1. DOR: Average Atomic Mass
1) Barium has four isotopes: Ba-130, Ba-133, Ba-137, and Ba The percent abundance of the isotopes is %, 12.44%, 45.57%, with the rest being composed of the heaviest isotope. Masses are grams, grams, grams, and 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 , Z-81 with a weight of , and Z-82 with a weight of The percent abundance of the three isotopes is: Z %, Z %, and Z %. What is the avg. atomic weight of element Z ?

2. Elemental Properties and Patterns
Periodic Trends
Elemental Properties and Patterns

3. 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.

4. 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.

5. 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.

6. 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

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

8. 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.

9. 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

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

11. Atomic Radius Trend
Decreases
Increases

12. 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.

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

14. 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

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

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

17. 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

18. 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.

19. 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

20. Ionization Energy Trend
Increases
Decreases

21. Ionization Energy

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

23. What does affinity mean?

24. 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

25. Electron Affinity Trend
Increases
Decreases

26. 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?

27. 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.

28. 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

29. 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

30. 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.

31. 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

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

33. 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

34. Metallic Character
Decreases
Increases

35. Nonmetallic Character
Atoms with a tendency to GAIN electrons
Increases
Decreases

36. 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

37. 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.

38. 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

39. 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!

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