All of the matters in the universe are composed of atoms or elements. These elements are very minute particles. Elements come in group to produce the matter that humans can see. Matters that have a specific proportion of the type of elements are called compounds. Water for example is composed of 2 parts hydrogen and 1 part oxygen by number of atoms. If in case a given substance contains 3 hydrogen atom and 1 oxygen atom, then even if it composed of hydrogen and oxygen, it will never be considered as water. Like elements, compounds are considered as pure substances. There are also combinations of substances that are not affected by the proportion of the combined substances and cannot be separated into elements by physical means. They can only be separated into elements using chemical means. These are called mixture. Example of these is a mixture of salt and water. Even if the proportion of salt to water in the mixture varies, the resulting mixture will still be a salt water mixture. Unlike compounds, mixtures are not considered as pure substance and can be separated into other substances by physical means (Kotz Treichel, 1996).
Compounds are generally named using the names of the elements that composed them. Hence, it a pure substance can be classified as either element or compound by knowing its name. A complete list of known elements and their chemical symbols is listed in many references. It the name of the pure substance is included in the list, it is an element. However, the reverse is not always true since there are compounds that are composed of only 2 or more of the same element. A more accurate way is by knowing its chemical formula. If the chemical formula of the pure substance is composed of different chemical symbols of elements or if it is composed of more than one atom of an element, then it is a compound. The disadvantage of this is that the chemical formula is not always readily available. Other methods are necessary, like line emission spectra. This technique utilizes the fact that an element possesses unique line spectra. If the pure substance showed line spectrum of different elements, then it is a compound.
Elements do not readily group with other elements to form a compound. Some rules are satisfied first before a compound is formed and these rules depend on the nature of element, such as its charge. If the elements to be combined are both negatively charged, the compound is called covalent compounds and the bonds that exist between the elements are called covalent bond. If it is composed of elements of opposite charge, it is called ionic compounds and the bonds that exist between the elements are called ionic bond (Carpi, 1999).
Ionic bond is easy to understand. It is well known that opposite charges attracts while same charges repeal. Since the charges of the elements present in ionic compounds are opposite, the elements will attract each other by electrostatic force. The charge also reflects the need to give up or attain electrons. A negative charge indicates that the atom requires additional electrons while positive charge indicates the need to give up electrons. Since the charges of elements in ionic compound are opposite, one must give up and while one must accept electron. In this process, the bond between elements in ionic compounds is produced. Example of these compounds are CaBr2 (calcium bromide) and NaCl (sodium chloride).
The bonds for covalent compounds are produced in a different way. It can be expected that the elements will repeal each other due to them having the same size, but in reality bonds are still formed. Since all the elements are negatively charged, all must accept electron. However, no other source of electron is present and so the only solution is for the elements to share electrons. The shared electron becomes property of the forming elements. Examples of these compounds are NF3 (nitrogen trifluoride) and PCl3 (phosphorus trichloride) (Kotz Treichel, 1996).
Compounds are generally named using the names of the elements that composed them. Hence, it a pure substance can be classified as either element or compound by knowing its name. A complete list of known elements and their chemical symbols is listed in many references. It the name of the pure substance is included in the list, it is an element. However, the reverse is not always true since there are compounds that are composed of only 2 or more of the same element. A more accurate way is by knowing its chemical formula. If the chemical formula of the pure substance is composed of different chemical symbols of elements or if it is composed of more than one atom of an element, then it is a compound. The disadvantage of this is that the chemical formula is not always readily available. Other methods are necessary, like line emission spectra. This technique utilizes the fact that an element possesses unique line spectra. If the pure substance showed line spectrum of different elements, then it is a compound.
Elements do not readily group with other elements to form a compound. Some rules are satisfied first before a compound is formed and these rules depend on the nature of element, such as its charge. If the elements to be combined are both negatively charged, the compound is called covalent compounds and the bonds that exist between the elements are called covalent bond. If it is composed of elements of opposite charge, it is called ionic compounds and the bonds that exist between the elements are called ionic bond (Carpi, 1999).
Ionic bond is easy to understand. It is well known that opposite charges attracts while same charges repeal. Since the charges of the elements present in ionic compounds are opposite, the elements will attract each other by electrostatic force. The charge also reflects the need to give up or attain electrons. A negative charge indicates that the atom requires additional electrons while positive charge indicates the need to give up electrons. Since the charges of elements in ionic compound are opposite, one must give up and while one must accept electron. In this process, the bond between elements in ionic compounds is produced. Example of these compounds are CaBr2 (calcium bromide) and NaCl (sodium chloride).
The bonds for covalent compounds are produced in a different way. It can be expected that the elements will repeal each other due to them having the same size, but in reality bonds are still formed. Since all the elements are negatively charged, all must accept electron. However, no other source of electron is present and so the only solution is for the elements to share electrons. The shared electron becomes property of the forming elements. Examples of these compounds are NF3 (nitrogen trifluoride) and PCl3 (phosphorus trichloride) (Kotz Treichel, 1996).
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