Atoms, Elements and Compounds：练习题

Which of the following describes a substance that is made up of two or more different types of atoms chemically bonded together in a fixed ratio?

A sample of gas is collected and found to consist of molecules where each molecule contains two oxygen atoms chemically bonded together. Another sample contains molecules consisting of one carbon atom and two oxygen atoms chemically bonded together. Which statement correctly identifies the classification of these two samples?

Which of the following correctly describes a compound compared to an element?

A scientist analyzes a substance and finds it can be broken down into simpler substances only through chemical means, such as electrolysis, but not by physical means like filtration. The substance has a fixed melting point. What is this substance most likely to be?

An atom of Fluorine has an atomic number of 9 and a mass number of 19. State the number of neutrons present in this atom.

A sample of magnesium reacts with oxygen to form magnesium oxide. Based on the concept of Atoms, Elements and Compounds, describe how the physical properties of the resulting compound differ from the original elements and state whether this change is physical or chemical.

In the context of Atoms, Elements and Compounds, a molecule of sulfuric acid is represented by the formula \( H_{2}SO_{4} \). Calculate the total number of atoms present in three molecules of sulfuric acid and identify how many different elements are involved.

Consider the concepts of Atoms, Elements and Compounds.

(a) An atom of Carbon-12 has an atomic number of 6 and a mass number of 12. State the number of protons, neutrons, and electrons in a neutral atom of Carbon-12. (3 marks)
(b) Distinguish between a compound and a mixture. Provide one example of each to illustrate your answer. (2 marks)

Chemical substances can be classified as atoms, elements, compounds, or mixtures.

(a) Using the Dalton model of the atom, explain the difference between a molecule of an element (e.g., \( O_{2} \)) and a molecule of a compound (e.g., \( H_{2}O \)). (2 marks)
(b) A sample contains iron filings and sulfur powder. Describe a physical method to separate them. If the mixture is heated strongly, a black solid (iron(II) sulfide) is formed. Is this black solid a mixture or a compound? Justify your answer with two reasons. (4 marks)
(c) Represent the formation of water from hydrogen and oxygen using a word equation. (1 mark)