Have you heard your parents speak of pure and impure water? Do you know what that means? In this chapter, we will tell you more about it! Here, we will cover the concepts of pure substances. You will get a detailed information about the types of pure substances and their properties. This is a very interesting concept and an important one from the exam point of view.
Types of Substances
Substances are basically classified into two types. They are:
- Pure Substance: The substances that are free from any kind of mixture and contain only one kind of particle are pure substances. Examples of pure substances include iron, aluminum, silver, and gold.
- Mixtures: Substances that have two or more different particles are mixtures. Examples of mixture include the salt solution which is a ‘mixture’ of two components, salt, and water.
Learn more about the Suspension: a Heterogeneous mixture of two or more substances.
Now that we know what are the basic types of substances, let us cover the concept of pure substances in more detail.
Types of Pure Substances
Based on their chemical composition, pure substances are classified into two categories:
A pure substance that has only one kind of atom and cannot be broken into two or more simpler substances by physical or chemical means is an element. Therefore, when you break down gold, you still get gold. It is an element.
Browse more Topics under Is Matter Around Us Pure
- Physical and Chemical Changes
- Introduction and What is a Mixture?
- Separating the Components of Mixture
- What is a Solution?
- Concentration of a Solution
- What is a Colloidal Solution?
- What is a Suspension?
Characteristics of Elements
- An element is homogeneous in nature; it is a pure substance, made up of only one kind of atoms. For example, iron and silver are made of only iron and silver atoms. Therefore, they are elements.
- An element cannot be broken down into simpler substances by any physical or chemical methods such as heat, light electricity, or chemical reactions with other substances. Therefore, when you break a piece of iron into smaller pieces or heat it, the piece still remains as the element iron.
- An atom is the smallest unit of an element that shows all the properties of it. Hence, an atom of iron shows all the properties of that metal.
- Elements have sharp melting and boiling points.
- Elements are classified as metals, non-metals, and metalloids.
Now, let us look at what metals are and what their properties are.
Metals are the elements that readily lose an electron to form a positive ion or a cation. Example: Gold, silver, copper, iron, potassium etc. Properties of Metals are:
- Metals have lustre. Example: Gold.
- Metals are good conductors of heat and electricity. As metals have free electrons in them, they are able to conduct heat and electricity. Example: Copper
- Metals are malleable, meaning that it’s easy to hammer them into thin sheets. Example: Aluminum
- Metals are ductile, which means they can be drawn into wires.
- Metals are sonorous. They give a ringing sound when they are hit by a hard iron rod. Example: copper.
- Almost all metals are solids at room temperature.
Yet, there are some exceptions to this. For example, Sodium and potassium are soft metals. Tungsten is a poor conductor of electricity and so on. Therefore, it is good if you are aware of the exceptions.
Non – metals are those elements that readily gain an electron(s) to form a negative ion or anion. Examples include Hydrogen, Oxygen, Iodine etc. Properties of non-metals are:
- Non-metals exist as solids, liquids, and gases. Example: Silicon and carbon are solids; bromine is a liquid; chlorine, fluorine, and oxygen are gases.
- Non-metals are non-lustrous, that is, they have a dull appearance. Example: The surfaces of sulfur and phosphorus do not shine.
- Most non-metals have very low density. Example: Oxygen and nitrogen are lighter than air.
- Yet, we have the diamond that is a form of carbon. Diamond is one of the strongest known substances.
- They are not malleable.
- Non-metals, except for carbon are not ductile.
- They are bad conductors of heat and electricity. Yet, graphite is a good conductor of electricity.
- Non-metals have low melting and boiling points.
The elements which have intermediate properties between those of metals and non-metals are called metalloids. They are amphoteric in nature. Metalloids react both with acids and bases. Examples include boron, silicon, and germanium.
A pure substance, basically composed of two or more elements and chemically combined in a fixed proportion is called a compound. Therefore, water is a compound. It has two elements, hydrogen and oxygen, combined in a fixed ratio.
Properties of a Compound
- A compound is homogeneous in nature, made up of the same type of molecules.
- The components of a compound cannot be separated by physical methods. But, you can separate them by chemical and electrochemical methods. Therefore, water can be broken down into hydrogen and oxygen by electrolysis.
- A compound has a fixed composition.
- It has a distinct set of properties which is not similar with the properties of its constituent elements.
- A compound has a sharp melting and boiling point.
Question For You
Q1. Name one non-metal good conductor of electricity.
Q2. Name one metal that exists in liquid form at room temperature.
Q3. Name one compound that you can break down by the process of electrolysis.
Q4. Which forms do non-metals exist in?
Ans: Solid, liquid and gas.