Compounds Anytime two atoms join together they make a molecule Everything around us is made up of molecules When atoms from two or more different elements bind together the molecule is a compound The chemical bond is so strong that the atoms from the different elements all behave like a single substance Compounds are not simply mixtures or blends but a bind that happens at the atomic level Sometimes an element will lose traits when it is bound in a compound An element that is reactive on its own meaning it will release energy in a chemical reaction with another element like sodium Na can become nonreactive when it binds with another element like chlorine Cl forming sodium chloride NaCl which is everyday table salt All compounds have a definite composition For example a compound you may have heard about before is H2O or water Water always has two hydrogen atoms and one oxygen atom If you take away one of the hydrogen atoms it is no longer water While we have only 118 elements in the periodic table there are millions and millions of compound combinations that are each unique Alloys Versus Compounds Alloys are not compounds An alloy is a mixture of metals or a metal and another element Brass is an alloy of copper and zinc which are both metals Steel is an alloy of iron a metal carbon a nonmetal and sometimes other elements The alloy components are usually melted at very high temperatures mixed and allowed to cool to a solid alloy In general alloys are stronger and more durable than their individual components Unlike compounds alloys do not have chemical bonds between the elements 12 ILLUSTRATED ENCYCLOPEDIA OF THE ELEMENTS
Liquid bleach NaClO common compouns Some compounds you might know by their common names Marble CaCO3 Baking soda NaHCO3 Rubbing alcohol CH3 2CHOH Milk of magnesia Mg OH 2 Table Salt NaCl Baking soda Bleach 30% isopropyl Alcohol Milk of Magnesia Sugar pure Granulated Sugar C12H22O11
All elements can exist in three different states of matter solid liquid or gas We use room temperature a comfortable temperature of about 70 Fahrenheit 21 Celsius as our consistent point of reference At room temperature the majority of the elements are solid eleven are gas and two are liquid Elements change from one state to another through heating and cooling When an element changes from one state to another the number of atoms remains the same but they arrange themselves in different ways When an element is in solid form atoms are attracted to each other and locked into a tight position Solids keep their shape and have a fixed volume volume is how much space an object takes up While some solids are soft and flexible they are still solid When an element is in liquid form the atoms move around and their attraction loosens Liquids take the shape of the container they are in but their volume remains fixed When an element is in a gas form the atoms are weakly attracted to each other and move in different directions A gas will fill any container no matter how large or small it is States of Matter Solid Liquid Gas 14
Alchemy and Ancient Chemistry Long before the periodic table was developed humans attempted to understand the unique and distinct substances that comprised everything in the known universe What are these essential elements Many ancient cultures like the Babylonians Chinese and Egyptians developed an idea of simple groups wood fire earth metal water and so on The ancient Greeks synthesized the world into just four elements earth water fire and air This theory became elemental to Western thought for 2,000 years The four elements were used to describe not only objects in the seen world but also the temperaments a person might experience and physical sensations in the body called the four humors Maintaining the balance of the four elements humors was thought to be essential not just to the natural world but also to a person’s mental and physical well-being Alchemists and Gold Diggers In the Middle Ages practitioners of alchemy a combination of scientific exploration and mysticism strove to understand the natural world and how to transform it Alchemists were interested in purifying and perfecting metals and sought to change ordinary metals like lead or mercury into gold The material that was thought to accomplish this task was known as the philosopher’s stone Of course no such substance existed but one alchemist Hennig Brand became the first person to chemically discover an element in his pursuit read about the gross idea that led to his discovery of phosphorus on page 43 Air Water Fire Earth The four elements according to the ancient Greeks A Scientific Revolution Building on the efforts and discoveries of the alchemists and riding the wave of new scientific methods pioneering chemists in the sixteenth century began to dismantle the idea of the four elements They discovered that what had been known as elemental earth for example was made up of many components Much of their research involved how different substances that the alchemists had isolated such as arsenic or zinc interacted with each other or other substances such as gases in the air Because some substances behaved similarly under certain circumstances scientists began to classify them into groups in the eighteenth century which was the beginning of the periodic table and our modern understanding of the elements ALCHEMY AND ANCIENT CHEMISTRY 15
