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Ionization of Transition Metals
K Ca Sr Ti V Cr Mn Fe
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Oxidation Numbers: Examples H2O
CH4
NH4Cl NaH CaH2
KCl RbNO3
SrSO4
CaBr2
CO CO2
Mg3N2
P4O10
(NH4)2S
BeF2
SO2
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CHAPTER 7Chemical Bonding
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Chemical Bonds Attractive forces that hold atoms together in
compounds are called chemical bonds. There are two main types of chemical bonds
Ionic bonds – resulting from electrostatic attraction between cations and anions
Covalent bonds – resulting from sharing of one or more electron pairs between two atoms
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Lewis Dot Formulas
Valence electrons Electrons which are involved
in chemical bonding These are usually the
outermost electrons These electrons are most
important chemically
Schematic representations of valence electrons in atoms
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Lewis Dot Formulas: Single Atoms We show only electrons in the
outermost occupied shell An electron pair is represented
as a pair of dots An unpaired electron is
represented as a single dot
Li
Na
F
Cl
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Formation of Ionic Compounds
Consider reaction between metallic sodium and gaseous chlorine Electron configurations of the elements
NaCl
Sodium atom has low ionization energy and easily looses the only 3s electron forming a cation of Na+
Chlorine atom has highly negative electron affinity and readily gains an electron becoming an anion of Cl–
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Formation of Ionic Compounds
Na – e– Na+
Cl + e– Cl–Na + Cl Na+ + Cl–
Na+ cations and Cl– anions are electrostatically attracted to each other resulting in an extended ionic lattice
The high energy of the lattice overcomes all other factors involved in the formation of NaCl from elemental sodium and chlorine
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Formation of Ionic Compounds
Na + Cl Na+ Cl– We can write this equation using
Lewis dot formulas
The complete equation is2 Na + Cl2 2 Na+ Cl–
It can also be written as
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Alkali Metals + Halogens Reaction with halogens leading to the formation
of ionic halides M+X– is a general chemical property of alkali metals
It is also a general chemical property of halogens2M(s) + X2 2MX(s)
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Ionic Bonding Electrostatic interaction Non-directional The central ion attempts to
maximize the number of interactions with the ions of opposite charge
Formation of an ionic compound involves loss of electrons by metal (oxidation) and gain of electrons by nonmetal (reduction)
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Alkali Earth Metals + Halogens
The remainder of the IIA metals and VIIA nonmetals react similarly:
M(s) + X2 M2+ (X–)2 (s)
Ca + F2
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Formation of Ionic Compounds
Li + O2
The remainder of the IA metals and VIA nonmetals react similarly:4M(s) + O2(g) 2(M+
2 O2–) (s)
2M(s) + X(s) M+2
X2– (s)X = S, Se, Te, Po
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Formation of Ionic Compounds
Mg + O2
The remainder of the IIA metals and VIA nonmetals react similarly:2M(s) + O2(g) 2(M2+ O2–) (s)
M(s) + X(s) M2+ X2– (s)X = S, Se, Te, Po
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ExampleWrite the reaction between calcium and nitrogen. Show what happens to valence electrons using Lewis dot formulas.
Learn Table 7-2
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Covalent Bonding If the difference in electronegativity
of two elements is not large enough, an electron cannot be transferred completely from one atom to the other
It becomes shared between both atoms and a covalent bond is formed
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Formation of H2 Molecule When two H atoms are indefinitely far
from each other, they do not interact If the separation decreases to a
certain distance, the 1s electron of each H atom is attracted by the nucleus of the other H atom, as well as by its own nucleus
If electrons from different atoms can occupy the same orbital, they will form a covalent bond
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H2 Molecule We can use Lewis dot formulas
to show covalent bond formation
The covalently bonded atoms are held at a distance corresponding to the lowest total energy
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Covalent Bond We say that the covalent bond is formed
by the overlap of atomic orbitals The covalently bonded atoms are held
together by a pair of shared electons The distance between their nuclei
corresponds to the lowest total energy Below this equilibrium distance the
nucleus-nucleus and electron-electron repulsions become too large, pushing the nuclei back to the equilibrium distance
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HF Molecule
F is more electronegative than H In this molecule the electron pair
will be shifted towards the F atom
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F2 Molecule
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H2O Molecule
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NH3 Molecule
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NH4+ Ion
Lewis formulas can also be drawn for polyatomic ions
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Bonding & Nonbonding Electrons
Representative elements usually attain stable noble gas electron configurations in most of their compounds
Electrons which are shared among two atoms are called bonding electrons
Unshared electrons are called lone pairs or nonbonding electrons
Lewis dot formulas are based on the octet rule
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The Octet RuleS = N - A
S = total number of electrons shared in bonds
N = total number of electrons needed to achieve a noble gas configuration 8 for representative elements 2 for H atoms
A = total number of electrons available in valence shells of the atoms A is equal to the periodic group
number for each element A-S = number of electrons in lone pairs
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Examples F2
H2O
CH4
CO2
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Covalent Bonding Covalent bonds are formed
when atoms share electrons If the atoms share 2 electrons a
single covalent bond is formed If the atoms share 4 electrons a
double covalent bond is formed If the atoms share 6 electrons a
triple covalent bond is formed
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For ions we must adjust the number of electrons available, A: Add one e- to A for each negative charge Subtract one e- from A for each positive charge
The Octet Rule
Example: NH4+
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Assignments & Reminders Go through the lecture notes Read Sections 7-1 through 7-5 Read Sections 4-5 & 4-6 of Chapter 4 Homework #3 due by Oct. 10 Monday (10/10) and Tuesday (10/11) –
lecture quiz #3 based on Chapters 5&6