Unit 4 Notes

ChemistryMr. Nelson

2009

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

• Polyatomic ions =– Many atom ions

• Naming monatomic ions– To name positive ions, just add the word “ion”– To name negative ions, drop the last part of the word,

and add “-ide ion”

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 gains 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 outAl3+ 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 naming

• Write the electron configuration for Iron. • Predict the oxidation number

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 BOY BAND. 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