1. Unit 3 Part 2
Chapter 5
Explain the trends of the periodic table based on the elements’ valence electrons and atomic numbers. (PS-2.3)

2. History of the Periodic Table
First list of known elements compiled by Antoine Lavoisier in late 1790s
Contained 23 elements
~70 known elements by 1870
1860s – search for relationships between atomic mass and elemental properties began

3. John Newlands (1837 – 1898) English chemist
Elements arranged by increasing atomic mass, properties repeat every 8th element
Pattern is called periodic b/c it repeats in specific manner
Law of octaves
Did not work for all known elements

4. Lothar Meyer (1830 – 1895) German chemist
Demonstrated connection between atomic mass and elemental properties

5. Lewis Reeve Gibbes (1810 – 1894) American chemist
Professor of Chemistry at the College of Charleston 1839 – 1892
1870 – 1874 generated “Synoptical Table of the Chemical Elements”
Not published until 1886

6. Dmitri Mendeleev (1834 – 1907) Russian chemist
1869 – published periodic table based on relationship between atomic mass and elemental properties
Used table to predict existence and properties of undiscovered elements
Left blank spaces in table
Predicted existence of Scandium, gallium and germanium

7. Henry Moseley
Errors in periodic table developed by Mendeleev (some elements in wrong groups)
1913 – Moseley regrouped elements by increasing atomic number
Problems with order of elements solved

8. Periodic Law
Periodic repetition of chemical and physical properties of the elements when they are arranged by increasing atomic number

9. Modern Periodic Table Periods Horizontal Rows Numbered 1 – 7
Groups
Vertical Columns
Numbered 1 – 18
Each member of the same group has the same number of valence electrons and similar properties
Chemical properties are not the same because elements have different numbers of non-valence electrons
Periods
Horizontal Rows
Numbered 1 – 7
Represents which energy level that the valence electrons can be found

10. Modern Periodic Table Representative Elements Transition Elements
Groups 1A – 8A
Possess wide range of chemical and physical properties
Transition Elements
Groups 1B – 8B

11. Metals Located left of the staircase Luster Malleable & ductile
Good conductors
High density
React with acids

12. Metals Alkali Metals Alkaline Earth Metals Transition Metals
Group 1A elements
Most reactive metals
Alkaline Earth Metals
Group 2A elements
Chemically reactive
Transition Metals
Inner Transition Metals
Lanthanide Series
Used as phosphors, emit light when struck by electrons
Actinide Series

13. Alkali Metals
Alkaline Earth Metals
Transition Metals
Lanthanide Series
Actinide Series

14. Nonmetals Right of Staircase Dull Nonmalleable, non-ductile
Poor conductors
Low density
Do not react with acids

15. Nonmetals Halogens Noble Gases Group 7A Highly reactive Group 8A
Extremely unreactive

16. Noble Gases
Halogens

17. Metalloids Along staircase
May have characteristics of metals and/or nonmetals

19. Organizing Elements by Electron Configuration
Valence Electrons
Atoms in the same group have similar chemical properties because they have the same # of valence electrons
Valence Electrons & Period
Energy level of valence e- indicates the period on the periodic table
Valence Electrons & Group Number
Representative element’s group number is the same as its number of valence electrons

20. HW Question
An unknown element has chemical behavior similar to that of silicon (Si) and lead (Pb). The unknown element has a mass greater than that of sulfur (S), but less than that of cadmium (Cd). Use the periodic table to determine the identity of the unknown element.

22. Periodic Table Trends Energy Levels
Left to right across a period (Pds. 1 – 3)
Energy level of valence electrons stays the same
For example, all elements in Period 3 have valence electrons located in the 3rd energy level.
Top to bottom down a group (Representative Elements)
Energy level of valence electrons increases by one
For example, Li has 1 valence electron in energy level 2 and Rb has 1 valence electron in energy level 5

23. Periodic Table Trends Valence electrons
Left to right across a period (Pds. 1 – 3)
Representative elements: # of valence electrons increases by 1
For example, Mg has 2 valence electrons in the 3rd energy level and P has 5 valence electrons in the 3rd energy level.
Top to bottom down a group (Representative Elements)
Elements in a group have an EQUAL number of valence electrons

24. Compare…
Compare the number and location of the valence electrons in the following sets of elements:
Ca & P
Li & Cs
Br & F
Al & Kr
Be & N