[Chemistry Class Notes] on Elements Pdf for Exam

An element of chemistry is defined as a pure substance composed of atoms where all atoms in their nuclei have the same numbers of protons. Chemical elements cannot be broken down by any reactions into simpler substances. The defining property of elements is the number of protons in their nuclei and it is referred to as an atomic number of elements. Atoms are rearranged into new compounds held together by chemical bonding when different elements undergo chemical reactions. Most of the elements are found as compounds or mixtures, only a few elements, such as silver and gold, are found uncombined as relatively pure native element minerals. 

History of Elements

The elements have been used for different purposes since ancient times. It is estimated that around 1000 years ago, gold (Au) was used for making ornaments during the period of the stone age. In Egypt, different types of metals such as silver (Ag), iron (Fe), lead (Pb), copper (Cu) and tin (Sn) were used for different objectives more than 5,000 years ago. The discovery of arsenic (As) has happened around A.D. 1250. Around twelve elements were known by 1700.

The concept of elements or we can say the theory that there are a limited number of fundamental pure substances out of which all other substances are made is credited to the ancient Greeks. There are four basic “roots” of all materials: earth, air, fire, and water was proposed by Empedocles (c. 495–435 B.C.). The famous philosopher Plato termed these four roots as stoicheia elements.

 

Examples of Elements

Some examples of elements are given below.

We use elements in everyday life. We are dependent on these elements for our survival. The most important examples of elements in everyday life are carbon, hydrogen, oxygen and apart from these chlorine, sulphur, calcium, iron, phosphorus, nitrogen, sodium, and potassium are also essential for everyday life. The four major elements that are used in the making of  96% of the human body are carbon (C), oxygen (O), hydrogen (H) and nitrogen (N). In the body of a human being, a large number of chemical reactions occur involving compounds of all of these elements as a result of these reactions the human body used to function.

The physically combined structures which can be separated back into their original components are known as mixtures. It is very rare to find pure samples of isolated elements in nature. In mineral samples from the crust of the earth most of the naturally occurring elements have all been identified, only a small minority of them can be found as recognizable, relatively pure minerals. Among the more common such native elements are copper, silver, gold, and sulphur. Carbon is an element that occurs naturally in diamonds, coal and graphite. The noble gases, for example neon and noble metals, for example mercury can also be found in their pure, non-bonded forms in nature. 

When the chemical bonds are formed between the atoms of two distinct elements that are chemically combined the result is called a chemical compound. Most of the chemical elements present on the earth make bonds with each other in order to form chemical compounds, for example when sodium ions and chloride ions combine they form NaCl. Another example of a chemical compound is water (H2O). 

The chemical elements are classified and placed in different groups in the periodic table. The table of chemical elements is the representation of the chemical elements in tabular form. There are a total of 118 elements placed at present in the periodic table among them 94 are natural elements and 24 elements are synthetic. The elements are placed in groups in the periodic table; the names of these groups are alkali metal, alkaline earth metal, pnictogen, chalcogen, halogen, and noble gases. The groups of the periodic table are referred to by their number. The list of elements placed in the periodic table is very long but some important examples of elements in chemistry are hydrogen, oxygen, iron, copper, potassium, calcium, helium, nitrogen, silver etc.

Elements are also used at home for a variety of purposes. In Incandescent light bulbs, argon and tungsten are used. Copper is an important element that is found in every home in the form of electric wiring or utensils. Mercury element is used in some thermostats and in switches. Gold and silver elements are used for jewellery purposes.

Do you Know?

• The elements which are found on mars are exactly the same as the elements of the earth. 

• In ancient times the elements were referred to as fire, earth, water, and air.

Conclusion

An element of chemistry is a pure substance that is composed of similar types of atoms.  Atoms of an element have an atomic number, which indicates the total number of protons present in the nucleus of a single atom of that element. We get all the necessary information related to elements and examples of elements compounds and mixtures, at home, in chemistry etc.