Atoms relative size from atomic radius

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Atoms relative size (from atomic radius)
100 pm
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Energies of Ion Formation
Ionization energy energy required to remove an
electron from an atom in the gaseous state Atom
Energy ? Cation Electron Electron affinity
energy released on adding an electron to an
atom in the gaseous state Atom Electron ?
Anion Energy Comparisons Small ionization
energy electron easily lost Small electron
affinity electron not easily gained (cation
formation is favored) Large ionization energy
electron not easily lost Large electron affinity
electron easily gained (anion formation is
favored)
Alkali metals
Halogens
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Ionization energy and Electron Affinity
It is difficult to remove an electron from noble
gases (stable octet)
It is energetically favorable to add an electron
to the halogens (stable octet)
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Reaction of Sodium and Chlorine
Oppositely charged ions organized to form an
ordered lattice. These are crystals.
Why is Cl- larger than Na ?
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Nomenclature of ions
If an s- or p-block element is ionized to form
its cation, then the cation takes the name of the
element, followed by the word ion Ca ? Ca2
2 e- calcium is ionized to calcium ion If an
element is ionized to form its anion, then the
anion take the first part of the name of the
element, followed by ide S 2 e- ?
S2- sulfur is ionized to sulfide N 3 e- ?
N3- nitrogen is ionized to nitride
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Transition Metal Ions
Transition metals have low ionization energies,
and tend to form cations. Transition metals can
form more than one cation Ex iron can lose
two electrons to form iron 2 or lose three
electrons to form iron 3 There are two ways to
name transition metal ions First method name
of the element (roman numeral of its positive
charge) Ex iron(II) is the ion that forms as
iron loses two electrons Second method use the
latin name of the element follow by ous or
ic -ous indicates the cation with lower chare,
where ic indicates the cation with higher
charge. Ex iron(II) ferrous ion Fe2 and
iron(III) ferric ion Fe3
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Polyatomic Ions
Some ions are made up of several atoms, and the
overall group has a charge. These are classified
as polyatomic ions.
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Lattice and the Formula Unit

• Sodium chloride is an ionic compound
• 2) It consists of sodium ions and chloride ions
• 3) The oppositely charged ions are attracted to
  one another (electrostatic attraction)
• 4) The ions form a repeating three-dimensional
  array (lattice) called a crystal
• 5) A crystal contains a large number of cations
  and ions one does not find a molecule of ions
• 6) The simplest formula of an ionic compound is
  called the formula unit
• 7) The formula unit indicates the numbers of each
  contributing ion in simplest proportion

Sodium chloride formula unit NaCl
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Formula Unit
The formula unit is always electrically
neutral. What is the formula unit for the ionic
compound composed of calcium ions and phosphate
ions? calcium ion Ca2 phosphate ion
PO43- The least common multiple of 2 and 3 is 6,
thus the formula unit will contain 6 charge from
the cations balanced by -6 charge from the
anions. 3 Ca2 2 PO43- Ca3(PO4)2 Note
the use of (parentheses) to indicate the
subscript 2 applies to the entire phosphate
anion.
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Bonding in Ionic Compounds
Ions are held together by electrostatic forces
between oppositely charged ions. The valence
electrons on the anion remain localized on the
anion. This is an ionic bond.


Ions prefer electrostatic stabilization from all
directions
exposed positive sphere
exposed positive sphere


(one does not typically find a sodium chloride
molecule)
Ions in the interior are stabilized by oppositely
charged nearest neighbors from several
directions. Only the surface ions have exposed
charge.
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Characteristics of Ionic Compounds
Ionic compounds have high melting points.
(difficult to break the electrostatic bonding)
Ionic compounds shatter. (breakage across
crystal planes) Many ionic compounds dissolve
in water however, many others are insoluble in
water. Dissolved ions in water allow electrical
conductance.
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Lewis Dot Structures
A simple method of accounting for electrons in
compounds. Only valence electrons are
shown. Valence electrons are represented using
dots ( ) Example Lewis dot structure of a
nitrogen atom nitrogen has 5 valence
electrons N Example Lewis dot structure of
a chloride anion chloride anion has 8 valence
electrons Cl




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Lewis Dot Structures
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Lewis Dot Structures
The Lewis Dot picture can help one understand the
formation of ionic compounds. Consider potassium
bromide (KBr) element dot structure ion dot
structure fate K K K K loses
electron Br Br Br- Br- gains electron



K Br ? K Br-

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Common Ions
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Problems

• Write electron dot (Lewis dot) symbols for the
  following atoms
• beryllium b) neon
• strontium d) aluminum
• Write equations for loss or gain of electrons by
  atoms that result in formation of the following
  ions from the corresponding atoms
• Ca2 b) Au
• F- d) Cr3
• Tell whether each statement about ions is true or
  false
• A cation is formed by addition of one or more
  electrons to an atom
• Group 4 elements tend to lose 4 electrons to
  yield ions with a 4 charge
• Group 4 elements tend to gain 4 electrons to
  yield ions with a -4 charge
• The individual atoms in a polyatomic ion are held
  together by covalent bonds