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Exploring Diversity of Matter by Its Chemical Composition

Learn how the world around us is made up of elements, compounds, and mixtures, and how to distinguish between them based on their properties and composition.

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Learning Outcomes

After studying this chapter, you should be able to:

• Understand how chemical composition of matter relates to our daily lives
• Identify the basic building blocks of matter and their chemically combined derivatives
• Distinguish between elements, compounds, and mixtures
• Explain the properties of different types of mixtures, including solutions and suspensions
• Apply knowledge of chemical composition to make informed decisions about materials and sustainability

To recycle waste materials correctly, we need to know what they are made up of. In Chapter 2, we learned about the physical properties of matter. In this chapter, we will learn about the chemical composition of matter, which is equally important for understanding how to safely and effectively manage the materials around us.

Let's Learn

• How is understanding the chemical composition of matter applicable to our daily lives?
• What are the basic building blocks of matter and their chemically combined derivatives?
• What matter comprises elements and/or compounds that are not chemically combined?
• How can we distinguish between elements, compounds, and mixtures?

Categories of Matter

Click on any category to learn more about its principles, examples, and properties.

Elements

The basic building blocks of matter that cannot be broken down into simpler substances through chemical means.

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Compounds

Substances formed when two or more elements chemically combine in a fixed proportion by mass.

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Mixtures

Combinations of two or more substances that are not chemically combined and can be separated by physical means.

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Solutions

A special type of mixture where one substance (solute) dissolves completely in another substance (solvent).

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Suspensions

Mixtures containing insoluble substances in a solvent, where particles can settle and separate over time.

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Real-World Applications

Understanding the chemical composition of matter has numerous applications in our daily lives:

Food and Nutrition

Understanding food ingredients and preservatives helps us make informed choices about what we eat. Food labels list compounds and elements that make up our food.

Recycling

Knowledge of what materials are made of helps in proper waste segregation. Recycling bins in Singapore are designed for specific types of materials based on their composition.

Medicine

Pharmaceutical companies design medications with specific chemical compositions to treat illnesses. Understanding how compounds interact with our bodies is crucial for medical advancement.

Construction

Building materials like concrete are carefully formulated mixtures. Different compositions provide varying properties for specific applications in construction.

Product Safety

Awareness of harmful substances like melamine helps prevent contamination incidents. In 2008, melamine in milk powder caused serious health issues due to its similar chemical structure to proteins.

Environmental Protection

Understanding air pollutants helps in creating standards like Singapore's Pollutant Standards Index (PSI). It helps individuals make informed decisions about outdoor activities during periods of poor air quality.

Materials Engineering

Creating new materials like steel (a mixture of iron, carbon, and other elements) that have superior properties to their constituent parts. Materials engineers develop innovative solutions like carbon fiber and self-cleaning paints.

Heritage Conservation

Traditional materials like chunam plaster, made from seashells and other natural ingredients, are used in conservation of heritage buildings in Singapore like St Andrew's Cathedral and the Arts House.

Understanding Matter

Matter can be classified into three main categories: elements, compounds, and mixtures. Each has distinct properties and characteristics.

Elements in the Periodic Table

There are 118 known elements, represented by chemical symbols and arranged in the Periodic Table based on their properties. Elements are the building blocks from which all matter is made.

Chemical Compounds

Compounds are formed when elements combine chemically in a fixed proportion. Water (H₂O), carbon dioxide (CO₂), and sodium chloride (NaCl) are common examples we encounter daily.

Comparison Between Elements, Compounds, and Mixtures

Property	Elements	Compounds	Mixtures
Composition	Only one element	Two or more elements	Two or more elements or compounds
Formation	Mostly a naturally occurring process	A chemical reaction	A physical change
Proportion of Constituents	-	Fixed	Not fixed
Properties of Constituents	-	Not retained	Retained
Separation of Constituents	-	Not easy	Easy

Common salt - a compound made of sodium and chlorine elements

Copper coins - made primarily of the element copper

Salt solution - a mixture of salt (solute) and water (solvent)

Dirty water - a suspension with insoluble particles in water

Did You Know?

In 2018, an artificial intelligence program called Atom2Vec successfully distinguished between different elements after analyzing names of compounds containing two or more elements. It was able to group elements according to their chemical properties, just like the periodic table!

Take Note!

Hydrogen and oxygen react chemically to form water. It takes a lot of energy to reverse this chemical reaction. However, not all chemical reactions are reversible. The burning of paper is a chemical reaction. Do you think you can recover the same piece of paper after it is burnt?

Test Your Knowledge

Check your understanding of the chemical composition of matter with this quick quiz!

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1. Which of the following best describes an element?

A substance that cannot be broken down into simpler substances by chemical means

A substance formed when two elements combine chemically

A combination of two or more substances that are not chemically combined

A mixture of different elements in any proportion

2. Which of the following is a compound?

Oxygen (O₂)

Water (H₂O)

Iron (Fe)

Air

3. What is the main difference between a compound and a mixture?

Compounds are naturally occurring; mixtures are man-made

Compounds contain only two elements; mixtures can contain more

Compounds have elements chemically combined in fixed proportions; mixtures do not

Compounds can be easily separated; mixtures cannot be separated

4. Which of the following is a mixture?

Sodium chloride (NaCl)

Carbon dioxide (CO₂)

Air

Water (H₂O)

5. In a solution, what is the substance that dissolves called?

Solute

Solvent

Solution

Suspension

6. Which property is characteristic of a suspension?

Light passes through it completely

Particles cannot be seen

Particles never settle

Insoluble particles can settle over time

7. What is the most abundant element in air?

Nitrogen

Oxygen

Carbon dioxide

Hydrogen

8. Which factors affect the rate of dissolving a solute in a solvent?

Only the size of solute particles

Only the temperature of the solvent

Only the rate of stirring

Size of solute particles, temperature of solvent, and rate of stirring

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Elements

Definition

Examples

Periodic Table

What Are Elements?

Elements are the basic building blocks of living and non-living matter. They cannot be broken down into simpler substances.

At present, there are 118 known elements. They are represented by chemical symbols and grouped in a table called the Periodic Table of Elements.

As the elements are arranged based on their properties, the periodic table allows us to predict patterns in the properties of different elements. For example, we can tell from the periodic table which elements are metals and which are non-metals.

The diversity of matter we see around us is made up of one or more elements in the periodic table.

Key Characteristics

• Elements contain only one type of atom
• They cannot be broken down by chemical means
• Each element has a unique chemical symbol
• Elements are arranged in the Periodic Table based on their properties
• Most elements occur naturally, but some are artificially created
• Examples include hydrogen (H), oxygen (O), carbon (C), and iron (Fe)

Scientific Endeavour

Technetium is element number 43, represented by the chemical symbol Tc in the Periodic Table of Elements. It is the first element to be artificially created in a laboratory. In early 1937, some researchers managed to create technetium using a sample of element number 42, which was obtained from an unwanted laboratory apparatus. They also proved that element number 43 cannot exist naturally due to its unstable nature. The creation of technetium was made possible due to the open-mindedness of the researchers involved. It encouraged other researchers to create new elements to add to the periodic table.

Examples of Elements in Everyday Objects

Copper (Cu) - Used in coins and electrical wiring

Aluminum (Al) - Used in cookware and packaging

Neon (Ne) - Used in illuminated signs

Carbon (C) - Used in pencil lead (graphite)

Liquid Nitrogen

Nitrogen (N) in liquid form is extremely cold (-196°C) and is used in making ice cream, freezing biological samples, and in dermatology.

Gold

Gold (Au) is a precious metal used in jewelry, electronics, and as a financial asset due to its rarity and resistance to corrosion.

Silicon

Silicon (Si) is the main component in computer chips, solar panels, and is the second most abundant element in Earth's crust.

Fun Fact

The oxygen we breathe doesn't exist as a single oxygen atom (O) but as a molecule made up of two oxygen atoms (O₂). When lightning strikes, it can convert oxygen to ozone, which consists of three oxygen atoms (O₃).

The Periodic Table of Elements

Properties of the Periodic Table

The Periodic Table organizes all known elements in rows (periods) and columns (groups) based on their properties. Elements in the same group have similar chemical properties.

Metals are generally found on the left side of the table, while non-metals are on the right. Elements can be classified as:

• Metals: Generally solid (except mercury), shiny, good conductors of heat and electricity
• Non-metals: Can be solid, liquid, or gas, usually poor conductors
• Metalloids: Have properties of both metals and non-metals

Reading the Periodic Table

Each element box in the Periodic Table typically contains:

• Atomic number (the number of protons)
• Element symbol (1-2 letters)
• Element name
• Atomic weight

The table is organized by increasing atomic number, and elements in the same group (column) have similar electron configurations and chemical behaviors.

Compounds

Definition

Examples

Properties

What Are Compounds?

Compounds consist of two or more elements that are chemically combined together. When elements combine chemically, they form a new substance with properties different from the original elements.

The constituent elements of a compound are always chemically combined in a fixed proportion by mass. This means that a pure compound always contains the same elements in the same ratio, regardless of how it was made or where it came from.

Once elements form a compound, they cannot be easily separated back into the original elements through physical means. It typically requires a chemical reaction to break down a compound.

Key Characteristics

• Compounds have different properties from their constituent elements
• Elements combine in fixed proportion by mass
• Compounds form through chemical reactions
• Cannot be separated by physical means
• Energy changes (usually heat) occur during formation
• Each compound has a unique chemical formula

hydrogen (gas) + oxygen (gas) → water (liquid)

2H₂ + O₂ → 2H₂O

Take Note!

Hydrogen and oxygen react chemically to form water. It takes a lot of energy to break down water into hydrogen and oxygen. A lot of energy is needed to break the chemical bonds in the water molecule.

Examples of Common Compounds

Sodium Chloride (NaCl) - Common salt used as a food preservative

Sodium Hydrogen Carbonate (NaHCO₃) - Baking soda used in cooking

Water (H₂O) - Essential for all life forms

Carbon Dioxide (CO₂) - Used in photosynthesis, present in air

Calcium Carbonate (CaCO₃)

Found in marble, limestone, and eggshells. Contains calcium, carbon, and oxygen. Used in building materials, antacids, and as a calcium supplement.

Silicon Dioxide (SiO₂)

The main component of glass. Formed by heating sand (silicon dioxide) with other compounds. Used for bottles, windows, and other containers.

Ammonia (NH₃)

Made up of nitrogen and hydrogen. Used in cleaning products, fertilizers, and refrigeration systems.

Fun Fact

Plastics are compounds made mainly of carbon, hydrogen, and oxygen. The versatility of carbon to form different types of bonds makes plastics so diverse in their properties and applications.

Properties of Compounds

Distinct Properties

Compounds do not have the same properties as their constituent elements. The chemical combination creates entirely new properties.

For example:

• Hydrogen and oxygen are gases at room temperature, but they form water, which is a liquid
• Sodium is a highly reactive metal and chlorine is a toxic gas, but they form sodium chloride (table salt), which is safe to eat
• Carbon is a solid and oxygen is a gas, but they form carbon dioxide, which is a gas

The drastic change in properties shows that a chemical reaction has taken place, forming a new substance with its own unique properties.

Energy Changes

The formation of compounds typically involves energy changes:

• Many compounds release energy when they form (exothermic reactions)
• Some compounds require energy to form (endothermic reactions)
• Breaking a compound back into its elements usually requires energy
• For example, electrolysis (shown in the textbook) uses electricity to break water into hydrogen and oxygen

These energy changes are evidence of the chemical bonds forming or breaking between atoms.

Electrolysis of water: An electric current is passed through water to break it down into hydrogen and oxygen gases.

Search It

What are some differences in the chemical and physical properties of some compounds and their constituent elements? Find out about the properties of sugar and sand, and of their constituent elements.

Mixtures

Definition

Examples

Properties

What Are Mixtures?

A mixture is made up of two or more elements and/or compounds that are not chemically combined. The components in a mixture retain their original properties and can be physically separated.

You might have taken a cough mixture to get well when you were ill. There is one mixture that we need all the time - air! Air contains various substances such as nitrogen, oxygen, carbon dioxide, and water vapor.

Mixtures can be made up of:

• Elements only (e.g., steel is a mixture of iron, carbon, and other elements)
• Compounds only (e.g., salt solution is a mixture of sodium chloride and water)
• Both elements and compounds (e.g., seawater contains compounds like sodium chloride and elements like iodine)

Key Characteristics

• Components are not chemically bonded together
• Components retain their individual properties
• Can be separated by physical methods
• No fixed proportion of components
• No chemical reaction occurs when creating a mixture
• Properties depend on the amounts of each component

The composition of air: nitrogen (78%), oxygen (21%), and other gases including carbon dioxide, water vapor, and dust particles (1%).

Fun Fact

The composition of air at high altitudes above sea level is the same as that at sea level. However, less air is present above sea level. Hence, less oxygen is available for breathing. Mountain climbers sometimes carry oxygen tanks with them so that they have enough oxygen for breathing when scaling mountains.

Examples of Different Types of Mixtures

Mixtures of Elements Only

Steel - a mixture of iron, carbon, and other elements

Pewter - a mixture of tin, copper, and silver

Mixtures of Compounds Only

Salt solution - sodium chloride and water

Coffee - water and various organic compounds

Mixtures of Elements and Compounds

Seawater - contains compounds and trace elements

Fuel - mixture of carbon compounds and elements

Milk - contains compounds and trace elements

Heritage Conservation

A mixture known as chunam plaster was used to treat the walls of some heritage monuments in Singapore, namely St Andrew's Cathedral and the Arts House. This mixture was made from baked seashells, egg whites, sugar, and other substances.

Properties of Mixtures

Retained Properties

A mixture has the same characteristics as its constituents. Each component in a mixture keeps its original properties.

For example, common salt tastes salty. When we mix common salt with water, the salt dissolves in the water and the resulting salt solution tastes salty too.

This is different from compounds, where the properties of the compound are not the same as its constituent elements.

Variable Composition

The constituents of mixtures do not have a fixed proportion. They can be separated from the mixtures easily.

For example, we can form salt solution by mixing a small or large amount of common salt with water. We can recover the salt from the salt solution using a separation technique, which we will learn about in Chapter 4.

This is in contrast to compounds, where the elements are always combined in the same fixed ratio.

Comparison Between Compounds and Mixtures

Property	Compounds	Mixtures
Formation	Chemical reaction	Physical mixing
Proportion of components	Fixed ratio	Variable
Properties	Different from constituent elements	Same as constituents
Separation	Difficult (requires chemical means)	Easy (physical means)
Energy changes	Often significant	Minimal or none

Solutions

Definition

Examples

Properties

What Are Solutions?

A solution is a mixture in which one substance dissolves completely in another substance. The substance that dissolves is called the solute. The substance in which the solute dissolves is called the solvent.

For example, sugar dissolves in water to form sugar solution. Sugar is the solute and water is the solvent.

In a solution, the particles of the solute can no longer be seen. If we shine a flashlight at the solution, light will be able to pass through it fully, indicating that the solute particles are completely dissolved.

Key Characteristics

• Transparent (light passes through)
• Homogeneous (uniform composition throughout)
• Particles of solute cannot be seen
• Solute does not settle out
• Cannot be separated by filtration
• Can be dilute or concentrated depending on solute amount

Formation of a sugar solution: Sugar (solute) dissolves in water (solvent) to form a homogeneous mixture.

Fun Fact

Most solvents are liquids, although there are some solvents in the solid and gaseous states. Water is such a good solvent for many substances that it is called the universal solvent.

Examples of Solutions

Salt water - sodium chloride dissolved in water

Soda water - carbon dioxide dissolved in water

Brass - zinc dissolved in copper (solid solution)

Air - oxygen, carbon dioxide dissolved in nitrogen (gas solution)

Dilute vs. Concentrated Solutions

Given a fixed volume of water, a solution with a low percentage of dissolved solute is known as a dilute solution, while a solution with a high percentage of dissolved solute is known as a concentrated solution.

Solubility and Rate of Dissolving

Rate of Dissolving

When a solute dissolves completely in a solvent, we say that it is soluble. Substances that do not dissolve in a given solvent are considered insoluble.

The rate of dissolving refers to how quickly a solute dissolves in a solvent. Some factors affecting the rate of dissolving are:

• Size of solute particles - smaller particles dissolve faster
• Temperature of solvent - higher temperature usually increases dissolving rate
• Rate of stirring - more stirring speeds up dissolution

Solubility

Solubility refers to the largest amount of solute that can dissolve in a fixed volume of a particular solvent at a specific temperature.

Some factors that affect solubility are:

• Type of solute - different substances have different solubilities
• Type of solvent - "Like dissolves like" (polar substances dissolve in polar solvents)
• Temperature - usually increases solubility for solids, decreases for gases
• Pressure - affects solubility of gases (higher pressure increases solubility)

Chalk is insoluble in water

Sugar is more soluble in water than salt

Salt is soluble in water but insoluble in oil

Search It

Find out about other factors that affect the rate of dissolving. For example, would the volume of a solvent affect the rate of dissolving if all other factors or variables are kept the same?

Suspensions

Definition

Examples

Comparison

What Are Suspensions?

A suspension is a mixture that contains insoluble substances in a solvent. The insoluble particles are large enough to be seen and will eventually settle to the bottom if left undisturbed.

For example, dirty water is a suspension as it contains substances that are insoluble in water. These insoluble substances can be seen and will settle at the bottom of a container over time.

If we shine a flashlight at a suspension, light will not pass through it fully because the insoluble particles block and scatter the light.

Key Characteristics

• Insoluble particles are visible
• Particles settle over time
• Light cannot pass through easily
• Heterogeneous (composition varies throughout)
• Can be separated by filtration
• Often appears cloudy or opaque

Dirty water is a suspension with insoluble particles that can settle over time and be removed by filtration.

Examples of Suspensions

Muddy water - soil particles suspended in water

Calamine lotion - used to treat skin irritations

Blood - red blood cells suspended in plasma

Paint - pigment particles suspended in a liquid medium

Wastewater

Wastewater contains numerous suspended particles from homes and industries. These particles need to be filtered out during water treatment processes.

Certain Soups

Many soups, especially homemade ones, contain visible food particles suspended in the broth. These particles will settle if the soup is left standing.

Differences Between Solutions and Suspensions

Property	Solution	Suspension
Appearance	Particles of the solute cannot be seen	Insoluble substances can be seen
Settling	The solute does not settle to form solid deposits	Insoluble substances can settle to form solid deposits
Light passage	Light can pass through fully	Light cannot pass through fully
Filtration	Cannot separate components by filtration	Can separate insoluble substances by filtration
Homogeneity	Homogeneous (uniform throughout)	Heterogeneous (varies throughout)

Visual comparison between a clear solution (left) and a cloudy suspension (right).

Note: The insoluble substances in a suspension can be removed by a process called filtration. We will learn more about filtration in Chapter 4.

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• Chemistry Guide
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• Separation Techniques
• Chemical Reactions
• Sustainability in Chemistry

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