Understanding Electron Dot Formulas: Bonding in Ionic and Covalent Compounds

1. Lesson Objectives • Draw electron dot formulas • Ionic compounds • Covalent compounds • Electron Dot Formulas

2. Bonding electrons – electrons used for bonding • Single dots on a side of the symbol • Nonbonding pairs – electrons not used for bonding • Paired dots on a side of the symbol • Bonding vs. Nonbonding Electrons nonbonding pair P bonding e- bonding e- bonding e-

3. Noble gases have octets of electrons • Noble gases have the most stable electron configurations • Stable–electron arrangement that resists spontaneous change • Octet rule– atoms gain, lose, or share electrons to fill their valence shells with eight electrons and achieve stability • Hydrogen and helium are octet rule exceptions • Follow the duet rule • Highest energy shell only holds two electrons • The Octet Rule Ex)

4. Valence Electrons and Bonding • Chemical bonds are created by the transfer or sharing of valence electrons • Covalent bonds are formed by electron sharing • Ionic bonds are formed by electron transfer

5. Ions form when electrons are lost or gained • Ionic charges are based on the number of electrons lost or gained • Losing or gaining electrons changes the ratio of positive particles (p+) to negative particles (e–) and causes an overall charge to form • Valence Electrons and Ion Formation Ex) Na lost 1 e– to become Na+ F gained 1 e– to become F- 10 e- 10 e- 11 p+ 9 p+ + + +1 charge -1 charge

6. Valence Electrons and Ion Formation • Generally, charge can be be determined by an ion’s group number • Metals lose valence electrons to form cations • Nonmetals gain valence electrons to form anions 1+ 3+ 2- 1- 3- 2+

7. Electron Dot Structures for Ions • Excess or deficit of electrons will be represented by • Number of electrons around the symbol • Charge outside the dot structure Ex) Neutral calcium becomes a calcium ion 2+ Ca Ex) Neutral sulfur becomes a sulfide ion 2- S

8. Ionic compounds are held together by the attraction between oppositely charged ions • Ionic Electron Dot Formulas Ex) Formation of KBr Br – Br K Transfer K+

9. Ionic Electron Dot Formulas Ex) Electron dot formula for Li2O 2- O O Li+ Li+  Li Li + +

10. Molecules and covalent compounds are held together by electron sharing • Covalent bonds are represented by lines drawn between atoms • Each line represents a pair of electrons that are shared between two atoms Covalent Electron Dot Formulas Ex) Br2 Br Br

11. Draw structure for central atom • Central atom is usually the least electronegative • Draw structures for surrounding atoms • Check for octets • Consider exceptions • Connect bonding electrons between atoms Covalent Electron Dot Formulas Ex) NH3 N H H H

12. Some compounds may require more than two electrons to be shared between two atoms to fill each atom’s octet • 4 shared electrons = double bond • 6 shared electrons = triple bond • Multiple Bonds • Ex) O2 O O • Ex) N2 N N

13. Covalent Electron Dot Formulas Ex) Electron dot formula for the synthesis of water 2H2(g) + O2(g)  2H2O(l ) O O + +  + O O H H H H H H H H