1. The Periodic Law
Chapter 5

2. Essential Question
What were the roles of Mendeleev and Moseley in the development of the periodic table?

4. Periodic Table groups Write the names of the groups of elements.
Yellow
Blue
Pink
Red
Green

5. Before 1860 More than 60 elements had been discovered.
There was no method to accurately determine an elements atomic mass or number of atoms of an element in a compound.
1860, Germany, first international congress of chemists
Stanislao Cannizzaro presented a method for accurately measuring relative atomic masses of atoms, it was accepted.
Chemists began to look for relationships between the atomic mass and other properties of an element.

6. Mendeleev and Chemical Periodicity
Mendeleev hoped to organize the elements by their properties while looking for other trends or patterns.
Mendeleev noticed that certain patterns and similarities appeared at regular intervals when the elements were arranged in order of increasing atomic mass.
Such a repeating pattern is referred to as periodic.

7. The First Published Periodic Table
Similar properties were grouped together
Elements listed in order of increasing atomic mass
Several empty spaces were left in the periodic table
With great accuracy, Mendeleev predicted the properties of the elements that would fit these spaces.
Periodic table was accepted and Mendeleev was given credit for discovering the periodic law.

8. The First Published Periodic Table

9. Stop and Think
What do you notice different about the first published periodic table and the now universally accepted periodic table? Find and write down the three main differences.

10. Moseley and The Periodic Law
Mendeleev’s periodic table left some unanswered questions.
Why could most of the elements be arranged by increasing atomic mass and others couldn’t?
What was the reason for chemical periodicity?
Moseley, while working with Ernest Rutherford found other patterns that Mendeleev didn’t find.
Moseley found that the elements fit into the periodic table better when they were arranged by the atomic number or number of protons in the nucleus.
This led to the definition of atomic number, and the recognition that atomic number not atomic mass as the basis for the organization of the periodic table.

11. Stop and Think
Why didn’t Mendeleev think of arranging the periodic table by the atomic number instead of the atomic mass?

12. The Periodic Law
The physical and chemical properties of the elements are periodic functions of their atomic numbers. (When elements are arranged in order of increasing atomic number, elements with similar properties appear at regular intervals on the periodic table.)

13. Stop and Think What patterns do you notice in the groups of elements?
What do you think that this pattern relates to?

14. The Modern Periodic Table
The periodic table is an arrangement of the elements in order of their atomic numbers so that elements with similar properties fall in the same column or group.
Groups added to Mendeleev’s modern periodic table by other scientist are:-
The Noble gases (group 8A/18)
The Lanthanides (elements –period 6)
The Actinides (elements –period 7)

15. The Noble Gases
1868- He was discovered as a component of the sun.(Strut and Ramsay)
1894- Ar was discovered (but was not considered important)
Both elements had a total lack of reactivity, so a new group was proposed by Ramsay.
1898- Kr and Xe were discovered and added to the group.
1900- Rn, the final noble gas was discovered and added to the group

16. Stop and Think
Why were He and Ar considered not important at the time of their discovery?

17. The Actinides and Lanthanide Series
The lanthanides are 14 elements with atomic numbers from 58 to 71.
Elements are very similar in chemical and physical properties.
The Actinides are 14 elements with atomic numbers from 90 to 103.

18. Lanthanides and Actinides
The actinides and lanthanides are placed below the main periodic table only to save space and to give the table a more uniformed appearance.

19. Periods and Blocks
The length of each period is determined by the number of electrons that can occupy the sublevels in that period.
The period of an element can be determined by the elements electron configuration by looking at the highest occupied energy level.

20. The s- Block Elements: Groups 1 and 2
Group 1- Alkali Metals
1 electron in their outermost shell
Silvery appearance
Soft enough to cut with a knife
Very reactive because of the one outer electron
Combine vigorously with nonmetals
React strongly with water to produce hydrogen gas and alkali solutions
Stored in kerosene because they also react with the air and any type of moisture.
Moving down the group they melt at successfully lower temperatures.

22. Hydrogen Hydrogen is the first element in the periodic table
Over ninety percent of all the atoms in the universe are hydrogen atoms
Reacts easily with most Halogens(group 7)
Found in the sun, plants and sugars, and used in cryogenics

24. Lithium The first metal encountered in the periodic table
Silvery colored solid when purified
Never found alone in nature
Found in batteries, medicine, rocks and soils, nuclear reactors, air conditions

26. Potassium Never found by itself in nature
Softer metals with a silver color
Found in bananas, crust of the earth, fireworks, fertilizer, oceans, and nuclear reactors.

27. Group 2- Alkaline Earth Metals
A pair of electrons in their outer shell
Ns2 electron configuration
Harder, denser, and stronger than group 1 (alkali metals)
Higher melting points
Less reactive than group 1
Too reactive to be found in nature as free elements

29. Berylium
Purified beryllium is a grey, hard, steel-like metal that is very poisonous
Non-magnetic metals are very useful in electronics
Never found alone in nature
Found in emeralds and gems, machine parts, space crafts, and satellites.

31. Magnesium Very light and silvery metal.
Used in many other metal alloys to increase strength without increasing the weight
Both humans and plants need magnesium to live and be healthy.
Found in medicine, chlorophyll, and camera flash bulbs.

33. Calcium
Calcium (Ca) is an important element that helps your bones stay strong
Your nervous system also uses calcium to help transmit impulses through your body
Hard silver-colored metal.

34. Hydrogen and Helium
Hydrogen’s properties are not similar to any of the other groups.
Can be placed in group one because it has one valance electron
Helium has a ns2 configuration, but is in group 18 because its highest shell/orbital is full
Stable because it cannot accept any electrons

35. The d-Block groups 3-12 Transitional metals
Typical metallic properties
Consists of 5 orbitals (holds 10 electrons)
Good conductors of electricity
High luster
Less reactive than groups 1 and 2
Some exist as free elements in nature
Palladium, platinum and gold are the least reactive and are found free in nature

36. The p- Block groups 13-18 All elements except He
Called main group elements
The right side of the block contains all nonmetals
Six metalloids are also in the p-Block
Brittle solids
Intermediate conductivity
Harder and denser than s block elements
Softer and less dense than d block metals

37. Group 17 Halogens Most reactive nonmetals
React vigorously with most metals to form salts
Seven electrons in the outer shell makes it very close to being stable.

38. Noble Gases Six noble gases (He, Ne, Ar, Kr, Xe, and Rn)
Oxidation n umber is 0
Maximum level of electron makes them very stable
Odorless and colorless
Monatomic gases
Largest ionization energy
Size increase down the periodic table

39. Electron Configuration
The electron configuration of an element tells you a number of things about that element.
Group
Period
Block
[Xe] 6s2
For example:
Tells you that the element is in the:
6th period
S block
Group 2 (2nd element in the block)
Does it have a high or low reactivity