Unit 4 Notes

ChemistryMr. Nelson

2008

Why do atoms bond?

Why DON’T some atoms bond? The noble gases – why? They have a full s and p subshell of electrons

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

bonded Bonds help atoms get full s and p subshells

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, giving it 8 electrons in its outer shell.

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

To be more stable, with a full s and p shell, atoms lose or gain electrons

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 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.

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 electron affinity 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 ion

Oxygen gains two electrons to become O2-

Oxide ion

Nitrogen loses three electrons to become N3-

Nitride ion

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

Write the formulas of 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 smallest common denominator that will make the charges on each ion cancel out

Al3+ O2-

3. Check the subscripts and divide them by their largest common factor to give the smallest whole number ratio of ions. Then write the formula.

Al2O3

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 When an atom can have different charges, you must use

ROMAN NUMERALS to indicate the charge when naming

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

EXAMPLE: copper (III) chloride is made of Cu3+ 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. It is just like an algebra problem

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 do not end in –ide, they are ates, ites

Writing formulas 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, put PARENTHESES ( ) around it.

Polyatomic ions

Naming compounds that contain polyatomic ions: it is 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 formula for potassium perchlorate

Write the formula for tin(IV) sulfate

Write the formula for Iron(II) chromate

Write the formula for ammonium sulfate

Covalent vs. Ionic bonding

Ionic bonds: Formed when a positive and negative ion bond. Example: Cu2+ + 2Cl- CuCl2 Electrons are transferred from one atom to

another See page 363 for nice pictures

Covalent bonds: Electrons are just “shared” and not fully

transferred This is because the atoms aren’t strong enough to

rip the other atom’s electrons off (low electronegativity, etc.)