Ion notes
Atom
• Fundamental structure of matter
• Cannot be broken by any chemical means.
• Have no charge (neutral) because the number of protons matches the number of electrons
Ion
• Charged atom – atom gives up or gains electrons to get a complete outer shell of electrons (like their nearest noble gas).
• Same number of neutrons and protons but different number of electrons than atom
Anions
• Gain electrons
• Negative charge (more electrons than protons)
• Non Metals
• Ion names have an –ide ending (eg. chloride)
Cations
• Lose electrons
• Positive charge (fewer electrons than protons)
• Metals
• Ions keep their regular names (eg. Sodium)
Ionic Compounds
• Ions do not form by themselves.
o If they need electrons to fill their valence shell they need to get them from somewhere.
o If they need to get rid of electrons to get down to a full shell they need to give them to something.
• This can happen when they form ionic bonds with other atoms.
Binary/Univalent Compounds •
Made of 2 ions – metal and a non-metal.
o Hydrogen sometimes acts as a metal.
• Transfer electrons from atom to the other ions!
o One negatively charged (Anion)
o One positively charged (Cation)
• Because ions are oppositely charged they are attracted to each other, ionic bond!
• Total charge of the compound must be Zero (neutral).
Writing Ionic Formulas
• Write down each ion - you can get the ionic charge of each atom from your periodic table.
Example: Ionic compound made up of potassium and fluorine.
K+ F-
• Determine how many of each you will need to make the compound neutral.
One K+ and one Fl- = zero charge
KF
Naming Ionic Compounds
• Entire name is written in lowercase letters.
• Name the calcium fluoride first using its full name.
• Name the sodium oxide second, changing its ending to “ide”.
Multivalent Ions
• Atoms of some elements can form more than one ion
• Mostly transition metals
o Cations (positive charge)
How do we know which ion is being used?
• Each ionic formula should have a neutral charge.
• We can get the negative charge from the anion(s) of the compound.
• The positive charge of compound needs to match the negative for the formula to be neutral.
• We can use the positive charge to figure out the charge of the cation(s).
Naming Multivalent Ions
• How do chemists tell people which ionic charge to use? Roman Numerals!
• Roman numerals are used after the cation name when naming to identify which ionic charge is being used (NOT how many of each ion there is.)
• Roman numerals only get used for multivalent ions.
Polyatomic Ions
• Ions that are made up of more than one element that are covalently bonded (share electrons) together.
• “Poly” – Many “Atomic” – Atoms
• Examples: o Ammonium - NH4 + o Carbonate – CO3 - o – SO4 2-
• Act together as a single ion.
• Polyatomic ion formulas and names are found in a table above the Periodic Table.
• Most polyatomic ions are anions and have a negative charge.
Common Polyatomic Ions
• hydroxide
• chlorate
• phosphate
• nitrate
• sulfate
• HSO4 -
• MnO4 -
• SCN-
• SO3 2-
Naming Polyatomic Ions
• All polyatomic ions keep their name, we don’t change the endings.
• NH4Cl, ammonium chloride
• CaSO4, calcium sulfate
• NaNO2, sodium nitrite
The names and charges of polyatomic ions can be found in lists and do not need to be memorized. However, it is a good idea to get to know the more common ones introduced in the practice below. Remember to form the name by combining the positive and negative ion:
Name = positive ion + negative ion