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 ?

DOR: Average Atomic Mass

Periodic TrendsElemental Properties and Patterns

The Periodic LawDimitri 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 LawMendeleev 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 LawMendeleev 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 LawAtoms 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 TrendsThere are several important atomic characteristics that

show predictable trends that you should know.

Atomic properties—Deal with only single atoms

Atomic RadiusEnables 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 RadiusHalf the distance between the nuclei of 2 bonded atoms.Radius of nonmetallic atoms

Ex. Br

2.86 Å1.43 Å 1.43 Å

Half the distance between nuclei of adjacent atoms in a metal

Radius of metallic atoms

2. Metallic Radius

Atomic Radius Trend

Decreases

Increases

Atomic RadiusThe 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 radii1) Ca, F2) Cl, O3) N, P

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

Larger size than original neutral atom Generally nonmetals Electrons repel as increase in number, causes

size to increase

Ionic Radii: 1) Anions

Smaller size than original neutral atom

Generally metals

Less electrons, more attractive force from nucleus

Ionic Radii: 2) Cations

Ionization EnergyTIf 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 atomRemoval 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.

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 (cont.)

Ionization Energy Trend

Increases

Decreases

Ionization Energy

Identify the highest ionization energy1) F, Mg2) Na, Rb3) 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 reactiveStable atoms—full octet

Electron Affinity Trend

Increases

Decreases

Metals, Nonmetals, MetalloidsHow 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 GroupingBesides the 4 blocks of the table, there is

another way of classifying element:MetalsNonmetalsMetalloids 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 shineThey are dull, brittle,

nonconductors (insulators).Gases at room temperature

Want to GAIN electrons Form negative ionsp block elements, H and He

Transition MetalsMiddle of the periodic tableForms positive ions, multiple

typesShine, malleable, ductile, good

conductorss/d orbitals—electrons lost from

these subshells.

Metalloids/Semi-MetalsMetalloids, 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 18Do NOT react with other

elements

Atomspheric gases

Naturally in elemental form , single atoms

Not completely unreactive

Metallic CharacterThis 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

Atoms with a tendency to GAIN electrons

Nonmetallic Character

Increases

Decreases

Classwork: Ionization Energy

Circle the atom with the highest first ionization energy.1) Al, B 5) Fr, Li 9) Se, Cl2) Mg, Na 6) Mg, Al 10) Rb, Mg3) P, As 7) C, F4) I, At 8) K, Sc

Classwork: Metal IdentityIdentify each element as a nonmetal, metal, or metalloid1) Na 6) Cl2) P 7) Mg3) Se 8) Al4) Ge 9) Sb5) 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.

1) Sodium, Nitrogen2) Potassium, Calcium3) Bromine, Iodine4) Sulfur, Phosphorus5) Phosphorus, Arsenic6) Carbon, Fluorine7) Selenium, Chlorine8) Rubidium, Magnesium9) Magnesium, Aluminum10) 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!

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

Homework