Ionic and Covalent Bonding Why Do Atoms Form

Ionic and Covalent Bonding

Why Do Atoms Form Compounds? ® To become more stable. ® Any atom that has 7 or less valence electrons is considered “unstable. ” ® Group 18 noble gases do not form compounds because they have 8 valence electrons.

How do atoms become more stable? ® They can gain electrons, lose electrons, or share electrons to make their outer energy level full. ® Example: Na. Cl ® Na has one valence electron and Cl has 7 valence electrons. ® Na “gives” its 1 valence electron to Cl so that Cl can have 8 valence electrons. ® Both atoms now have a stable outer electron orbital.

How do bonds form? ® When atoms gain, lose, or share electrons, an attraction forms between the atoms. ® This force that holds them together is called a chemical bond. ® There are 2 different types of chemical bonds ® 1. Ionic bonds ® 2. Covalent bonds

Ionic Bonds ® Form when one atom “gives” its valence electrons to another atom. ® The atoms that “gives up” electrons becomes positive, and the atom that “receives” the electrons becomes negative. ® The 2 atoms then attract each other because they have opposite charges. ® Example: Na. Cl ® Na gives up 1 electron to have a charge of +1 and Cl gains 1 electron to have a charge of – 1, so they attract.

Ionic compounds ® Example – salt Na. Cl ® Metals and nonmetals usually combine by ionic bonding. ® The ionic bonds in these compounds are very strong. They have high melting and boiling points ® They are hard and brittle solids. ® They are good conductors of electricity when dissolved in water. ® ® Form a crystal lattice, which is very hard to take apart. ® Made from alternating positive and negative ions.

Covalent bonds ® Form when atoms share electrons. ® The particle that forms from covalent bonds is called a molecule. ® The atoms in group 14 form covalent bonds because it is much easier to share their 4 valence electrons than to gain or lose them. ® There are 3 types of covalent bonds Single – share 2 electrons. ® Double – share 4 electrons. ® Triple – share 6 electrons. ®

Covalent compounds ® Example – sugar ® Attraction between individual molecules is very weak. ® Have ® low melting and boiling points. Sugar melts at 108 o. C and salt melts at 801 o. C. ® Form soft solids. ® Poor electrical and thermal conductors. ® Usually form between nonmetals, especially those in group 14.