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Key takeaways
- Gold is the only substance in the list that is not a compound; it is a pure element.
- A compound must contain two or more different elements chemically bonded.
- Silicon dioxide (SiO₂), water (H₂O), and sugar (C₁₂H₂₂O₁₁) all have multiple elements and are compounds.
- To distinguish a compound from an element, check whether the chemical formula shows only one element symbol.
Direct Answer: Gold Is Not a Compound
Among the four substances listed — silicon dioxide (SiO₂), water (H₂O), sugar (C₁₂H₂₂O₁₁), and gold (Au) — gold is not a compound. A compound must contain at least two different elements chemically bonded. Gold consists only of gold atoms, making it an element, not a compound. This distinction is fundamental in chemistry for classifying matter into elements, compounds, and mixtures.
The question “Which is not a compound?” tests understanding of the difference between a pure element and a chemical compound. Silicon dioxide, water, and sugar each contain two or more different elements, whereas gold is a single element on the periodic table.
What Is a Compound?
In chemistry, a compound is a substance formed when two or more different elements bond chemically. Its properties usually differ from those of its constituent elements. For example, water (H₂O) is a liquid at room temperature, while hydrogen and oxygen are gases. Compounds have a fixed elemental ratio defined by a chemical formula.
To identify a compound, check whether the formula contains more than one element symbol. If the formula shows only one element symbol (like Au for gold or O₂ for oxygen), the substance is an element, not a compound. This rule directly applies to the four items in the question.
| Aspect | Explanation |
|---|---|
| Definition | A substance formed by chemical bonding of two or more different elements in fixed proportions |
| Formula | Contains more than one element symbol (e.g., H₂O, CO₂) |
| Properties | Properties differ from those of constituent elements |
| Examples | Water, silicon dioxide, sugar, salt |
| Non-examples | Pure elements like gold, oxygen gas, iron |
Why Silicon Dioxide Is a Compound
Silicon dioxide has the formula SiO₂: each molecule contains one silicon atom and two oxygen atoms. Because it includes two different elements, it qualifies as a chemical compound. For details on the mineral composed of silicon dioxide, refer to our guide. Silicon dioxide is commonly found as quartz and sand, and it exhibits distinct properties that highlight the key advantages of silicon dioxide.
The presence of more than one type of atom in a fixed ratio is the key criterion. Silicon dioxide meets it, so it is undoubtedly a compound, and silicon dioxide as filler is a separate application.
Why Water Is a Compound
Water is represented by H₂O, consisting of two hydrogen atoms and one oxygen atom. Hydrogen and oxygen are different elements that form covalent bonds to create water molecules. Water is a common example of a compound, and its chemical behavior is completely different from that of hydrogen or oxygen gas.
Because water contains two different elements in a definite proportion, it is a compound. This makes water a classic reference point for understanding compounds.
Why Sugar Is a Compound
Table sugar (sucrose) has the formula C₁₂H₂₂O₁₁, containing carbon, hydrogen, and oxygen atoms. With three different elements and a specific bonding structure, sugar is a compound classified as a carbohydrate. Its properties, such as sweetness and solubility, arise from the arrangement of these elements.
Since sugar consists of more than one element chemically combined, it meets the definition of a compound. Among the four options, sugar is clearly a compound.
Why Gold Is Not a Compound
Gold is represented by the symbol Au on the periodic table. It contains only gold atoms and no other elements. A substance made of only one type of atom is an element, not a compound. Therefore, gold is the only item in the list that is not a compound.
This distinction is crucial: elements cannot be broken down into simpler substances by chemical means, while compounds can be separated into their constituent elements. As a pure element, gold does not qualify as a compound.
Summary: Recognizing Compounds vs. Elements
To determine whether a substance is a compound, check its chemical formula. If the formula includes two or more different element symbols (e.g., SiO₂, H₂O, C₁₂H₂₂O₁₁), it is a compound. If the formula contains only one element symbol (e.g., Au, O₂, N₂), it is an element. In the given list, gold is the only element, making it the correct answer to “Which is not a compound?”.
This knowledge is foundational for chemistry students and anyone studying matter. Understanding the difference between elements and compounds helps in classifying substances and predicting their behavior.
Frequently asked questions
Is sugar a compound?
Yes, table sugar (sucrose) is a compound with the formula C₁₂H₂₂O₁₁, containing carbon, hydrogen, and oxygen atoms bonded together.
Is gold an element or a compound?
Gold is an element. Its symbol is Au, and it consists only of gold atoms, not a combination of different elements.
What makes silicon dioxide a compound?
Silicon dioxide (SiO₂) is a compound because it contains two different elements—silicon and oxygen—chemically bonded in a fixed ratio.
Can elements be compounds?
No, elements are pure substances made of only one type of atom, while compounds are made of two or more different elements. They are mutually exclusive categories.
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