Properties of water

Here's a decent video about water's unique properties. Watch the video and answer the following questions:

1. Describe the shape of a water molecule
2. What is cohesion? 
3. What property water molecule makes it cohesive?
4. What property of water is attributed to its cohesive nature?  (hint: think back to the paper clip activity!)
5. What is adhesion?
6. What is capillary action?  Does it occur because of water's cohesive nature or adhesive nature?
7. How does a droplet of water compare to a droplet of alcohol?  Which has stronger cohesive forces?
8. Does mercury have more or less cohesion than water?
9. Go back into your notes or to p. 75 of your textbook:  What are other terms used to describe cohesive and adhesive forces?

If you'd like, fill out a diagram or table that lists water's cohesive and adhesive properties.

Transition Metal Cations

So far, we have only discussed 4 families of elements: the alkali metals, the alkaline earth metals, the halogens, and the noble/inert gases.  Now we are going to pay attention to all those elements in between!

Take a look at groups 3 to 12.  They are all metals, right?  Well, we group these elements into a category called the "transition metals."  This isn't a chemical family; in fact, transition metals really only have a few things in common:

1) They are all metals
2) They all have 4 or more electron orbitals (these are called d-orbitals)
3) They all form cations in ionic compounds

Because of their unique d-orbitals, these transition metals don't follow the same patterns of other metals we've learned about.  It is difficult to predict what cation a transition metal will form and some transition metals can form two different cations!  Let's break it down...

• Take a look at your Periodic Table of the elements.  Can you identify the transition metals?
• Find the element iron (period 4, group 8).  You may notice that there are two integers included in its cell.  +3, +2.  These integers represent the cations that iron can form in an ionic compound.  So, you could have Fe3+ or Fe2+.  This means that iron can give away 3 valence electrons (Fe3+) or two valence electrons (Fe2+).  What are the two cation charges for palladium (period 5, group 10)?

• You'll notice that some elements only form one cation (Zn2+, for example) and that others form two (Cu2+ or Cu1+).  If there are two possible cations, the first integer represents the cation it is most likely to form.

So, take a look at the following two examples and see if you cannot determine which cation of iron is used in each:

1. FeO
2. Fe2O3

Figure it out?  First thing you should ask is "what is the charge of the anion?"  Oxygen has 6 valence electrons and can receive two more.  Therefore, in an ionic compound, oxygen is always O2-.  Now you have to figure out the charges of the cations which will create a stable (no charge) ionic compound.

1. Fe2+  and O2-  will create FeO
2. 2 x Fe3+ (total positive charges = 6) and 3 x O2- (total negative charges = 6) will create Fe2O3

More about transition metals:

• http://www.bbc.co.uk/schools/gcsebitesize/science/edexcel/patterns/transitionmetalsrev1.shtml  (please note that this website labels the groups on the periodic table different from what we have been learning.  Transition metals are in groups 3-12.)
•  

Ionic Compounds

What I need to know about ionic compounds:

• Formed between metallic and non-metallic elements
• Electrons are transferred  from the metal to the non-metal.  This only happens between the valence energy shells (outer orbitals) of the atoms.
• When this occurs, both atoms become ions (charged)
• The metal, having lost negative electrons, is now positively charged and is called a cation.
• The non-metal, having gained negative electrons, is now negatively charged and is called an anion.
• These ions will combine in proportions that allow the metals to give away all their unpaired electrons and the non-metals to acquire a full octet of electrons.

Extra reading:

• Ions: http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/atomic/ionicrev1.shtml
• Ionic Bonds: http://www.teachersdomain.org/resource/lsps07.sci.phys.matter.ionicbonding/
• Chemical bonds: http://www.teachersdomain.org/resource/lsps07.sci.phys.matter.chembonds/
• Chemical bonds: http://www.visionlearning.com/library/module_viewer.php?mid=55