PERIODICITYGuys, Groups,

Trends, Creations

Guys

•Dimitri MendeleevDimitri Mendeleev—published his periodic table in 1869 according to similarities based upon atomic mass; applied “eka” to the missing element names

•Lothar MeyerLothar Meyer—arranged the elements according to their atomic volume and had a similar periodic table to Mendeleev’s just too late

•Henry MoseleyHenry Moseley—student of Rutherford who used X-ray diffraction to prove atomic charge and thus atomic number and suggested arranging in order of increasing atomic number; died in 1915 at the age of 27

Groups

An Element on Its Own:Hydrogen

• nonmetal• highly reactive• most abundant in the universe

Group 1 (IA) Elements:The Alkali Metals

• soft (can be cut with a dull knife)• highly reactive (especially with

water)• make basic solutions in water• good conductors of electricity (Na

is used in street lights)• have one valence electron

Group 2 (IIA) Elements:The Alkaline Earth Metals

• harder than Alkali Metals• reactive (but not as reactive as

Alkalis)• make basic solutions in water• found in compounds with structural

integrity (emeralds, aircraft, marble)• have two valence electrons

Groups 3-12 (B) Elements:The Transition Metals

• harder than Groups 1 & 2 Metals• not very reactive• have varying properties• most are good conductors• all are solid at RT except ???• all are natural except Tc

Lanthanide & Actinide Series:

The Inner Transition Metals• Lanthanides are shiny and

reactive– some are useful: Nd in magnets

• Actinides all have at least one radioactive isotope– transuranium elements are Atomic

#93 and up and are all synthetic and radioactive

The Metalloids

• B, Si, Ge, As, Sb, Te• semiconductors—means that

sometimes they conduct and sometimes they insulate

Group 17 (VIIA) ElementsThe Halogens

• most reactive nonmetals• combine easily with metals to

form salts—”halogen” means “salt-former”

• consist of two solids, one liquid, and two gases at RT

• have seven valence electrons

Group 18 (VIIIA) ElementsThe Noble Gases

• virtually nonreactive nonmetals

• stable• happy valence levels (2

valence electrons in He, and the rest have 8)

Trends

Atomic Radius• Measured from the centers of two

atoms in a diatomic molecule.

Rb—distance/2= 0.248nm

Atomic Radius•Shielding Effect—the reduction of the attractive force between a nucleus and its outer electrons due to the blocking effect of inner electrons

Atomic Radius• As you move across a period,

more electrons are added to the same energy level.

• As you move down a group, more electrons are added to farther and farther away energy levels.

• THUS…

Atomic Radius Decreases going across a

period

Incre

ase

s goin

g d

ow

n a

gro

up

Ionization energy• the energy required to remove an

electron from an atom or an ion—measured in kJ/mol

• As you move across a period, the size gets smaller thus the electrons are held more tightly by the nucleus

• As you move down a group the electrons are farther away from the nucleus and are not held as tightly

• Thus…

H—1312kJ/mol He—2300kJ/mol

K—420kJ/mol

Ionization Energy Increases going across a period

Decre

ase

s goin

g d

ow

n a

gro

up

Electronegativity• the ability of an atom in a molecule

to attract electrons to itself• As you move across a period, there

are more and more electrons in the same energy level getting closer to a noble gas

• As you move down a group, the electrons become farther away from the nucleus

• Thus…

H—2.1 F—4.0

Fr—0.7

Electronegativity Increases going across a period

Decre

ase

s goin

g d

ow

n a

gro

up

Electron Affinity• The energy change associated with the

addition of an electron to a gaseous atom—measured in kJ/mol

• As you move across a period, there are more and more electrons in the same energy level getting closer to a noble gas

• As you move down a group, the electrons become farther away from the nucleus

• Thus…

H= -73kJ/mol F= -329kJ/mol

Cs= -45kJ/mol

Electron Affinity Increases going across a period

Decre

ase

s goin

g d

ow

n a

gro

up

Trendy Practice• Arrange the following elements in

order of increasing atomic size: chlorine, oxygen, fluorine, polonium

• Arrange the following elements in order of increasing ionization energy: boron, helium, lithium, nitrogen

F<O<Cl<Po

Li<B<N<He

Trendy Practice• Arrange the following elements in

order of decreasing electronegativity: carbon, fluorine, francium, lithium

• Arrange the following elements in order of increasing electron affinity: cesium, potassium, rubidium, sodium

F>C>Li>Fr

Cs<Rb<K<Na

Creations

Natural Elements

• are atomic numbers 1-92, excluding 43, Tc

• three other elements occur so infrequently in nature that they are almost considered unnatural…Pr, At, and Fr

• are made in stars and result from the violent reactions that occur… the left over stuff makes up all of the naturally occurring elements

Fusion Reactions

• 1º source of energy• 4 H nuclei fuse to

form 1 He nucleus• mass of the He

nucleus < mass of the 4 H nuclei…that means mass was not conserved!!!

Nuclear Fusion• Primary fusion reaction in stars

4 H He +11

42 ? energy

E = mc2

Fusion Reactions

• Thus, magically, mass was exchanged for energy following the concept put forth in E=mc2

• The He nuclei will then fuse to form all of the other elements that are naturally occurring.

Fusion Reactions

• A star dies when it no longer has the fusionable stuff to make new elements.

• Planets result when lots of dead stars come together as one big blob of all of those fun elements.

Man-made fusion reactions

• were first performed in the 1950’s and resulted in the Hydrogen-bomb

• cannot be contained in any physical container due to the high heat (>20 million ºC); so must be contained in a magnetic bottle

Fission reactions

• allow us to make new elements by hitting existing elements with really fast particles

• this violent act results in the breaking apart of the original element or the absorption of the really fast particle

• This was first done using those alpha-particles that Rutherford used.

Fission reactions

What is the missing particle?• Lawrence (as in Lr) developed the

1st cyclotron in 1930.• Frédéric and Irène Joliet-Curie were

the first to make normally stable isotopes radioactive by bombardment in early 1930’s.

147N + 4

2He 11H + ?

Fission reactions

• Then truly synthetic elements (those that did not previously exist) were made.

• The first was ???

Fission reactions (Tc, in particular)

• In 1937 technetium was created by bombarding molybdenum targets with deuterons (particles consisting of a p+ and a n). Because technetium is not part of the decay series of any naturally radioactive element, scientists had thought that technetium does not occur in nature.

Fission reactions (more on Tc)

• In 1988, however, minute quantities of it were detected in ore from a deep molybdenum mine in Colorado.

Fission reactions

• Up to atomic number 100, they are made by firing nuclear bullets at existing nuclei to force them to become new elements

Fission reactions

• Nuclear Bullets– protons– neutrons– alpha particles (really just He

nuclei)– beta particles (really just

electrons)

Synthetic Elements• Atomic #’s 101 and higher are made by

using whole nuclei of heavier elements (heavier than He) at existing elements

C + Cm No + 2 n12 6

244 96

254102

1 0

Things to ponder for your quiz

1. The guys and what their tables were based upon

2. Properties of elements in specific groups

3. Atomic radii4. Ionization energy5. Electronegativity6. Electron affinity

Things to ponder for your quiz

7. Fusion & fission reactions8. Synthetic elements