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Chemical bonding

A chemical bondis an attraction between atoms thatallows the formation of chemicalsubstances that containtwo or more atoms. The bondis caused by the electrostaticforce of attraction between opposite charges, eitherbetween electrons and nuclei, or as the result of a dipoleattraction.

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Chemical bonding is one of the most basic fundamentals of chemistry

that explains other concepts such as molecules and reactions. Without

it, scientists wouldn't be able to explain why atoms are attracted to each

other or how products are formed after a chemical reaction has taken

place. To understand the concept of bonding, one must first know the

basics behind atomic structure.Introduction

A common atomcontains a nucleus composed of protons and neutrons,

with electrons in certain energy levels revolving around the nucleus. In

this section, the main focus will be on these electrons. Elements are

distinguishable from each other due to their "electron cloud," or the area

where electrons move around the nucleus of an atom. Because eachelement has a distinct electron cloud, this determines their chemical

properties as well as the extent of their reactivity (i.e. noble gases are

inert/not reactive while alkaline metals are highly reactive). In chemical

bonding, only valence electrons, electrons located in the orbitals of

the outermost energy level (valence shell) of an element, are involved.

http://chemwiki.ucdavis.edu/Physical_Chemistry/Atomic_Theoryhttp://chemwiki.ucdavis.edu/Physical_Chemistry/Quantum_Mechanics/Atomic_Theory/Electrons_in_Atoms/Electronic_Orbitalshttp://chemwiki.ucdavis.edu/Physical_Chemistry/Quantum_Mechanics/Atomic_Theory/Electrons_in_Atoms/Electronic_Orbitalshttp://chemwiki.ucdavis.edu/Physical_Chemistry/Atomic_Theory

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Bonding types Ionic or electrovalent Bond

Covalent Bond

Coordinate bond Metallic bond

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Definition:-An ionic bond is formed by the attraction of oppositely chargedatoms or groups of atoms. When an atom (or group of atoms)gains or loses one or more electrons, it forms an ion. Ions haveeither a net positive or net negative charge. Positively chargedions are attracted to the negatively charged 'cathode' in an

electric field and are calledcations

.Anions

are negativelycharged ions named as a result of their attraction to the positive'anode' in an electric field

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Characteristics of Ionic compounds

Some important characteristics of ionic compounds are asfollows.1. Ionic compounds are hard and rigid due to strong forcesof attraction between the oppositely charged ions.2. Ionic compounds have high melting and boiling points,again due to strong forces of attraction between the ions.

3. Ionic compounds dissolve easily in water.4. Solid Ionic compounds do not conduct electricitybecause their constituent ions are fixed in their positions.But, when melted or dissolved in water, they conductelectricity because the ions become free in a solution.5. Ionic compounds are crystalline due to the orderly

distribution of ions in them. This gives characteristicgeometrical shapes to the ionic compounds.

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Examples of Ionic Bonds:

1. Sodium chloride - NaCl - table salt2. Calcium chloride - CaCl2rock salt3. Sodium hydroxide - NaOH - Lye used insoap

4. Sodium fluoride - NaF fluoride intoothpaste5. Iron Oxide Fe2O3- rust6. Calcium hydroxide Ca(OH)2basic salt inantacid tablets

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Definition:- A covalent chemical bond results from the sharing of electrons between twoatoms with similar electronegativities A single covalent bond represent the

sharing of two valence electrons (usually from two different atoms). The

Lewis structure below represents the covalent bondbetween two hydrogen

atoms in a H2molecule.

http://www.chem.ufl.edu/~chm2040/Notes/Chapter_11/covalent.htmlhttp://www.chem.ufl.edu/~chm2040/Notes/Chapter_11/covalent.html

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Some elements form very large molecules by forming covalent bonds. When these

molecules repeat the same structure over and over in the entire piece of material,

the bonding of the substance is called network covalent. Diamond is an example of

carbon bonded to itself. Each carbon forms 4 covalent bonds to 4 other carbonatoms forming one large molecule the size of each crystal of diamond.

Silicates, [SiO2]xalso form these network covalent bonds. Silicates are

found in sand, quartz, and many minerals.

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Definition:

it is a special type of covalent bond it may be

Defined as a covalent bond in which both electrons of the

shared pair are contribute by one of the two atoms It is alsocalled as

dative bond

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Both the ammonium ion and hydronium ion contain onecoordinate covalent bond each. A lone pair on the oxygen atomin water contributes two electrons to form a coordinatecovalent bond with a hydrogen ion to form the hydronium ion.

Similarly, a lone pair on nitrogen contributes 2 electrons toform the ammonium ion. All of the bonds in these ions areindistinguishable once formed, however.

Ammonium (NH4+) Hydronium (H3O+)

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Formation of ammonium ion (NH4) Formation of Hydronium Ion (H3o)

Combinaton of Ammonia & Borontriluoride

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The valence electrons of pure metals are not strongly associated withparticular atoms. This is a function of their low ionization energy.Electrons in metals are said to be delocalized(not found in onespecific region, such as between two particular atoms).Since they are not confined to a specific area, electrons act like aflowing sea, moving about the positively charged cores of the metalatoms.Delocalization can be used to explain conductivity, malleability, andductility.Because no one atom in a metal sample has a strong hold on itselectrons and shares them with its neighbors, we say that they arebonded.

In general, the greater the number of electrons per atom thatparticipate in metallic bonding, the stronger the metallic bond.

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