1. Unit 5: Periodicity

2. History of the Periodic Table
Dimitri Mendeleev ( )
Russian chemistry professor
Noticed that as he was arranging elements according to their properties that they generally were organized in order of increasing atomic mass.

3. Genius of Mendeleev’s Work
Left spaces for elements not yet discovered.
He predicted that some still-unknown elements must exist to fit in the holes.

4. Dmitri Mendeleev (1869) His handwritten periodic table.

5. Mendeleev’s Periodic Table
Contained 1 inconsistency.
He placed the elements in order of atomic mass
Forced to break pattern a couple times to preserve the patterns he had discovered.

6. Henry Moseley
Once the proton was discovered by Rutherford, Moseley worked with X-rays to determine how many protons elements had.
He arranged the elements in order of increasing atomic number.
The eliminated the inconsistencies seen in Mendeleev’s table.
He was killed at the age of 28 in WWI.

7. Periodic Law
Periodic Law: The properties of the elements are periodic functions of their atomic numbers.
What this means is that if we arrange the elements in order of increasing atomic number, we will periodically encounter elements that have similar chemical and physical properties.
These elements appear in the same vertical column (group).

8. Elements
Science has come along way since Aristotle’s theory of Air, Water, Fire, and Earth.
Scientists have identified 92 naturally occurring elements, and created about 28 others.

9. Periodic Table
We can learn a lot about an element based on where it is located.
You can predict the physical and chemical properties and how an element will react.

10. Nonmetals
Metalloids
Metals

11. Properties of Metals Good conductors of heat and electricity. Shiny
Ductile (can be stretched into thin wires).
Malleable (can be pounded into thin sheets).
Reacts with water which results in corrosion.

12. Metals

13. Properties of Non-Metals
Sulfur
poor conductors of heat and electricity.
not ductile or malleable.
Solid non-metals are brittle and break easily.
dull
Many non-metals are gases.
Bromine

14. Properties of Metalloids
Metalloids (metal-like) have properties of both metals and non-metals.
They are solids that can be shiny or dull.
They conduct heat and electricity better than non-metals but not as well as metals.
They are ductile and malleable.

15. Columns of elements are called groups or families.
Elements in each family have similar but not identical properties.
For example, lithium (Li), sodium (Na), potassium (K), and other members of family 1 are all soft, white, shiny metals.
All elements in a family have the same number of valence electrons.

16. Each horizontal row of elements is called a period.
The elements in a period are not alike in properties.
In fact, the properties change greatly across even given row.
The first element in a period is always an extremely active solid. The last element in a period, is always an inactive gas.

17. Families

18. Hydrogen
The hydrogen square sits atop Family 1, but it is not a member of that family. Hydrogen is in a class of its own.
It’s a gas at room temperature.
It has one proton and one electron in its one and only energy level.
Hydrogen only needs 2 electrons to fill up its valence shell.

19. Alkali Metals first column of the periodic table 1 valence electron
They are shiny, have the consistency of clay, and are easily cut with a knife
That is Sodium!

20. Alkali Metals most reactive metals react violently with water
never found as free elements in nature. They are always bonded with another element.
That is sodium on top of the water.

21. Alkaline Earth Metals
never found alone in nature, always bonded with something else.
two valence electrons

22. Transition Metals elements in the d-block (Groups 3-12)
These are the metals you are probably most familiar

23. Transition Metals
The compounds of transition metals are usually brightly colored and are often used to color paints.
1 or 2 valence electrons, which they lose when they form bonds with other atoms. Some transition elements can lose electrons in their next-to-outermost level.

24. Transition Elements
Transition elements have properties similar to one another and to other metals, but their properties do not fit in with those of any other family.
Many transition metals combine chemically with oxygen to form compounds called oxides.

25. Boron Family
The Boron Family is named after the first element in the family.
3 valence electrons
This family includes a metalloid (boron), and the rest are metals.
This family includes the most abundant metal in the earth’s crust (aluminum).

26. Carbon Family 4 valence electrons
This family includes a non-metal (carbon), metalloids, and metals.
The element carbon is called the “basis of life.” There is an entire branch of chemistry devoted to carbon compounds called organic chemistry.

27. Nitrogen Family
The nitrogen family is named after the element that makes up 78% of our atmosphere.
This family includes non-metals, metalloids, and metals.
5 valence electrons. They tend to share electrons when they bond
Other elements in this family are phosphorus, arsenic, antimony, and bismuth.

28. Oxygen Family 6 valence electrons
Most elements in this family share electrons when forming compounds.
Oxygen is the most abundant element in the earth’s crust. It is extremely active and combines with almost all elements.

29. Halogen Family
7 valence electrons, which explains why they are the most active non-metals. They are never found free in nature.
Halogen atoms only need to gain 1 electron to fill their outermost energy level.
They react with alkali metals to form salts.

30. Noble Gases
Noble Gases are colorless gases that are extremely un-reactive.
One important property of the noble gases is their inactivity. They are inactive because their outermost energy level is full.
Because they do not readily combine with other elements to form compounds, the noble gases are called inert.
The family of noble gases includes helium, neon, argon, krypton, xenon, and radon.
All the noble gases are found in small amounts in the earth's atmosphere.

31. Rare Earth Elements
The thirty rare earth elements are composed of the lanthanide and actinide series.
One element of the lanthanide series and most of the elements in the actinide series are called trans-uranium, which means synthetic or man-made.

33. Octet Rule Octet means to have 8 valence electrons.
Is associated with the stability of the noble gases.
Helium (He) is stable with 2 valence electrons
Valence Electrons
He 1s
Ne 1s2 2s2 2p
Ar 1s2 2s2 2p6 3s2 3p6 8
Kr 1s2 2s2 2p63s2 3p6 4s2 3d10 4p6 8

34. Electron Shielding
Shielding electrons are those electrons in the energy levels between the nucleus and the valence electrons.
They are called "shielding" electrons because they "shield" the valence electrons from being pulled closer to the nucleus.
Remember, the nucleus has a positive charge!

37. Periodic Trends
Trends in properties of the elements that follow a pattern down a group and across a period in the periodic table.
down a group
across a period

38. Trends in Atomic Radius (size)
atomic radius: distance from center of nucleus to edge of electron cloud

39. Atomic Radius group trend: increases going down a group.
As you move down a group, you add energy levels, thus increasing the size of the electron cloud, so the atoms get larger.

40. Atomic Radius
periodic trend: decreases going left to right across a period.
Why?: You are not adding energy levels, you are adding protons. As you do this, the nucleus gets a greater positive charge which pulls the electrons closer to it, decreasing the radius.

41. Atomic Radius
Atomic Radius
Increases to the LEFT and DOWN

42. Ionization Energy
ionization energy: the energy required to remove a valence electron.

43. Trends in Ionization Energy
group trend: decreases going down a group
This is due to the shielding effect - an electron in the outer energy level of a large atom is easier to remove because it is well-shielded from the pull of the nucleus by the inner electrons.
periodic trend: increases going across a period
This is due to nuclear charge - across a period, nuclear charge increases, so they hold onto their electrons tighter.
metals have a much greater tendency to lose electrons than nonmetals do.

44. Ionization Energy
Ionization Energy
Increases UP and to the RIGHT

45. Trends in Electron Affinity
electron affinity (electron-liking): the energy change that accompanies the addition of an electron to an atom.
group trend: EA decreases going down a group.
Why? It is harder to add an electron when it is so far away from the nucleus. The nucleus cannot “grab onto it”.
periodic trend: EA increases going across a period.
Why? As the nuclear charge becomes more positive, it is able to hold onto electrons better.
Note that this periodic trend supports the idea that nonmetals have a much greater tendency to gain electrons than metals do.

46. Electron Affinity
Electron Affinity
Increases UP and to the RIGHT

47. Trends in Electronegativity
electronegativity: the tendency of an atom to attract electrons to itself when it is chemically bonded with another element.
Diagram of water molecule:
In H2O, oxygen is more electronegative than hydrogen, so it pulls the electrons closer, and thus obtains a partially negative charge.

48. Trends in Electronegativity
group trend: decreases down a group.
Larger atoms have more energy levels, so it is harder for them to attract electrons to the nucleus (shielding effect).
periodic trend: increases across a period.
The nuclear charge is greater with more protons and can hold onto electrons closer to the nucleus.

49. Electronegativity
Electronegativity
Increases UP and to the RIGHT

50. Summary of Periodic Trends
Ionization Energy, Electron Affinity, and Electronegativity
Increases UP and to the RIGHT
Atomic Radius
Increases to the LEFT and DOWN
IE EA EN AR
IE EAEN AR