1. The Periodic Table J.W. Dobereiner Triads
Groupings of 3 elements with similar properties

2. The Periodic Table In the early 1860’s, about 60 elements were known.
There was no reliable method for measuring the atomic masses of atoms.
Different chemists would find different formulas were being used to represent the same compound

3. The Periodic Table
In September of 1860, at the 1st International Congress of Chemistry, Stanislao Cannizzaro revealed a method for accurately measuring relative masses of atoms.

4. The Periodic Table 1863 John Newlands creates the Law of Octaves
It states that every 8th element in order of increasing atomic mass should have similar properties.
This works for some smaller atoms, but does not work as atoms become progressively larger

5. The Periodic Table Dmitri Mendeleev
He arranged the elements by patterns and by similar properties of elements
He noticed that similarities occurred in elements when they were arranged by increasing atomic mass
He left gaps in his table for elements that he thought existed but had not been discovered
He could make very good predictions about the properties of these elements

6. The Periodic Table
Moseley, who had worked with Rutherford, rearranged the periodic table by increasing numbers of protons and atomic charge. This led to using the atomic number as the basis for the organization of the periodic table
The Periodic Law
The law stating that many of the physical and chemical properties of the elements tend to recur in a systematic manner with increasing atomic number.

7. The Periodic Table s-block Group 1 The Alkali Metals Very Reactive
Not found freely in nature
Have 1 outer electron
Tend to lose 1 electron in compounds
Silvery
Soft. They can be easily cut with a knife
Low melting points
More reactive toward the bottom of the group

8. The Periodic Table Group 2 The Alkaline Earth Metals
Have 2 outer electrons
Harder, denser, stronger, higher melting points than Group 1 elements
Still very reactive, but less reactive than Group 1 elements
Not found freely in nature
More reactive towards bottom of group

9. The Periodic Table Hydrogen Has 1 outer electron
Is sometimes considered to be a group 1 element and at other times is considered to be its own group
It is a gas at room temperature
If frozen until solid, hydrogen is a metal
99% of the atoms in the universe are hydrogen atoms
76% of the mass of the universe is hydrogen

10. The Periodic Table Helium
A stable and filled outer energy level places it with the noble gases even though it has only 2 outer electrons.
23% of the mass of the universe is helium

11. The Periodic Table d-block Transition Elements
Sometimes called the transition metals
Groups 3-12
All are metals
Generally hard, dense, high melting points when compared to s-block elements
Not as reactive as s-block elements
Some can be found freely in nature
Tend to have 1-3 outer electrons
Tend to lose 1-3 electrons in compounds
Cause colors in gemstones as impurities in crystal structures

12. The Periodic Table p-block Groups 13-18
Main block elements-elements in the s and p blocks
Have 3-8 outer electrons
Elements with 4 or more electrons normally share or gain electrons in compounds
Metalloids are found in this region

13. The Periodic Table Group 17 The Halogens Very Reactive
Fluorine is the most reactive element
7 outer electrons
Gain 1 electron to achieve a structure like a noble gas
The word halogen means “salt former”

14. The Periodic Table Group 18 Noble Gases
Unreactive due to filled and stable outer energy level
Very few compounds can be made with Kr, Xe, and Rn.
There are no known compounds using He, Ne, or Ar

15. The Periodic Table
Helium Pierre Janssen discovered it in solar spectra
Sir William Ramsay confirmed helium on earth in 1895
Neon discovered by Ramsay
Argon-1894 discovered by Ramsay and John William Strutt(Lord Raleigh)
Krypton-1898 Ramsay
Xenon-1898 Ramsay
Radon Friedrich Ernst Dorn

16. The Periodic Table Lanthanides Mostly discovered in early 1900’s
Elements 58-71
Also called Rare earth elements
They comprise less than 0.1% of the earth’s crust
Actinides
Elements
All are radioactive
Elements above 92, Uranium, are synthetic
Transuranium elements-synthetic elements that are past Uranium, the last of the naturally occurring elements on the periodic table

17. Periodic Trends Atomic Radii Decreases across a period
As the number of protons increases in atoms across a period, the attractive forces of the nucleus on the electrons in the atom also increase. This increase in attractive force allows the nucleus to pull electrons closer to the nucleus, making for smaller atoms.
Increases down a family
Every new family adds an energy level where electrons can reside. As more energy levels are added, each outer orbital is farther from the nucleus than the last.

18. Periodic Trends Ionic Radius Cations Cations are positive ions
Metals tend to lose electrons and become cations
Cations are smaller than the neutral atom
The same amount of force pulls on electrons regardless of how many electrons are present in a given atom. The removal of electrons increases the amount of pull that is distributed among the remaining electrons, holding the electrons closer to the nucleus.
Anions
Anions are negative ions
Nonmetals tend to form anions
Anions are larger than the neutral atom
The same amount of force pulls on electrons regardless of how many electrons are present in a given atom. If electrons are added to the atom, the electrons each feel less nuclear pull than they did in the neutral atom and move farther away from the nucleus, increasing the atomic radius.

19. Periodic Trends Valence electrons
Electrons found in the s and p sublevels of the outermost energy level
Atoms will gain or lose enough electrons to have an octet
Metals will lose electrons to have an electron configuration like the previous noble gas, becoming cations
Nonmetals will gain electrons to have an electron configuration like the next noble gas, becoming anions
The Electron Dot structure shows how many valence electrons an atom has and how many it will gain or lose as it becomes an ion

20. Periodic Trends Electronegativity
The measure of an atom’s ability to attract electrons in a compound
The lowest value is 0.7(Cs,Fr)
The highest value is 4.0(F)
Electronegativity increases across a period because atoms that tend to gain electrons to become ions will also attract electrons when in a compound
Electronegativity decreases down a family because atoms that are larger are not as effective at attracting electrons because of the distance that outer electrons will be from the nucleus

21. Periodic Trends Ionization Energy
The energy required to remove an electron from an atom
Each electron that is removed results in the next electron being even more difficult to remove because each remaining electron is held more tightly.
A huge increase in the energy required for removing electrons occurs when the atom’s electron configuration is the same as a noble gas.
Ionization Energy increases across periods
Ionization Energy decreases down a family

22. Periodic Trends Shielding Effect
Inner electrons block some of the nuclear pull on outer electrons, making them easier to remove
Shielding effect is constant across a period since no new energy levels are added to the atom
Shielding effect increases down a family because new energy levels of electrons are added with each new row on the periodic table

23. Periodic Trends Electron Affinity
The energy change when a neutral atom acquires an electron
Can be endothermic (absorbing energy) or exothermic (releasing energy)
Electron Affinity increases across a period
Electron Affinity decreases down a family

24. Periodic Trends