The Periodic TableThe Periodic Table

What it SaysWhat it Says

How to Read ItHow to Read It

AtomsAtoms

Hopefully you have already seen the Hopefully you have already seen the Atoms slide showAtoms slide show

Briefly, all the complicated matter in the Briefly, all the complicated matter in the Universe is made from atomsUniverse is made from atoms Neutrinos, quarks, and other sub-atomic Neutrinos, quarks, and other sub-atomic

particles are exceptions, being smaller than particles are exceptions, being smaller than atoms themselvesatoms themselves

Every atom of an element is the same, and Every atom of an element is the same, and elements are fundamentally different from elements are fundamentally different from each other.each other.

Aside from hydrogen, some helium, and a Aside from hydrogen, some helium, and a little bit of lithium that were made in the Big little bit of lithium that were made in the Big Bang, all the elements in the Universe (up Bang, all the elements in the Universe (up to Uranium) have been made in the interior to Uranium) have been made in the interior of a starof a star

Attempts to organize these 114 elements Attempts to organize these 114 elements (as of 2011) into some kind of table was a (as of 2011) into some kind of table was a major task of 19major task of 19thth century chemists and century chemists and physicistsphysicists They did not know all 114 then!They did not know all 114 then!

The 1869 Periodic Table of the Elements by The 1869 Periodic Table of the Elements by Dmitri Mendeleev (men dell A’ ev) serves as Dmitri Mendeleev (men dell A’ ev) serves as the standardthe standard

http://www.webelements.com/http://www.webelements.com/

The elements are arranged in rows (periods) and The elements are arranged in rows (periods) and columns (groups)columns (groups)

Rows have increasing electron configurations up to Rows have increasing electron configurations up to fully populated shells on the right*fully populated shells on the right*

Elements in a column have similar chemical propertiesElements in a column have similar chemical properties Light elements are at the top, heavy sink to the bottomLight elements are at the top, heavy sink to the bottom

*later

How to read each elementHow to read each element Each element block has four pieces of Each element block has four pieces of

informationinformation The symbol comes from the original name The symbol comes from the original name

(Latin, German, etc.) for the element; the (Latin, German, etc.) for the element; the English name is belowEnglish name is below

The atomic weight, The atomic weight, AA, is the mass in grams of one , is the mass in grams of one molemole of atoms of the element of atoms of the element

A mole is like a dozen, only biggerA mole is like a dozen, only bigger 6.022 X 106.022 X 102323 items per mole items per mole

So a mole of Iron has a mass of 55.845 gramsSo a mole of Iron has a mass of 55.845 grams When rounded to the nearest whole number, it When rounded to the nearest whole number, it

can tell you the average number of neutrons by can tell you the average number of neutrons by abundance*abundance*

*hang on

The atomic number, The atomic number, ZZ, is how many , is how many protons an element hasprotons an element has

ZZ makes each element unique makes each element unique It also gives the element a numerical It also gives the element a numerical

name, e.g. element 26 is Ironname, e.g. element 26 is Iron In a neutral element In a neutral element ZZ also indicates the also indicates the

number of electronsnumber of electrons

Hydrogen has 1 proton/electronHydrogen has 1 proton/electron Helium has 2 protons/electronsHelium has 2 protons/electrons Potassium has 19 protons/electronsPotassium has 19 protons/electrons Krypton has 36 protons/electronsKrypton has 36 protons/electrons

FlavorsFlavors

While each element has a unique number of While each element has a unique number of protons, Z, each can have a range of Nprotons, Z, each can have a range of N

The differing numbers of neutrons makes a The differing numbers of neutrons makes a different flavor, called an different flavor, called an isotopeisotope, of the , of the elementelement Think chocolate: there’s white, Belgium, dark, Think chocolate: there’s white, Belgium, dark,

Swiss, German—but it’s all chocolate!Swiss, German—but it’s all chocolate! When Chemists average out how much of When Chemists average out how much of

each isotope exists, called its abundance, the each isotope exists, called its abundance, the atomic weight always turns out to be a atomic weight always turns out to be a number with decimal placesnumber with decimal places

To find the number of neutrons, To find the number of neutrons, NN, round the , round the atomic weight atomic weight AA to the nearest whole number to the nearest whole number and subtract the atomic number and subtract the atomic number ZZ from it. from it. The remainder is The remainder is NN, the number of neutrons:, the number of neutrons:

N = A – ZN = A – Z 56 – 26 means typical Iron has 30 neutrons56 – 26 means typical Iron has 30 neutrons

Electron ShellsElectron Shells

It’s beyond the scope of our course It’s beyond the scope of our course to lay out all the electron to lay out all the electron configurations in all the atomsconfigurations in all the atoms

It’s enough to know that the outer It’s enough to know that the outer shell, or orbital, of an atom can have shell, or orbital, of an atom can have at most 8 electronsat most 8 electrons

Chemistry happens because of <8 Chemistry happens because of <8 electrons in that shellelectrons in that shell See a Chemist for an explanation!See a Chemist for an explanation!

Just if you’re curious…Just if you’re curious…

All the groups (columns) have the All the groups (columns) have the same number of electrons in that same number of electrons in that outermost shelloutermost shell That’s what makes them chemically similarThat’s what makes them chemically similar

All the periods (rows) start on the left All the periods (rows) start on the left with 1 electron in the outer shell and with 1 electron in the outer shell and end with 8 electrons in the outer shell end with 8 electrons in the outer shell on the righton the right Inner shells get filled up along the wayInner shells get filled up along the way

What about those two rows at the bottom?What about those two rows at the bottom? They are the lanthanide and actinide series, They are the lanthanide and actinide series,

chemically a little different from the otherschemically a little different from the others You can think of it as the Periodic Table would You can think of it as the Periodic Table would

have to be inconveniently wide to fit them inhave to be inconveniently wide to fit them in

Let’s look at just these, Z > 92Let’s look at just these, Z > 92 These These transuranictransuranic elements* are made only in the elements* are made only in the

laboratory in small, sometimes infinitesimal laboratory in small, sometimes infinitesimal quantitiesquantities

They tend to have very short half-lives, meaning They tend to have very short half-lives, meaning they don’t last long before they shed protons and they don’t last long before they shed protons and neutrons and become lighter elementsneutrons and become lighter elements

* Technetium and Promethium are also laboratory elements

That’s pretty much all you need to know hereThat’s pretty much all you need to know here So, as we go along, discussing So, as we go along, discussing

nucleosynthesis and other fun things, it nucleosynthesis and other fun things, it might be a good idea to have a handy copy might be a good idea to have a handy copy of the PTOE, (or your text open to that page!)of the PTOE, (or your text open to that page!)