Chemistry: Difference between revisions

Chemistry is the science of chemical elements and compounds.

Chemistry is the science of chemical elements and compounds, and how these things work together. It is the study of the materials (things) that make up our bodies and everything in the world around us.

History

Before 1600, people studied substances to figure out how to do things like turn lead into gold, but no one managed to do that. This was called alchemy. Alchemists (people that did alchemy) did discover some useful things, though. Sulfuric acid and nitric acid were two substances that they discovered.

Only a few elements were known. Some of them are mercury, silver, gold, and carbon.

Chemistry began as a true science during the 1600s. This is when chemists discovered the simplest substances that make up all other substances. These simple substances are called elements. One of the things that they learned is that gold and lead are made of two different elements, so you can not change one into the other by a chemical reaction. The first element discovered after 1600 was phosphorus, a strange white glowing solid.

Elements were discovered more and more rapidly. People separated the air into many parts and isolated the noble gases from it. They also processed special minerals from a mine in Sweden to get rare earth metals. Radioactivity was also discovered. Today chemists have discovered 118 different elements. Some are very common, like oxygen. Many are very rare and expensive, like platinum. Some cannot be found on earth and can only be made in labs, like rutherfordium.

Types of chemistry

There are several types of chemistry. Analytical chemistry looks at things to see what chemicals they have in them. A sample job would be to see how much arsenic is in food. Organic chemistry looks at things that have carbon in them. A sample job would be making acetylene. Inorganic chemistry looks at things that do not have carbon in them. A sample job would be making an integrated circuit.

A large area of chemistry is polymer chemistry. It looks at plastics. A sample job would be making nylon. Because plastics are made of carbon, polymer chemistry is part of organic chemistry. Then there is biochemistry. It looks at the chemistry of the human body. A sample job would be seeing how arsenic poisons people. Biochemistry is also part of organic chemistry. There are many other small branches of chemistry.

Concepts of chemistry

Basic concepts

The basic unit of an element is called an atom. An atom is the smallest thing that you can cut an element into without the element breaking down. A chemical compound is a substance made up of two or more elements. In a compound, the atoms of each element are joined together to form a molecule. The tiniest speck of dust, or drop of liquid, that you can see is made up of many millions or billions of these molecules. Mixtures are substances where chemicals are mixed but not reacted. An example would be mixing sand and salt. It is just a mixture. If it is put in water, the salt will dissolve, leaving the sand behind. Chemical compounds are broken down by a chemical reaction. An example would be heating sodium bicarbonate, common baking soda. It will make water, carbon dioxide, and sodium carbonate.

Mole

A mole is a very large amount of atoms (602,200,000,000,000,000,000,000 atoms). The atomic mass of an element can be used to see how much of the element makes a mole. For example, the atomic mass of copper is about 63.55. That means about 63.55 grams of copper metal has a mole of atoms. The atomic mass of chlorine is about 35.45. That means 35.45 grams of chlorine has a mole of atoms in it.

Moles can be used to see how many molecules are in chemical compounds, too. Copper(II) chloride is an example. CuCl₂ is its chemical formula. There is one copper atom (63.55) and two chlorine atoms (35.45 · 2 = 70.90). Add all the molar masses of the elements together and the molar mass of the chemical compound is gotten. (63.55 + 70.90 = 134.45) That means in 134.45 grams of copper(II) chloride, there is one mole of copper(II) chloride molecules. This concept is used to calculate how much chemicals are needed in a chemical reaction if no reactants (chemicals that are reacted) should be left. If too much reactant is used, there will be some reactants left in the chemical reaction.

Acids and bases

Acids and bases are common chemicals. Acids release H⁺ ions when in water, and bases release OH⁻ ions when in water. Acids can react with bases. The H⁺ ion is taken from the acid by the base. This makes water, H₂O. A salt is also made when an acid and a base react together. An example would be reacting hydrochloric acid (HCl) and sodium hydroxide (NaOH). Hydrochloric acid releases H⁺ and Cl^- ions in water. The base releases Na⁺ and OH^- ions. The H⁺ and the OH^- react to make water. There is a solution of sodium chloride (NaCl) left. Sodium chloride is a salt.

Usefulness

Chemistry is very common in normal life and makes up the foundation of much of science. Most objects are made by chemists (people who do chemistry). Chemists are constantly working to find new and useful substances. Chemists make new drugs and materials like paints that we all use every day.

Safety

This chemist is wearing glasses, a lab coat and gloves. He is looking at a rock from the moon.

Although there are some chemicals that are harmless, many chemicals are dangerous. For example, mercury(II) chloride is very toxic. Chromates can cause cancer. Tin(II) chloride pollutes water easily. Hydrochloric acid can cause bad burns. Some chemicals like hydrogen can explode or catch fire. To stay safe chemists experiment with chemicals in a chemical lab. They use special equipment and clothing to do reactions and keep the chemicals contained. The chemicals used in drugs and in things like bleach have been tested to make sure they are safe if used correctly.

Other pages

• Periodic table
• List of common elements
• Common chemical apparatus
• Laboratory techniques
• Chemical techniques
• Aerosol
• Ask a chemistry question