Grade 6 ↓
Introduction to Chemistry
Chemistry is a branch of science that studies the properties, structure, and changes of matter. It gives us an understanding of the building blocks of the universe and how they come together to form the substances we see every day. Chemistry is often called the "central science" because it connects other sciences such as physics, biology, and environmental science.
What is the matter?
Matter is everything that has mass and occupies space. Everything around us is made up of matter, from the air we breathe, the water we drink, to even our own bodies. Matter can exist in different states, mainly solid, liquid, and gas. Let's take a closer look at these states.
States of matter
Solids: Solids have a definite shape and volume. The particles in a solid are tightly packed together and cannot move around freely. This is why solids maintain their shape. Examples of solids are ice, wood, and metal.
Fluids: Fluids have a definite volume but no definite shape. The particles in a fluid are close together but can move past one another, causing the fluid to flow and take the shape of its container. Examples of fluids are water, oil, and juice.
Gases: Gases have no definite shape or volume. The particles in a gas are far apart and move around freely, expanding to fill their container. Examples of gases include air, helium, and carbon dioxide.
Elements and atoms
Everything in the universe is made up of more than 100 basic substances called elements. An element is a pure substance that cannot be broken down into another substance by chemical means. Each element is made up of tiny particles called atoms.
Structure of the atom
An atom is the smallest unit of an element that retains the properties of that element. Atoms are made up of three main particles:
- Proton: Protons are positively charged particles located in the nucleus of the atom.
- Neutrons: Neutrons are neutral particles that also reside in the nucleus.
- Electrons: Electrons are negatively charged particles that orbit the nucleus.
Each element has a specific number of protons, called its atomic number. For example, hydrogen has an atomic number of 1, which means that each hydrogen atom has one proton.
Compounds and mixtures
While elements are pure substances made of only one type of atom, compounds are substances made of two or more different types of atoms that are chemically bonded together. Mixtures are combinations of two or more substances that are not chemically bonded.
Examples of compounds
A common compound is water (H2O
), which consists of two hydrogen atoms and one oxygen atom bonded together. Another example is carbon dioxide (CO2
), which is made up of one carbon atom and two oxygen atoms.
HHO , O <- water O = C = O <- carbon dioxide
Examples of mixtures
Mixtures can be divided into two types: homogeneous and heterogeneous. Homogeneous mixtures have a uniform composition, while heterogeneous mixtures have visible separate parts. An example of a homogeneous mixture is salt water, where the salt is evenly distributed in the water. An example of a heterogeneous mixture is a salad, where you can see the different ingredients.
Chemical reactions
A chemical reaction occurs when substances undergo chemical changes to form new substances. During a chemical reaction, atoms in the reactants rearrange to form different molecules in the products. Chemical reactions can be identified by changes such as color changes, formation of a precipitate, gas production, or temperature changes.
Example of a chemical reaction
An example of a simple chemical reaction is the reaction between vinegar (acetic acid) and baking soda (sodium bicarbonate). When they react, they form carbon dioxide gas, water, and sodium acetate.
C2H4O2 (aq) + NaHCO3 (s) → CO2 (g) + H2O(l) + NaC2H3O2 (aq)
Periodic table
The periodic table is a chart that arranges all known elements based on their atomic number, electron configuration, and recurring chemical properties. The elements are arranged in rows called periods and columns called groups or families. The periodic table allows us to quickly find information about each element, including its chemical symbol and atomic mass.
Understanding the periodic table
Columns or groups in the periodic table represent elements with similar properties. For example, Group 1 contains the alkali metals, which are very reactive. Group 18 contains the noble gases, which are mostly inert.
Rows or periods represent elements with increasing atomic numbers. As you move from left to right across a period, the atomic number increases by one.
Chemistry in everyday life
Chemistry plays an important role in our daily lives. It is involved in cooking, cleaning, medicine, and even our emotions. When we cook, chemical reactions take place that transform ingredients into delicious food. Medicines are developed through chemistry to help us stay healthy. Cleaning products contain chemicals that react with dirt and bacteria to clean surfaces.
Chemistry also plays a part in our emotions. For example, the feeling of happiness is associated with the release of certain chemicals in our brain, such as serotonin and dopamine.
Summary
Chemistry is a fascinating and integral part of our world. By understanding the basics of matter, elements, compounds, mixtures, and chemical reactions, we can better understand the complexity and wonder of the universe. The periodic table serves as a valuable tool for organizing and identifying elements, connecting chemistry to various aspects of life and other scientific fields.