02 Med Biochemistry

7/23/2019 02 Med Biochemistry

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Biochemistry 2

FUNDAMENTALS

Periodic Properties

and Atomic Structure

AUSOM


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Summary

The Periodic Law and Table. The properties of elements tend torepeat in a regular (periodic) way when the elements are arrangedin order of increasing atomic numbers. This periodic law is the basisof the arrangement of elements called the periodic table in which anelement belongs to a vertical grouping called a group or family, anda horizontal grouping called a period. All elements in a group or

family tend to have similar chemical properties.

Electronic Arrangements in Atoms. Niels Bohr proposed a theoryfor electronic arrangements in atoms based on the idea that theelectrons of atoms move around atomic nuclei in fixed circular orbits.Electrons change orbits only when they absorb or release energy.The Bohr model was modified as a result of continued research. It

was found that precise Bohr orbits for electrons could not bedetermined. Instead the energy and location of electrons could notbe specified in terms of shells, subshells, and orbitals which areindicated by a notation of numbers and letters.


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The Shell Model and Elemental Properties. The modified Bohrmodel or shell model of electronic structure provides an explanationfor the periodic law. The rules governing electron occupancy inshells, subshells, and orbitals result in a repeating pattern of valenceshell electron arrangements. Elements with similar chemicalproperties turn out to be elements with identical numbers and types

of electrons in their valence shells.

Electronic Configurations. The arrangements of electrons inorbitals, subshells, and shells are called electronic configurations.Rules and patterns have been found that allow these configurationsto be represented in a concise way. Written electronic configurationsallow details of individual orbital, subshell, and shell electron

occupancies to be seen readily. Also, the number of unpairedelectrons in elements is easily determined.


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Other Electronic Configuration Representations. Electronicconfigurations can be represented by using noble gas symbols torepresent some of the inner electrons, or by using Lewis structuresin which the valence electrons are represented by dots.

Another Look at the Periodic Table. Correlations betweenelectronic configurations for the elements and the periodic

arrangements of elements make it possible to determine a numberof details of electronic structure for an element simply on the basisof the location of the element in the periodic table. Special attentionis given to the last or distinguishing electron in an element.Elements are classified according to the type of subshell (s,p, etc.)occupied by this electron. The elements are also classified on the

basis of other properties as metals, nonmetals, or metalloids.


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Formative Assessment


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Question 1

Which of the following elements is

found in the same period as Lithium?

Sodium

MagnesiumRadon

Carbon


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Carbon


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Question 2

What group VIII element is located at

period 3 on the Periodic Table?

Argon

HeliumLead

Oxygen


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Argon


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Question 3

According to the Bohr model for the

atom:

electrons are located in similar orbitals.

electrons have identical energiesprotons spin counterclockwise

electrons can only occupy specific orbitals


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electrons can only occupy specific

orbitals


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Question 4

The maximum number of electrons that

can occupy a 2s subshell is:

2

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8

varies


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2


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Question 5

Which of the following has the same

number of valence electrons as

Sodium?

magnesiumhydrogen

chloride

oxygenpotassium


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hydrogen, potassium


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Question 6

The total number of unpaired electrons

in carbon is:

0

12

3

4


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02 Med Biochemistry