More on Chemistry: The Meaning of Chemistry

denz By denz, 31st Mar 2012 | Follow this author | RSS Feed | Short URL
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Chemistry is the science which treats of the composition of substances and of the changes which these substances may undergo. Chemistry is the science that is concerned with the characterization, composition, and transformations of matter.

More on Chemistry: The Meaning of Chemistry

What is Chemistry?
Chemistry is the science that is concerned with the characterization, composition, and transformations of matter. The modern science took centuries to develop from its roots in the practical arts of ancient civilizations and the theories of the ancient Greeks through alchemy and phlogiston chemistry. The modern period was ushered in by the work of Antoine Lavoisier, who based his work on the law of conservation of mass.

The classification of matter rests on the identification of elements, substances that cannot be decomposed into simpler substances and from which all other types of matter are made. Compounds are composed of two or more elements in fixed proportions. They are produced by chemical reactions and can be decomposed only by chemical means. Elements and compounds are called pure substances.

Mixtures are formed from two or more pure substances in variable proportions and may be separated into these components by physical means. Mixtures that appear uniform throughout are called homogeneous; those that are not uniform throughout are called heterogeneous.

Definitions of the following:

The atoms are elements that composed of extremely small particles.
The periodic table is very useful device for correlating the properties of the elements.
The elements found in a horizontal row in the table are collectively called a period.
The elements that appear in a given vertical column in the table make up what is called a group or family.
A metal is an element that in general has a characteristic luster, conducts heat and electricity well, and can be pounded into various shapes without breaking. A nonmetal, on the other hand, is an element that is not lustrous, is a poor conductor of heat and electricity, and is brittle in the solid state.

The meaning of Isotopes
All atoms of a given element have the same atomic number. Some elements, however, consist of several types of atoms that differ from one another in mass number. Atoms that have the same atomic number but different mass numbers are calledisotopes.

The mass spectrometer is used to determine the types of isotopes present in an element, the exact masses of these isotopes, and the relative amount of each isotope present.

The meaning of Molecules and Ions

A molecule is a particle that is formed from two or more atoms that are bound tightly together. In chemical and physical processes, molecules behave as units. Some elements and many compounds exist as molecules.

An ion is a particle that is made up of an atom or a group of atoms and that bears and electric charge.

The two types of ion: cation that has a positive charge and anion with a negative charge.

The meaning of chemical equations:

Chemical equations are representation of chemical reactions in terms of the symbols and formulas of the elements and compounds involved. The substance that enter into a reaction are called reactants, and the substances formed in a reaction are called products. In a chemical equation, the formulas of the reactants are indicated on the left and those of the products on the right. An arrow is used instead of the customary equal sign of the algebraic equation

Knowledge of modern chemistry is a basic requirement for an intelligent understanding of the various chemicals and cosmetics being used in beauty salons. Through advances in chemistry, new and better products are being developed for the benefit of their users.

Chemistry is the science which treats of the composition of substances and of the changes which these substances may undergo.

Organic chemistry is that branch of chemistry which treats of carbon and its compounds, which may be derived from the animal and vegetable sources.

Inorganic chemistry is that branch of chemistry that treats of substances found in or on the earth and are generally of mineral extraction, such as is found in the air, water, and bones.

A substance is any definite variety of matter showing the same properties.

The physical state of a substance is dependent on temperature and pressure. A solid may be changed to a liquid by raising the temperature. A liquid may be changed to a gas by raising the temperature or lowering the pressure. The temperature at which a solid changes to a liquid is its melting point; from a liquid to a solid, its freezing point.

Matter is that which occupies space. There are three forms of matter: solids, liquids and gases. Wood is a solid. It has a definite shape and definite volume. Water is a liquid. It has no definite shape but definite volume. It takes the shape of the vessel that holds it. A gas has neither definite shape nor definite volume. Air is a mixture of gases.

A physical change is an alteration of the properties without the formation of any new substance. (Example: Ice melts at a certain temperature and water freezes at a certain temperature. There are no changes in the inherent nature of the water but merely a change in form. This is a physical change. No new substance has been formed).

A chemical change is one in which a new substance or substances are formed, having properties different from the original substance or substances. For example, soap is formed from the chemical reaction between an alkaline substance (potassium hydroxide) and an oil or fat. The soap does not resemble the alkaline substance or the oil from which it is formed.

Elements, Compounds and Mixtures

Matter exists in the form of elements, compounds and mixtures.

An element is a simple substance made up of similar atoms that cannot be decomposed by chemical means. Iron, sulphur, oxygen, zinc and silver are some of the elements. The elements are the units from which more complex substances are built.

Anatom is the smallest quantity of an element that can exist and still retain its chemical properties

Compounds - when two ore more elements unite chemically they form a compound. (Example: Iron, when it is left in the damp air, rusts. The iron combines with the oxygen in the air and forms a new substance know as iron oxide. Each element has lost it identifying features. The new substance formed by iron and oxygen cannot be separated by any mechanical means).

Compounds are divided into four classes:

1. Oxides - are compounds of any element with oxygen. (Example: carbon + oxygen = carbon dioxide).

2. Acids - are compounds of hydrogen, a non-metal, and sometimes oxygen. (Example: sulphuric acid - hydrogen, sulphur, oxygen).

3. Base - is a compound of a metal, oxygen, hydrogen. (Example: sodium hydroxide - sodium, oxygen, hydrogen).

4. A salt is a compound of a metal, a non-metal and sometimes oxygen. (Example: sodium carbonate - sodium, carbon, oxygen).

Chemical compounds are known by the symbols of the elements composing them. One atom of sodium (NA) combined with on atom of chlorine (Cl) makes one molecule (smallest particle of the compound) of the resulting product, sodium chloride (NaCl) or common salt. Two atoms of hydrogen (H) combined with one atom of oxygen (O) form one molecule of water, for which the formula is H2O.

Analysis is a chemical reaction in which a substance or compound is separated into its component parts or elements.

Synthesis is a chemical reaction in which two or more substances or compounds combine to form an entirely new product.

A mixture is a combination of substances which retain their individual identities as separate substances, however thoroughly mingled, such as air and salt water.

Difference between mixture and compounds. In a compound, the resulting properties from the chemical union, such as density, color, solubility, etc. are generally completely different from those of the substances combined. Every particle looks and acts like every other particle in the compound. A compound may never be separated by purely mechanical means. In making a compound, there are always energy and matter changes.

IN a mixture, the resulting properties are the same as they were originally. The particles of one substance differ from another. Mixtures may be separated by mechanical means. In making a mixture, there are no changes in energy.

Properties of Common Elements, Compounds and Mixtures

The properties of some of the most common elements, compounds and mixtures can be advantageously studied by the cosmetologist.

Oxygen (O) - is the most abundant element, being found both free and in compounds, and composes about half of the earth's crust, half of the rock, one-fifth of the air, and 90% of the water. It is a colorless, odorless, tasteless, gaseous substance, combining with most other elements to form an infinite variety of compounds called oxides. One of the chief characteristics of this element is that substances burn more readily in oxygen than in air.

Hydrogen (H) - is a colorless, odorless and tasteless gas. It is the lightest element known, being used as a unit of weight. It is inflammable and explosive when mixed with air. It is found in chemical combination with oxygen in water, and with other elements in acids, bases and organic substances such as wood, meat, fish, sugar and butter.

Air - is the gaseous mixture which makes up the earth's atmosphere. It is odorless, colorless and consists of about 1 part by volume of oxygen and 4 parts of nitrogen. These proportions vary somewhat according to conditions. It also contains a small amount of carbon dioxide, ammonia, nitrites and organic matter, which are essential to plant and animal life.

Hydrogen peroxide (H2O2) - is a compound of hydrogen and oxygen. It is a colorless liquid with a characteristic odor and a slightly acid taste. Organic matter, such as silk, hair, feathers, and nails are bleached by hydrogen peroxide, because of its oxidizing power. The 20 to 40 volume hydrogen peroxide solution is used as a bleaching agent for the hair. A 3% or 10 volume solution of hydrogen peroxide possesses antiseptic qualities.

Oxidizing agents - a substance which readily gives up its oxygen is known as an oxidizing agent. Hydrogen peroxide releases oxygen which oxidizes the hair pigment to a colorless compound. The bleaching agent is reduced and the pigment is oxidized. When oxygen is taken away from any substance it is known as a reduction. The substance which attracts the oxygen is the reducing agent. Oxidation is always accompanied by reduction.

Nitrogen (N) - is a colorless, gaseous element found free in the air. It constitutes part of the atmosphere, forming about four-fifths of the air. It is necessary to life because it dilutes the oxygen. It is found in nature chiefly in the form of ammonia and nitrates.

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Antoine Lavoisier, Chemical Property, Chemical Reaction, Chemistry, Isotope, Mixture, Molecule, Periodic Table

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