CHAPTER 5

The Periodic Table

5 .1

Organizing the Elements

Organizing Elements Game

How did you arrange the table?Based on your arrangement, where would

you put a card for an element that is a liquid with an atomic mass between 9 and 13? What would its atomic mass actually be?

Historic Overview Article

Trace the evolution of the current Periodic Table by creating a detailed timeline. Show important steps in the history of arranging

elements in meaningful ways. Include every step that is listed in the article!

Describe the basic tenets of each model for arranging elements

Questions

What is the periodic law?

What is an outlier?

What element did Mendeleev start his “game of cards” with? Why did he pick this element (in other words, why not hydrogen or helium?)

Why did Mendeleev leave spaces on his version of the periodic table?

More Questions

What does interpolated mean?

What element is named after Mendeleev? What is its atomic number? How many protons does it have?

Dmitri Mendeleev

http://www.youtube.com/watch?v=kuQ0Um4Wcz0

Search for Order

Brings order to seemingly unrelated facts Helped chemists predict the existence of

elements that weren’t discovered yet Groups elements according to their

chemical and physical properties

Dmitri Mendeleev

Thought of a way to approach the problem of organizing the elements while playing solitaire

Mendeleev made playing cards of the elements that included the mass and properties of the elements, then arranged them in order of increasing mass

Mendeleev’s Periodic Table

Strategy for organization: What

did he look at? chemical properties physical properties atomic mass density color melting point Valence electrons

Mendeleev’s Proposal

Elements arranged in rows based on increasing mass.

Elements with similar properties are in same column.

Chart was a Periodic Table arrangement of elements in columns based on a set of

properties that repeat.

Mendeleev’s Prediction

Table incomplete– elements not yet discovered

Left spaces in table for undiscovered elements

Evidence Supporting Mendeleev’s Table

Close match between Mendeleev’s predictions and the actual properties of new elements showed how useful table was.

Ex. Discovery of: Aluminum, Gallium, Scandium, and Germanium

5 .2

The Modern Periodic Table

The Periodic Law

Elements are arranged by increasing atomic number

Periods Rows of the periodic table The period number tells us how many energy levels an atom of

a particular element will have

Groups (or Families) Columns of the periodic table Properties of elements repeat in a predictable way when atomic

numbers are used to arrange elements into groups Elements in vertical groups have similar electron configurations,

which determines the chemical properties of an element

The pattern of repeating chemical and physical

properties that exists in groups of the periodic

table

Periodic Law

Atomic Weight (or Atomic Mass)

A value that depends on the distribution of an element’s isotopes in nature and the masses of those isotopes.

Calculating Atomic Weight

In nature, most elements exist as a mixture of two or more isotopes.

Example: There are two natural isotopes of Chlorine that Chlorine – 35 Chlorine – 37

How are these different?

Weighted Averages

Some isotopes occur more frequently in nature than do other isotopes

Distribution of Chlorine Atoms in Nature

Isotope Percentage Atomic Mass

Chlorine-35 75.78% 34.969

Chlorine – 37 24.22% 36.966

Classifying Elements

Can be classified in three ways: By state of mater at room temperature (solid, liquid or

gas) By those that occur naturally and those that do not Based on their general properties we can divide them

into METALS, NONMETALS & METALLOIDS

Periodic Table Coloring Activity With a marker, draw solid lines around the following

elements B, Si, Ge, As, Sb, Te, Po, At

Trends in the PT

Across a period from left to right, the elements become less metallic and more non-metallic in their properties

The most reactive metals are on the left side of the PT

The most reactive non-metals are in Group 17

Complete Side 1 of Element Classification Graphic Organizer

Valence Electrons

An electron that is in the highest occupied energy level of an atom

Elements in a group have similar properties because they have the same number of valence electrons

We can illustrate valence electrons using electron dot diagrams

Valence electrons are the electrons that participate in bonding between atoms

Electron Dot Diagram

How do we find the number of valence electrons?

Look at the Group number! The group number tells you how many electrons are in

the outer shell of an atom

Group 1 – 1 valence electronGroup 2 – 2 valence electronsGroup 13 – 3 valence electronsGroup 14 – 4 valence electronsGroup 15 – 5 valence electrons

Making Dot Diagrams

Write down the chemical symbol of the element

Determine the number of valence electronsUse a dot to represent each valence electron

by drawing dots around the chemical symbol Pretend there is a box around the chemical symbol,

putting single electrons on the edges of the box. After you have put a single dot on each edge, then start paring up dots with any remaining electrons.

Example - Carbon

C

Valence Electron Practice

Dot Diagram Game

4 TeamsRacing to make correct dot diagramsWinning Team gets a HW pass for ONE HW

assignmentEveryone on your team MUST participate