Chemical bonding

INORGANIC Pharmacy-II

Presentation On-Chemical Bonding

SUBMITTED TOMD.ASSADUJAMAANLecturer, Dept. Of Pharmacy, NUB

SUBMITTED BY

1. Saidur Rahman , ID-9382. Mubassera Anee , ID-9403. Zakia Sultana , ID-9514. Malvin Sajib , ID-9555. Abdul Hannan , ID-9596. Swarnali Sultana , ID-960

CHEMICAL BONDING

A chemical bond is defined as the attractive force that hold two or more atoms together in a molecule or an ion.

WHY DO ATOMS COMBINE

Atoms combine because they are not stable unless their valence orbital is full of electrons. In order to fill this outer orbital they will share, give, or take electrons from other atoms.

HOW DO ATOMS COMBINE

Atoms can atoms combine in the following two ways :

1. Transfer of one or more electrons from the valence shell of one atom to the valence shell of another atom.

2. One , two or three electron pairs of the valence shell of both the combining atoms are shared between them.

TYPES OF CHEMICAL BONDS

Two types:• Strong Bonds• Weak Bonds

Strong Bonds:I. Ionic BondII. Covalent BondIII. Coordinate or Dative Covalent BondIV. Metallic Bond

Weak BondI. Hydrogen BondII. Vander Waals Interaction

IONIC BOND

An ionic bond is a type of chemical bond that involves a metal and a non-metal ion (or polyatomic ions such as ammonium) through electrostatic attraction. In short, it is a bond formed by the attraction between two oppositely charged ions.

How are ionic BONDS FORMEDThe metal donates one or more electrons, forming a positively charged ion or cation with a stable electron configuration. These electrons then enter the non metal, causing it to form a negatively charged ion or anion which also has a stable electron configuration. The electrostatic attraction between the oppositely charged ions causes them to come together and form a bond.

For example, common table salt is sodium chloride. When sodium (Na) and chlorine (Cl) are combined, the sodium atoms each lose an electron, forming cations (Na+), and the chlorine atoms each gain an electron to form anions (Cl−). These ions are then attracted to each other in a 1:1 ratio to form sodium chloride (NaCl).

The removal of electrons from the atoms is endothermic and causes the ions to have a higher energy. There may also be energy changes associated with breaking of existing bonds or the addition of more than one electron to form anions. However, the attraction of the ions to each other lowers their energy.

Factors or conditions for favoring ionic compounds

I. Ionization Enthalpy (Energy) : Lesser the value of ionization enthalpy, greater the tendency of the atom to form cation. For example, alkali metals form cations easily because of the low value of ionization energies. 

II. Electron gain enthalpy : Greater the value of electron gain enthalpy, more the tendency of the atom to form anion .For example ,halogens have high electron gain enthalpies within the respective periods and form ionic compounds easily . 

III. Lattice enthalpy : It is the energy released when the close packing of the gaseous ions of the opposite charge forms one mole of ionic solid. Magnitude of lattice energy gives an idea about the inter-ionic forces and it also gives the measure of the stability of the ionic compound which depends upon the following factors. 

IV. Size of the ion : Smaller the size of the ion s, lesser the inter nuclear distance and greater the inter ionic interaction, hence, larger the magnitude of lattice energy 

V. Charge on the ions : Larger the magnitude of the charge on the ions greater will be the attractive forces and higher the negative value of lattice energy. 

covalent BOND

A chemical bond in which two atoms share some of their valence electrons, thereby creating a force that holds the atoms together.

Usually each atom contributes one electron to form a pair of electrons that are shared by both atoms.

A clear example is the molecule of chlorine, chlorine occurs in nature as a molecule composed of 2 atoms of chlorine, chlorine atoms are linked by a covalent bond produced by the sharing of 2 electrons.During this process two atoms are join together to form one molecule, ignoring the molecular orbital theory, bonding / anti bonding and in order to explain it simply, we can say that 2 atomic orbital (Cl + Cl) combine to form a new molecular orbital (Cl2).The orbital are defined as regions of the atoms or molecules where the electrons are localized.

There are three types of covalent bond depending upon the number of shared electron pairs.

I. SINGLE COVALENT BONDII. DOUBLE COVALENT BONDIII. TRIPLE COVALENT BOND

SINGLE COVALENT BONDA covalent bond formed by the mutual sharing of one electron pair between two atoms is called a “Single Covalent bond”

 Examples: 

DOUBLE COVALENT BONDA covalent bond formed between two atoms by the mutual sharing of two electron pairs is called a "double   covalent bond".

Examples:

TRIPLE COVALENT BONDA covalent bond formed by the mutual sharing of three electron pairs is called a "Triple covalent bond".

Examples:

POLAR COVALENT BONDA covalent bond formed between two different atoms is known as Polar covalent bond.For example when a Covalent bond is formed between H and Cl , it is polar in nature because Cl is more   electronegative than H atom . Therefore, electron cloud is shifted towards Cl atom. Due to this reason a   partial -ve charge appeared on Cl atom and an equal +ve charge on H atom.Examples:

NON-POLAR BOND A covalent bond formed between two like atoms is known as Non-polar bond. Since difference of  electro negativity is zero therefore, both atoms attract electron pair equally and no charge appears on any atom and the whole molecule becomes neutral.

Examples:

Coordinate or Dative Covalent Bond

A dipolar bond, also known as coordinate link, coordinate covalent bond, dative bond, or semi polar bond, is a description of covalent bonding between two atoms in which both electrons shared in the bond come from the same atom.

The reaction between ammonia and hydrogen chloride

• If these colorless gases are allowed to mix, a thick white smoke of solid ammonium chloride is formed.

• Ammonium ions, NH4+, are formed by the transfer

of a hydrogen ion from the hydrogen chloride to the lone pair of electrons on the ammonia molecule.

When the ammonium ion, NH4+, is formed, the fourth hydrogen

is attached by a dative covalent bond, because only the hydrogen's nucleus is transferred from the chlorine to the nitrogen. The hydrogen's electron is left behind on the chlorine to form a negative chloride ion.Once the ammonium ion has been formed it is impossible to tell any difference between the dative covalent and the ordinary covalent bonds. Although the electrons are shown differently in the diagram, there is no difference between them in reality.

metallic bond

The chemical bond characteristic of metals, in which mobile valence electrons are shared among atoms in a usually stable crystalline structure.

The structure of a metallic bond is quite different from covalent and ionic bonds. In a metal bond, the valence

electrons are delocalized, meaning that an atom's electrons do not stay around that one nucleus. In a

metallic bond, the positive atomic nuclei (sometimes called the 'atomic kernels') are surrounded by a sea of delocalized electrons which are attracted to the nuclei

 Positive atomic nuclei (+) surrounded by delocalized electrons (∙)

PROPERTIES OF METALIC BOND

Formed between atoms of metallic elements

Electron cloud around atoms Good conductors at all states,

lustrous, very high melting pointsExamples; Na, Fe, Al, Au, Co

hydrogen bond

 An electrostatic attraction between a hydrogen atom in one polar molecule (as of water) and a small electronegative atom (as of oxygen, nitrogen, or fluorine) in usually another molecule of the same or a different polar substance

Hydrogen bonds only form between hydrogen and oxygen (O), nitrogen (N) or fluorine (F). Hydrogen bonds are very specific and lead to certain molecules having special properties due to these types of bonds. Hydrogen bonding sometimes results in the element that is not hydrogen (oxygen, for example) having a lone pair of electrons on the atom, making it polar. Lone pairs of electrons are non-bonding electrons that sit in twos (pairs) on the central atom of the compound. Water, for example, exhibits hydrogen bonding and polarity as a result of the bonding. This is shown in the diagram below. Because of this polarity, the oxygen end of the molecule would repel negative atoms like itself, while attracting positive atoms, like hydrogen. Hydrogen, which becomes slightly positive, would repel positive atoms (like other hydrogen atoms) and attract negative atoms (such as oxygen atoms). This positive and negative attraction system helps water molecules stick together, which is what makes the boiling point of water high (as it takes more energy to break these bonds between water molecules). In addition to the four types of chemical bonds, there are also three categories bonds fit into: single, double, and triple. Single bonds involve one pair of shared electrons between two atoms. Double bonds involve two pairs of shared electrons between two atoms, and triple bonds involve three pairs of shared electrons between two atoms. These bonds take on different natures due to the differing amounts of electrons needed and able to be given up.

Vander Waals Interaction

Van der Waals forces include attractions between atoms,

molecules, and surfaces. They differ from covalent andionic bonding in that they are caused by correlations in

thefluctuating polarizations of nearby particles (aconsequence of quantum dynamics).