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 Inner Transition

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 1 st energy level). Using the octet rule, you can predict which ions will likely form. Neon has full outer shell : 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

NaCl

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 1 st 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 outer electrons 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

Noble Gas