Ionization of Transition Metals

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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 7

• Chemical 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

• Schematic representations of valence electrons in
  atoms

• Valence electrons
• Electrons which are involved in chemical bonding
• These are usually the outermost electrons
• These electrons are most important chemically

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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
F
Na
Cl
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Formation of Ionic Compounds

• Consider reaction between metallic sodium and
  gaseous chlorine
• Electron configurations of the elements
• Na
• Cl
• 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 is
• 2 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 MX is a general chemical
  property of alkali metals
• It is also a general chemical property of
  halogens
• 2M(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
Ca F2 ?

• The remainder of the IIA metals and VIIA
  nonmetals react similarly
• M(s) X2 ?? M2 (X)2 (s)

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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(M2 O2) (s)
• 2M(s) X(s) ?? M2 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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Example
Write 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 Rule

• S 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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The Octet Rule

• 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

• 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 56