4.1 ionic bonding & structure
DESCRIPTION
Understandings Positive ions (cations) form by metals losing valence electrons Negative ions (anions) form by non-metals gaining electrons The number of electrons lost or gained is determined by the electron configuration of the atom The ionic bond is due to electrostatic attractions between oppositely charged ions. Under normal conditions, ionic compounds are usually solids with lattice structures.TRANSCRIPT
4.1 Ionic Bonding & Structure
Mrs. Page IB Chem Understandings Positive ions (cations) form by
metals losingvalence electrons Negative ions (anions) form by
non-metalsgaining electrons The number of electrons lost or gained
isdetermined by the electron configuration of theatom The ionic
bond is due to electrostatic attractionsbetween oppositely charged
ions. Under normal conditions, ionic compounds areusually solids
with lattice structures. Application & Skills Deduction of the
formula and name of an ioniccompound from its component ions,
includingpolyatomic ions Explanation of the physical properties of
ioniccompounds (volatility, electrical conductivity, andsolubility)
in terms of their structure. Nature of Science Use theories to
explain natural phenomenon molten ionic compounds conduct
electricity butsolid ionic compounds do not. The solubility
andmelting points of ionic compounds can be usedto explain
observations. Introduction to Bonding
Chemical bond: an interaction between atomsor ions that results in
a reduction of thepotential energy of the system, therebybecoming
more stable Three types of bonds: ionic, metallic, andcovalent The
bond type depends on the atomselectronegativity values More Bonding
Basics If the atoms have very differentelectronegativity values,
then ionicbonding occurs If they both have high
electronegativityvalues, then covalent bonding occurs If they both
have low electronegativityvalues, then metallic bonding occurs
Practice: What Kind of Bond?
Na and Cl Sr and O C and O Ni and Fe N and O Li and N Ti and Cr
Ionic Covalent Metallic Valence Electrons Valence electrons are the
electrons in theoutermost energy level, which is the
highestoccupied energy level They are the electrons responsible for
thechemical properties of atoms Electron transfers result in nobal
gas electronconfigurations. Core electrons are those in the energy
levelsbelow. Keeping Track of Electrons
Atoms in the same group have the sameouter electronic structure and
thereforethe same number of valence electrons. The number of
valence electrons iseasily determined. It is the groupnumber Group
2:Be, Mg, Ca, etc. Each has 2 valence electrons Electron Dot (Lewis
Dot)diagrams
A way of showing & keeping track ofvalence electrons. Write the
symbol - it represents thenucleus and inner (core) electrons Put
one dot for each valence electron(8 maximum) First two electrons
placed as a pair (sorbital) Then they dont pair up until they
haveeach have 1 (Hunds rule) X The Electron Dot Diagram (Lewis
Structure) for Nitrogen
Nitrogen has 5 valenceelectrons to show. First we write the symbol.
N Place 1st pair Then add 1 electron at a time to each side. The
Octet Rule The noble gases are unreactive in chemical
reactions
In 1916, Gilbert Lewis used this fact toexplain why atoms form
certain kinds ofions and molecules The Octet Rule: in forming
compounds,atoms tend to achieve a noble gasstructure; 8 in the
outer level is stable Each noble gas (except He, which has2) has 8
electrons in the outer level Formation of Cations Metals become
oxidized (lose electrons) to attaina noble gas structure. They make
positive ions (cations) If we look at the electronic structure, it
makessense to lose electrons: Na:2, 8, 1 shows 1 valence electron
Na1+: 2, 8This is a noble gas structure with 8electrons in the
outer level. Electron Dots For Cations
Metals have few valence electrons (usually 3or less); calcium has
only 2 valenceelectrons Ca Electron Dots For Cations
Metals will lose the valence electrons Ca Electron Dots For
Cations
Form positive ions Ca2+ This is namedthe calciumion. No dots are
now shown for the cation. Electron Configurations: Anions
Nonmetals are reduced (gain electrons)to attain noble gas
electronicstructures. They make negative ions (anions) S = 2,8,6 =
6 valence electrons S2-= 2,8,8 = noble gas structure. Halide ions
are ions from chlorine orother halogens that gain electrons
Electron Dots For Anions
Nonmetals will have many valence electrons(usually 5 or more) They
will gain electrons to fill outer shell. 3- P (This is called the
phosphideion, and should show dots) Stable Electron
Configurations
All atoms react to try and achieve a noble gasstructure. Noble
gases have 8 valence electrons and so arealready stable This is the
octet rule (8 in the outer level isparticularly stable). Ar Ionic
Bonding Anions and cations are held together bythe electrostatic
attraction due to theopposite charges (+ and -) Simplest ratio of
elements in an ioniccompound is called the formula unit. The bond
is formed through the transferof electrons (lose and gain)
Electrons are transferred to achievenoble gas structure. Ionic
Bonding Na Cl The metal (sodium)is oxidized (loses itsone electron)
from the outer level. The nonmetal (chlorine) is reduced (gainsone
electron) to fill its outer level, and willaccept the one electron
that sodium is goingto lose. [ ] Cl - Na+ Ionic Bonding
Notes:
[ ] Cl - Na+ Notes: Remember that no dots are now shown forthe
cation Brackets must be shown in Lewisstructures to show overall
charge of ion This step involving the formation of ions isa
critical step to show in the formation ofionic bonds Ionic Bond
Negative charges are attracted to positive charges.
Negative anions are attracted topositive cations. The result is an
ionic bond. A three-dimensional crystal lattice ofanions and
cations is formed. Ionic Compounds The ionic substance is held
together bystrong electrostatic attractions in allthree dimensions
No molecules present An ionic lattice-type structure isformed This
gives them distinct physicalproperties NaCl CsCl TiO2 Properties of
Ionic Compounds
Hard, brittle crystalline solids Relatively high melting and
boilingpoints Do not conduct electricity whensolid, but do when
molten or inaqueous solution Are more soluble in water than
othersolvents - Page 198 The ions are free to move when they
aremolten (or in aqueous solution), and thusthey are able to
conduct the electric current. Preserve Electroneutrality
When ions combine, electroneutralitymust be preserved. In the
formation of magnesiumchloride, 2 Cl- ions must balance a Mg2+ ion:
Mg Cl- MgCl2 Predicting Ionic Charges
Group 1A: Lose 1 electron to form 1+ ions H+ Li+ Na+ K+ Rb+
Predicting Ionic Charges
Group 2: Loses 2 electrons to form 2+ ions Be2+ Mg2+ Ca2+ Sr2+ Ba2+
Predicting Ionic Charges
Group 13: B3+ Al3+ Ga3+ Loses 3 electrons to form 3+ ions
Predicting Ionic Charges
Nitride Group 15: P3- Phosphide As3- Arsenide Gains 3 electrons to
form 3- ions Predicting Ionic Charges
Oxide Group 16: S2- Sulfide Se2- Selenide Gains 2 electrons to form
2- ions Predicting Ionic Charges
Group 17: F- Fluoride Br- Bromide Cl- Chloride I- Iodide Gains 1
electron to form 1- ions Predicting Ionic Charges
Stable noble gases do not form ions! Full octets. Group 18:
Predicting Ionic Charges
Many transition elements have more than one possible oxidation
state. Note the use of Romannumerals to show charges Iron (II) =
Fe2+ Iron (III) = Fe3+ Polyatomic Ions (MUST KNOW!)
Because these are ions they also are involvedin ionic bonding! Ion
Name NH4+ ammonium OH- Hydroxide NO3- Nitrate HCO3- Hydrogen
Carbonate CO32- Carbonate SO42- Sulfate PO43- Phosphate Upcoming
Dates: December 6 Final Exam Topics 1-3
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