Elements and their symbols - Their origin and Groups

Elements and their Symbols

Around 400 B.C., a Greek scholar, Democritus, suggested that matter is made up of tiny particles. We call these particles atoms. More than 2000 years later, in 1808, John Dalton (1766-1844), an English scien­tist, suggested that each element has its own kind of atom. He also sug­gested that compounds are made up of combinations of different kinds of atoms. When explaining his model, Dalton represented elements by symbols and compounds by combinations of symbols.
Dalton's model has been useful in explaining many properties of matter. Over the years, the model has been modified as scientists have gained new knowledge, but much of it has remained the same. However, Dalton's system of symbols was never widely used.
Simpler symbols based on Dalton's model were suggested by Jons Jakob Berzelius (1779-1848). He suggested that all elements be repre­sented by the first letter of their name in Latin, or by the first letter and another letter from the name. The first letter of the symbol would always be capitalized, and the second letter would be lower case. Berzelius's suggestion seemed so convenient to other scientists that his system became widely accepted and is still used today. These same symbols are now used in all languages, even those that use a different alphabet. In this way, the symbols are truly international.
The origin of symbols or the elements 
You may wonder why the symbols for the elements are based on their Latin names. First, some of the elements were known to the Latin­speaking Romans as early as two thousand years ago and were there­fore named by the Romans. A few elements occur in nature in almost pure form. Thus, they are easy to separate and identify. An example of such an element is gold (aurum in Latin), whose symbol is Au.
Second, for more than a thousand years, Latin was used throughout Europe and was considered to be the language of learning. Long after the Roman Empire had collapsed, scholars in Europe continued to use Latin for their writings. As alchemists and scientists discovered new elements, it was natural for them to give the elements Latin names. To keep the system consistent, even elements discovered very recently are given Latinized names. Examples are uranium, einsteinium, and californium.
The English names of certain elements are the same as or very similar to their names in Latin, so it is easy to recognize these symbols. Example are carbon (from carbonem in Latin, meaning charcoal), whose symbol is C, and sulfur (sulfur in Latin), whose symbol is S. Other elements, how­ever, have English names that are very different from the Latin names.
Sorne English words are related to the Latin names for elements. For example, the Romans used lead pipes in their water systems. The Latin rd for lead is plumbum, so people who work with pipes and water sys­ms today are called plumbers. A plumb bob is a heavy weight hung m a string. It is used for finding vertical lines. Since lead a high density, it makes a good weight, and so lead, or plumbum, ,gave plumb bobs their name.
Groups of Elements
There are 109 elements. Although each elements is different from every other, ther are groups of elements that have similar properties. When elements are grouped according to their properties, naming the compounds they form becomes easier.
Metals and non-metals 
Based on experiments on many elements over many years, elements with certain characteristics are considered to be metals. Metals typically have the following properties:

• They are shiny. 
• They are ductile; that is, they can be pulled (stretched) into wires. 
• They are malleable; that is, they can be beaten into sheets. 
• They are good conductors; that is, they are able to conduct (transfer) electricity and heat. 

Non metals are elements that do not have these properties. If you look The Periodic Table of the Elements, you will see that all the elements are grouped together on the left-hand side of the table, and all the non-metals, except hydrogen, are grouped together to the right of the metals.
As in nature, however, things are not so simple. Some elements fit very well into either group. Other elements have properties of both groups. Hydrogen is a gas, but when it forms compounds, it b­ehaves as a metal would. Aluminum has the properties of a typical metal, but it sometimes acts like a non-metallic elements. Silicon and germanium have both metallic and non-metallic properties.

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Posted in Chemistry

Chemical Reacitons

CHEMICAL REACTIONS 
Another term for chemical change is chemical reaction. There are :rrany kinds of chemical reactions. They may be spectacular and explosive, like the reactions in a fireworks displays. Or they may quite slow, like the formation of rust.
In every chemical reaction, a new substance is produced. A reac­tant is any substance that you start with. A product in a chemical reaction is any substance produced in the action. There may be one or uore reactants and one or more products in a chemical reaction. The products have properties that are different from the properties of the reactants.
In the three chemical reactions above, elements or compounds react to produce a new substance. In another type of chemical reaction, a com­pound breaks down to produce two or more products. For example, when hydrogen peroxide breaks down, it forms water and oxygen.
hydrogen peroxide ---->  water + oxygen
SOME COMMON CHEMICAL REACTIONS 
Chemical reactions are going on all around you. When you cook a hamburger, bake cookies, or allow glue to harden, you are carrying out a chemical reaction. When you eat, the glucose in the food reacts with the oxygen in the air you breathe. This reaction produces the energy you need to run, study, and stay alive.
As you have already learned, rusting of iron is another type of chemical reaction. Rusting is an example of corrosion, or the eating away of metal through a chemical reaction.
Corrosion poses problems in many aspects of life, from bridge con­struction to car manufacturing to the production of computer chips.
Corrosion is a constant problem with boats and ships. Without some protection, the metal parts corrode quickly in water. This is an especially serious problem for ships in salt water.
Paint and other surface coverings can be used to slow corrosion.
Corrosion can also be stopped by fastening reactive metal to a ship or at. A metal that is reactive reacts more easily than other metals. When a reactive metal is attached to a ship, that metal corrodes instead of the more important, less reactive parts of the ship. Zinc and magnesium are two reactive metals used to halt corrosion.
In some metals, corrosion produces a protective surface covering. aluminum is one example. When the surface of a piece of aluminum is scratched, it is shiny, but it soon becomes dull. Some of the alu­minum has combined with oxygen from the air to produce aluminum xide. The aluminum oxide sticks to the surface of the aluminum and protects the rest of it from further reaction. As a result, objects made of aluminum keep their original strength under certain conditions, in :ontrast to iron objects, which are weakened by rusting. Aluminum can therefore be used in making outdoor furniture, snow shovels, and other items exposed to weather. However, pure alu­minum does corrode rapidly in salt water.
Another common type of chemical reaction is combustion, which is another name for burning. Combustion is a chemical reaction in which oxygen is one of the reactants and in which heat is produced. Many substances, such as wood, kerosene, natural gas, and diesel fuel, can undergo combustion. These substances burn easily in air, which is only about 20 percent oxygen. In pure oxygen, they burn much more intensively.

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Posted in Chemistry

Matter and changes in matter

MATTER AND CHANGES IN MATTER

Matter and Changes in Matter

Matter is anything that has mass and volume, including all solids, liquids, and gases. To understand changes in matter, you need to know that the sample of matter was like before the change and what it is like after the change. You also need to be able to describe and classify atter. There are many ways in which matter could be classified, but s.:ientists have found it useful to classify matter according to its properties, or characteristics. Properties are ways of describing things so that we can identify them. Any kind of matter can be classified as a mixture or a pure substance.

Physical and Chemical changes

When matter changes, what happens to it? After some changes, mat­ter may still have the same properties. When you tear paper into small pieces, for example, each piece still has the properties of the original paper. When a balloon bursts, the rubber is still the same color and is still just as soft and stretchy as it was in the balloon. When ice melts, the water is still the same substance-it can easily be arranged back into ice if it is cooled. These are physical changes, changes in which no new substance is produced.

During some changes, a new substance may appear. For example, if you leavve your bicycle out in the rain, a reddish-brown crumbly substance may form on it. This substance-rust-is quite different from the shiny, hard etal that was used to make the new bicycle. Changes such as this, in which new substances are produced, are called chemical changes. If one or more new substances are produced-substance(s) with prop­erties that are different from the properties of the starting material(s) then a chemical change has occurred. Chemical changes may involve energy; heat or light may be given off during the change. Most chemical changes, cannot be easily reversed.

Differentiating between physical and chemical change

It is not always easy to tell the difference between a physical change and a chemical change. Some chemical changes may pro­duce flames, sparks, and noise, but many do not. The chemical changes that take place when you bake a cake, polish brass, or clean the oven are much less spectacular. However, cer­tain clues may tell you that a chemical change has occurred:

• A new color may appear. 
• Heat or light may be given off. 
• Bubbles of gas may be formed. 
• Solid material may form in a liquid. 
• The change may be difficult to reverse. 

Any of these clues could also be part of a physical change. You need to consider several clues in order to determine which type of change has taken place.

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Posted in Chemistry , Physics