Atom and Element (Chemistry)

 All matter is composed of atoms; each atom is a very small, chemically indivisible particle. The word 'atom' is from the Greek work "atmos" which means "cannot be cut apart". Elements are the basic building blocks of all matter. The chart given below gives the relationship between matter, pure substances, elements, compounds, atoms, molecules etc.

Both elements and compunds are pure substance. Atoms are the smallest particles that can be identified as a particular element, and molecules are the smallest particles that can be identified as a particular compound.

ELEMENT

Any material that is composed of only one type of atom is called a basic element, or just an element. Elements are different because they can be composed of different types of atoms. Elements can also occur in a molecular form in which the same type of elements (atoms) are chemically combined, such as two oxygen atoms, O, which form molecular oxygen, O₂, when chemically combined. There are some elements, which you should know, that only occur naturally (under normal conditions) in their molecular forms. They are called diatomic molecules or, sometimes, molecular elements and they are: hydrogen, H₂; nitrogen, N₂; oxygen, O₂; fluorine, F₂; chlorine, Cl₂; bromine, Br₂; iodine, I₂. 

ATOM 

Atoms consist of three subatomic particles:

• electrons
• electrons are negatively charged particles.
• protons
• protons are positively charged particles.
• neutrons
• neutrons have no charge..

The atoms of different elements are different from each other because they have different numbers of protons.For example, the atoms in hydrogen are identical to each other. However, the atoms of oxygen are different from the atoms of hydrogen. Each type of atom has properties different from other atoms. For example, each type of atom has different properties, one of which is mass--the mass of a carbon atom weighs 12 times that of a hydrogen atom


MOLECULE

A molecule is a combination of two or more atoms in a definite arrangement held together by chemical bonds.  The atoms may be of the same type of element, or they may be different. Molecule is created by bonded atoms when electrons fill up the outer orbit of each atom. For example H2, CO2, N2


COMPOUND

Compounds, like water, are formed by combining the atoms of different elements together according to some chemical formula. In other word, compounds are composed of two or more atoms chemically combined in fixed proportions. For example, water, H₂O, always occurs in a ratio of 2 hydrogens : 1 oxygen--if the ratio were anything else it would not be water, H₂O₂ with a ratio of 2 : 2 is peroxide, certainly not water.


IONS

The nucleus of an atom (containing protons and neutrons) remains unchanged after ordinary chemical reactions, but atoms can readily gain or lose electrons.
If electrons are lost or gained by a neutral atom, then the result is that a charged particle is formed - called an ion.

For example, Sodium (Na) has 11 protons and 11 electrons. However, it can easily lose 1 electron. The resulting cation has 11 protons and 10 electrons, for an overall net charge of 1+ (the units are electron charge). The ionic state of an atom or compound is represented by a superscript to the right of the chemical formula: Na⁺, Mg²⁺ (note the in the case of 1+, or 1-, the '1'is omitted). In contrast to the Na atom, the Chlorine atom (Cl) easily gains 1 electron to yield the chloride ion Cl^- (i.e. 17 protons and 18 electrons).

In general, metal atoms tend to lose electrons, and nonmetal atoms tend to gain electrons.

A T O M & E L E M E N T from roszelan



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atom, molecules, ions

Ion image