1. Elements, Their Properties, and the Periodic Table

2. What is an Element?
Element- a pure substance that cannot be separated into simpler substances by physical or chemical means.
It consists of only one type of atom
Pure substance-  a substance that has only one type of particle.

3. Dmitri Mendeleev Arranging the Elements
By 1869, 60 elements had been identified,
but was there a pattern or a way to organize
them?
Dmitri Mendeleev, a Russian chemist, came up with the Periodic table.  He took the name and properties of the elements, and wrote them out on cards.  He included density, atomic mass, appearance, melting point, and other information.  He found a repeating pattern of the properties.  
   
The properties of the elements are periodic, meaning they have a regular, repeating pattern.  
Mendeleev recognized there were elements missing and he predicted the properties of those missing elements.  

4. Dmitri Mendeleev Changing the Arrangement
Mendeleev was perplexed because some of the elements in the table were not in the correct place according to their properties. He figured he had made a mistake figuring the atomic masses of the elements and in time more accurate atomic masses would be made and the table would be corrected.
In 1914, a British chemist, Henry Moseley, solved the problem.  
He had determined the number of protons in atoms of the elements.  He then placed the elements according to their atomic number, the number of protons in an atom.  Doing this allowed each element to fall into place.  Thus, in the modern version of the periodic table, the elements are arranged by atomic number and not by atomic mass. (weight)
Periodic Law-  
States that the chemical and physical properties of elements are periodic functions of their atomic numbers.  

5. Finding your way around the Periodic Table
Atomic Number
(# of protons in the nucleus)
(# of electrons in a neutral atom)
Classes of elements-
Metals
Nonmetals
Metalloids (seimiconductors)
Chemical Symbols
    - each element is identified by a symbol
    - usually consists of one or two letters
     - 1st letter is always capitalized, second letter is lowerecase
Atomic Mass
(basically the total number of particles in an atom's nucleus)

6. We now know that Elements are pure substances made up of only ONE kind of atom…
But are all atoms of an element really the same? Remember when you made a hydrogen atom in your notes? You know, “the simplest of atoms”? Draw that atom again. Now I want you to draw another atom. This atom has the atomic number of one, but has an atomic mass of amu. What is different about this new atom?

7. Isotopes
Let's say an atom is missing a neutron or has an extra neutron. That type of atom is called an isotope.
Isotopes are still the same element, they are just a little different from every other atom of the same element.
For example, there are a lot of carbon (C) atoms in the Universe. The normal ones are carbon-12. Those atoms have 6 neutrons. There are a few straggler atoms that don't have 6. Those odd ones may have 7 or even 8 neutrons. As you learn more about chemistry, you will probably hear about carbon-14. Carbon-14 actually has 8 neutrons (2 extra). C-14 is considered an isotope of the element carbon.

8. Messing with the Mass
If you have looked at a periodic table, you may have noticed that the atomic mass of an element is rarely an even number. That happens because of the isotopes.
You can identify each isotope of an element by its mass number.
We write the name of the element followed by a hyphen and the mass number of the isotope.
The mass number is sum of the protons and neutrons in an atom. Electrons are not included because they are so small.
(THE MASS NUMBER IS CLOSE, BUT DIFFERENT
FROM THE ATOMIC MASS!)

9. Calculating the Mass of an Element
Most elements found in nature contain a mixture of two or more stable isotopes.
Atomic mass is the weighted average of the masses of all the naturally occurring isotopes of an element.
To calculate the atomic mass of an element, multiply the mass number of each isotope by its percentage abundance in decimal form then add those amounts together to find the atomic mass. Let’s practice a few…

10. Take a Look at your Periodic Table Again…
Rows are called Periods
    *each horizontal row is called a period.  
Ex.  The row starting with lithium (Li) and ending with neon (Ne)  is Period 2.
*the elements in a row become less metallic from left to right.
   
Columns are called Groups or Families
*elements in the same group often have similar chemical and physical properties.

11. Properties of Elements
Elements are classified by their properties
Think of all the different breeds of dogs. There are hundreds!! These breeds are sometimes classified into categories such as sporting breeds, hunting breeds, hounds, spaniels, purebreds, giant breeds, toy breeds, mixed breeds, just to name a few.
Like dogs, there are many kinds of elements and scientists group/classify these elements by their properties.

12. Properties of Elements
Work with your partner to make observations and group/classify the following items in your SNB however you think is best:

13. Properties of Elements
Characteristic properties-  a unique set of properties for each element that allows scientists to identify that element.
        *Physical properties-   boiling point, melting point, and density.
        *Chemical properties- reactivity with acid.

14. Ex. Cobalt, Iron, and Nickel
Ex.  Cobalt, Iron, and Nickel             *All three have some properties in common, especially color.
Cobalt-
    Melting point- 1,495oC
    Density- 8.9 g/cm3
    Conducts electrical
    current and thermal
    energy.
     Un-reactive with
oxygen
Iron-
  Melting point-1,5350C
   Density-7.9g/cm3
   Conducts electrical
energy and thermal
energy.
   Combines slow with
oxygen in the air to
form rust.
Nickel-
   Melting Point-1,4550C
    Density-8.9 g/cm3
    Conducts electrical
current and thermal
energy.
   Unreactive with oxygen
in the air.

15. Back to our Dog Breed Example… Elements are Grouped into Categories Too!
     *classified according to their shared properties.
    *All 3 above are Metals,
*They’re all shiny, hard, and conduct electrical current and
thermal energy.
        * Not all metals are alike, but they all have shared properties.
If you know the category, you know the properties.
    Ex.  Movie Rental stores or Redbox
        *How are the movies categorized?
        *If you come across the title of a movie that you don’t recognize, and it is in the
          ”Horror” section, what can you assume about that
          movie?  
    Likewise, you can predict some of the characteristics of elements if you know what category they are in.

16. There are Three Main Categories of Elements:
Metals
Non-Metals
Metalloids
You will notice on the periodic tables you were given today, that these main categories have been divided even further into 10 smaller categories. For now, we will focus on just these three.

17. Metals

18. Non-Metals

19. Metalloids