Electron Dot Formulas Chemistry 7(C) Lesson Objectives Draw electron dot formulas Ionic compounds Covalent compounds Electron Dot Formulas Valence Electrons Valence electrons electrons found in the highest occupied energy level Outermost electrons of the electron cloud Establish the chemical characteristics of elements Only electrons represented in Lewis electron dot structures Symbolized by dots Number of valence electrons is the same as the group number of representative elements Electron Dot Periodic Table Number of valence electrons corresponds to the group number of representative elements Ex) Group 5A elements have 5 valence electrons N is in group 5A N Writing Electron Dot Structures 1.Identify the number of valence electrons using the periodic table 2.Place the corresponding number of electron dots around the symbol First assign one dot per side If there are still more dots to assign, assign a second dot Ex) Dot Structure for Phosphorus Writing Electron Dot Structures P 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 P nonbonding pair bonding e- 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) 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 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 10 e - 11 p charge 10 e - 9 p charge Na lost 1 e to become Na + F gained 1 e to become F - Ex) Valence Electrons and Ion Formation Generally, charge can be be determined by an ions group number Metals lose valence electrons to form cations Nonmetals gain valence electrons to form anions 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 Ca 2+ Ex) Neutral sulfur becomes a sulfide ion S 2- Electron Dot Structures for Ions Ionic compounds are held together by the attraction between oppositely charged ions Ionic Electron Dot Formulas Ex) Formation of KBr K+K+ Br Ex) Electron dot formula for Li 2 O + Li + Li O + O 2- Li + Ionic Electron Dot Formulas 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) Br 2 Br 1.Draw structure for central atom Central atom is usually the least electronegative 2.Draw structures for surrounding atoms 3.Check for octets Consider exceptions 4.Connect bonding electrons between atoms Ex) NH 3 N H H H Covalent Electron Dot Formulas Some compounds may require more than two electrons to be shared between two atoms to fill each atoms octet 4 shared electrons = double bond 6 shared electrons = triple bond Multiple Bonds O O Ex) O 2 N N Ex) N 2 Ex) Electron dot formula for the synthesis of water + H H 2H 2 (g) + O 2 (g) 2H 2 O(l ) O O H H + O H H + O H H Covalent Electron Dot Formulas Lesson Objectives Draw electron dot formulas Ionic compounds Covalent compounds Electron Dot Formulas