Ions and Ionic Compounds

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Ions and Ionic Compounds

• Chapter 5

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Chemical Reactivity

• How much an element reacts depends on the
  electron configuration of its atoms.
• For example, oxygen will react with magnesium. In
  the electron configuration for oxygen, the 2p
  orbitals, which can hold six electrons, have only
  four
• O 1s22s22p4
• Neon has no reactivity. Its 2p orbitals are full
• Ne 1s22s22p6

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Chemical Reactivity, continuedNoble Gases Are
the Least Reactive Elements

• The noble gases, which are found in Group 18 of
  the periodic table, show almost no chemical
  reactivity.
• The noble gases have filled outer energy levels.
• This electron configuration can be written as
  ns2np6 where n represents the outer energy level.
  

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Chemical Reactivity, continuedNoble Gases Are
the Least Reactive Elements, continued

• The eight electrons in the outer energy level
  fill the s and p orbitals, making these noble
  gases stable.
• In most chemical reactions, atoms tend to match
  the s and p electron configurations of the noble
  gases.
• This tendency to have either empty outer energy
  levels or full outer energy levels of eight
  electrons is called the octet rule.

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Chemical Reactivity, continuedAlkali Metals and
Halogens Are the Most Reactive Elements

• An atom whose outer s and p orbitals do not match
  the electron configurations of a noble gas will
  react to lose or gain electrons so the outer
  orbitals will be full.
• When added to water, an atom of potassium (an
  alkali metal) gives up one electron in its outer
  energy level.
• Then, it has the s and p configuration of a noble
  gas.
• 1s22s22p63s23p64s1 1s22s22p63s23p6

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Chemical Reactivity, continuedAlkali Metals and
Halogens Are the Most Reactive Elements

• Chlorine, a halogen, is also very reactive.
• An atom of chlorine has seven electrons in its
  outer energy level.
• By gaining just one electron, it will have the s
  and p configuration of a noble gas.
• 1s22s22p63s23p5 1s22s22p63s23p6

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Valence Electrons

• The electron configuration of phosphorus, P, is
  Ne3s23p3.
• Each P atom has five valence electrons two in
  the 3s orbital and three in the 3p orbital.

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Valence Electrons, continuedAtoms Gain Or Lose
Electrons to Form Stable Ions

• All atoms are uncharged because they have equal
  numbers of protons and electrons.
• For example, a potassium atom has 19 protons and
  19 electrons.
• After giving up one electron, potassium still has
  19 protons but only 18 electrons.
• Because the numbers are not the same, there is a
  net electrical charge.

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Valence Electrons, continuedAtoms Gain Or Lose
Electrons to Form Stable Ions, continued

• An ion is an atom, or molecule that has gained or
  lost one or more electrons and has a negative or
  positive charge.
• The following equation shows how a potassium atom
  forms an ion with a 1 charge.
• K ? K e?
• An ion with a positive charge is called a cation.

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Valence Electrons, continuedAtoms Gain Or Lose
Electrons to Form Stable Ions, continued

• In the case of chlorine, far less energy is
  required for an atom to gain one electron rather
  than give up its seven valence electrons to be
  more stable.
• The following equation shows how a chlorine atom
  forms an ion with a 1- charge.
• Cl e? ? Cl?
• An ion with a negative charge is called an anion.

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Some Ions with Noble-Gas Configurations
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Some Stable Ions Do Not Have Noble-Gas
Configurations

• Not all stable ions have an electron
  configuration like those of noble gases.
  Transition metals often form ions without
  complete octets.
• With the lone exception of rhenium, Re, the
  stable transition metal ions are all cations.
• Also, some elements, mostly transition metals,
  form stable ions with more than one charge.

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Stable Ions Formed by the Transition Elements and
Some Other Metals
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Atoms and Ions

• Nearly all metals form cations
• The atoms of all nonmetal elements form anions.

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Ionic Bonding

• Pyrite is a mineral that is shiny like gold, but
  it is made of iron cations and sulfur anions.
• Because opposite charges attract, cations and
  anions attract one another and an ionic bond is
  formed.
• The iron cations and sulfur anions of pyrite
  attract one another to form an ionic compound.

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Ionic Bonds Form Between Ions of Opposite Charge

• When sodium and chlorine react to form sodium
  chloride, sodium forms a stable Na cation and
  chlorine forms a stable Cl? anion.
• The force of attraction between the 1 charge on
  the sodium cation and the 1? charge on the
  chloride anion creates the ionic bond in sodium
  chloride.
• Sodium chloride is a salt, the scientific name
  given to many different ionic compounds.

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Ionic Bonds Form Between Ions of Opposite Charge

• All salts are electrically neutral ionic
  compounds that are made up of cations and anions
  held together by ionic bonds in a simple,
  whole-number ratio.
• However, the attractions between the ions in a
  salt do not stop with a single cation and a
  single anion.
• One cation attracts several anions, and one anion
  attracts several cations.
• They are all pulled together into a tightly
  packed crystal structure.

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Transferring Electrons Involves Energy Changes

• Ionization energy is the energy that it takes to
  remove the outermost electron from an atom.
• The equation below shows this process for sodium.
• Na energy ? Na e?
• With some elements, such as chlorine, energy is
  released when an electron is added.
• Cl e? ? Cl? energy

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Formation of Sodium Chloride
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Ionic Bonding

• The energy released when ionic bonds are formed
  is called the lattice energy.
• This energy is released when the crystal
  structure of a salt is formed as the separated
  ions bond.
• Without this energy, there would not be enough
  energy to make the overall process spontaneous.

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Ionic Compounds

• The ratio of cations to anions is always such
  that an ionic compound has no overall charge.
• Ionic Compounds Do Not Consist of Molecules
• Water is a molecular compound, so individual
  water molecules are each made of two hydrogen
  atoms and one oxygen atom.
• Sodium chloride is an ionic compound, so it is
  made up of many Na and Cl? ions all bonded
  together to form a crystal. There are no NaCl
  molecules.

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Ionic Compounds Have Distinctive Properties

• Most ionic compounds have high melting and
  boiling points because of the strong attraction
  between ions.
• When a salt melts or dissolves, the ions can move
  about and are excellent electrical conductors.

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Ionic Compounds Have Distinctive Properties

• Hard means that the crystal is able to resist a
  large force applied to it.
• Brittle means that when the applied force becomes
  too strong to resist, the crystal develops a
  widespread fracture rather than a small dent

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Salt Crystals

• Despite their differences, the crystals of all
  salts are made of simple repeating units.
• These repeating units are arranged in a salt to
  form a crystal lattice, the regular pattern in
  which a crystal is arranged.
• These repeating patterns within a salt are the
  reason for the crystal shape that can be seen in
  most salts.

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Crystal Structure Depends on the Sizes and Ratios
of Ions

• Formulas indicate ratios of ions.
• For example, the formula for NaCl indicates there
  is a 11 ratio of sodium cations and chlorine
  anions.
• Example, the salt calcium fluoride has one Ca2
  ion for every two F? ions.
• Because of the size differences of its ions and
  their ratio in the salt, the crystal lattice
  structure of calcium fluoride is different from
  that of sodium chloride.
• All salts are made of repeating units. The
  smallest repeating unit in a crystal lattice is
  called a unit cell.

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Naming Ionic Compounds

• Rules for Naming Simple Ions
• Simple cations borrow their names from the names
  of the elements.
• For example, K is known as the potassium ion.

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Naming Ionic Compounds, continuedRules for
Naming Simple Ions

• When an element forms two or more ions, the ion
  names include roman numerals to indicate charge.
• For example, the names of the two copper ions
  are
• Cu copper(I) ion Cu2 copper(II) ion
• The name of a simple anion is also formed from
  the name of the element, but it ends in -ide.
• For example, Cl? is the chloride ion.

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Naming Ionic Compounds

• The name of a binary ionic compound is made up of
  just two words the name of the cation followed
  by the name of the anion.
• NaCl sodium chloride CuCl2 copper(II) chloride
• ZnS zinc sulfide Mg3N2 magnesium nitride
• K2O potassium oxide Al2S3 aluminum sulfide