Study Portal 4 – Chapter 4

Structure of Molecules

 

Introductions

Q1.      Define structure of molecules.

Ans.     In chemistry the structure determination is the basic and most essential element. The properties of matter lie in the structure of compounds, and structure of compound is largely influenced by the type of bonding in the compound.

Q2.   What is chemical bond? Why atoms form chemical bond?

Ans.    The force of attraction which keeps the atoms in substance is called a chemical bond e.g. in oxygen molecule (O2) two atoms are held together by chemical bond. Similarly in NaCl, sodium and chloride are held together by chemical bond. In this word, every thing tends to get stability e.g. water flows from higher level to lower level. Similarly electricity flows from higher potential to lower potential. In the same way atoms tend to decrease their energy and get stability. In the periodic table the most stable electronic structure is of the noble gasses, so all the other atoms react to attain the electronic structure of these noble gasses. Helium has two electrons and all other members have eight electrons in their last shells. It is known as octal rule. For this purpose atoms lose, gain or share electrons and form different types of bonds.

Q3.      Name types of bond.

Ans.    Depending upon their nature there are following 4 types of chemical bonds:

  • The ionic bond
  • The covalent bond
  • The co-ordinate covalent bond
  • Metallic bond

Q4.      Define ionic bond.

Ans.    This type of bond is formed when one or more electrons are completely transferred from atom to the other as results of these transfer ions are formed. One of these ions is positively charged and other is negatively ions charged. These ions attract each other by strong electrostatic force and hence ionic bond is formed between these ions ionic bond have high melting and boiling point.

Q5.      What is covalent bond?

Ans.    The covalent bond is formed by mutual sharing of electrons between two atoms. The shared pairs of electrons are counted towards the stability of both the participating atoms. These two atoms may be similar or dissimilar. In this way, they acquire the stable configuration of the nearest noble gas. The electron that pair up to form a chemical bond are called ‘bond pair’ electron depending upon the number of bond pairs, covalent bond is classified into following three types.

  • Single Covalent Bond:- When one electron is contributed by each bonded atom, one bond pair is formed and it forms a single covalent bond e.g. H2, Cl2, HCl etc. it is represented by a single line (-) e.g. H-H or H2
  • Double Covalent Bond:- When each bonded atom contributes two electrons, two bond pairs are shared and a double covalent bond is formed e.g. O2, C2H4 it is represented by two short lines (=) e.g. O = O or O2
  • Triple Covalent Bond: – When each bonded atoms contributes three electrons, three bond pairs are involved in bond formation. This type is called triple covalent bond e.g. N2 and C2H2 it is represented by three short lines (≡) e.g. N N or N2

Q6.      What is meant by a coordinate covalent bond or dative bond?

Ans.    It is that type of a bond which is formed when the shared electron pair is provided by one of the combining atoms. The atom which provides the electron pair is termed as the donor atom whiles the other atom which accepts it is called the acceptor atom. Such a bond is also known as dative bond. Coordinate covalent bond is represented by an arrow pointing towards the acceptor atom. e.g.

Q.7.  Define and explain non-polar and polar covalent bond.

Ans.    Polar Covalent Bond

The covalent bond formed between unlike atoms which differ in their electronegativity is said to be a polar covalent bond. When a covalent bond is formed between two atoms of different elements then the bonding pair of electrons does not like exactly midway between the two atoms. It lies more towards the atom which has more electronegative.

Non-Polar Covalent Bond

This bond formed between two atoms of the same element. The electrons are shared equally between the two atoms in such molecules. The shared electron pair lies exactly midway between the two atoms.

Q8.      What is meant by a metallic bond?

Ans.    The force of attraction that binds positive metal ions to the number of electron with in its sphere of influence is called metallic bond. The crystalline solids in which metal atoms are held together by metallic bonds are known as metallic solids.

Q9.      What is meant by intermolecular forces?

Ans.    These are the forces of attraction presented between the molecules to bring them closer and to bind molecules. These are quite different from intermolecular forces or bonds. Which are present between the atoms to form a molecule?

Q10.  Define dipole-dipole forces and its properties.

Ans.    The attractive forces between positive end of one polar molecule and negative end of other polar molecule are known as dipole-dipole forces. The dipole-dipole forces are present in Hydrochloric acid, acetone and chloroform.

Properties

  • These forces are formed in all polar molecules.
  • These forces operate reasonably in liquids.
  • They are about one percent as effective as a covalent bond.
  • Due to greater distance among the gas molecules these forces are very weak in gasses.
  • Stronger the dipole-dipole forces, higher will be the thermodynamic properties like melting point, boiling point, heat of sublimation heat of vaporization and heat of fusion.

Q11.  Define Hydrogen Bonding.

Ans.    “The bond between hydrogen atom of one molecules and a more electronegative atom of an other molecules is called hydrogen bond”

Properties of compounds are greatly affected by hydrogen bonding e.g.

  • Under the normal temperature conditions, the pure compounds like water, ethanol and carboxylic acid have their molecules associated due to hydrogen bonding.
  • The compounds having hydrogen bonding, the melting and boiling points are comparatively higher than the hydrides of the same.

What is a Nature of Bonding?

The type of bonding greatly effects both physical and chemical properties of compounds. It is so important that generally the compounds are classified on the bases of type of bonding the physical properties e.g. M.P, B.P, density, color, surface tension, viscosity, refraction index, solubility, bond energy, vapor pressure, lattice energy etc may be predicted from knowing the type of bonding.

Q12. Describe the nature of bonding and ionic compounds.

Ans.    The ionic compounds which have a strong type of bonding are hard, solid and very high melting and boiling points. The ionic compounds although have ions but they conduct electricity only in molten state, because of the limited mobility in solid state and high mobility in liquid state. The ionic compounds which are strongly polar are generally soluble in the polar solvents like water, as concerned with reactions, ionic compounds are more reactive and the rate of reaction is very fast.

Q13. Describe the properties of covalent compounds according to nature of bonding.

Ans.    The covalent compounds have sharing of electrons and thus there does not exist strong interactions among the constituting particles like that of ionic compounds, hence they have low melting and boiling points and mostly the covalent compounds are gasses. The covalent compounds do not conduct electricity unless they are ionized by some factor, so the pure water does not conduct the electricity. But when some ionizing material is added to the water, which makes it ionized and thus the flow of charge particles becomes possible.

Q14.   Describe the nature of bonding and polar and non-polar compounds.

Ans.    The behavior of polar and non-polar compounds is well understand in terms of the ionic and covalent compounds, where the polarity also counts greatly in determining the properties of these compounds, the non-polar compounds are mostly gases and have low melting and boiling points and do not conduct electricity on the other side the polar compounded have relatively high melting and boiling points and conduct electricity.

Q15.   Describe the nature of bonding and metals.

Ans.    The metals have a very special type of bonding and thus their characters also are very interesting in the metals there exists a positive center around which is a sea of negative sphere exists. The negative sphere which consists of free electron gives the metals a high conductor character for both the electricity and heat. More over the metals have lustrous surface due to transition of electron.

%d bloggers like this: