds, occur between metal atoms and involve a 'sea of electrons' that are delocalized. Choice D, hydrogen bonds, are much weaker interactions between hydrogen atoms and other electronegative atoms like oxygen or nitrogen.

5. What is the name for the horizontal rows of the periodic table?

A. groups
B. periods
C. families
D. sets

Correct answer: B

Rationale: In the periodic table, 'periods' are the horizontal rows. Each period corresponds to the energy level occupied by the elements in that row. The other terms mentioned, such as groups, families, and sets, are not used to describe the horizontal rows but rather refer to different aspects of the periodic table organization. 'Groups' are the vertical columns, 'families' are groups of elements with similar properties, and 'sets' is a more generic term not specifically used in the context of the periodic table.