Chemical Combinations II

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Welcome to class! 

In today’s class, we will be talking more about chemical combinations. Enjoy the class!

CHEMICAL COMBINATIONS II

HYDROGEN BOND

A hydrogen bond is a dipole-dipole intermolecular force of attraction which exists when hydrogen is covalently bonded to a highly electronegative element of small atomic size. The electronegative element can be N, O, F, Cl, Br or I.

The highly electronegative element has a very strong affinity for electrons. Hence, they attract the shared pair of electrons in the covalent bond toward themselves, resulting in the formation of a dipole which leaves a partial positive charge on the hydrogen atom and a partial negative charge on the electronegative atom. An electrostatic attraction between two dipoles is set up when the positive pole of one molecule attracts the negative pole of the other. This attractive force is known as a hydrogen bond.

IMPORTANCE OF HYDROGEN BOND

It accounts for the solubilities of some compounds containing O, N and F in certain hydrogen-containing solvents such as water. The crystalline shape of solid water (ice) is due to a hydrogen bond.

EVALUATION

1. Define hydrogen bond
2. State two importance of hydrogen bond.

METALLIC BOND

Metal atoms are held together in the solid crystal lattice by a metallic bond. each metallic atom contributes its outer (valence) electron to the electron cloud, thus becoming positively charged. The resulting positively charged metallic ions tend to repel each other but are held together by the moving electron cloud and overlapping residual electron orbits. Thus, a metallic bond is a force of attraction between the positive metal ions and the free mobile electrons.

VAN DER WAALS’ FORCES

The attractive forces which make it possible for non-polar molecules like nitrogen and CO^­₂ molecules to form liquid and solid is called van der Waals’ force. This force though very weak when compared to ionic and a covalent bond is important in the liquefaction of gases and the formation of molecular lattices as in iodine and naphthalene crystals.

GENERAL EVALUATION/REVISION

1. Using electron dot representation, show the formation of MgO and O₂ molecule
2. Define hydrogen bond
3. How is a metallic bond formed?
4. Describe how you will separate a mixture of NaCl, Iodine and PbCl₂

READING ASSIGNMENT

New School Chemistry for Senior Secondary School by O.Y Ababio, Pg 55-66

WEEKEND ASSIGNMENT

1. Noble gases are stable because they A. are volatile B. have octet configuration C. have no neutron in their nucleus forms ions easily
2. The bond type in diatomic nitrogen gas is A. double covalent bond          triple covalent bond                   C. single covalent bond              D. double electrovalent bond
3. In electrovalency, valence electrons are transferred and the atomic number is  A.  reduced   B.   stabilized   C.   unaffected   D.   increased
4. An element Y having an atomic number of 19 combines with another element Z with atomic number 17. The likely compound formed is  A. Y₂Z    B.    Y₃Z₂    C.  YZ   D.  Y₂Z₂
5. The type of attractive force which exist between discrete molecules is called      A.   metallic bond   B.    hydrogen bond   C.   dative bond       D. van der Waals’ forces

THEORY

1. Illustrate the formation of the compound AlCl3 using electron dot representation
2. State two properties of the compound
3. Define hydrogen bond

 

In our next class, we will be talking about Identification and Types of Alloys.  We hope you enjoyed the class.

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