Ch. 6 Chemical Periodicity Fall 2014

I. Organizing the Elements A. The Periodic Table Revisited 1. Dmitri Mendeleev arranged the elements in He based his arrangement on the atomic mass of the elements and the common properties. 3. He left gaps in his table that suggested that other elements were yet to be discovered.

I. Organizing the Elements B. Today’s Periodic Table 1. After the discovery of the subatomic particles, the arrangement of the periodic table was slightly changed. 2. Henry Mosley determined that the atomic number is known for each element. 3. The modern table is arranged by the increasing atomic number. 4. The chemical and physical properties of elements change as you move across (left to right) the periodic table and repeats as you move from one period to the next. 5. There is also a pattern of chemical and physical properties as you go down a periodic group. 6. This pattern is called the periodic law.

I. Organizing the Elements C. Metals, Nonmetals, and Metalloid 1.Metals donate electrons. 2. Located on the left hand side of the zigzag line of the Periodic Table. 3. Metallic properties: a. Luster b. Ductile - May be drawn into wire. c. Malleable - Can be hammered into thin sheets. d. Good conductors of heat and electricity. e. Tend to give up electrons in making bonds. f. Can be identified by spectral analysis techniques- when materials give off excess energy in the form of different colors of light.

I. Organizing the Elements C. Metals, Nonmetals, and Metalloid 4. Nonmetals gain electrons. 5. Located on the right side of the zig-zag line of the Periodic Table (except column 18 or 8A) 6. Nonmetallic properties: a. Brittle b. Good insulators c. Tend to take in electrons in making bonds.: 7. Also called "inert gases". 8. Located in Group Rarely react ( the outer energy level is full). 11. Special elements identified as B, Si, Ge, As, Sb, Te, Po and At. 12. Properties: Metalloids have properties of both metals and nonmetals.

II. Classification of the Elements A. Using the Periodic Table 1. The discovery of the subatomic particles affected the arrangement of the elements of the periodic table. 2. The atomic number (mainly electrons) is now how the table is arranged. 3. The electrons are what determine the chemical and physical properties of the elements. 4. Element are classified in four categories based on electron configuration. a. Noble Gases b. Representative Elements c. Transition Metals d. Inner Transition Metals

II. Classification of the Elements A. Using the Periodic Table 5. The representative elements are the following groups: a. Alkali Metals ( Group 1) b. Alkaline Earth Metals (Group 2) c. Halogens ( Group 17) 6. When groups 1 or 2 react with group 17, they form what we call a salt.

II. Classification of the Elements B. Classifying Elements by Electron Configuration 1.TRANSITION ELEMENTS are special metals are in Groups (all B metals) 2. Properties: a. Can be magnetized. b. Strong characteristic colors. 3. NOBLE GASES are also called "inert gases” because they rarely react ( the outer energy level is full). Located in Group 18.

III. Periodic Trends A. Trends in Atomic Size and Ionic Size 1. As the principal quantum number (energy level or row of the periodic table) increases, the size of the electron cloud increases. (Group Trend) 2. So what happens when you go DOWN the chart? Each period (or row) as you go down the chart represents an additional orbit in your solar system. This is a new shell or energy level for the atom’s electrons. Since you have gained a whole orbit, this will automatically make the radius bigger, in spite of the magnetic pull of the protons.

3. As the atomic number increases, the atomic radius decreases. (Periodic Trend) 4. The exception to this is the noble gases 5. You have discovered that as each element progresses from left to right on the periodic table, it gains protons. Thus, its total positive charge (gravity) increases. When this happens, the pull on the electrons is greater, so the electrons move closer. The atomic radius SHRINKS from left to right on the table.

6.Now you know the trends for atomic radius: from left to right, the radius decreases due to a greater nuclear magnetic pull on the electrons. From top to bottom, the radius increases due to gaining additional energy levels. The trend looks much like this: III. Periodic Trends A. Trends in Atomic Size and Ionic Size

7. So, what happens when an atom gains or loses electrons to form an ion? Remember, the octet rule states that atoms want to have 8 electrons in their valence (or outer) shells (orbits). In order to accomplish this, atoms form ions. An ion is an atom with a charge because its electrons and protons are no longer equal. An atom that loses electrons is called a cation. This atom initially had the same number of protons as electrons. Once it loses electrons to follow the octet rule, it will have more protons than electrons. It will then have a positive charge.

8. Since a cation loses a shell when losing electrons, its radius as an ion gets smaller. This new radius is called the ionic radius. Since metals act as cations, metals will have a smaller ionic radius than atomic radius.

9. Because the nonmetal atom is gaining electrons without gaining additional protons, the negative electrons will push each other away (like charges repel), but there is no extra force pulling the electrons in toward the nucleus. The electrons take advantage of the extra space outside the atom to push further away, slightly expanding the radius.

B. Trends in Ionization Energy 1. The energy that is required to remove an electron from an atom is called the ionization energy. 2. The first ionization energy refers to the loosely held electrons. a. As the atomic number increases, the ionization energy increases. b. As the principal quantum level increases, the ionization energy decreases.

B. Trends in Ionization Energy 3. The decrease in ionization energy as you go down the periodic table is caused by the shielding affect of the outer electrons distance from the nucleus. 4. The increase in ionization energy as you go across the periodic table is caused by the increase in the nuclear charge (number of protons) in the nucleus. 5. Ionization energy is the energy needed to remove an electron from a neutral atom. 6. Because metals would rather lose electrons to satisfy the octet rule, it is easy to remove electrons. They have a low ionization energy. However, as they gain protons, the magnetic pull on the electrons also increases, making it more difficult to remove them. This is why ionization energy increases from left to right.

7. Nonmetals want to gain electrons, not lose them! Thus, they have very high ionization energies. These are located at the top right of the periodic table. Thus, the ionization energy, like electronegativity, increases from bottom to top and left to right.

D. Trends in Electronegativity 1. The energy needed to attract and remove and electron is called electronegativity. 2. Electronegativity is the tendency of atoms to gain electrons. Since nonmetals want to gain electrons to satisfy the octet rule while metals want to lose electrons, nonmetals have a higher electronegativity than metals. Nonmetals are located in the upper right corner of the periodic table. Thus, electronegativity increases left to right and bottom to top. 3. As the atomic number increases, the electronegativity increases. As the principal quantum level increases, the electronegativity decreases.

How does it all work together?

Assignments! Put the elements C, K, N, Sr, and P in order by: 1) Increasing atomic radius 2) Decreasing electronegativity 3) Decreasing ionic radius 4) Increasing ionization energy Assignment : Write four paragraphs explaining how each of the four trends works and what causes the trend from left to right and top to bottom.