{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Ch_04_summary - CHAPTER 4 BONDING(IB TOPICS 4 AND 14...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
CHAPTER 4 BONDING (IB TOPICS 4 AND 14) SUMMARY © IBID Press 2007 1 A chemical bond is the interaction between atoms within a molecule, between molecules or between ions of opposite charges. Bond formation is an exothermic process; it gives out energy and leads to a more energetically stable state. Bonding in liquids and solids 1. Covalent bonding results from electron sharing between non-metals or a non-metal and a metal of higher electronegativity. The electron pair is attracted by both nuclei leading to a bond that is directional in nature. (i) van der Waals’ Forces : For a non-polar molecule, only weak, temporary, instantaneous dipole-dipole interaction called van der Waals’ forces exist between molecules. These molecules are low melting point solids and low boiling point liquids and gases. Larger the molecule, stronger the van der Waals’ forces, higher its boiling and melting points. (ii) Dipole-dipole Interaction : In a polar molecule, besides weak van der Waals’ forces, the molecules experience stronger permanent dipole-dipole interaction. (iii) Hydrogen Bonding : Elements of high electronegativity (F, O, N), bonded to a (tiny) hydrogen atom give rise to a special case of dipole-dipole interaction called H-bonding. This is important in determining solubility, melting and boiling points, and stability of crystal structures. Hydrogen bonding also plays an important role in biological systems. Hydrogen bonded molecules experience stronger hydrogen bonding in addition to van der Waals’ forces and dipole-dipole interaction. Strength of bonding: van der Waals’ < dipole-dipole < H-bond << covalent bond ionic bond. However, van der Waals’ forces can become extensive depending on the size of the molecules, e.g., in polymers and long chain hydrocarbon molecules. 2. Ionic bonding occurs as a result of electron transfer from active metals of Groups 1, 2, 3 to active non-metals of Groups 6, 7, leading to electrostatic attraction between ions of opposite charges. Ionic crystals are regular repeating arrays of positive and negative ions, packed so that each positive ion is surrounded by negative ions and vice versa in a 3 dimensional lattice structure. Ionic crystals have high melting and boiling points, are
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}