Unit 5 Chemical Bonding

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UNIT 5 CHEMICAL BONDINGChapter 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 diagramDot diagram emphasizes valence

electrons (inner shells hidden)

ELECTRON CONFIGURATION AND LEWIS DOT DIAGRAMS

Lewis Dot Diagram

Both of these mean the same thing

LEWIS DOT DIAGRAM

Element symbol represents:Nucleus

ANDAll 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 = A Negative ION] Example: Chlorine

atomic # 17Halogen Family/Group 7A

7 Valence ElectronsNeutral (but not stable) - 17 protons and 17

electronsTo 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 # 11Alkali Metal Family/Group 1A

1 Valence Electron Neutral (but not stable) -11 protons and 11 electronsTo become stable – lose the 1 electron in outer e-

shell Now has 1 more proton than electron = 1+ net charge

Symbol is written Na+ or Na1+

FORMATION OF IONS

Naming Cations:Use the normal element name

Na+ is called a sodium ion Li+ is the lithium ionCs+ is the cesium ionFr+ 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”

themThese elements “lose” valence electrons

Those with >4 valence electrons “BORROW” themThese elements “gain” electrons

FORMATION OF IONS & BONDING

Sodium reacts with chlorine electron transferred from sodium to

chlorine

Each atom ends up more stable

chlorine

IONIC BONDING

Chemical bond = force that holds atoms or ions together as a unit.

Opposites attractParticle(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

IONIC BONDING

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 1 chlorine 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

PROPERTIES OF IONIC COMPOUNDS

The properties of sodium chloride are typical of ionic compounds.High melting point

sodium chloride melts ~800°CWhen solid - poor conductor of

electric currentWhen 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

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