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.)