Question

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

Short answer

(a) Hydrogen is an element, (b) Water is a compound, (c) Gold is an element, (d) Sugar is a compound

Step-by-step solution

Classify Hydrogen

Firstly, it's important to note that hydrogen is listed in the periodic table of elements. Hence, hydrogen is an element.

Classify Water

Water, scientifically known as H2O, is formed by the combination of two elements: two Hydrogen molecules and one Oxygen molecule. As a result of this, water (H2O) is classified as a compound.

Classify Gold

Gold is a chemical element with the symbol Au (from Latin: aurum) and atomic number 79 making it an element, not a compound.

Classify Sugar

Sugar, which is typically represented by the formula C12H22O11, is formed from the combination of the three elements: Carbon, Hydrogen, and Oxygen. Therefore, Sugar is classified as a compound.

Key concepts

Chemical Elements

Let's delve into the fascinating world of chemical elements. Chemical elements are pure substances consisting of only one type of atom. They serve as the building blocks for all matter in the universe. Each element has a unique number of protons in its nucleus, known as the atomic number. This defines the element and its properties. Examples include hydrogen (H), gold (Au), and oxygen (O).
Elements are represented by symbols, usually one or two letters, that are universally recognized. For instance, gold is represented by 'Au' and hydrogen by 'H'.

• They cannot be broken down into simpler substances by chemical means.
• They can exist in various forms, such as gases (like hydrogen and oxygen), solids (like gold and copper), or even liquids (like mercury at room temperature).

Understanding elements is essential for comprehending the complex world of chemistry, as they combine in countless ways to form different substances.

Compounds

Compounds are a crucial concept in chemistry as they are substances formed from two or more different elements that are chemically bonded together. The properties of a compound are distinct from the properties of the elements that compose it. For example, water is a compound made from hydrogen and oxygen, and it behaves quite differently from either of those elements alone.
Each compound has a definite and constant composition, symbolized using chemical formulas. Water, for instance, is represented by H_2O:

• Compounds are pure substances with consistent properties and composition.
• They can be broken down into simpler substances (elements) through chemical reactions.
• Common compounds include water (H_2O), carbon dioxide (CO_2), and sugar (C_12H_22O_11).

Grasping the nature of compounds is essential for understanding a wide range of chemical reactions and biological processes.

Periodic Table

The periodic table is like a roadmap for chemists. It's a comprehensive chart that organizes all known chemical elements based on their atomic number, electron configurations, and recurring chemical properties. Invented by Dmitri Mendeleev, the periodic table provides critical information about the elements, such as their symbol, atomic number, and relative atomic mass.
Here's why it’s so useful:

• Elements in the same column, or group, have similar properties. For instance, the noble gases like helium and neon are all in the same group and share lack of reactivity.
• Periods are the rows in the table, indicating energy levels for electrons.
• It allows chemists to predict the behavior of elements in reactions and find elements with similar chemical properties easily.

The periodic table is a tool that, despite its inception in the 19th century, continues to be indispensable in modern chemistry.