Chapter 7: Ionic Bonding & the Formation of Ionic Compounds

Matter is made of Atoms!

Nothing would “matter” without “Atoms”

Atoms can bond together . . .

Types of Bonds Oh yeah, these too. . . Covalent Bond Ionic Bond

Chemical Bonds Chemical compounds are divided into two broad classes called ionic compounds and molecular compounds Ionic compounds tend to have high melting points and are good conductors of electricity - when melted or dissolved only Molecular compounds, generally have lower melting points and can be gases, liquids, or low-melting solids at room temperature.  They are poor conductors of electricity.

Chemical bonds - the attractive forces that hold atoms together Ionic bonds - the transfer of electrons from one atom or group of atoms to another. Covalent bonds - the sharing of one or more pairs of electrons between atoms.

Two fundamental concepts that are common to both the ionic and covalent bonding models:  1.  Not all electrons in an atom are available for bonding. Those that are, are called valence electrons. 2. Certain arrangements of electrons are more stable than other arrangements.  (Can you guess which ones?)

Valence Electrons and Electron-Dot Structures Valence electrons are all those electrons in the outermost electron level, that is, in the shell with the highest shell number.   Determine the number of valence electrons present in: Mg Cl Se Next page please…

Mg has two valence electrons You could have just looked at the element's group number!

Cl has seven valence electrons

6 Se has six valence electrons.                                                       This is too easy!

Electron-Dot Structure A shorthand system for designating numbers of valence electrons uses electron-dot structures An electron-dot structure consists of an element's symbol with one dot for each valence electron placed about the elemental symbol.  Electron-dot structures are also called Lewis dot structures

Mg 2 → How many valence electrons are in Mg? Electron Dots = Valence Electrons Symbol = inner electrons & the nucleus Each position (up, down, right, left) around the element symbol represents an _____________, which can hold no more than _________ electrons. orbital two

Lewis Dot Diagrams of Selected Elements                                                                                                        

H Cl Typically, an element in group: one 1A forms ___________ bond 2A forms ___________ bonds 3A forms ___________ bonds 4A forms ___________ bonds 5A forms ___________ bonds 6A forms ___________ bonds 7A forms ___________ bond H two three Cl four three two one

Electron-Dot Structures Hydrogen Oxygen Chlorine

Important Generalizations 1.  Representative elements in the same group of the periodic table have the same number of valence electrons. 2.  The number of valence electrons for representative elements in a group is the same as the periodic table group number. 3.  The maximum number of valence electrons is eight.

Is there a specific way the electrons dots are arranged around an element? As long as there are no more than 2 electron dots per side - - - - you are O.K. NO! Draw the electron dot structure for the following elements: Lone pairs - electrons that typically are not shared during bonding. P K Unpaired electrons - participate during bonding. Cl

Draw electron dot structures for: Mg S Br

The Octet Rule A key concept is that certain arrangements of valence electrons are more stable than others.   The outer shell electron configurations possessed by the noble gases (He, Ne, Ar, Kr, Xe, and Rn) are the most stable

For helium, this most stable electron configuration involves two outer shell electrons.  The rest of the noble gases have eight outer shell electrons. He: 1s2 Ne:  1s2 2s2 2p6 Ar:  1s2 2s2 2p6 3s2 3p6 Octet Rule: In forming compounds, atoms of elements lose, gain, or share electrons in such a way to produce a noble gas electron configuration.

The Ionic Bond Model Compounds can be formed from the combination of a negative ion and a positive ion.  Such compounds are called ionic compounds.  The negative and positive ions of the compound are held together by an ionic bond.

Use the electron dot structure to show how Na can become an ion: Sodium atom (electrically neutral, i.e. charge = 0 ) → Loses one electron [Na]+ Sodium Ion (charge = +1) + e- 1 electron

Use the electron dot structure to show how Mg can become an ion: + 2e- 2 electrons Mg Mg atom (electrically neutral: charge = 0) → Loses 2 electrons [Mg]2+ Mg Ion (charge = 2+)

Use the electron dot structure to show how Cl can become an ion: Cl atom (electrically neutral: charge = 0) Cl ion (charge = -1) Cl ] [ -1 → Gains 1 electron e- +

[ ] [ ] The Ionic Bond Model Example - Show the formation of Na2O:         Na2O [ ] [ ]

Show the formation of CaCl2 + [ ]

Show the formation of the following ionic compounds using electron-dot structures: a)  K3P b) NaF c)  Al2O3 d) KF e)  Li2O f)  Ca3P2

Exceptions Continued: Ni: [Ar] 4s2 3d8 Ni+2: [Ar] 3d8 Fe: [Ar] 4s2 3d6 Fe+2: [Ar] 3d6 [Ar] 3d5 Fe+3:

Let’s Review . . . WAKE UP

lose gain A. Atoms will _________ or _______ electrons to become like the nearest _____________ gas, which has ______________ valence electrons or a full __________________. noble eight octet → Octet rule: Atoms will lose or gain electrons to have a stable electron structure; like a noble gas that has eight valence electrons. compounds Elements will also form _________________ to become stable & share or steal each other’s electrons to have a full ____________. octet Atoms will form octets in their ____________ existing or remaining energy level. highest

→ Halogens will gain one electron & become a ______________ ion. metallic 1. Cations are ______________ elements that will ________ their valence electrons to become stable & obey the octet rule. lose nonmetallic 2. Anions are ______________ elements that will ________ their valence electrons to become stable & obey the octet rule. gain → Halogens will gain one electron & become a ______________ ion. halide

Ionic Bonds anions A. Ionic bonds are formed between __________ & ______________ which are held together by ___________________ forces. cations electrostatic lost B. A cation has ______________ its electron & an anion has ________________ an electron. gained C. In ionic bonds, the elements do not share their electrons but ___________________ their electrons. transfer or steal