Ionic Bonding

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Ionic Bonding
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Ionic Bonding

• Occurs when electrons are transferred from one
  atom to another, forming two ions
• The ions stay together because of electrostatic
  attractions
• Ionic bonds NEVER form molecules
• Ionic bonds form easily between alkali metals and
  halogens

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The Octet Rule

• Atoms tend to gain, share, or lose electrons in
  order to obtain a full set of valence electrons
  (in most cases this equals 8)
• An octet of electrons consists of full s and p
  sublevels on an atom.
• Exceptions transition elements and rare earth
  elements

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Example
-

Na
Cl
Na

Cl

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Properties of Ionic Compounds

• Ionic compounds do not form molecules they form
  a crystal lattice
• The green spheres are Na and the red spheres are
  Cl -

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This is a crystal of CaCl2. Each ion is held
rigidly in place by strong electrostatic forces
that bond it to several oppositely charged ions
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Other Properties

• Normally form between metals and nonmetals
• Ionic compounds have ions that form very strong
  bonds, which makes them hard and brittle
• They have high melting points and high boiling
  points
• When dissolved in water, the solution will
  conduct electricity

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Types of Ionic Compounds

• Ionic compounds will be a combination of a metal
  and a nonmetal (if the cation is monatomic)
• There are two types of ionic compounds
• Binary Ionic Compounds contains the ions of only
  two elements (NaCl, CaCl2)
• Polyatomic Ionic Compounds contain at least one
  polyatomic ion (CaCO3, Mg(OH)2)
• The names DO NOT indicate the ratio of ions
  present, but the formulas do

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Types of Ions

• There are two types of ions
• Monatomic cation or anion that consists of a
  single atom. Examples Na and Cl-
• Polyatomic two or more atoms that act as a
  single ion (or particle). Examples (CO3)2- and
  (OH)-

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Names of Charged Particles

• When electrons are lost, the ion has an overall
  positive charge and is called a cation Examples
  Na, Ca2
• When electrons are gained, the ion has an overall
  negative charge and is called an anion Examples
  F-, S2-
• The negative ions will attract the positive ions
  and form a bond
• All ionic compounds are electrically neutral

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Ionic Charges

• Monatomic ions
• Ions that consist of only one atom
• Charges often can be determined by using the
  periodic table
• Many of the transition metals have more than one
  charge
• The charge on the ion is indicated by using a
  Roman numeral next to the name of the element
• Cu has a 1 and a 2 charge. Cu 1 is called
  Copper I, and Cu2 is called Copper II
• A few transition metals have only one charge
• The names of these do not have to include a Roman
  numeral
• Zn, Cd

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Monatomic Ions
Group Atoms that commonly form ions Charge on ions
1 H, Li, Na, K, Rb, Cs 1
2 Be, Mg, Ca, Sr, Ba 2
13 B, Al 3
15 N, P, As 3-
16 O, S, Se, Te 2-
17 F, Cl, Br, I 1-
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Ionic Compounds

• Writing formulas for binary ionic compounds
• Compounds composed of two elements are called
  binary compounds
• When the formula is written, the charge of the
  cation must be balanced by the charge of the
  anion
• The overall charge of the ion combination must be
  zero
• The cation is always written first in the formula

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Writing Formulas for Ionic Compounds

• To write the formula for an ionic compound
• Write the chemical symbol and overall charge of
  the cation or polyatomic cation Na, Ca2, NH4
• Write the chemical symbol and overall charge of
  the anion or polyatomic anion Cl-, O2-, NO3-
• Add the charges
• If equal, write the chemical symbols together,
  e.g. NaCl, CaO, NH4NO3
• If not equal, crisscross values of the charges
  and make them subscripts, e.g. Ca(NO3)2, CaCl2

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Crisscross Method (also called Drop and Swap

• Na can combine with S2-
• The value of the charge on Na, which is 1,
  becomes the subscript for S S
• The value of the charge on S, which is 2, becomes
  the subscript for Na Na2
• The resulting formula is Na2S

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Naming Ionic Compounds

• Naming binary ionic compounds
• It is important to know the Stock naming system
  and the charges on cations before naming ionic
  compounds
• The process is the reverse of writing formulas

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Polyatomic ionic compounds

• Compounds that contain atoms of three different
  elements
• They usually contain a polyatomic ion must be
  recognized first to be able to name the compound
  correctly
• Tightly bound groups of atoms that behave as a
  unit and carry a charge
• Have the suffix ite and ate
• These ions will be given to you on a sheet you
  will not have to memorize them
• Hydroxide and cyanide are the only common
  polyatomic ions that end in ide

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Common Polyatomic Ions
Ion Name Ion Name
NH4 Ammonium NO2- Nitrite
NO3- Nitrate OH- Hydroxide
CO32- Carbonate SO42- Sulfate
O22- Peroxide C2H3O2- Acetate
SO32- Sulfite ClO3- Chlorate
You will get these on a chart for tests and
quizzes!!
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How Do I Write the Formulas for Polyatomic Ions?

• Put parentheses around any polyatomic ion and add
  subscripts to the outside of the parentheses.
• Never change the subscript of a polyatomic ion
  (it will change the composition of the ion)
• Ca(OH)2, Ca3(PO4)2
• Include the subscript inside the parentheses

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Practice

• Sodium combines with fluorine
• Chlorine combines with hydrogen
• The nitrite ion combines with calcium
• The ammonium ion combines with nitrogen

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Percentage Composition

• The percent by mass of any element in a compound
  can be found by dividing the mass of the element
  by the mass of the compound and multiplying by
  100
• Example 65g of element X and 45g of element Y
  in 110 g of compound
• X (65g 110g) x 100 59
• Y (45g 110g) x 100 41

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Examples

• What is the percentage of oxygen in H2O?
• What is the percentage calcium in Ca(OH)2?

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Representing Chemical Compounds

• The Laws of Definite and Multiple Proportions
  must be obeyed
• Law of Definite Proportions
• States that in samples of any chemical compound,
  the masses of the elements are always in the same
  proportions (e.g. H and O always combine as H2O
  to form water)
• Law of Multiple Proportions
• Whenever element combine to form a compound, they
  will always combine in small, whole-number ratios
  with each other (e.g. H2O, CO2, H2CO3, etc)

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What is molar mass?

• Mass of 1 mole of a compound
• Measured in grams
• It is the mass in grams of one mole of a given
  substance
• It is equal to the average atomic mass of that
  element, written in grams
• It depends on the masses of the elements that
  make up the substance

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How to find molar mass

• Find the molar mass of Na2SO4
• Find the molar mass of MgSO4 7H2O

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How do I convert from moles to mass?

• You must use molar mass
• How many moles of water are in 18.01 g of water?
• What is the mass of 15.2 moles of CO2?

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What is empirical formula?

• Empirical formula gives the simplest whole
  number ratio of the atoms of the elements
• Gives the ratio of the atoms, but doesnt
  necessarily give a correct molecular formula

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To find empirical formulas

• To calculate
• Convert the mass (g) of each element in the
  compound to moles
• Compare the moles in a ratio
• Put the ratio in lowest terms by dividing by the
  smallest number in the ratio
• Round the ratio to whole numbers
• It is easy to go from composition to empirical
  formulas by assuming the percentage is the amount
  of element in grams (i.e., drop the and replace
  with a g).

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Examples

• What is the empirical formula of the compounds
  below?
• 59.95 O 40.05 S
• 48.64 C 8.16 H 43.20 O

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Molecular vs Empirical Formulas

• Molecular gives actual number of atoms of each
  element in a molecule
• Always a whole multiple of empirical formula
• Empirical gives ratios of each element in each
  compound
• Subscripts always in lowest possible whole number

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To Determine Molecular Mass

• Divide the molar mass of the unknown compound by
  the molar mass of the empirical formula
• This lets you know what multiple of the empirical
  formula the formula of the unknown is
• molecular formula (empirical formula)n

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Example

• A compound was found to contain 65.45 C, 5.45
  H, and 29.09 O. The molar mass of the compound
  is 110.0 g/mol. What is the molecular formula?

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Example

• A colorless liquid composed of 46.68 N and
  53.32 O has a molar mass of 60.01 g/mol. What
  is the molecular formula?