CHEMISTRY: BALANCING EQUATIONS

There are 2 tricks to balancing equations.  First, spelling the technical word:
                       STOICHIOMETRY

Second, insuring that there are an equal number of atoms of each element on both sides of the equation, following the Law of Conservation of Mass.

The left side of a balanced equation is called the reactant(s).  The right side is called the product(s).

The number of atoms is determined by multiplying the coefficients and subscripts.

To balance a chemical equation, change only the coefficients.  This changes the number of elements or molecules used or produced without changing the element or molecular configuration itself.

Let’s balance an easy one...

We have 2 H’s on the left, so we need 2 on the right.

And now the 2 Cl’s on the right match the 2 on the left.  We’re in balance.

Here’s one with more steps:

Start with the most complicated configuration, maybe Pb3
on the right.   We need 3 Pb’s on the left.

 

That gives us 12 Cl’s on the left, so we need the same number on the right.

Now there are 12 Na’s on the right, so we need the same number of Na atoms on the left. 

TIP:  Because the PO4 on the right is held together with parentheses, keep the PO4 on the left as a single entity as well.

And counting up the PO4’s shows that we have 16 on both the left and the right.  We’re in balance.  Notice that we didn’t have to write the coefficient ‘1’ because it is implied.

TIP:  In the balancing act, it is easier to make the final adjustments if there is a reactant that stands alone, a single element.  Try to save these until last.

BALANCING with FRACTIONS

Sometimes when balancing an equation, you'll wind up with terms that can't be split up.  What if you have O2 on one side and O3 on the other?

Assume that O3 is the more complicated entry so we need to get 3 oxygens from the diatomic O2 on the left.  Think of fractions.  We need one and a half O2s or 3/2.

Even though this equation is technically "in balance," most teachers will want you to use only whole numbers as coefficients in chemical equations.  Think about what you would do in a simple Algebra equation to get rid of a fraction.  You'd multiply by a common denominator, so do the same here.  Multiply ALL terms on BOTH SIDES by the denominator 2 to yield

TIP:  The diatomic oxygen is so frequently involved in these fraction situations, that I try to "balance" the oxygens last.  

Although these examples seem simple, the concept itself is simple also, regardless of how complicated a balancing question may appear.  Just remember

MATTER CAN BE NEITHER CREATED NOR DESTROYED.

FIRST STEP IN CHEMISTRY - The ATOM

 An activity to introduce the atom.

Building an Atom reinforces the concepts of Periodic Table organization, atomic number, atomic mass, proton-electron pairing, shells and subshells, order in which shells and subshells are filled, future study of valence electrons, electron-sharing bonds, ions, and isotopes.

 

This example represents NEON, element #10, with 10 protons and 10 neutrons in the nucleus, and 10 electrons in the subshells.  The first ring (1s) carries 2 electrons, the second (2s) another 2, and the third (2p) a whopping 6!!






Chemistry isn't normally listed as a discrete subject until high school.  We dabble in it at the lower grades with little activities or "experiments" (Isn't it fun to make bubbles and to see the soda pop erupt from the bottle?), and in middle school we introduce a more scholastic approach to some of the foundational concepts.  But when studied at greater depth in high school, some students get stumped at the very beginning by the Periodic Chart (with all of its imbedded detail), the structure of the atom (which seems more like fiction than fact since we never actually "see" it with our own eyes), and the confounding electron cloud. 

At Tutoring Resources, the Summer Preview in Chemistry recognizes the seemingly abstract aspect of the subject and employs ways for a variety of students to gain an intrinsic understanding by doing activities that may not be possible in a classroom of 30 kids.  This year, we've expanded the program to middle school students with great success, proving once again that younger students can rise to the challenges of higher level learning.

This blog explains an activity to explore the structure of the atom through arts and crafts.  It can be completed at home with some basic craft supplies.

Supplies you'll need:
     -- wire rings, embroidery hoops, or thick wire to simulate the subshells.  Each successive shell should be of larger diameter than the previous one.
     -- styrofoam balls, wooden balls, beads, or similar objects to represent protons, electrons, and neutrons, each component of a different color to differentiate them.
     -- paint, to achieve different colors.  Use a paintbrush, not spray paint on styrofoam.  I've had the unfortunate experience of spray paint melting styrofoam.  Although this may be an interesting reaction in a chemistry experiment, physical and chemical changes come much later in the curriculum.
     -- glue or glue gun to affix the components in place.  The younger the student, the less advisable is a hot glue gun!!  I've had strapping football players react strongly to hot glue on fingers.  I've also seen a clear plastic ornament used for the nucleus -- quite attractive and allows the protons and neutrons to move around inside.
     -- string, fishing line, or thread to tie the rings together, attach the nucleus at the center of the innermost ring, and hang the "atom" for display.
     -- a periodic chart for guidance.

Building several "atoms" has pinpointed a few tips that make the construction easier and more effective.
     §  Make the nucleus first by gluing "protons" and "neutrons" together in sort of a sphere.  Before adding the last few components, glue in the string that will be used to tie the nucleus to the shells.
     §  Tie the appropriate number of rings together using the scouting method for connecting teepee poles.  This will help to spread the rings for a more spherical presentation.
     §  I tried sawing an opening in the metal rings so the styrofoam balls could be strung on, but that was a lot of effort.  I settled on cutting a slit in the styrofoam and pressing each one onto the ring.  A squirt of glue closes the slit and keeps the balls from sliding to the bottom.
     §  When cutting a length of string for tying, longer is better.  It's easier to cut off excess thread than it is to tie a square knot with only an inch to work with.
     §  A dab of glue is an effective method of setting a knot, especially in fragile threads.

STEPS:
1.  Decide the element to be constructed.*
2.  Determine the number of protons, neutrons, and electrons needed.
3.  Assemble materials.  Paint components if necessary.
4.  Construct nucleus.
5.  Tie rings together.
6.  Tie nucleus so it hangs in the center of the innermost ring.
7.  Affix electrons to appropriate rings.
8.  Tie string as a hanger and suspend far enough from a wall to allow the "atom" to move with the breezes.

* To make the exercise more challenging, I prepared a few styrofoam balls in three different colors.  The students needed to count how many of each color were available and then select an element that would need no more components than they had at their disposal.  This approach reinforced the idea of protons and electrons being equal and the value of an element's atomic number.

Did the activity work?  Well, from the social media posts, the enthusiasm of requests to "make another one," and the fluency with which the kids can now speak the names of  the first 10 elements, I think atom building will be a feature of the Chemistry Preview for many years to come.

Atom display: (L to R) Neon, Helium, Lithium, Hydrogen, Boron





EXTENSIONS:  The concepts introduced here can be expanded to introduce Periodic Table BLOCKS, electron configuration, elements with higher atomic numbers, isotopes, and ions.

An anecdote from the experience of a seventh grader:  In working on the valance shell, the student dropped one of the electrons and questioned what had happened to the element.  This became a learning opportunity to introduce ions.