1. Organizing the Elements Prentice-Hall Chapter 6.1 Dr. Yager
The Periodic Table
Organizing the Elements
Prentice-Hall Chapter 6.1
Dr. Yager

2. Objectives
Explain how the elements are organized in the periodic table.
Compare early and modern periodic tables.
Identify three broad classes of elements.

3. History By 1700 only 13 elements were known
Scientists suspected others existed
five new elements discovered
(3 gases H2, O2, N2)
1829 Dobereiner published the first classification system
Elements were grouped into triads

4. Example of a Triad
Chlorine, bromine, and iodine have very similar chemical properties.
Properties of middle element fell midway:

5. John Newlands
In 1865, the English chemist John Newlands arranged the known elements according to their properties and in order of increasing atomic mass.
Newlands noticed that all of the elements in a given row had similar chemical and physical properties.
Because these properties seemed to repeat every eight elements, Newlands called this pattern the law of octaves.

6. Demitri Mendeleev In 1869, 63 elements were known.
Mendeleev developed his table while writing a textbook for his students.
He wrote the symbol for each element, along with the physical and chemical properties and atomic mass of the element, on a card.
He arranged the elements in order of increasing atomic mass.

7. Demitri Mendeleev
Mendeleev started a new row each time he noticed that the chemical properties of the elements repeated.
He placed elements in the new row directly below elements of similar chemical properties in the preceding row.
Mendeleev made two interesting observations:
1) the table contained gaps that elements should fill
2) the elements did not always fit neatly in order of atomic mass
Mendeleev predicted the properties of missing elements!

8. An Early Version of Mendeleev’s Periodic Table

9. Henry Moseley
Mendeleev wrote some elements out of order using atomic mass. (i.e. “Te and I” and amu)
In 1913 Henry Moseley arranged elements by atomic number.

10. Periodic Table Seven rows called Periods
10  2 elements, 20  8 elements  18 elements, 60  32 elements
Each period corresponds to a principal energy level n = 1, 2, 3, 4….
Higher number of elements in higher periods; therefore more orbitals
Properties change across a period
Groups are columns of elements with similar properties

11. Periodic Law
When elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties.
Properties of the elements change as you move across a period.
The pattern of properties within a period repeats as you move from one period to the next.
Similar chemical properties in groups

12. Three Broad Classes of Elements
Metals
Non-metals
Metalloids

13. Metals, Nonmetals and Metalloids

14. Metals Compose about 80% of the elements
Good conductors of heat and electricity
High luster or sheen
Solid at room temp (except Hg)
Ductile or easily drawn into wire
Malleable or can be hammered into thin sheets

15. Metals

16. Nonmetals Elements in the upper right hand corner
Greater variation of physical properties
Many are gases at room temperature
Sulfur and Phosphorus are solid
Bromine is liquid
Properties generally opposite of metals
Poor conductors of electricity and heat (ex. carbon)
Brittle – shattered when hit with a hammer

17. Nonmetals

18. Metalloids Separates the metals from nonmetals
Depending on conditions, they can act like metal or like nonmetal
Often used as a semiconductor
Si poor conductor; add a little boron to make a good electrical conductor
“Transistor” current valve

19. Metalloids

20. 1. The modern periodic table has elements arranged in order of
colors.
melting and boiling points.
increasing atomic mass.
increasing atomic number.

21. 1. The modern periodic table has elements arranged in order of
colors.
melting and boiling points.
increasing atomic mass.
increasing atomic number.

22. 2. Mendeleev arranged the elements in his periodic table in order of
increasing atomic number.
number of protons.
number of electrons.
atomic mass.

23. 2. Mendeleev arranged the elements in his periodic table in order of
increasing atomic number.
number of protons.
number of electrons.
atomic mass.

24. 3. Which one of the following is NOT a general property of metals?
Ductility
Malleability
Having a high luster
Poor conductor of heat and electricity

25. 3. Which one of the following is NOT a general property of metals?
Ductility
Malleability
Having a high luster
Poor conductor of heat and electricity