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7/30/2019 Chapter 2 Molecules & Ions & Compounds
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Copyright (c) 1999 by Harcourt Brace & Company
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Molecules, Ions &Their Compounds
NaCl, salt
Buckyball, C60
Ethanol, C2H6O
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Compounds & Molecules
COMPOUNDSare a combination of 2 ormore elements in definite ratios by mass.
The character of each element is lost when
forming a compound.
MOLECULESare the smallest unit of acompound that retains the characteristics of
the compound.
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MOLECULAR FORMULAS
Formula for glycine is C2H5NO2 In one molecule there are
2 C atoms
5 H atoms
1 N atom
2 O atoms
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WRITING FORMULAS
Can also write glycine formula as
H2NCH2COOH
to show atom ordering
or in the form of a structural formula
C
H
H C
H
H
O
O HN
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MOLECULAR MODELING
C
H
H C
H
H
O
O HN
Ball & stick Space-filling
Structural formula
of glycine
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Molecular & Ionic Compounds
Heme NaCl
Fe
N
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ELEMENTS THAT EXIST AS
MOLECULES
Allotropes of C
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ELEMENTS THAT EXIST ASDIATOMIC MOLECULES
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ELEMENTS THAT EXIST ASPOLYATOMIC MOLECULES
White P4 and polymeric
red phosphorus
S8 sulfurmolecules
7/30/2019 Chapter 2 Molecules & Ions & Compounds
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IONS AND IONIC COMPOUNDS
see Screen 3.5
IONSare atoms or groups of atoms with apositive or negative charge.
Taking away an electron from an atom gives a
CATION with a positive charge
Adding an electron to an atom gives an
ANION with a negative charge.
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Forming Cations & Anions
A CATION forms
when an atom
loses one or
more electrons.
An ANION forms
when an atom
gains one or
more electrons
Mg --> Mg2+ + 2 e- F + e- --> F-
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Active figure 3.5
7/30/2019 Chapter 2 Molecules & Ions & Compounds
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PREDICTING ION CHARGES
In general
metals (Mg) lose electrons ---> cations
nonmetals (F) gain electrons ---> anions
See CD-ROM Screen 3.5 and book Figure 3.7
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Charges on Common Ions
+3
-4 -1-2-3+1
+2
By losing or gaining e-, atom has same
number of e-s as nearest Group 8A atom.
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Predicting Charges on Monatomic Ions
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METALS
M ---> n e- + Mn+where n = periodic group
Na+ sodium ion
Mg2+ magnesium ion
Al3+ aluminum ion
Transition metals --> M2+ or M3+are common
Fe2+ iron(II) ion
Fe3+ iron(III) ion
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NONMETALS
NONMETAL + n e- ------> Xn-where n = 8 - Group no.
C4-,carbide N3-, nitride O2-, oxide
S2-, sulfide
F-, fluoride
Cl-, chloride
Group 7AGroup 6AGroup 4A Group 5A
Br-, bromide
I-, iodide
Name derivedby adding -ideto stem
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Valence Electrons
3Li
7
4Be
9.4
9F
19
5B
11
7N
14
6C
12
8O
16
Li BBe C N O F
10Ne
19Ne
The Octet Rules
Lewis
electron dot
diagrams
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Sodium can loose one electron to expose
an octet
Chlorine can gain one electron to
complete an octet
11Na
23Na
17Cl
35.5Cl
[Na]+
+
Cl
+
-
V l
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Valence Atoms differ in their combining
power or valence.
Na combines with one Cl, NaCl, whileCa combines with two, CaCl2
We say that Ca has a valence of twoand sodium a valence of one whencompared to Cl.
Cl, a non metal is given a valence of
1-, in contrast to Na which is 1+or Ca= 2+.
Sulfur has a valence of 2- so it forms
Na2S.
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Valence and Charge
Atoms with positive valence formpositive ions by loosing electrons.
Atoms with negative valence form
negative ions by gaining electrons. The charge of an ion is determined
by the difference between the
number of protons and the numberof electrons.
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Ionic charge from theperiodic table
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Ionic Compounds
The atoms of ionic compounds existas charged ions and are heldtogether by strong electrostaticforces creating a crystal lattice.
NaCl, FeCl2, NaHCO3, (NH4)2SO4
Water molecules are sometimesincorporated into the lattice creatingcompounds called hydrates.
CuSO45H2O
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Ionic Compounds Electrostatic forces attraction
and repulsion by two chargedspecies
The force of attraction betweentwo oppositely charged ions isgreater as their charges increaseand the distance (d) decreases
Generally arranged in a crystallattice network
M t l i C ti
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Metal ions- CationsCations are named with the name of the element.
Na+ -sodium
H+ - hydrogen
K+ -potassium
Ca2+ - calcium
Some Cations have common names and may exist with
several different ionic charges; these are denoted with Romannumerals showing the amount of positive charge on the ion.
Fe2+ Iron(II) Ferrous ion
Fe3+ Iron(III) Ferric ion
Cu2+ Copper(II) Cupric ion
Cu1+ Copper(I) Cuprous ion
Lead(II), (IV), Mercury(I), (II), Tin(III), (IV) are only some of
the other metals forming multiple ions
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Negative Ions - AnionsAnions are named by changing the ending of the element
name to ide.
Cl1- Chloride
O2- Oxide
H1- Hydride
N3- Nitride
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POLYATOMIC IONSCD Screen 3.6
Groups of atoms with a charge.
MEMORIZE the names and
formulas in Table 3.1, page 107.
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Note: many Ocontaining anions
have names ending
inate (or -ite).
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CATION +
ANION --->COMPOUND
A neutral compd.
requires
equal number of +
and - charges.
COMPOUNDSFORMED FROM
IONS
Na+ + Cl- --> NaCl
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IONIC COMPOUNDS
NH4+
Cl-
ammonium chloride, NH4
Cl
7/30/2019 Chapter 2 Molecules & Ions & Compounds
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Some Ionic Compounds
Mg2+ + NO3- ---->
Mg(NO3)2
magnesiumnitrate
Fe2+ + PO43- ---->
Fe3(PO4)2
iron(II) phosphate(See CD, Screen 3.11 for naming
practice)
calcium fluoride
Ca2+
+ 2 F-
---> CaF2
roperties o Ionic
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roperties o IonicCompounds
Forming NaCl from Na and Cl2
A metal atom cantransfer anelectron to a
nonmetal. The resulting
cation and anionare attracted to
each other byelectrostaticforces.
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Electrostatic Forces
The oppositely charged ions in ionic compounds are
attracted to one another by ELECTROSTATIC
FORCES.These forces are governed by COULOMBS LAW.
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Electrostatic Forces
COULOMBS LAW
As ion charge increases, the attractive force
_______________.
As the distance between ions increases, theattractive force ________________.
This idea is important and will come upmany times in future discussions!
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Electrostatic Forces
COULOMBS LAW
Active Figure 3.10
7/30/2019 Chapter 2 Molecules & Ions & Compounds
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Importance of Coulombs Law
NaCl, Na+ and Cl-,
m.p. 804 oCMgO, Mg2+ and O2-
m.p. 2800 oC
Naming Ionic
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Naming IonicCompounds
Positive ion name goes firstfollowed by the negative ion
CaBr2
Mg(OH)2
KCl
AgSO4 NH4CO3
Molecular
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MolecularCompounds
Binary compounds:
use valence to write formulas as if theywere ionic.
use prefixes: mono-1, di-2, tri-3,tetra-4,
penta-4, hexa-6.for both anion andcation.
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Molecular CompoundsCompounds without Ions
CH4 methane
CO2 Carbon dioxide
BCl3 boron trichloride
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Naming MolecularCompounds
CH4 methaneBCl3
boron trichloride
CO2 Carbon dioxide
All are
formed from
two or more
nonmetals.
Ionic
compounds
generallyinvolve a metal
and nonmetal
(NaCl)
Naming Binary
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Naming BinaryCompounds
Usually put the the elements inincreasing atomic number
Use prefixes such as di-, tri-, etc
There are some common namesthat are still used for somecompounds (see page 96)
Example: water, ammonia,methane
N i Bi
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Naming BinaryCompounds
NF3
Nitrogen trifluoride
N2O4
Dinitrogen tetraoxide
SF6
Sulfur hexafluoride
NO2
Dinitrogen dioxide