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Lesson Objectives Draw electron dot formulas Ionic compounds Covalent compounds - PowerPoint PPT Presentation


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

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Lesson Objectives

  • Draw electron dot formulas

    • Ionic compounds

    • Covalent compounds

  • Electron Dot Formulas


  • 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-


  • 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

  • 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


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+


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


  • Ionic Electron Dot Formulas

Ex) Formation of KBr

Br –

Br

K

Transfer

K+


Ex) Electron dot formula for Li2O

2-

O

O

Li+

Li+

Li

Li

+

+


  • Molecules and covalent oppositely charged ionscompounds 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


  • Draw structure for central atom oppositely charged ions

    • 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


  • Multiple Bonds

  • Ex) O2

O

O

  • Ex) N2

N

N


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


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