Science: Atom & Molecules

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|Atoms and Molecules | |Everyday Science | | An atom is the smallest "piece" of an element that still has the properties of that element. A molecule is a combination of two or more | |atoms bonded together. |

Table of Content

Constituents of Atoms3

Isotopes of an Element4

But the Orbits Are Quantized6

Atomic Excitation and De-excitation7

Ionization of Atoms8

Chemical reactions and molecules9

Molecular science10

Molecular size11

Molecular geometry11

Molecular spectroscopy11

Molecular Orbtials........................................................................................................................…...12

The Molecules…………………………………………………………………………………………13

References………………………………………………………………………………………………………………………………………..17

Atom and Molecules
Atom:
An atom is the smallest "piece" of an element that still has the properties of that element. For example, an atom of gold is the smallest piece of gold that still acts like gold — divide that atom any further and the particles inside are no longer gold. Atoms are much too small to see or feel with our human senses, but evidence from scientific instruments and studies clearly indicates that they are at the heart of all objects and matter in the universe. When many atoms come together, atoms tend to form molecules. Molecule:

A molecule is a combination of two or more atoms bonded together. For example, a molecule of water (designated by the symbol H2O) consists of two hydrogen atoms and oxygen atoms which are in a "relationship" — held together by an electric attraction. The basic building blocks of the "normal" matter that we see in the Universe are atoms, and combinations of atoms that we call molecules. We first consider atoms and then molecules. However, we shall see that although "normal matter" is composed of atoms and molecules, most of the matter in the Universe is not in the form of atoms or molecules, but rather in the form of a plasma. We discuss plasmas in the next section. Constituents of Atoms

Atoms are composed of three classes of constituents, as illustrated in the following table

.
|Constituent |Symbol |Charge |Mass | |Electrons |e- |-1 |9.1 x 10-28 g | |Protons |p+ |+1 |1836 x electron mass | |Neutrons |n |0 |Approximately that of p+ |

Thus, most of the mass of atoms resides in the neutrons and protons which occupy the dense central region called the nucleus (see the Bohr atom below). The number of protons (or the number of electrons) is called the atomic number for the atom. The total number of protons plus neutrons is called the atomic mass number for the atom. Atoms are electrically neutral because the number of negatively-charged electrons is exactly equal to the number of positively-charged protons. The number of neutrons is approximately equal to the number of protons for stable light nuclei, and is about 1-2 times the number of protons for the heavier stable nuclei. Isotopes of an Element

Atoms having the same number of protons (and therefore the same number of electrons) but different numbers of neutrons are called isotopes of the element in question. Thus, the isotopes of an element have the same atomic number but differ in their atomic mass number. A compact notation for isotopes of an element is illustrated by the following examples. [pic]

In this notation...
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