Unit 5 Chemical Bonding

Unit 5 Chemical Bonding Chapter 6.1 Lewis Dot Diagrams & Ions

Stable Electron Configurations • When is an atom unlikely to react? • When the outer shell (highest occupied energy level) is filled with electrons • 8 e- for Octet Rule • Noble gases are the most stable elements. • The highest occupied energy level is completely filled. • Elements tend to react to achieve electron configurations similar to those of noble gases.

Stable Electron Configurations • Chemical properties of an element depend on the number of valence electrons. • Electron dot diagram - [Lewis Dot Model] is alternative to standard electron shell diagram • Dot diagram emphasizes valence electrons (inner shells hidden)

F F Electron Configuration and Lewis Dot Diagrams Lewis Dot Diagram Both of these mean the same thing

F Lewis Dot Diagram • Element symbol represents: • Nucleus AND • All inner core electrons • Dots represent: • Valence electrons (outer shell – Highest occupied energy level)

Stable Electron Configurations – Lewis Dot Diagrams

Formation of Ions • When an atom gains or loses an electron(s)  atom is no longer neutral. • # of Protons NO LONGER EQUAL # of electrons Definition: • ION = atom (or group of atoms) with positive (+) or negative (-) net electric charge.

Formation of Ions • ANION = Ion with a negative (-) charge • [Memory aid: anion = ANegative ION] • Example: Chlorine • atomic # 17 • Halogen Family/Group 7A • 7 Valence Electrons • Neutral (but not stable) - 17 protons and 17 electrons • To become stable – gain 1 electron in outer e- shell • Now have 1 more e- than proton = -1 net charge • Symbol is written Cl- or Cl1-

Formation of Ions • Naming Anions: • Part of element name + suffix “ide” • Example: Chlorine ion becomes “chlor” + “ide” • Cl-is called a chloride ion • F- is the fluoride ion (“fluor” + “ide”) • Br-is the bromide ion (“brom” + “ide”) • I- is the iodide ion (“iod” + “”ide”)

Formation of Ions • CATION = Ion with a positive charge • Example: Sodium • atomic # 11 • Alkali Metal Family/Group 1A • 1 Valence Electron • Neutral (but not stable) -11 protons and 11 electrons • To become stable – lose the 1 electron in outer e- shell • Now has 1 more proton than electron = 1+ net charge • Symbolis written Na+ or Na1+

Formation of Ions • Naming Cations: • Use the normal element name • Na+ is calleda sodium ion • Li+is the lithium ion • Cs+ is the cesium ion • Fr+ is the francium ion

Bonding • Elements achieve stable electron configurations by transferring or sharing electrons between atoms • Transferring Electrons - • Those with <4 valence electrons “LEND” them • These elements “lose” valence electrons OR • Those with >4 valence electrons “BORROW” them • These elements “gain” electrons

Formation of Ions & Bonding • Sodium reacts with chlorine  electron transferred from sodium to chlorine • Each atom ends up more stable

IonicBonding • Chemical bond = force that holds atoms or ions together as a unit. • Opposites attract • Particle(s) with negative charge attracts particle(s) with positive charge. • Ionic bond • Force that holds cations and anions together and which involves the transfer of electrons. • Bond occurs between a metal and a nonmetal

IonicBonding • Ionic Compounds • What is the chemical formula for magnesium chloride? • Mg and Cl • First determine the Lewis Dot Diagram and Ions for each element: Mg2+ , Cl- Ions Lewis Dot

Ionic Bonding • Mg atom cannot reach a stable electron configuration by giving up just 1 valence electron or reacting with just 1chlorine atom. Mg+ 2Cl OR

Ionic Bonding • Mg transfers 2 electrons, one to each of the 2 Cl atoms. • After transfer  • Charge on the magnesium ion is 2+ • Charge on the 2 chloride ions is 1-

Ionic Bonding • Formula for magnesium chloride is MgCl2 - - 2+

Properties of Ionic Compounds • The properties of sodium chloride are typical of ionic compounds. • High melting point • sodium chloride melts ~800°C • When solid - poor conductor of electric current • When liquid (melted) - good conductor of electric current. • Brittle - crystals shatter when struck with a mallet

Exit Slip • Draw the Lewis Dot Diagrams for the Nitrogen Family. • Provide and name the ions for Oxygen, Calcium, and Sulfur. • What is the chemical formula for Aluminum Fluoride? • Show the steps you used to determine the formula.

Unit 5 Chemical Bonding