5 Steps to a 5 AP Chemistry

Although this filling pattern conveys a lot of information, it is bulky. A shorthand

method for giving the same information has been developed—the electronic configuration.

Electronic Configurations

The electronic configurationis a condensed way of representing the pattern of electrons

in an atom. Using the Aufbau build-up pattern that was used in writing the energy-level

diagram, consecutively write the number of the shell (energy level), the type of orbital

(s, p, d, etc.), and then the number of electrons in that orbital shown as a superscript. For

example, 1s^2 2s^1 would indicate that there are two electrons in the s-orbital in energy level

(shell) l, and one electron in the s-orbital in energy level 2. Looking at the energy-level

diagram for silicon above, the electronic configuration would be written as:

The sum of all the superscripts should be equal to the number of electrons in the atom

(the atomic number, Z). Electronic configurations can also be written for cations and anions.

Periodic Table

If chemistry students had to learn the individual properties of the 100+elements that are now

known, it would be a monumental and frustrating task. Early scientists had to do just that.

Then several scientists began to notice trends in the properties of the elements and began

grouping them in various ways. In 1871, a Russian chemist, Dmitri Mendeleev, introduced

the first modern periodic table. He arranged the elements in terms of increasing atomic mass.

He then arranged columns so that elements that had similar properties were in the same

column. Mendeleev was able to predict the existence and properties of elements that were

then unknown. Later, when they were discovered, Mendeleev’s predictions were remarkably

accurate. Later the periodic table was rearranged to sequence the elements by increasing

atomic number, not mass. The result is the modern periodic table shown in Figure 5.4.

This is not the periodic table supplied on the AP exam. The one in this book has

family and period labels. Become familiar with these labels so that you can effectively use

the unlabeled one. You may wish to add labels to the one supplied with the AP exam.

Each square on this table represents a different element and contains three bits of infor-

mation. The first is the element symbol. You should become familiar with the symbols of

the commonly used elements. Secondly, the square lists the atomic number of the element,

usually centered above the element. This integer represents the number of protons in the

element’s nucleus. The atomic number will always be a whole number. Thirdly, the square

lists the element’s mass, normally centered underneath the element symbol. This number is

not a whole number because it is the weighted average (taking into consideration abun-

dance) of all the masses of the naturally occurring isotopes of that element. The mass

number can never be less than the atomic number.

Arrangement of Elements

There are a number of different groupings of elements on the periodic table that may be uti-

lized. One system involves putting the elements into three main groups—metals, nonmetals,

and metalloids (semimetals). Look at Figure 5.4. Notice the heavy, stair-stepped line starting

at boron (B) and going downward and to the right. The elements to the left of that line

(except for H, Ge, and Sb) are classified as metals. Metalsare normally solids (mercury being

an exception), shiny, and good conductors of heat and electricity. They can be hammered

silicon sspsp:1 2 2 3 322 62 2

50  STEP 4. Review the Knowledge You Need to Score High

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