Chapter 6

Periodic Table and Periodic Law

• The Periodic Table got its name because of the repeating pattern of chemical & physical properties.

• Mendeleev ordered his periodic table with elements arranged in order of increasing atomic mass.

• He started new rows so that the elements having the same properties would be aligned in each column.

• Mendeleev left “holes” for elements he predicted, but weren’t discovered until a later time.

Holes for undiscovered elements

Similar properties in each column

• In the modern Periodic Table, elements are arranged in order of increasing atomic number.

• The horizontal rows are called periods.

• The vertical columns are called groups.

• The patterns of properties repeat in each new row, so elements in the columns, have similar chemical and physical properties. This is called the periodic Law.

Similar properties in each column

• The group A elements (the s&p blocks) are called the representative elements.

1A 2A 3A 4A 5A 6A 7A 8A

• The group B elements (the d block) are called the transition elements.

• The group B elements (the f block) are called the inner transition elements.

Transition

InnerTransition

• There are 3 main classes of elements: metals, nonmetals, metalloids.

Metals, Nonmetals, Metalloids

• There is a zig-zag or staircase line that divides the table.

• Metals are on the left of the line, in blue.

• Nonmetals are on the right of the line, in orange.

• Metals are located on the left side of the Table. Metals are generally shiny solids, good conductors of heat and electric current, and have high melting and boiling points.

• They are also malleable and ductile.

Metals

• Metals are lustrous (shiny), malleable, ductile, and are good conductors of heat and electricity.

• They are mostly solids at room temp.

• What is one exception?

• Located on the upper right side of the table, nonmetals are generally gases or brittle solids at room temp, and poor conductors.

Nonmetals

• Nonmetals are the opposite.

• They are dull, brittle, nonconductors (insulators).

• Some are solid, but many are gases, and Bromine is a liquid.

• The elements that border the heavy stair-step line on the table are called metalloids, which have some characteristic of both metals and nonmetals.

Metalloids• Metalloids, aka semi-metals

are just that.• They have characteristics of

both metals and nonmetals.• They are shiny but brittle.• And they are

semiconductors.• What is our most important

semiconductor?

• The electron structure of an atom determines many of its chemical & physical properties. For the group A elements, the group number equals the number of valence electrons.

• (Except for Helium=2)

• The Octet rule states that atoms lose, gain, or share electrons in order to gain a full set of 8 valence electrons.

• This noble gas configuration is very stable. (the exceptions are Hydrogen and helium which will have a stable set of 2 electrons in the 1st energy level). Using the octet rule, you can predict which ions will likely form.

Neon has full outershell : stable & nonreactive

• Metals are electron donors. They tend to lose electrons and become + charged ions. Called a cation.

Na has 1 valence electron

Must lose 1 electron to have full outer shell (easier to lose 1 than gain 7)

Creates a ion with a +1 charge

• Nonmetals are electron acceptor. They tend to gain electrons and become – charged ions. Called an anion.

Chlorine has 7 valence electrons

Need 1 more electron to gain full outer shell

Creates -1 ion

Na Cl

Periodic trends• Atomic radius: Tends to decrease across

the period. Electrons are being added in the same energy level so increased attraction between the larger number of + protons pulls the – electrons closer.

Periodic trends

• Atomic radius: Tends to increase down the group, because you are adding energy levels, which shield the valence electrons from the pull of the nucleus.

Ionic radius• Losing electrons produce + charged ions,

which are smaller than the parent atom.

Cation Formation

11p+

Na atom

1 valence electron

Valence e- lost in ion formation

Effective nuclear charge on remaining electrons increases.

Remaining e- are pulled in closer to the nucleus. Ionic size decreases.

Result: a smaller sodium cation, Na+

Ionic radius

• When atoms gain electrons, they become – charged ions, which are larger than

the parent atom.

Anion Formation

17p+

Chlorine atom with 7 valence e-

One e- is added to the outer shell.

Effective nuclear charge is reduced and the e- cloud expands.

A chloride ion is produced. It is larger than the original atom.

Ionic radius• As with the atomic radius size, decrease across

the periods an increase down the group. • Notice difference between cations & anions;

but trends are still same

decreases

increases

Ionization energy• Is the amount of energy required to pull the 1st

valence electron away from the atom. Elements with high ionization energy are [unlikely, likely] to lose electrons. Atoms with low ionization energy [easily, don’t really] lose electrons

Ionization energy

• Generally metals have low ionization energies and easily form positive ions… nonmetals have high ionization energies and tend to form – ions.

Mostly +2 & +3

Noble gases: do not form ions

Ionization energy• Ionization energies increase across the period,

because the atoms are getting smaller and the electrons closer to the nucleus and harder to pull away.

Increases

Ionization energy• Ionization energies decrease moving

down the group because the size of the atom is larger so the electrons are farther away and easier to remove.

In other words the outerelectrons are shielded from the pull of the nucleus by the inner shells

decreases

Electronegativity • Indicates the elements relative ability to gain

electrons in a chemical bond. The greater the electronegativity the greater the attraction for electrons.

• How strongly the element “wants” the electron, so metals are low; nonmetals are high

Electronegativity • Fluorine is the most electronegative element

are Francium is the least. Increases across the periods and decreases down the group.

0

Fr

F

decreases

increases

NobleGas