Concept Development

The material things around us are all various types of matter. Matter is anything that takes up space and has mass. Aluminum, water, air, glass, and you are different kinds of matter. Ideas, light and heat are not matter. They do not take up space or have mass. (Chemistry, pg. 5)

Mixtures are matter composed of two or more physically blended substances. Each substance retains its own properties. Mixtures differ from pure substances because they have a variable composition. Most materials found in nature are mixtures. We all recognize beef stew as a mixture of meat, vegetables, and gravy. On the other hand, the identification of air or brine as mixtures is much less obvious. (Air is a mixture of gases. Brine is a mixture of salt and water.) The component parts of these mixtures cannot be distinguished even under a microscope.

Mixtures can be heterogeneous or homogeneous. A heterogeneous mixture I not uniform in composition. If we were to sample one portion of a mixture, its composition would be different from another sample. Soil is a heterogeneous mixture. It contains bits of decayed material along with sand, silt and/or clay. By contrast, a homogeneous mixture is completely uniform in composition. Its components are evenly distributed throughout the sample. Salt water from the ocean is a homogeneous mixture. It is the same throughout a sample.

By separating mixtures into their parts we obtain pure substances. Substances are uniform and have a definite composition. There are two groups of substances, elements and compounds. Elements are the simplest forms of matter that cannot be further decomposed by ordinary chemical means. Compounds are matter that can be decomposed into two or more simpler substances by ordinary chemical means. Compounds are made up of elements. Every element and every compound has its own unique set of properties. We can identify mixtures, compounds, and elements by using the following diagram. (Chemistry pg.7)

Physical Properties of Solids

Physical properties of matter can be easily seen or measured without altering the identity of that substance. Physical properties in many cases can be identified by just looking at the substance. Some physical properties include: color, hardness, odor, melting point, boiling point, magnetism, electrical conductivity, density, and solubility (ability to dissolve). Those physical properties that can not be identified by sight, feel, or smell must be measured. When measuring a physical property you should still have the same substance when you are finished. For example, by putting salt into water we can see that it will dissolve, if we allow the water to evaporate we are left with just sugar. Thus, we still have the same substance that we started with even though we changed its state of matter.

Elements are matter and have certain physical properties. Metals, nonmetals, and metalloids can be distinguished by their physical properties. Some physical properties of metals are as follows:

Some physical properties of metalloids are as follows:

Some physical properties of non-metals are as follows:

Not only do all forms of matter have physical properties but they also have chemical properties. Chemical properties describe the ways in which a substance can be changed into different substances with an entirely different set of properties. In other words chemical properties describe the ability a substance has to undergo a chemical reaction and to form new substances. There are several ways to identify if a chemical change has occurred. One way is to compare the physical properties of the beginning substance to that of the ending substance. If there is a difference than a chemical change has occurred. Another way to identify if a substance is undergoing a chemical reaction is to look for one of the five evidences of a chemical reaction.

1. Gas given off (bubbles)
2. Color change
3. Light given off
4. Temperature change (heat/cold)
5. Precipitate forms. (solid falls out of a liquid)

 The periodic table is made up of all the known elements. Each of these elements has a symbol to represent them. These symbols are assigned by using the name of the element. Here are a few rules for assigning symbols.

0. The second letter is never capitalized.
1. The second letter is one whose sound is conspicuous when the name of the element is pronounced.
2. Some symbols come from the Latin name, not the common English name.

The Periodic Table

The periodic table consists of all known elements, their atomic masses, and atomic numbers. The table has been in development for many years, and many scientists have contributed to it. John Newlands, in 1865, found that properties were repeated after each series of eight elements. This became known as the Law of Octaves.

By the mid-1800s there were only 70 elements that had been discovered and described. Dmitri Mendeleev, a Russian chemist, created his periodic system in one day by puzzling over cards containing 63 known elements with chemical and physical properties and atomic weights. He listed the elements in several vertical columns in order of increasing atomic mass. He soon noticed a recurrence of their physical and chemical properties.

Mendeleev left numerous bland spaces in the table because there were no known elements with the appropriate properties. He noted the properties of the elements adjacent to the blank spaces. Then he and others were able to predict the physical and chemical properties of the missing elements. Eventually these missing elements were discovered and found to have properties similar to those predicted. (Chemistry, pg. 272)

In 1913 Henry Moseley determined the atomic numbers of the elements. The periodic table is today arranged by increasing atomic number.

 Let's take a closer look at the periodic table, the properties of the elements and some of the trends that occur within the table.

There are nine elements that have been known since ancient times. They are carbon, iron, sulfur, copper, silver, gold, mercury, lead, and tin.

In this century since the 1945 the following elements have been discovered or made; californium, promethium, berkelium, einsteinium, fermium, mendelevium, nobelium, and lawrencium. These are all located in the inner transition metals or rare earth metals. This is the very bottom of the table.

Many elements are found in the earth's crust. The most abundant of these elements are sodium, mercury, potassium, calcium, iron, aluminum, silicon, and oxygen.