A Chemist’s View of Explosives:

I. Chemical bond: a mutual electrical attraction between the nuclei and valence electrons of different atoms that binds the atoms together. Another way to describe a chemical bond is to say the attractive forces between atoms or ions in compounds. In ionic compounds, it is an attractive force between positive and negative ions.

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In ionic bonding, an electron(s) is(are) actually TRANSFERRED because a non-metallic atom is so much more electronegative and it can, therefore, pull the electron(s) away from the less electronegative atom.

However, sometimes the more electronegative atom is not "powerful' enough to completely take away the electron(s) from another atom so what happens is that these atoms SHARE electrons. This sharing of electrons is called a covalent bond.

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Ionic Bonding occurs between metals and nonmetals.Bonds (and compounds) form in order to obtain an electron configuration like that of noble gases!

II. Formation of Ionic Bonds and Ionic Compounds

A. Ionic compounds-compounds made of positive and negative ions that are combined so that the numbers of positive and negative charges are equal.

• Formula unit: the simplest collection of atoms from which an ionic compound’s formula can be established. A formula unit is to an ionic compound as a molecule is to a covalent compound.

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B. Bonding - involves the valence electrons that are electrons in the HIGHEST OCCUPIED ENERGY LEVEL.

How can we use a diagram to show the placement and the transfer of valence electrons? By using electron-dot structures or Lewis dot structures, valence electrons can be illustrated. Rules to remember are:

1. Valence electrons are (a) outer shell "s" and "p” electrons and (b.) any high-energy electron ("d" or "f") which is NOT stable. (Stable: full, empty, half full)

2. Electrons are not drawn randomly! They are arranged around the element's symbol to correspond to the elements electron configuration.

3. Because it is the "s" and "p" electrons that are illustrated for the representative or main group elements, the Lewis dot diagram has no more than 8 electrons represented for each atom.

               

               

               

                                   

                                   

                                   

                                   

                       

                           

                           

               

               

               

                                   

                                   

                                   

                                   

                       

                           

                           

1. illustrating atoms-Write the element's symbol and place the appropriate number of dots to represent the "s" and "p" electrons around the symbol. (Write out the E.C. and draw the orbitals to help you decide how many dots to draw.)

C. Lewis dot diagrams -

a.) calcium - [Ar]4s2

b.) Li - [He]2s1

c.) Be - [He]2s2

d.) O - [He]2s22p4

e.) Br - [Ar]4s23d104p5

2. illustrating ions- Why do ions form? Because of the Octet rule that states, "Atoms react by changing the number of their electrons so as to acquire the stable electron configuration of a noble gas.”

* for representative or main group elements - These elements lose or gain electrons in their s and p energy levels.

a. Sodium, Na - loses it's one valence electron to have the E.C. of neon.

b. Fluorine:

Types of Ions

(1.) cations - these are atoms that have LOST valence electrons. Write their symbol and the charge on the ion. There are NO dots because there are NO valence electrons! Again, write out the E.C. and orbitals for each atom first. This will help you see what happens when it ionizes.

Mg atom, Mg becomes Mg +2

Ca atom, Ca becomes ___________

Li atom, Li becomes ____________

(2.) anions-these are atoms that have GAINED valence electrons. Write their symbol and the charge on the ion. There will MORE dots on the ion than there were on the atom because it has GAINED electrons! Write out the E. C. for the atom first.

S atom S becomes S -2

O atom, O becomes _______________

Br atom, Br becomes ________________

N atom, N becomes ________________

E. Draw Lewis dot structures to correspond with the appropriate number of valence electrons.

1. F

2. Na

3. P

4. Al

F. Characteristics of ionic compounds (compared to covalent or molecular compounds)

-higher melting points-higher boiling points-generally hard, brittle solids-when melted or dissolved in water they

can conduct electricity-shapes are crystalline in nature (page

177) – square/cube

G. Lewis dot diagrams to illustrate formation of a compound:

1. Write the Lewis dot diagrams for each of the elements involved. Na Cl

2. Draw arrows from the electrons of the metallic atom to the non-metallic atom. This shows the transfer of electrons.

Na Cl

3. Write the dot diagram for the new ionic compound, including charges.

A. Lewis Dot Structures for Ionic Compounds (compounds held together by ionic bonds – usually a M

Example: NaCl

Na + Cl [ Na ]+ + [ • Cl• ]-

• •• ••••

•••

••••

All 3 steps must be shown when you are asked to show the formation of an ionic compound.

Examples- show formation of ionic bond between magnesium and bromine. (MgBr2)

Practice:

1. aluminum and oxygen aluminum oxide

2. calcium and flourine calcium flouride

3. sodium and nitrogen sodium nitride

Writing Ionic Compounds

• Monotomic Ions- Ions formed from a single atom (are either positive or negative). To determine the ion formed for main group elements look to its placement on the periodic table. For elements in groups 3-12, most have either a +2 or +3 charge. For now some will have to be memorized.

• Noble gases to do not form ions except in rare cases.

• Hydrogen can either gain or lose an electron, depending on the other elements with which it combines

Polyatomic Ions

• - 2 or more elements (nonmetals) bonded together that have lost or gained electrons and now have a charge. Compounds have a zero charge but a polyatomic ion has a charge. You must memorize several polyatomic ions.

Writing Formulas

• - formed from (1) a positive ion and a negative ion

• The charge on an ionic compound must always equal zero!!!!

Writing Formulas for Binary Ionic Compounds

• - those containing only 1 metal and 1 nonmetal.

• Write the cation (metal ion) first and the anion (nonmetal ion) second. Determine the smallest whole number ratio of cations to anions that would make the charge 0.

Example

• Write the formula for sodium chloride. Na+1 Cl1-

• NaCl charges equal 0

Example

• Write the formula for sodium oxide

• Na+1 O -2

Example

• Write the formula for aluminum nitride. Ca 2+ N 3-

Ca3N2 charges equal 0

Practice: • Magnesium phosphide____________________ • iron(II) bromide______________________• Calcium oxide __________________________ • sodium sulfide _____________________• Copper (II) iodide __________________________ • lead (IV) nitride ____________________•

tin (II) chloride _________________• Silver fluoride __________________________ • mercury (I) phophide ________________• Copper (II) oxide ___________________________ • potassium bromide __________________• Iron (III) fluoride _______________________ • Tin (II) oxide ______________________

B. Writing Formulas For Ternary Ionic Compounds

• – those containing polyatomic ions• (It is imperative that you know the correct charges

on these ions!!!!!)• Write the cation first and the anion second.

Determine the smallest whole number ratio of cations to anions that would make the charge 0. If a subscript must be added to a polyatomic ion, place the polyatomic ion in parentheses

Example:

• Write the formula for sodium phosphate. Na 1+ PO4 3-

Na3PO4

Example:

• Ammonium sulfide NH4 1+ S 2-

(NH4)2S

Naming Ionic Compounds – 2 naming systems

• IUPAC – International Union of Practical and Applied Chemistry is the newest system-this system uses Roman numerals to give the charges or oxidation number of positive ions ONLY if the positive ion has variable charges.

• “ous” and “ic” system – oldest system and still very commonly used. May be used ONLY if the positive ion has a variable charge and exhibits only 2 oxidation numbers.

• cuprum, stannum, plumbum, ferrum

Names for Binary Ionic Compounds

• - those containing only 1 metal and 1 nonmetal.

• 1. The correct full name of the cation (positive ion) is written first. (Do not forget about the roman numerals on some of the metal ions!)

• 2. The last syllable in the anion (negative ion) is dropped and –ide is added.

Example:

NaCl Sodium Chloride

CuS Copper (II) Sulfide or Cupric Sulfide

MgCl2 ?

Names for Ternary Ionic Compounds

• - those containing polyatomic ions. (It is imperative that you know the correct names of these ions!!!!)

• 1. The correct full name of the cation (metal ion or polyatomic ion) is written first.

• (Do not forget about the roman numerals on some of the metal ions!)

• 2. The correct full name of the anion__________ (polyatomic ion or nonmetal ion) is written second. If the anion is a polyatomic ion do not change the ending. If the anion is a nonmetal ion then the ending is dropped and –ide is added.

Example

NH4Cl ammonium chloride

KNO3 potassium nitrate

Na3PO4 ?