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Matter in our surroundings, Elements, Compounds, Mixtures
Matter is any thing which has mass and occupies space. All solids, liquids and gases around us are made of matter. Scientist believe that matter is made of tiny particles that clump together. You cannot see these particles but you can see the matter, for example, a book, a car, a letter, a hand set, a piece of wood, tree, a bag etc.
A substance is a pure kind of matter having only one kind of constituent particle (atom or molecule). Water, iron, gold, copper, aluminum and oxygen are examples of substances. All substances are matter but all forms of matter are not substances.
Elements
Elements All substances are made up of chemical elements. A chemical element is a basic form of matter that cannot be chemically broken down into simpler substances. A chemical element is a pure substance and it consists of one type of atom distinguished by its atomic number. Examples of some elements are : helium, carbon, iron, gold, silver, copper, aluminum, hydrogen, oxygen, nitrogen, sulphur, copper, chlorine, iodine, uranium, and plutonium.
Elements are the building blocks of the Universe. In total, 114 elements have been listed so far. Out of the total 114 known elements, about 90 occur naturally on Earth and the remaining have been synthesized artificially by nuclear reactions. Only two elements namely hydrogen (92%) and helium (7%) make up about 99% of the total mass of the Universe. The remaining elements contribute only 1% to the total mass of the Universe.
Out of about 90 elements found naturally on Earth, two elements silicon and oxygen together make up almost three-quarters of the Earth’s crust. Our body is also composed of elements but the composition of elements in human body is very much different from that of the Earth’s crust.
Compounds
Chemical compound, any substance composed of identical molecules consisting of atoms of two or more chemical elements.
All the matter in the universe is composed of the atoms of more than 100 different chemical elements, which are found both in pure form and combined in chemical compounds. A sample of any given pure elementis composed only of the atoms characteristic of that element, and the atoms of each element are unique. For example, the atoms that constitute carbon are different from those that make up iron, which are in turn different from those of gold. Every element is designated by a unique symbol consisting of one, two, or three letters arising from either the current element name or its original (often Latin) name. For example, the symbols for carbon, hydrogen, and oxygen are simply C, H, and O, respectively. The symbol for iron is Fe, from its original Latin name ferrum. The fundamental principle of the science of chemistry is that the atoms of different elements can combine with one another to form chemical compounds. Methane, for example, which is formed from the elements carbon and hydrogen in the ratio four hydrogen atoms for each carbon atom, is known to contain distinct CH4 molecules. The formula of a compound—such as CH4—indicates the types of atoms present, with subscripts representing the relative numbers of atoms.
Chemical compounds show a bewildering array of characteristics. At ordinary temperatures and pressures, some are solids, some are liquids, and some are gases. The colours of the various compounds span those of the rainbow. Some compounds are highly toxic to humans, whereas others are essential for life. Substitution of only a single atom within a compound may be responsible for changing the colour, odour, or toxicity of a substance. So that some sense can be made out of this great diversity, classification systems have been developed. An example cited above classifies compounds as molecular or ionic. Compounds are also classified as organic or inorganic. Organic compounds (see below Organic compounds), so called because many of them were originally isolated from living organisms, typically contain chains or rings of carbon atoms. Because of the great variety of ways that carbon can bond with itself and other elements, there are more than nine million organic compounds. The compounds that are not considered to be organic are called inorganic compounds.
Within the broad classifications of organic and inorganic are many subclasses, mainly based on the specific elements or groups of elements that are present. For example, among the inorganic compounds, oxidescontain O2? ions or oxygen atoms, hydrides contain H? ions or hydrogen atoms, sulfides contain S2? ions, and so forth. Subclasses of organic compounds include alcohols (which contain the ?OH group), carboxylic acids (characterized by the ?COOH group), amines (which have an ?NH2 group), and so on.
Mixtures
Mixtures are the substances composed of two or more forms of matter. You can separate them by physical methods. Examples include a solution of salt and water, mixture of sugar and water, different gases, air, etc. In any mixture, the various components do not combine through any kind of chemical changes. Therefore, the components do not lose their individual properties.
When a sample of matter has the same composition throughout, we call that substance a homogeneous substance. A cup of water will have the same chemical composition throughout (symbol for water). That makes it a homogeneous substance. A piece of gold will also have the same chemical composition, making it a homogenous substance. Homogeneous Mixtures behave in a similar way — the substance formed appear to have the same chemical composition. Alloys and Solutions are Homogeneous mixtures.
A mixture can also result in two or more phases clearly separated by boundaries. Very often, the separation can be clearly seen by the eye. A heterogeneous mixture is one that does not have uniform properties and composition. Take a look at a bowl of cereal with nuts. A spoon full will surely have a different number of nuts than a second spoonful taken at random. Another example—take some sea-sand into your palms. Look at it closely and you will notice that some sand particles are bigger than others, and the colors of some particles may be different too.