Test Your Knowledge of Molecules and Compounds Quiz
This quiz will challenge your understanding of how atoms combine to form molecules and compounds, including chemical formulas, bonding types, and properties of different substances. It’s a great way to reinforce your knowledge and master the fundamentals of chemistry.
MOLECULES AND COMPOUNDS QUIZ – 25 QUESTIONS
1. A molecule is formed when
A. Atoms bond chemically
B. Elements are mixed physically
C. Atoms gain electrons
D. Electrons move freely
2. A compound contains
A. Only one element
B. Two or more elements chemically combined
C. Mixtures of elements
D. Ions only
3. Water (H₂O) is an example of
A. Element
B. Molecule
C. Mixture
D. Salt
4. Molecular formula shows
A. Number of atoms and type of elements in a molecule
B. Only elements present
C. Mass of atoms
D. Type of bond only
5. Ionic compounds are formed between
A. Two metals
B. Metal and non-metal
C. Two non-metals
D. Proton and neutron
Molecules And Compounds Quiz
6. Covalent compounds are formed by
A. Sharing electrons between atoms
B. Transferring electrons
C. Losing protons
D. Gaining neutrons
7. The chemical formula for carbon dioxide is
A. CO
B. CO₂
C. C₂O
D. C₂O₂
8. Salt (NaCl) is an example of
A. Molecular compound
B. Ionic compound
C. Element
D. Mixture
9. Oxygen molecule (O₂) is held together by
A. Ionic bond
B. Covalent bond
C. Hydrogen bond
D. Metallic bond
10. A mixture differs from a compound because
A. Its components are chemically bonded
B. Its components can be separated physically
C. It has a fixed ratio of elements
D. It has new chemical properties
Molecules And Compounds Quiz
11. Empirical formula shows
A. Actual number of atoms in a molecule
B. Simplest ratio of atoms of elements
C. Types of bonds only
D. Molecular weight
12. Molecular weight of a molecule is
A. Sum of atomic numbers
B. Sum of relative atomic masses of all atoms in the molecule
C. Number of electrons
D. Number of moles
13. Hydrogen chloride (HCl) is
A. Ionic compound
B. Covalent compound
C. Mixture
D. Salt
14. Covalent bonds usually form between
A. Metals only
B. Non-metals only
C. Metals and non-metals
D. Metals and metals
15. Ionic bonds usually form between
A. Two metals
B. Non-metals only
C. Metal and non-metal
D. Hydrogen and helium
Molecules And Compounds Quiz
16. Molecules of a compound
A. Always have the same proportion of elements
B. Can have varying proportions
C. Are never bonded
D. Are mixtures
17. Carbon monoxide (CO) is
A. Ionic compound
B. Covalent compound
C. Element
D. Mixture
18. Hydrogen bonding is
A. A weak attraction between a hydrogen atom and electronegative atom in different molecules
B. A strong covalent bond
C. A type of ionic bond
D. Metallic bonding
19. Molecular compounds are generally
A. Conductors of electricity in solid state
B. Poor conductors of electricity
C. Metals
D. Insoluble in all solvents
20. Ionic compounds generally
A. Conduct electricity when solid
B. Conduct electricity when molten or dissolved in water
C. Are always gases
D. Are always liquids
21. Electrolytes are substances that
A. Dissolve in water to give free ions
B. Are insoluble
C. Form covalent bonds in water
D. Never conduct electricity
22. The lattice structure in ionic compounds
A. Gives them high melting and boiling points
B. Makes them soluble only in non-polar solvents
C. Makes them soft
D. Makes them liquids at room temperature
23. Molecular polarity affects
A. Boiling and melting points
B. Solubility in water
C. Physical and chemical properties
D. All of the above
24. Oxygen (O₂) and nitrogen (N₂) are examples of
A. Diatomic molecules
B. Triatomic molecules
C. Polyatomic molecules
D. Monatomic elements
25. A chemical reaction that forms a compound from its elements is called
A. Decomposition
B. Combination (Synthesis) reaction
C. Displacement
D. Combustion
Molecules And Compounds Quiz Answers And Explanations
1. A – A molecule is formed when two or more atoms chemically bond, resulting in a distinct particle with new properties. Physical mixing or electron movement alone does not produce molecules.
2. B – A compound contains two or more elements chemically combined in a fixed ratio. Unlike mixtures, compounds have properties different from their constituent elements.
3. B – Water (H₂O) is a molecule because it consists of hydrogen and oxygen atoms bonded covalently.
4. A – The molecular formula indicates the exact number and type of atoms in a molecule, e.g., H₂O has 2 H and 1 O atom.
5. B – Ionic compounds form between metals and non-metals where electrons are transferred from metal to non-metal.
6. A – Covalent compounds form when atoms share electrons to achieve stable outer shells.
7. B – Carbon dioxide has the formula CO₂, meaning one carbon atom and two oxygen atoms per molecule.
8. B – NaCl is ionic because sodium (metal) transfers an electron to chlorine (non-metal), forming a lattice of ions.
9. B – Oxygen molecule (O₂) is held together by a double covalent bond, sharing two pairs of electrons between atoms.
10. B – Mixtures can be separated physically because their components are not chemically bonded. Compounds require chemical methods to separate elements.
11. B – Empirical formula shows the simplest whole-number ratio of elements in a compound. For example, CH₂O for glucose (C₆H₁₂O₆).
12. B – Molecular weight is the sum of relative atomic masses of all atoms in the molecule, e.g., H₂O = 2(1) + 16 = 18.
13. B – HCl is covalent in the gas phase but forms ions in water. In pure form, the hydrogen and chlorine share electrons.
14. B – Covalent bonds form between non-metal atoms sharing electrons.
15. C – Ionic bonds usually form between metals and non-metals through electron transfer.
16. A – Molecules of a compound have fixed proportions of elements; this ensures consistent chemical properties.
17. B – CO is a covalent compound with one carbon atom triple-bonded to one oxygen atom.
18. A – Hydrogen bonding is a weak intermolecular attraction, critical in water’s high boiling point and DNA structure.
19. B – Molecular compounds are poor conductors because they do not have free ions in solid form.
20. B – Ionic compounds conduct electricity when molten or in solution because ions are free to move.
21. A – Electrolytes dissociate in water into ions, allowing conduction of electricity.
22. A – Ionic lattices create strong electrostatic attraction, resulting in high melting and boiling points.
23. D – Molecular polarity affects solubility, melting/boiling points, and other physical and chemical properties.
24. A – Oxygen (O₂) and nitrogen (N₂) exist as diatomic molecules, two atoms bonded covalently.
25. B – Combination (synthesis) reactions involve forming a compound from two or more elements, e.g., 2H₂ + O₂ → 2H₂O.
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