Unit 5 Notes

ChemistryMr. Nelson

2009

Chemical Bonds• Today we will learn about ionic bonds

– Ionic• Electrostatic attraction between ions

Why do atoms bond?

• Why DON’T some atoms bond?– The noble gases – why?

• Why do other atoms bond, then?– They are more chemically stable when bonded

How do atoms bond?

• The octet rule– The octet rule, or rule of eight, says that an atom will

strive for a full s and p subshell

– Atoms will either lose or gain electrons to get 8 in the outer shell

– NOTE: when an atom loses or gains electrons, it’s nucleus remains the same – only the outer electron shell has changed!!!

Bonding and energy changes

• Energy is the ability to do work

• Stability is a measure of inability to do work– So, the lower the energy, the more stable something is!

• When atoms bond, the process favors stability (lower energy). Things will never go from a stable to an unstable state on their own!

Electrons, bonding, and IONS

• When they do this, they get a CHARGE, because protons (+) and electrons (-) are no longer equal. They are now IONS

• Positive and negative IONS come together and balance each other out in IONIC BONDS.

Cations and Anions

• Remember:+ + +A “plussy cat”

An “antion”

Ionic Bonding

• Sodium wants to GIVE an electron, Chlorine wants to GET an electron.

Ionic Bonding

• The low ionization energy of sodium and the high electronegativity of chlorine is one reason this works so well.

•

Naming ions

• Monatomic ions = – One atom ions

• Naming monatomic ions– To name positive ions, just add the word “ion”

• Example: Magnesium’s ion is Magnesium ion

– To name negative ions, drop the last part of the word, and add “-ide ion”

• Oxygen’s ion is called oxide

Naming monatomic ions

Rubidium loses an electron to become Rb+

Rubidium ion

Calcium loses two electrons to become Ca2+

Calcium ion

Chlorine gains an electron to become Cl-

Chloride

Oxygen gains two electrons to become O2-

Oxide

Nitrogen loses three electrons to become N3-

Nitride

Compounds made of two monatomic ions

• These are called BINARY COMPOUNDS

• You always put the positive part first and the negative part last: Na+ + Cl- NaCl

• Names = name of the positive ion + name of the negative ion: Sodium Chloride

Examples: Name the following

Back to ions: Writing Ionic Formulas

• The nomenclature (naming system):1. Write the symbols for the ions side by side. Write

the cation first.Al3+ O2-

2. Find the lowest common multiple that will make the charges on each ion cancel out

Al3+ O2-

3. Check the subscripts for the lowest whole number ratio of ions. Then write the formula.

Al2O3

Write the formulas of the following:

d-block• The d-block (yo) has its own rules

– Metals in the d-block have variable charges– All d-block metals must get a ROMAN NUMERAL to

indicate the charge

– EXAMPLE: copper (I) chloride is made of Cu1+ and Cl-

– EXAMPLE: copper (II) chloride is made of Cu2+ and Cl-

– Don’t use roman numerals if you don’t have to

Examples

• Write the formulas for– Tin(II) iodide

– Cobalt(III) chloride

Working backward• If you are given the formula you need to calculate

the charge of the d-block metal.

• Assume the anion did not change its charge (they are very consistent)

• Example: FeO, to write the name we need the charge of iron.

A few more examples

• PbS2

• MnBr3

• Cu3P2

Polyatomic ions

• When two or more ions are clumped together it is a polyatomic ions.

• They usually end with –ates or -ites

Nomenclature of Oxyanions

• They are not standard!– Example Sulfate vs Phosphate

• Nomenclature examples– Perchlorate– Chlorate Nitrate– Chlorite Nitrite– hypochlorite

Writing formulas for compounds with polyatomic ions

• Polyatomic ions should ALWAYS be treated like a LUMP. Don’t ever break it up!

• If you need more than one polyatomic ion to balance a charge, use PARENTHESES ( )

Polyatomic ions

• Naming compounds that contain polyatomic ions:– The steps are the same:– the name of the first ion + the name of the second:

• NH4+ = ammonium ion (polyatomic)

• Cl- = chloride ion (monatomic)

• NH4Cl = ammonium chloride

Example

• Write the formulas for:

• potassium perchlorate

• tin(IV) sulfate

• Iron(II) chromate

• ammonium sulfate

Ionic vs. Metallic bonds

• In an IONIC BOND, the electrons of one atom (that wants to lose electrons) are donated to the electrons of another atom (that wants to gain electrons). The charges on each ion balance each other out and equal ZERO.

• In a METALLIC BOND, all the atoms are the same (all copper, for example) and the electrons don’t belong to any one atom. They move around a lot – that’s why electricity is conducted.

Metallic Bonds

• A “sea” of mobile outer electrons.

• Low ionization energies means the atoms don’t hold electrons well.