Chemistry

The study of the substances of which matter is composed.

When you hear the word “chemistry,” you may think of a scientist working in a lab, pouring liquids into tubes. But did you know that chemistry is all around you every day, and that it impacts many aspects of your daily life? Chemistry affects how your body digests food, how your water is made safe to drink, how your winter coat keeps you dry, how your computer's battery functions, how your rubber ball bounces, and how your favorite t-shirt gets its blue or red color. In everyday life, you're doing something that involves chemistry when you cook, when you take medicine, when you wipe off the counter with a cleaning detergent, when you apply sunscreen, or when you paint a picture. Chemistry is everywhere! Let's learn more about the science of chemistry.

Everything that has weight or mass and takes up space is called matter. Matter is the “stuff” in our world. Reach out and touch the nearest piece of furniture. That is matter. So are the clothes you are wearing, the hair on your head, and the air you are breathing. Everything that you can touch, see, feel, and smell — everything on Earth and even in the universe beyond — is made of matter.

Chemistry is the study of matter. When we learn about matter, we are learning about chemistry. Chemistry explores and explains the ways that matter changes, combines, and transforms to create the world we know. Since matter is all around us, chemistry is part of almost everything we do.

All matter is made of small particles known as atoms. Atoms are the basic building blocks of matter; they make up the air, the water, our bodies, food, trees, cars, and even the computer on which you are viewing this website. Atoms are so small that you cannot see them. But in the period at the end of this sentence, there are billions of atoms.

Atoms are made of three subatomic particles known as protons, neutrons, and electrons. The protons and the neutrons huddle together to make the nucleus in the center of the atom. The electrons orbit around the nucleus. Protons have what is called a positive (+) charge, while electrons have a negative (-) charge. Neutrons are not charged, but they affect the mass of the atom.

There are different types of atoms, and atoms combine in special ways to make up all of the matter in our world. That is why cat fur is so different from the steel bumper on a car. But both are still made of atoms. Atoms are different in the number of protons, neutrons, and electrons they contain.

When atoms join together, they form molecules. Molecules may be made up of the same kind of atom, or they may be made up of two or more different atoms. Although there are only 118 types of atoms, there are millions of types of molecules because the atoms combine in different ways.

Matter can exist on earth in different states or phases. The three states of matter you are most familiar with are solid, liquid, and gas. In solids, the atoms are packed tightly together and do not move past each other. Solids hold their shape at regular room temperature. With liquids, there is more space between atoms. Liquids do not hold their shape at room temperature, but instead take on the shape of the portion of the container they occupy – a glass, a pitcher, or the banks of a lake. Gases have so much room between atoms that they move freely and rapidly, and they spread out to fill all the available space in a container.

You can easily observe water in all three of these states. Water is a solid when it is ice, a liquid when we drink it, and a gas when it is steam. How does matter move from one state to another? If the motion of the atoms is altered by pressure or temperature, the state can change too. The atoms and molecules do not change, but the way they move about does. By lowering the temperature of water, it can freeze into ice which is a solid. By heating water, it can become steam which is a gas. Deep underground, extreme pressure causes solids to become liquid magma. Other substances need conditions produced in a laboratory setting in order to change states. But no matter which state, the molecular structure of the substance remains the same. Whether solid, liquid, or gas, water is still water.

To learn more, take a look at these animations of the behavior of solids, liquids and gases.

A chemical is a substance that has specific properties that we can use to identify it. Atoms of a substance help give it the physical properties that we use to describe an object. Some physical properties of matter are color, odor, texture, hardness, and magnetism. If a substance allows heat or electricity to flow through it, the property is referred to as conductivity, while the ability to dissolve in a liquid is called solubility. Density, another physical property, describes how tightly atoms are packed together. An object with a higher density will have greater mass than a low-density object of the same size. The boiling point, the temperature at which a substance changes from liquid to gas, and melting point, the temperature at which a substance changes from solid to liquid, are also physical properties.

Atoms also give an object its chemical properties, but chemical properties cannot be determined just by looking at or touching an object. Chemical properties are identified by an object's ability to change given the right conditions. The ability of an object to ignite, for example, is a chemical property. The ability of an object to rust or tarnish is a chemical property, as is the toxicity of a substance, or its ability to damage a living organism.

Matter can change in different ways. A physical change happens when we crumple up a piece of paper. It is still paper, just a different shape. We could change the temperature of a cup of water, mix two different paint colors together, cut a banana into slices, whip cream into peaks, or drop a glass jar and see it shatter into pieces. Despite all these different changes, the substances are still water, paint, banana, cream, or glass. Changes in size, shape, or states of matter are all physical changes.

Physical changes only affect the way that matter looks or feels. A physical change does not affect the chemical makeup of the object.

Chemical changes happen when changes are made to matter at the molecular level. Bonds between atoms are broken and new kinds of molecules are created. A chemical change creates a new substance that wasn't there before. When a chemical change happens, it is possible that you will see a change in color or odor, or you may find that heat, light, bubbles, fizzing, flames, or gases are given off. When you strike a match, for example, there is a sound of fizzing, there is heat, and there is a strong smell as gases are given off. These are signs that a chemical change has happened. You've actually created a new substance.

Chemical changes happen all around us. When a piece of fruit ripens, that is a chemical change. You cannot change the fruit back into its un-ripened state. When you put bleach in the washing machine to clean your clothes, a chemical change breaks down molecules in the stains. When wood burns in a campfire and produces smoke and ash, the atoms have been rearranged into new combinations, and the properties of the starting materials have changed.

Sometimes a chemical change happens in a slow reaction, as when rust is produced. Rust happens over a long period of time when iron is exposed to oxygen. But rust is a new chemical. It isn't iron and it isn't oxygen; it is rust.

The process by which substances are changed into other substances is called a chemical reaction. Chemical reactions are part of everyday life. When you eat, your body uses chemical reactions to break down food into energy. Photosynthesis in green plants, where plant food and oxygen are produced from water, sunlight, and carbon dioxide, is a chemical reaction.

Everything in the universe is made from elements. Elements make up the basic ingredients of all matter. We know of 94 elements that occur in nature, but several more have been created by scientists for a total of 118. An element is a pure substance that is made from one single type of atom. For example, gold is an element that is made up of gold atoms – it cannot be broken down into smaller components and still be called gold. Oxygen is an element made up of oxygen atoms. Copper is an element made up of copper atoms.

The most common and abundant elements make up most of the matter on Earth. Although your body is made of trillions of atoms, just four elements – hydrogen, carbon, oxygen, and nitrogen – account for more than 96% of those atoms inside you. And as far as we know, elements make up matter throughout the universe. Iron atoms found on Earth are identical to iron atoms found in meteorites and in the red soil of Mars.

The Periodic Table of Elements is used to organize the elements by their atomic number, or the number of protons in the nucleus. For example, oxygen has 8 protons, so its atomic number is 8. Chemical symbols stand for each element. There is much more you can learn about atoms and elements from the periodic table.

Although a few things in our world are made of just one element, such as oxygen, carbon, or gold, most are a combination of two or more elements. While there are only 118 elements, there are millions of combinations of elements, making different types of molecules. When different elements are chemically bound together, they are known as compounds. When a compound is created from different kinds of atoms, the new substance created does not have the same physical or chemical traits of the original elements. Each compound has its own unique properties.

Compounds are written with formulas showing which elements from the periodic table are combined. One very familiar compound is water. Water is made of two elements chemically bound together. When two hydrogen atoms (H2) combine with one oxygen atom (O), it makes the compound H2O, which we know as water. The formula H2O tells us that there are 2 atoms of hydrogen bound to each atom of oxygen. All water molecules have this same combination of atoms. Water is not hydrogen or oxygen. You couldn't pour oxygen and hydrogen atoms on a fire and expect to put it out. But when they are bonded together as water molecules, they behave like water.

The same elements in different amounts can build very different compounds. If you took those two hydrogen atoms and joined them to two oxygen atoms (instead of one), you would wind up not with water but with H2O2, a very different compound called hydrogen peroxide – and you wouldn't want to drink it!

There are many other compounds that are already familiar to you. When one sodium atom (Na) combines with one chlorine atom (Cl), it makes the compound NaCl, which you know as salt. Every time you breathe out, your breath contains CO2, a compound of one carbon atom (C) and two oxygen atoms (O2) that we call carbon dioxide. Sometimes more than two elements make up a compound. A sugar molecule (glucose) is a compound of 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms, written as C6H12O6. These specific atoms in these exact numbers make up a sugar molecule.

Sometimes substances may combine without forming a compound. A compound requires a chemical reaction where bonds are formed between atoms and a new substance is created. Without that chemical reaction, combined substances may instead form a mixture. The components of a mixture keep their original properties and can easily be separated. For example, a mixture of fruits in a salad can be separated back into groups of different fruits. Salt and water can be combined in a mixture, but water is still water, and salt is still salt. To separate the two components, the water can be evaporated so that the salt can be collected. Sand and water can be separated by using a filter. The ocean, rocks, blood, and even the air we breathe are mixtures rather than compounds.

Chemists often describe liquid chemicals as acids or bases. Acids have a sour taste. Some acids, such as lemon juice and vinegar, are foods we can eat. Our stomachs use acids to help digest foods and to kill bacteria that could make us sick. Other kinds of acids are used in car batteries to make them run. Those strong acids are dangerous and should never be handled by students.

Bases are the opposite of acids. They have a bitter taste. Soap is a common base found around the house. If you have ever accidentally gotten shampoo in your mouth while washing your hair, you have experienced its bitter taste. Other common bases are baking soda and toothpaste. Very strong bases can be dangerous and can harm living cells.

Sometimes people use an antacid to treat their upset stomach. An antacid is a base which, when dissolved in the stomach's acid, neutralizes that acid and takes away its acidic qualities. The acid no longer bothers the person's stomach and they feel better. That is chemistry at work in our lives.

To determine if a substance is an acid or a base, chemists can test it using special paper known as litmus paper which changes color when exposed to chemicals. This is known as testing the pH of a substance. By comparing the color of the changed paper, chemists can tell whether the substance is an acid or a base. Chemists use a scale between 0 and 14 to describe how strong the acid or base is. Pure water is 7, right in the middle, and most everyday liquids are in the middle range. Very strong acids (with a pH near zero) and very strong bases (with a pH near 14) are dangerous and should be handled only by people who are trained to work with them. Chemicals should never be tasted without adult supervision.

Chemistry really is everywhere! Everything you hear, see, smell, taste, and touch involves chemistry and matter. Chemical reactions power all life on Earth and keep our bodies functioning. Chemistry allows scientists to create medicines that keep us well. Chemistry is responsible for turning used milk jugs into carpets for homes and schools, and for creating sunscreen that keeps us from getting sunburned. Chemistry has been used to enrich soil for growing crops, to measure levels of pollution in the environment, and to make stronger metals, fibers, and building materials. Chemistry allows scientists to determine what kinds of matter make up the planets and stars, even from millions of miles away. Nearly everything you see around you at home is some type of chemical compound, from vinegar to nail polish remover to baking soda to aspirin. Chemistry has even come up with fun products such as glow sticks, silly string, and marshmallows!

Scientists are learning more and more about chemistry all the time. The work of chemists is to research all aspects of matter and its properties and changes, and then create new substances that improve people's lives. Sometimes such substances are discovered by accident, like the glue used in Post-it notepads and the fabric protectant known as Scotchgard. Both chemicals were invented in chemical laboratories, but they were discovered as an accidental application of the chemist's work.

Learn more at Science Trek's websites for Compounds and States of Matter. Keep learning all you can about chemistry. Perhaps you will be the future chemist who finds a way to power cars using the air we breathe!