Question

Classify each of the following substances as an element or a compound: (a) hydrogen, (b) water, (c) gold, (d) sugar.

Short answer

(a) Element, (b) Compound, (c) Element, (d) Compound.

Step-by-step solution

Understand the Difference

An element is a pure substance that cannot be broken down into simpler substances by chemical means. A compound is a substance composed of two or more elements chemically combined in a fixed proportion.

Classify Hydrogen

Hydrogen is a gas found on the periodic table with the atomic number 1. It is composed of only one type of atom, which categorizes it as an element.

Classify Water

Water is composed of two hydrogen atoms and one oxygen atom, chemically combined in the formula \( H_2O \). This makes it a compound.

Classify Gold

Gold is a pure substance found on the periodic table with the atomic number 79. It consists of only one type of atom, classifying it as an element.

Classify Sugar

Sugar, such as sucrose, is composed of carbon, hydrogen, and oxygen atoms in a chemical formula \( C_{12}H_{22}O_{11} \). It is therefore a compound.

Key concepts

Element

An element is one of the simplest substances in chemistry. It consists of only one type of atom and cannot be broken down into anything simpler by any chemical means. You will find elements arranged in the periodic table, where they are organized by increasing atomic number. Each element has unique properties, like its own symbol and atomic structure. Examples include hydrogen, which is the lightest element, and gold, known for its high density and glossy appearance. Understanding elements is crucial because they are the building blocks of all matter around us.

Compound

A compound is a substance formed when two or more different elements join together chemically. When the atoms of these elements bond, they create a substance with its own unique characteristics, different from the individual elements it contains. For example, water is a compound made of hydrogen and oxygen. Compounds always have a fixed proportion of elements, represented by chemical formulas, such as the formula for water, \( H_2O \). Compounds are everywhere, from the sugar you sweeten your tea with, to the carbon dioxide you exhale.

Atomic Number

The atomic number of an element is a fundamental concept in chemistry. It is the total number of protons found in the nucleus of an atom of the element. Since each element has a unique number of protons, the atomic number uniquely identifies it on the periodic table. For instance, hydrogen's atomic number is 1, which means it has one proton, while gold's atomic number is 79, indicating it has 79 protons. The atomic number not only determines the position of an element on the periodic table but also influences the element's chemical properties.

Chemical Formula

Chemical formulas are essential for representing compounds. They show us what elements are in a compound and in what proportion. A chemical formula uses element symbols and numerical subscripts to convey this information. For example, the chemical formula for water \( H_2O \) indicates two hydrogen atoms for every oxygen atom within each water molecule. Similarly, sugar, or sucrose, is represented by the complex formula \( C_{12}H_{22}O_{11} \), showing it consists of carbon, hydrogen, and oxygen. Understanding these formulas is key to grasping how compounds are structured.