Atoms, Ions, and Electrolytes

Matter and Elements

Everything that tangibly exists in the universe in known as matter.  What, exactly does that mean?  Can I hold it in my hand?  Breathe it in?  Matter has mass, so it takes up space, and it has a state of charge.  I’m sure you are thinking positive and negative charge, but there is also the state of having no charge. 

Elements are identities of matter.  Some things are made of oxygen, carbon, and nitrogen. They also include all the other elemental identities listed in the Periodic Table of Elements.  Usually, this is the point where some students ask where atomsThe smallest units of matter that retain the properties of an element. and moleculesGroups of atoms bonded together. come into play.  Soon. 

You will come to know the abbreviations for many of these elements.  Some are intuitive, such as O for oxygen, H for hydrogen, and so on.  But some abbreviations refer to a Latin root word.  The prefix natur- stands for sodium(Na⁺): Major ECF cation; important for fluid balance, nerve function., making its abbreviation Na.  The prefix kal- stands for potassium(K⁺): Major ICF cation; essential for muscle and nerve function.. It gives it the K abbreviation. It’s often confused for calci-, which is the prefix for calcium (which is Ca).  Notice how the second letter of the abbreviation is always in lowercase.  The numbers that you see here are called the atomic numbers.  These all indicate something about electronsNegatively charged subatomic particles found in atoms..  We’ll just leave it at that for now.

Atoms

An atom is the smallest packet of matter that we know of.  Actually, that’s not true.  We believe that there are smaller structures called subatomic particles, but we have never directly viewed them. The subatomic particle are protons, neutronsElectrically neutral particles in an atom’s nucleus., and electrons. They all have different charges and different locations in an atom. Neutrons are uncharged. They are not negatively charged. They possess no charge. Neutrons exist in the juicy center of the atom called the nucleusThe control center of the cell that contains DNA and directs cellular activities..  With them are protons, which are positively charged. Protons and neutrons never leave the nucleus.  If a proton tries to leave, there’s a big explosion and movies like The Hills Have Eyes.

The number of protons an atom has depends on which element it is.  The atomic number of each element from the Periodic Table tells you. It shows how many protons an atom of that element will have. For example, hydrogen has 1 proton, oxygen has 8 protons, and sodium has 11.  In both these diagrams of a carbon atom, there are 6 protons and 6 neutrons in the nulcei. 

The negatively charged electrons are not fixed in location.  They move around and so we get this kind of…cloud as to where they are.  The diagram on the left is called a planar model of a carbon atom.  But the diagram on the right is more accurate that the electrons fly around the nucleus creating a cloud.  Why don’t they fly away?  Because each electron is attracted to a proton in the nucleus.   Positive and negative attract. 

We are talking about atoms on this slide.  An atom, by definition, has the same number of protons and electrons.  This also means that, by definition, atoms have no charge.  

Electron Shells

Electrons don’t just fly around the nucleus randomly in factA statement based on direct observation that is repeatedly confirmed. an atom is much like a peanut M&M. The peanut is the nucleus and it is dipped into chocolate to make the first shell.  Then you dip it again to make the second shell, then again, and so forth.  These planar models are in 2-D and you have to think of them in 3D.  For example, electrons do not orbit the nucleus, in a predetermined path, like the planets rotate around the sun.  An electron would have an infinite number of orbits around the nucleus, forming a shell.  We call these areas shells and shells hold a different number of electrons. 

Before we get started looking at valence shells, you should know the two preferences of the universe. Shells like to be full. Electrons like to be in pairs.

The first shell for any and every atom in the world holds two electrons.  You can see this in the diagrams on the right and left which are oxygen and carbon, respectively.  Let’s just look at those two for now. Oh, we know they are atoms. The number of protons in each of them is equal to the number of electrons.  Count them.  I’ll wait.  

As we draw these planar models, we put the protons and neutrons in the nucleus lockdown.  We draw a line for the first shell of chocolate. It covers the juicy nucleus. We put two electrons in that first shell.  This is good, the shell is full and the electrons are shared.  Let’s move to the second shell, which CAN hold 8 electrons.  Oxygen’s atomic number is 8, so we draw the remaining six electrons into the second shell.  This valence shell is not full and that is bad. Oxygen could give these 6 away.  Have you ever re-homed a litter of stray cats?  I dare you to try and find 6 people that want a cat.  It is much easier for oxygen to find another atom wanting to donate or share 2 electrons. It is harder to find someone willing to take all 6 electrons in the valence shell.  Now, take a look at carbon on the right and apply the same rules.  We put 2 electrons in the first shell and the rest in the second shell.  This time, we have 4 out of 8 electrons present.  So, carbon could potentially bond with 4 other things.  That’s a lot of bonding.  It is also always determined by the valence shell.

The middle atom of hydrogen defies all expectations.  This lonely electron is in the outer most or valence shell. Unfortunately, for the proton in the nucleus of the middle atom, everything else in the world has as many. Many things have even more protons.  This electron is attracted to anything but its original proton.  So, hydrogen atoms are rarities. 

Ions

An ion is an atom that has lost or gained electrons from its valence shell.  By doing so, we get positively charged and negatively charged structures.  Don’t be fooled that you can make an ion by gaining or losing a proton.  You can’t.  Remember?  Big explosion, radiation sickness, bad B horror movies?

The planar model on the left is a sodium atom.  It’s atomic number is 11 and so it has 11 electrons.  Two electrons go into the first shell. Eight electrons go in the second shell. We have this lonely electron all by itself in the 3^rd shell.  Again…bad.  Sodium would like to give this electron away.  If it does, the second shell, which is full, will be its valence shell and it will be happy. 

The planar model on the right is a chlorine atom.  Its atomic number is 17. Simply put, it has 7 electrons in its valence shell. This shell wants to hold eight.  It is almost a match made in heaven here right?  Sodium has one extra electron and chlorine wants one electron.  KISMET!

This is how salt is formed…a sodium atom gives an electron to a chloride atom.  The sodium becomes a positively charged ion called a cation, because now it has 11 protons but only 10 electrons. The chloride atom becomes a negatively charged ion called an anionA negatively charged ion., because now it has one extra electron. 

It’s really all about that outer shell.  It determines the ability of atom to make bonds with other atoms, molecules, compounds, and other chemistry nouns.  By trying to fulfill those two rules, bonds are made, bonds are broken, and ionsCharged atoms or molecules. are formed.  This is what is happening inside of you right now.  RIGHT NOW!

Electrolytes

In my general biology class, we talk about ions.  Here in A&P, we talk about electrolytes.  You have electricity running through your body.  A thought is really just the movementA fundamental property of life involving motion of the body or its parts. of electricity.  Move your big toe.  Electricity zapped through your spineProminent ridge on the posterior scapula dividing it into supraspinous and infraspinous fossae. and sciatic nerveThe largest nerve in the body, arising from the sacral plexus.. It delivered the message to your toe muscles. They should contract.  The electricity that your body uses to move information depends on ions present in your blood. It also depends on the ions in your interstitial fluids between cellsThe basic structural and functional units of life. and your cells. 

Therefore, we call salts electrolytes, which is a word that denotes the ability to conduct an electrical currentThe flow of electrical charge, as in ions moving across a neuron’s membrane..  When a salt enters your blood from your small intestine, it breaks apart quickly. It splits into its anion and cation.  The salt you ingested at lunch split immediately. It formed the sodium cation and the chloride anion when it hit your blood. This splitting is called dissociation.  That is what you see in that flask on the right of the picture.  The cations and anions are fully separated because NaCl is a very strong electrolyte.  There are also weak electrolytes.  As you can see in the picture weak electrolytes don’t dissociate completely in your blood.  Anything that isn’t an electrolyte doesn’t dissociate.  This molecule in the flask on the left could be an alcohol. It stays intact when you put it into waterThe universal solvent essential for life..