Question

The formula of water is \(\mathrm{H}_{2} \mathrm{O}\). Which of the following is indicated by this formula? Explain your answer. a. the mass of hydrogen is twice that of oxygen in each molecule. b. there are two hydrogen atoms and one oxygen atom per water molecule. c. the mass of oxygen is twice that of hydrogen in each molecule. d. there are two oxygen atoms and one hydrogen atom per water molecule.

Short answer

The correct answer is (b). The formula of water, H₂O, indicates that there are two hydrogen atoms and one oxygen atom per water molecule.

Step-by-step solution

Understanding the Chemical Formula

In the given chemical formula for water, H₂O, H represents hydrogen, and O represents oxygen. The subscript number ₂ after H indicates that there are two hydrogen atoms in a water molecule. There is no subscript number after O, which means that it's just one oxygen atom in a water molecule.

Analyzing the Statements

Let's analyze each statement provided: a. The mass of hydrogen is twice that of oxygen in each molecule. The chemical formula H₂O doesn't reflect anything about the mass of hydrogen and oxygen in the molecule. This statement is not correct. b. There are two hydrogen atoms and one oxygen atom per water molecule. We already established that the formula H₂O indicates that there are two hydrogen atoms and one oxygen atom in each molecule. This statement is correct. c. The mass of oxygen is twice that of hydrogen in each molecule. This statement is also incorrect because it doesn't relate to the ratio of hydrogen and oxygen atoms in the molecular formula H₂O. d. There are two oxygen atoms and one hydrogen atom per water molecule. The formula H₂O doesn't indicate two oxygen atoms and one hydrogen atom. The correct proportion is two hydrogen atoms and one oxygen atom. This statement is incorrect.

Final Answer

Based on our analysis of the chemical formula for water, H₂O, and the given statements, the correct answer is: b. There are two hydrogen atoms and one oxygen atom per water molecule.

Key concepts

Chemical Formula

The chemical formula of a substance provides insight into the elements that make up the substance and the number of atoms of each element present in a molecule. For water, the chemical formula is \(\mathrm{H}_2\mathrm{O}\). This formula is concise and informative both. It indicates that a water molecule is composed of hydrogen and oxygen elements. The subscripts in the formula indicate the number of atoms of each element present. A chemical formula, like \(\mathrm{H}_2\mathrm{O}\), also helps in conveying information about the molecular structure and can give hints towards establishing the proportions of different elements. It is important to understand that while the chemical formula shows the counts of each atom, it does not typically reflect the mass or spatial structure.

Atomic Composition

The term 'atomic composition' refers to the types and numbers of atoms present in a molecule. For water (H₂O), the atomic composition includes:

• Two hydrogen (H) atoms
• One oxygen (O) atom

The subscript numbers in a chemical formula denote the number of each type of atom in one molecule of a substance. In \(\mathrm{H}_2\mathrm{O}\), the subscript 2 following H indicates that each water molecule contains two hydrogen atoms. If no subscript is present, as with oxygen in this case, it means there is only one atom of that element per molecule. This fundamental understanding of atomic composition allows scientists and students alike to understand how simple molecules like water are formed.

Molecular Structure

While the chemical formula \(\mathrm{H}_2\mathrm{O}\) tells us about the types and ratios of atoms, the molecular structure gives us insight into how these atoms are arranged spatially. Water has a bent or angular shape at about 104.5 degrees, coming from the two hydrogen atoms bonded to the oxygen atom. This bent shape is due to the way electrons are distributed in the molecule and the repulsion between electron pairs. The spatial arrangement of atoms impacts the physical properties of water, such as its boiling and melting points, as well as its ability to form hydrogen bonds, which is crucial for many chemical reactions.

Hydrogen and Oxygen Atoms

In a water molecule, the hydrogen and oxygen atoms play crucial roles.

• Hydrogen atoms: Comprising two parts of the water molecule, hydrogen is the simplest and most abundant element in the universe. It consists of one proton and one electron.
• Oxygen atom: The oxygen atom in water is more complex, with eight protons, eight neutrons, and eight electrons. Oxygen is highly electronegative, which means it strongly attracts electrons.

In the \(\mathrm{H}_2\mathrm{O}\) molecule, the oxygen atom is more electronegative than the hydrogen atoms, leading to a polar covalent bond. This means electrons are shared between the oxygen and hydrogen atoms but are pulled more towards the oxygen. This polarity is what gives water its unique properties, like its ability to dissolve many substances or its surface tension.