Chapter 3, Sec 2: Organizing the Elements Periodic Table Compare to a Calendar

A way to arrange and categorize elements

1869: 69 elements had been discovered

These 69 elements had many different properties

Pattern Did these properties follow any sort of patter?

Dmitri Mendeleev, Russian scientist, discovered a pattern

Mendeleev Discovered that some elements have similar chemical and physical properties

Ex: fluorine and chlorine are both gasses that form similar compound and have the same effect

How to find the pattern…

Mendeleev wrote down several things about each element:

-melting point

- density

- color

- atomic mass number

- number of chemical bonds the element could form

Mendeleev Wrote each of these properties on cards

Started arranging by trying to find different patterns

HE NOTICED THAT A PATTERN OF POROERTIES APPEARED WHEN HE ARRANGED THE ELEMENTS IN ORDER OF INCREASING ATOMIC MASS

Mendeleev Also noticed that elements with a similar atomic mass tended to react in the same ways

HOWEVER grouping by atomic number only did not always put similar elements together

He then moved several around so that elements with simple properties were together

Mendeleev After arranging his periodic table he had 3 empty spaces

Mendeleev predicted these were elements that had not yet been discovered

Mendeleev even predicted the PROPERTIES of those undiscovered elements

Mendeleev

(he’s a pretty smart guy!)

1869 Mendeleev published the first periodic table

Within three years scientists had found those three missing elements– scandium, gallium, germanium

What is all that stuff in each square?

Atomic number– usually on top of the symbol, tells how many protons an atom contains in its nucleus

Atomic mass– usually a long number with a decimal point, this is the average mass of an elements atoms

What is all that stuff in each square?

Symbol– one to three letters that are used to identify the element, (does not always start with the same letter the element does)

Element name– lists the name of the element in each square

Periodic Table of Today Periods

Henry Moseley

Rows (horizontally) Properties of each element

repeat in each period Contains a series of

elements (like a calendar contains a series of seven days)

Discovered how to measure the positive charge of an atom, then arranged by atomic number not atomic mass

Periodic Table of Today Periodic Table

Groups

The properties of an element can be predicted from its location in the periodic table

Vertical columns

18 total

Can also be called families

Have similar characteristics

Use your periodic table Take out your

highlighters

Make yourself a key for each of these!

Highlight in one color the Atomic number

Highlight in a different color the Chemical symbol

In another color the Element name

In a different color the Atomic mass

Still keep out your highlighter

Still use a KEY!!

Highlight the GROUP all the way on the LEFT

Highlight the 5th period

With a pen number the periods and groups