AnaChem_Chapter1

8/19/2019 AnaChem_Chapter1

1/6

1

The Atomic Theory

In 1804, John Dalton proposed the existence of atoms. He not only postulated thatatoms exist, as had ancient ree! philosophers, "ut he also attri"uted to the atomcertain properties. His postulates #ere as follo#s$

1. e%lements are composed of indi&isi"le particles, called

atoms.'. All atoms of a (i&en element ha&e the same mass, and

the mass of an atom of a (i&en element is di)erent fromthe mass of an atom of any other element.

*. +hen elements com"ine to form a (i&en compound, theatoms of one element com"ine #ith those of the otherelements- in a denite ratio to form molecules. Atoms arenot destroyed in this process.

4. Atoms of t#o or more elements may com"ine in di)erentratios to form di)erent compounds.

/. The most common ratio of atoms is 1$1, and #here morethan one compound of t#o or more elements exists, themost sta"le is the one #ith 1$1 ratio of atoms.

The Atomic Structurerom /0 to 100 years after Dalton proposed his theory, &arious disco&eries

#ere made that sho# that the atom is not indi&isi"le, "ut really is composed of parts. The most important su"atomic particles are listed in Ta"le 1.a, alon( #iththeir most important properties. The protons and neutrons are found in a &ery tinynucleus plural, nuclei-. The electrons are found outside the nucleus.

Table 1.a. Subatomic Particles

The Law of Conservation of Mass states that mass is neither created nor destroyedin a chemical reaction or physical chan(e.

The Law of Denite Proportions states that e&ery chemical compound is made up ofelements in a denite ratio "y mass.

The Law of Multiple Proportions states that #hen t#o or more di)erent compoundsare formed from the same elements, the ratio of masses of each element in thecompounds for a (i&en mass of any other element is a small #hole num"er.

There are t#o types of electric char(es that occur in naturepositi&e and ne(ati&e.2har(es of these t#o types are opposite one another, and cancel the e)ect of the

3repared "y$%n(r. elissa . A"ansi


2/6

'

other. 5odies #ith opposite char(e types attract one another6 those #ith the samechar(e type repel one another. If a "ody has e7ual num"ers of char(es of the t#otypes, it has no net char(e and is said to "e neutral .

The 3eriodic Ta"le

Table 1.b. Important elements

The periodic table is an extremely useful ta"ulation of the elements. It isconstructed so that each &ertical column contains elements that are chemicallysimilar. The elements in the columns are called groups, or families. %lements insome (roups can "e &ery similar to one another. %lements in other (roups are lesssimilar. or example, the elements of the rst (roup resem"le one another morethan the elements of the fourth (roup from the end, headed "y .- %ach ro# in theta"le is called a period.

%lectronic 2on(uration of the Atom

Quantum Numbers : “Address of an Electron”%ach electron is specied in terms of its four 7uantum num"ers that (o&ern itsener(y, its orientation in space, and its possi"le interactions #ith other electrons.

Thus, listin( the &alues of the four 7uantum num"ers descri"es the pro"a"lelocation of the electron, some#hat analo(ously to listin( the section, ro#, seat, anddate on a tic!et to a roc! concert.



3/6

*

The last entry in an electronic con(uration is a representation of the elementlocation in the periodic ta"le.

i.e. 3s2 9 element is in the *rd ro#, 'nd column. ∴ a(nesium The 4 :uantum um"ers

1. 3rincipal :uantum um"er, n ;the ener(y le&el


4/6

4

-! -2 -1 0 1 2 !

f sublevel

4. pin 7uantum num"er, ms ;direction of thearro#


5/6

/

%xample$ 3redict the char(e on a ma(nesium ion and that on a uoride ion,

and deduce the formula of ma(nesium uoride.

'E()SE'E$T%#N

*#T

N#TAT)#N

To representthe formationof "onds"et#eenatoms, it iscon&enient to use a system !no#n as electron dot notation. In this notation, thesym"ol for an element is used to represent the nucleus of an atom of the elementplus all the electrons except those in the outermost &alence- shell. The outermostelectrons are represented "y dots or tiny circles or crosses-. or example, the dotnotations for the rst 10 elements in the periodic ta"le are as follo#s$

A. )onic +ondin,

%xamples$

1- a

'- 2a'



6/6

*- 2aG

+. $oalent +ondin,

refer to /reious notes.


Documents

AnaChem_Chapter1