Tugas Atomic Structure

7/23/2019 Tugas Atomic Structure

1/14

Chemistry: Atomic Structure

Name: ___________________ Hr: ___

Objectives of this Unit

In this unit, we will learn how our understanding of the atom has changed over time. We

will study the structure of the atom and the particles that make it up. We will also cover how

atoms differ from one another. The objectives of this unit are:

Describe the organiation of the modern periodic table.

!se the periodic table to obtain information about the properties of elements.

Identify common metals, nonmetals, and metalloids.

"ist the basic principles of Dalton#s atomic theory.

Describe the various models of the atom.

$ompare and contrast the properties of electrons, protons, and neutrons.

Describe an atom#s atomic structure in terms of atomic number and mass number.

!se the periodic table to write the electron configurations for various atoms.

Organization of the Modern Periodic Table

The modern periodic table shows all the elements that scientists recognie, and is

organied so that a large amount of information about any element can be located relatively

%uickly. In this unit and the ne&t, we will e&plore the periodic table in detail' in particular, wewill discover that the periodic table is organied byproperties.

An element is where it is on the Table because of its structure and, therefore, its properties.

egions of the Periodic Table

There are three main regions of the periodic table.

metals ! largest region of the table; left-and-down portion

What are some properties of metals( good conductors (poor insulators) of heat

and electricity, ductile, malleable, most are solids at room temp.

nonmetals ! second largest region; right side

What are some properties of nonmetals( good insulators (poor conductors) of

heat and electricity, most are either brittle solids or gases at room temp.

metalloids ! locatedbetween the metals and nonmetals


2/14

)etalloids have properties of both metals and nonmetals. semiconductors

*or this class, the metalloids are: B, Si, e, As, Sb, Te

The periodic table can be divided into groups and periods.

gro"# ! a !ertical column on the periodic table; range from " to "#

#eriod ! a hori$ontal row on the periodic table; range from " to %

+lements in the same group have very similar properties. iven what we learned at

the start of this unit, why must this be( they must ha!e similar structures

The properties of an element depend -"/ on the structure of the element&s atoms.

+lements close to each other in the same period are somewhat similar, but -T as

similar as elements in the same group.

Other egions of the Table

al$ali metals ! group "; !ery reacti!e elements

al$aline earth metals ! group '; not as reacti!e as the alali metals

transition elements ! groups -"'

main bloc$ elements ! groups ",', "-"#; e!erything e*cept the transition elements

coinage metals ! group ""+ u, Ag, Au

lanthanides !part of the inner transition elements; elements /#-%"

actinides !part of the inner transition elements; elements 01-"1

halogens ! !ery reacti!e; react w2metals to form salts; means salt-former in 3atin

noble gases ! !ery unreacti!e; 45B36

The essential elementsare the ones we need for health, such as 000000000000000.

The %tom Today

atom ! the fundamental building bloc of all matter

1ll atoms of the same element are essentially 2but not e&actly3 the same. In terms of

chemical reactivity, any o&ygen atom will react e&actly as any other o&ygen atom.

n"cle"s ! the center of the atom; it contains the protons and neutrons

2


3/14

The masses of atoms are far too small for us to measure using conventional units. *or

e&ample, a single carbon atom has a mass of about 4 & 56 748g, a number too small to

imagine. Instead, we measure the masses of single atoms using the atomic mass

"nit, abbreviated 9amu.

Parts of the %tom

Particle Mass&lectricalCharge

'ocation (ithinthe %tom

7roton 8" amu "9 nucleus

6lectron "2"#%amu; ($ero) "-surround

nucleus; far from

nucleus

4eutron 8" amu no charge nucleus

Particles of the %tom

The atom contains s"batomic #articles, which are very small particles that make up an

atom. Three of these types of particles we have seen already: #rotons, ne"trons,

and electrons.

The identity of an atom is determined by how many #rotonsit has.atomic n"mber ! the number of protons an element has

Ne"tronsadd mass to the atom. eutrons were discovered by the ;ritish scientist

protons, 5? neutrons, and 5@ electronsA

13 What is the atom#s net charge( ("/9) 9 ("#-) -

;3 What is the atomic number of the atom( "/ What is the mass number( "

3


4/14

$3 This is an atom of what element( phosphorus, 7

)am#le Problem +: *or an atom with 8? protons, 85 neutrons, and 8B electronsA

13 What is the atom#s net charge( (


5/14

total mass of the products total mass of the reactants

In 5F==, the *rench chemist


6/14

". Atoms are 45T indi!isible @ they can be broen apart into 79, neutrons, and e-.

'. Atoms can be changed from one element to another, but not by chemical means

(chemical reactions). an do it by nuclear reactions.

. Atoms of the same element are 45T all e*actly alie isotopes

illiam Croo$es25@F6#s3: +nglish physicist. $rookes used

a gas7discharge tube 2$rookes tube3 and called the particles

that appeared cathode rays. $rookes tubes are now called

cathode-ray tubesand are used as T and computer monitors, and radar screens.

In particular, $rookes discovered that his 9cathode rays were deflected by a

magnetic field. Without knowing it, $rookes had discovered electrons.

8585 Thomsen25@=F3: +nglish scientist. Thomsen e&perimented with the same type of

cathode7ray tube that $rookes had used. Thomsen noted that 9cathode rays were

deflected by an electric field, and he also noticed that the 9cathode rays were

attracted to the positive electrode, called the anode.

What conclusion did Thomsen draw from his observations( e- has (-) charge

*urther e&periments showed that the mass of the electron was only about 5H4666of the

mass of the smallest element, hydrogen. 1nd since the atom was known to be

electrically neutral, Thomsen proposed his famous #l"m #"dding model.

tiny (-) charges embedded in alarge mass of (9) particles

&rnest "therford25=6?3: ;ritish scientist

In 5=6?, utherford and his graduate assistants, eiger and )arsden, conducted the

famous .old'eaf &;#eriment. This e&periment used alpha particles 2helium atoms

with a 4J charge3, a thin gold leaf, and a fluorescent screen coated with inc sulfide.

Why did utherford#s team use gold instead of aluminum or tin(

gold can be rolled !ery, !ery thin

When the beam was directed at the gold

foil, most of the beam passed straight through,

while much of the rest of the beam was

deflected at a slight angle.

6


7/14

What conclusion did utherford draw from this evidence(

the atom is mostly empty space

1 small percentage of the alpha particles, however, bounced back toward the

radiation source. utherford concluded that the J particles of the atom must

-T be spread out evenly as Thomsen had suggested in his plum pudding

model, but instead must be concentrated at the center of the atom. The tiny

central region of the atom was called the n"cle"s, which is "atin for little nut.

*urthermore, utherford suggested that the electrons travel around the

positively7charged nucleus.

The +"ant"m Mechanicswhich is the idea that

energyis,"antizedK energy has only certain allowable !alues; other !alues

are 45T allowed

In an atom, where are the electrons, according to the %uantum mechanical model(

we cannot say for sure, but the e:uations of uantum Cechanics can tell us the

probability that we will find an electron at a certain distance from the nucleus

)"mmary of the %tomic Model

7


8/14

The atomic model has changed over time, and continues to change as we learn more.

% Closer 'oo$ at &lectrons: here are they in the %tom?

+lectrons are located within energy levels, which range from " to %. The higher the

energy level the electron is inA

5. the farther the electron is from the nucleus

4. the more energy the electron has

Within each energy level, there e&ist s"blevels, which differ from each other by slight

differences in energy. In each sublevel there are 9paths, called orbitals, that an electron

can travel on.

orbital ! a region of an atom in which there is a high probability of finding electrons

+ach orbital can hold a ma&imum of 0000 electrons.

In every s s"blevel, there is 0000 orbital, which holds a total of 000 electrons

In every # s"blevel, there are 0000 orbitals, which hold a total of 000 electrons

In every d s"blevel, there are 0000 orbitals, which hold a total of 000 electrons

In every f s"blevel, there are 0000 orbitals, which hold a total of 000 electrons

"et#s use an analogy to try to e&plain thisA

8


9/14

In what order do orbitals fill up( low-energy orbitals first, then higher-energy orbitals

Orbitals 4ill U# in

this Order

N"mber of this Ty#e

of Orbital

Total @ of &lectrons

in these Orbitals

"s " '

's " '

'p <

s " '

p <

=s " '

d / "1

=p <

This chart could go on, but let#s just give the order of the orbitals:

5s 4s 4p 8s 8p Bs 8d Bp >s Bd >p ?s Bf >d ?p Fs >f ?d Fp

riting the &lectron Config"ration for an %tom

9


10/14

The %uestion is: Dhere are the electrons in the atomE

The format for the electron configuration is, for e&ample: * s +

5 K the energy le!el

s K the suble!el, or orbital

4 K the number of electrons in that suble!el

ow to Write an +lectron $onfiguration

5. 3ocate the element on the periodic table.

4. Fill the orbitals in the proper order.

8. hec that the total number of electrons you ha!e e:uals the atomic number for

that element.

&;am#les: Write the electron configurations for the following elements.

carbon 2$3

lithium 2"i3

sodium 2a3

chlorine 2$l3

potassium 2L3

iron 2*e3

Using )horthand Notation for the &lectron Config"ration

Gut the noble gas that precedes the element in brackets, then continue filling the

rest of the orbitals in order, as usual.

&;am#les: sodium 2a3

chlorine 2$l3

potassium 2L3

iron 2*e3

The )ignificance of the &lectrons Config"rations

Asoto#es

Interestingly enough, -T all atoms of an element are e&actly the same in every respect.

$hemically, all atoms of an element react e&actly the same. 1ll atoms of an element

have a particular number of protons. What could be different about 4 or more atoms of

the same element( different radioacti!e beha!ior, different masses (diff. G of neutrons)

isoto#es ! atoms of the same element that ha!e different numbers of neutrons

10


11/14

&;am#le *: 1ll carbon atoms have how many protons( < (atomic number)

)ost carbon atoms have ? neutrons. What is their mass number( "'

Come carbon atoms have @ neutrons. What is their mass number( "=

-"' and -"= are isotopes of carbon

&;am#le +: ydrogen has 8 isotopes, protium 2753, deuterium 2743, tritium 2783.

ow many protons, neutrons, and " 79 " 79 " 79

electrons are in a neutral atom of 1 n1 " n1 ' n1

each of the isotopes of hydrogen( " e- " e- " e-

&;am#le B: ow many neutrons are in a sodium748 atom( "'

Cometimes, we use isoto#e notationto designate a particular isotope of an

element. This is particularly useful when balancing nuclear reactions.

Asoto#eNotation

Protons Ne"trons &lectrons

48@

!=4

0' "=< 0'

48

a55

"" "' ""

48>

!=4

0' "= 0'

%verage %tomic Mass

Cince all atoms of an element do not have the same mass, it is useful to find the average

mass of the atoms of an element. That is, if we took a random sample of a large number

of atoms of that element, what would the average mass of those atoms be(

average atomic mass 0atomic massD1 ! the a!g. mass of all isotopes of an element

The average atomic mass takes into account what percentage of each isotope have

a particular mass.*or an element with isotopes 91, 9;, etc., the average atomic mass can be

found using the e%uationA

AAC (Cass A)(H abundance of A) 9 (Cass B)(H abundance of B) 9 I

E ab"ndancetells what percentage of the element#s atoms are of each isotope.

/ou must use the decimal form of the percentage, such as using 6.4> for 4>M.

11


12/14

&;am#le *: /ou have > samples of concrete: B of them have a mass of 56.> kg and5 has a mass of @.8 kg. What is the average mass of the concrete samples("1.1

Documents

Tugas Atomic Structure