DOR: Average Atomic Mass 1) Barium has four isotopes: Ba-130, Ba-133, Ba-137, and Ba-139. The percent abundance of the isotopes is 16.06%, 12.44%, 45.57%, with the rest being composed of the heaviest isotope. Masses are 129.9860 grams, 133.0002 grams, 137.0265 grams, and 139.4511 grams, respectively. What should be the reported average atomic weight for barium? 2) Another element - Z - has three isotopes: Z-78 with a weight of 77.989, Z-81 with a weight of 81.000, and Z-82 with a weight of 82.003. The percent abundance of the three isotopes is: Z-78 34.050%, Z-81 50.720%, and Z- 82 15.230%. What is the avg. atomic weight of element Z ?

Elemental Properties and Patterns Periodic Trends Elemental Properties and Patterns

The Periodic Law Dimitri Mendeleev (1869/1871) was the first scientist to publish an organized periodic table of the known elements. He was taking a chemistry course in Russia and tried to find a way to organize the periodic table.

The Periodic Law Mendeleev even went out on a limb and predicted the properties of 2 at the time undiscovered elements. He was very accurate in his predictions, which led the world to accept his ideas about periodicity and a logical periodic table.

The Periodic Law Mendeleev understood the ‘Periodic Law’ which states: When arranged by increasing atomic number, the chemical elements display a regular and repeating pattern of chemical and physical properties.

The Periodic Law Atoms with similar chemical properties and behavior appear in groups or families (vertical columns named by Roman numerals with A or B) on the periodic table. They are similar because they all have the same number of valence (outer shell) electrons, which governs their chemical behavior. Periods– horizontal rows on periodic table

Periodic Trends There are several important atomic characteristics that show predictable trends that you should know. Atomic properties— Deal with only single atoms

Atomic Radius Enables us to gain information on atom’s size Outer electrons hard to locate Radius is the distance from the center of the nucleus to the “edge” of the electron cloud. Measurement of distance between nuclei of 2 atoms Since a cloud’s edge is difficult to define, scientists use define covalent radius, or half the distance between the nuclei of 2 bonded atoms.

1. Covalent Radius Half the distance between the nuclei of 2 bonded atoms. Radius of nonmetallic atoms Ex. Br 2.86 Å 1.43 Å

2. Metallic Radius Half the distance between nuclei of adjacent atoms in a metal Radius of metallic atoms

Atomic Radius Trend Decreases Increases

Atomic Radius The effect is that the more positive nucleus has a greater pull on the electron cloud. The nucleus is more positive and the electron cloud is more negative. The increased attraction pulls the cloud in, making atoms smaller as we move from left to right across a period.

Identify the atom with the largest radii 1) Ca, F 2) Cl, O 3) N, P

Ionic Radii Affected by distance between nuclei of 2 ions Defined by the distance between the nuclei occupied by the particular ion Studies with crystal structures Radii related to original atomic radii Isoelectronic— Atoms/ions with SAME number of electrons SO ------ electron configuration same as well

Ionic Radii: 1) Anions Larger size than original neutral atom Generally nonmetals Electrons repel as increase in number, causes size to increase

Ionic Radii: 2) Cations Smaller size than original neutral atom Generally metals Less electrons, more attractive force from nucleus

Ionization Energy TIf an electron is given enough energy (in the form of a photon) to overcome the effective nuclear charge holding the electron in the cloud, it can leave the atom completely. Amount of energy needed to remove ONE electron from a neutral atom Removal from ground state in neutral atom of gaseous state to form positive ion

Ionization Energy (cont.) The energy required to remove an electron from an atom is ionization energy. The larger the atom is, the easier its electrons are to remove. Ionization energy and atomic radius are inversely proportional.

Ionization Energy (cont.) 1st ionization energy Energy required to remove 1st electron from atom Taken from highest energy level Easiest to remove Energy increases as more electrons are removed

Ionization Energy Trend Increases Decreases

Ionization Energy

Identify the highest ionization energy F, Mg Na, Rb P, O

What does affinity mean?

Electron Affinity energy change that occurs when electrons added to gaseous atom Greater value with smaller atoms Energy released when electron added Exothermic, negative value An atom’s “desire/affinity” for more electrons, wants to get more electrons ! ! ! Metals—decrease electron affinity. Nonmetals—increase electron affinity, more reactive Stable atoms—full octet

Electron Affinity Trend Increases Decreases

Metals, Nonmetals, Metalloids How can you identify a metal? What are its properties? What about the less common nonmetals? What are their properties? And what the heck is a metalloid?

A Different Type of Grouping Besides the 4 blocks of the table, there is another way of classifying element: Metals Nonmetals Metalloids or Semi-metals. The following slide shows where each group is found.

Metals Metals are shiny, malleable, ductile, and are good conductors of heat and electricity. They are mostly solids at room temp. Want to LOSE valence electrons Form positive ions s block (not H and He), d/f blocks, some p block elements

Nonmetals Nonmetals are the opposite. No color, no shine They are dull, brittle, nonconductors (insulators). Gases at room temperature Want to GAIN electrons Form negative ions p block elements, H and He

Transition Metals Middle of the periodic table Forms positive ions, multiple types Shine, malleable, ductile, good conductors s/d orbitals—electrons lost from these subshells.

Metalloids/Semi-Metals Metalloids, aka semi-metals are just that. They have characteristics of both metals and nonmetals. They are shiny (like metals) but brittle. And they are semiconductors. “on the fence, middle of the road” B, Si, As, Te, At, Ge, Sb, Po

Noble Gases Group 18 Do NOT react with other elements Atomspheric gases Naturally in elemental form , single atoms Not completely unreactive

Metallic Character This is simply a relative measure of how easily atoms lose or give up electrons. Tendency to LOSE electrons Related to atomic radius/ionization energy, how easy to remove electrons

Metallic Character Decreases Increases

Nonmetallic Character Atoms with a tendency to GAIN electrons Increases Decreases

Classwork: Ionization Energy Circle the atom with the highest first ionization energy. Al, B 5) Fr, Li 9) Se, Cl Mg, Na 6) Mg, Al 10) Rb, Mg P, As 7) C, F I, At 8) K, Sc

Classwork: Metal Identity Identify each element as a nonmetal, metal, or metalloid Na 6) Cl P 7) Mg Se 8) Al Ge 9) Sb N 10) Si Look at row 3 on the periodic table. Write 1 paragraph describing which elements are metals, nonmetals, and metalloids. Also describe their properties and how these properties change as row 3 goes across the periodic table.

Write the electron configuration, identify the atom with the lowest ionization energy and circle which electron would be removed. Sodium, Nitrogen Potassium, Calcium Bromine, Iodine Sulfur, Phosphorus Phosphorus, Arsenic Carbon, Fluorine Selenium, Chlorine Rubidium, Magnesium Magnesium, Aluminum Potassium, Scandium

Writing Prompt Medeleeff developed the arrangement of the periodic table while in a chemistry class in school and assigned the task of placing the element properties together. If you were given this task before the table was developed, how would you go about arranging the elements? Write one paragraph explaining of why and how you would arrange this element table. Draw a diagram of your table. Your explanation and drawing must be logical ! Be creative!

Homework Problems in this lecture are for your practice if you need additional review Read pp. 315-329 Problems p. 333 #49, 51, 53, 57, 61