THE ‘EVERYTHING YOU NEED TO KNOW’ EVEN THOUGH ‘YOU COULD CARE
LESS’ CHEAT SHEET
NAMING COMPOUNDS
1.
Is it ionic or covalent? How do you know?
2.
Name your ionic compound by answering the following questions:
a. Is it binary? (only two elements) If so, name the cation (+ ion) as it appears on periodic table and
then change the ending of the anion (- ion) to ‘ide’ Then see “c”
3.
If its ionic, continue to # 2 --- If its covalent, skip to # 3
b.
Is ternary? (three elements) If so, name the cation (+ion) as it appears on the periodic table and then
look for the name of the polyatomic ion on the back of your periodic table. Then see “c”
c.
Finally, check to see if your cation is a transition metal. If it is, you must add Roman Numerals to
represent the CHARGE on the metal --- the Roman Numeral does not represent how many atoms
there are.
* To determine the charge on the transition metal, you must first determine the total
charge on the negative ion by multiplying the subscript by the charge of the negative
ion. The total positive charge must be equal but opposite. If all else fails, uncross-cross!
Name your covalent (molecular) compound by writing the name of the first element as it appears on the
periodic table and changing the ending of the second element to “ide”. Then add a prefix to each name
to show how many of each is in the formula. The prefix before the name should match the subscript for
that element in the formula. DO NOT CRISS CROSS anything.
WRITING FORMULAS
1.
Ionic Formulas: all will start with name of a metal except “Ammonium ____________”
a. Write the symbol and the charge for the metal.
Use the charge we wrote at the top of each “A” Group or if it’s a
Transition metal – the ROMAN NUMERAL in the name WILL BE THE CHARGE
b. Write the symbol and the charge for the non metal (which may be a polyatomic ion)
Most of the polyatomic ions end in “ate” or “ite” so you know to look on the
back of your table. The non metals on the periodic table end in ‘ide’
COMMON EXCEPTION: hydroxide (OH-) is a polyatomic ion that ends in ‘ide’
c. Calculate how many positive ions and negative ions you need to make the overall charge =
zero and add subscripts to balance. Criss-cross usually works, but not 100%.
Your final formula SHOULD NOT HAVE ANY CHARGES.
2.
Covalent Formulas: YOU WILL NOT USE CHARGES ON THE PERIODIC TABLE. NO CRISS CROSSING.
a. Underline the prefixes and determine their value. No prefix means there is only one.
b. Write the symbol for both elements and then add the subscript for each element based on its
prefix value.
LEWIS STRUCTURES
Represent the valence electrons only. Valence electron values are equal to the Roman Numeral of the ‘A’
Groups. IA, IIA, --- VIIIA. Make sure you have your periodic table numbered correctly. The valence
electrons on ‘B’ group transition metals have to be given to you.
For Ionic Compounds: Only the non metal will have electrons around it because the metal will be giving
its electrons to it.
For Covalent Compounds: Use the Needs (or wants), Has, Shares, Left over method. (NHSL). All
elements should end up with 8 electrons (dots) except Hydrogen which will need only 2.
DETERMINING MOLECULAR SHAPES AND POLARITY
1.
2.
3.
Ionic compounds will be polar --- because the nonmetal part of the molecule is negatively charged
and the metal part of the molecule is positive creating “unequal” ends.
Covalent molecules can be polar or nonpolar, depending on their shape which is determined by their
shape and surrounding electrons. To find the shape, you need to draw the Lewis Structure. Once the
Lewis structure is drawn, look carefully for left over, ‘unbonded’, or ‘lone pairs’ of electrons. The
presence or absence of lone pair electrons, determines the shape and polarity of molecules.
You will be able to use your “Shape Sheet” on the test.
PROPERTIES OF IONIC AND COVALENT COMPOUNDS
IONIC
High melting point
High boiling point
Conductors
Soluble in water
COVALENT_______________________
Low melting point
Low boiling point
Non conductors
Not soluble in water
WHAT’S WITH ALL THE NUMBERS??????
+ and – charges indicate how many electrons an ion will gain or lose. They are used to balance the
overall charge of a compound so the net charge is zero. They can be found at the top of
our “A” groups on the periodic table or by a Roman Numeral given in the name of an ionic
compound. These are the numbers you criss-cross when writing ionic formulas. Charges are written
as superscripts and should never appear in a formula.
Subscripts – in a formula tell you how many ions of each element you need to balance the charges.
Multiplying the subscript by the charge of each ion gives you the total positive charge or total
negative charge. When correctly balanced the sum of the two should be zero.
Roman Numerals you need to know two sets.
1. The Roman Numerals we wrote in on our periodic table for the “A” groups, tell how many
valence electrons the elements in that group have. They are used to determine
the charge on the ion once it forms, BUT it is NOT the charge itself.
2. The Roman Numerals that appear in the name of an ionic compound with a Transition metal DO
INDICATE THE CHARGE.