vineri, 9 mai 2014

ANALIZA CATIONILOR IN GRUPE ANALITICE

ANALIZA CATIONILOR IN GRUPE ANALITICE

  In cazul solutiilor care contin un amestec de mai multi ioni diferiti,  
nu este posibila punerea in evidenta pe cale directa a fiecaruia dintre ioni cu ajutorul unui reactiv specific corespunzator, datorita faptului ca ionii straini impiedica reactia respectiva.
   Deoarece numarul reactivilor specifici este din ce in ce mai limitat , pe masura ce se gasesc mai multi ioni in solutie, este necesara indepartarea in prealabil a acestora respectiv separarea lor folosind tipurile de reactie studiate si folosind conditiile unor separari foarte corecte si totale.
   Este rational insa sa se recurga la o separare sistematica a amestecului de ioni pe fractiuni ( grupe ) distincte care contin un numar mai mic de ioni, folosind acidul clorhidric, hidrogenul sulfurat, sulfura de amoniu, carbonatul de amoniu, carbonatul de amoniu, etc. Astfel, a aparut ideea clasificarii analitice a cationilor ( metalelor ), clasificare ce a fost elaborata de mai bine de 150 de ani, intr-o forma asemanatoare cu cea de astazi.
    Clasificarea ionilor in chimia analitica se bazeaza pe diferentade solubilitate a sarurilor si a hidroxizilor care se formeaza, diferenta care permite separarea unor grupe de ioni unele de altele.
 Altfel, potrivit clasificarii actuale, cationii se impart in cinci grupe analitice, in functie de solubilitatea clorurilor lor, a sulfurilor, respectiv a carbonatilor. Asa de exemplu ionii de Ag+, Pb2+, Hg22+,
dau cu ionul de Cl din HCl ( reactivul grupei a I - a analitice ) cloruri greu solubile .


Grupa a II a cuprinde cationii: Hg2+, Cu2+, As3+, As5+, Sb3+, Sb5+, Sn2+



Sn4+, si care dau cu ionul S2- sulfuri insolubile in mediul acid. Reactivul grupei este H2S in solutie acida HCL sau HNO3 . In functie 



de solubilitatea sulfurilor in mediu alcalin aceasta grupa se imparte 



in doua subgrupe:



- subgrupa sulfurilor insolubile in mediul alcalin ( sulfobaze )


- subgrupa sulfurilor insolubile in mediul acid ( sulfoacizi ).
























duminică, 12 mai 2013

NANOTECHNOLOGY

NANOTECHNOLOGY



Nanotechnology is ranked as the greatest discovery of the XXI century. It is a multidisciplinary field that combines great achievements in Physics, Chemistry, Mathematics, Strength of materials at the level of atoms and molecules at the nanoscale materials endowed with artificial intelligence.

Nanotechnology is a modalitatae materials are modified by atomic or molecular level, giving them unique properties and 
making them o behave in a different way from conventional material. Creations the nanotechnology

Material that cleans itself

Two Chinese researchers, Ming Long and Deyong Wu, claimed to have developed cotton clothes that have the ability to clean themselves of stains and bacteria when exposed to sunlight.
The invention was created by coating cotton with a layer consisting of a compound of titanium dioxide, a white material used in a wide range of products, from paint to sunscreen lotions.
This material has the ability to remove dirt and germs when exposed to different types of light. It is already used for self-cleaning windows, tiles for the bathroom and kitchen, but the socks which emit odors.

Nano - gold wires

      A team of American researchers have successfully use gold nano-wires to increase the electrical conductivity of a tissue created in the lab. Scientists believe that they could provide people with heart problems May 1 buan chance of survival.The threads used by researchers have a thickness of 30 nanometers and a length of 2-3 microns.
Researchers say this technology can be applied on any tissue can be stimulated electrically, including in the case of neural tissue
Microparticles that we can live without breathing
A team of researchers from the Boston Cildren's Hospital has created microparticles filled with oxygen can be injected directly into the patient's bloodstream to quickly oxygenate their blood.
Microparticles consist of a single layer of lipids inside is filled with oxygen. The microparticles are then injected by means of a liquid solution.
The researchers used high-intensity sonics to mix lipids with oxygen, thus obtaining particles with a diameter of 2-4 micrometers, in which oxygen is trapped inside the lipid coating.
Solution containing particles in which oxygen is 70% of the volume can easily mix with human blood. Microparticles thus obtained can carry 3-4 times more blood than red blood cells.


The most accurate scale in the world

      A team of researchers from the Catalan Institute of Nanotechnology in Barcelona has developed the most accurate scale in the world, able to distinguish the smallest unit of measurement of mass Yoctogramul. A yoctogram is a billionth of a billionth of a gram million. To measure such precision team of scientists have turned to the nanotubes, vibrating at different frequencies depending on the mass of the particles or molecules that are on them.
1,000 maps drawn on a grain of salt

     A team of scientists working in the I.B.M. drew the lowest 3D world that will be approved as such in the Guinness Book of Records. 1000 this took place on a map of salt granules. Map drawn on a tiny fragment of the polymer, measures 22 x 11 micrometers and consists of 500,000 pixels, each measuring 20 square nanometers.
     Even more remarkable is that it was created very quickly in just 2 minutes and 23 seconds. Although, at first glance, the map does not seem to have any practical use, their implementation representation is a very big step in terms of technology.

Nanovaccin against diabetes

    A group of Canadian researchers has developed a nanovaccin able to stop the progression of type 1 diabetes, restoring normal blood sugar levels.Nanovaccinul s - proved able to induce remission of type 1 diabetes in the experiments conducted by scientists in mice. Type 1 diabetes is a chronic pathology, caused by the destruction of pancreatic cells that produce insulin, operated by specific cells of the immune system T cells

Extremely small needle syringe

    A very small needle syringe was invented by researchers at the University of Illinois. Is able to penetrate the cell membrane to inject some substance molecules in the cytoplasm. It's applications are not limited to nano-needle 
so can be used as electrochemical probe to investigate the properties of intracellular environment, or optical biosensor. Nano-needle  is made - a tube made of a special chemical, boron nitride.

Nanotube is attached to the end of a glass pipette and covered with a thin layer of aur. Load to be inserted into the cell is attached to the gold layer using special molecules, the role of communication (linker molecules). Once inserted nano-needle  in the cytoplasm or nucleus of a cell, releasing loads unravel these links.

 N
ano-needle which has a diameter of only 50 nanometers (1 nanometer = 1 millionth of - a meter) causes minimum disruption to the membrane, where it enters the cell and for the first time, the introduction of foreign substances into the cell can be precisely controlled and recorded . With this technology, the inventors say, will be studied with great precision many biophysical and biochemical processes at the cellular level.

NANOTEHNOLOGIA

NANOTEHNOLOGIA


        Nanotehnologia este clasata ca fiind cea mai mare descoperire a secolului XXI. Este un domeniu multidisciplinar care combina marile realizari din Fizica, Chimie, Matematica, Rezistenta materialelor la nivel de atomi si molecule la scala nanometrica a unor materiale dotate cu inteligenta artificiala.

    Nanotehnologia este o modalitatae prin care materialele sunt modificate la nivel atomic sau molecular, dandu-le proprietati unice si facandu-le sa se comporte intr-un fel diferit fata de materialul conventional.
   Creeatii la nivelul nanotehnologiei

Materialul care se curata singur 
    
    Doi cercetatori chinezi, Ming Long si Deyong Wu, sustin ca au dezvoltat haine din bumbac care au capacitatea de a se curata singure de pete si bacterii atunci cand sunt expuse la lumina soarelui.
    Inventia a fost creata prin acoperirea bumbacului cu un strat format dintr-un compus din dioxid de titan, un material alb folosit intr-o gama larga de produse, de la vopsea pana la lotiuni de protectie solara.
    Acest material are abilitatea de a inlatura murdaria si microbii atunci cand este expus la diferite tipuri de lumina. El este deja, utilizat in cazul ferestrelor care se curata singure, a gresiei pentru baie si bucatarie, dar si al sosetelor care degaja mirosuri neplacute  . 

Nano - firele de aur

    O echipa de cercetatori americani au fol0osit cu succes nano- firele de aur pentru a creste conductibilitatea electrica a unui tesut creeat in laborator. Oamenii de stiinta cred ca acestea ar putea oferi oamenilor cu probleme cardiace o mai buna sansa de supravietuire.
Firele folosite de cercetatori au o grosime de 30 de nanometri si o lungime de 2 - 3 microni.

   Cercetatorii spun ca aceasta tehnologie poate fi aplicata asupra oricarui tesut ce poate fi stimulat electric, inclusiv si in cazul tesutului neuronal

Microparticule prin care putem trai fara sa respiram

    O echipa de cercetatori din cadrul  Boston Cildren's Hospital a creeat microparticule umplute cu oxigen care pot fi injectate direct in fluxul sangvinal pacientilor, pentru a oxigena rapid sangele acestora.

    Microparticulele constau intr-un singur strat exterior de lipide interiorul fiind umplut cu oxigen. Microparticulele sunt apoi injectate prin intermediul unei solutii lichide. 
    Cercetatorii au folosit unde sonice de intensitate  mare pentru a amesteca lipidele cu oxigenul, obtinand astfel particule cu diametrul de 2 - 4 micrometri, in care oxigenul este prins in interiorul invelisului lipidic.

Solutia ce contine particulele si in care oxigenul reprezinta 70% din volum se poate amesteca usor cu sangele uman. Microparticulele astfel obtinute pot transporta  de 3 - 4 ori mai mult sange decat globulele rosii din sange.

  Cel mai precis cantar din lume

    O echipa de cercetatori de la Institutul Catalan de Nanotehnologie din Barcelona a conceput cel mai precis cantar din lume, capabil sa distinga cea mai mica unitate de masura a masei Yoctogramul. Un yoctogram reprezinta o miliardime de miliardime de milion dintr-un gram. Pentru a putea masura o asemenea precizie echipa de oameni de stiinta au apelat la la nanotuburi, ce vibreaza la frecvente diferite in functie de masa particulelor sau moleculelor ce se afla pe ele.
   
1.000 de harti desenate pe o granula de sare

    O echipa de stiinta ce lucreaza in cadrul I.B.M. a desenat cel mai mic mapamond 3D, ce va fi omologat ca atare si in Cartea Recordurilor. 1000 de astfel de harti au avut loc pe o granule de sare. Harta desenata pe un fragment minuscul de polimer, masoara  22 x 11 micrometri si este alcatuita din 500.000 de pixeli, fiecare masurand 20 de nanometri patrati. 
    Inca si mai remarcabil este faptul ca a fost creeata foarte repede in numai 2 minute si 23 de secunde.
Desi, la prima vedere, harta nu pare a avea vreo utilitate practica, realizarea lor reprezentarea reprezinta un pas foarte mare din punct de vedere tehnologic.

Nanovaccin impotriva diabetului

   Un grup de cercetatori canadieni a pus la punct un nanovaccin capabil sa opreasca progresia diabetului de tip 1, restabilind nivelurile normale ale glicemiei.
Nanovaccinul s - a dovedit capabil sa induca remisia diabetului de tip 1 in cadrul experimentelor realizate de oamenii de stiinta pe soareci. Diabetul de tip 1 este o patologie cronica, provocata de distrugerea celulelor pancreatice care produc insulina, operata de celule specifice ale sistemului imunitar, celule T.

   Ac de seringa extrem de mic

   Un ac de seringa extrem de mic a fost inventat de cercetatorii de la Universitatea din Illinois. Este capabil sa patrunda prin membrana celulara pentru a injecta cateva molecule de substanta in citoplasma . Aplicatiile lui nu se marginesc la atat nanoacul poate fi utilizat si ca sonda electrochimica, pentru a cerceta proprietatile mediului intracelular, sau ca biosenzor optic. Nanoacul este fabricat dintr - un tub constituit dintr-o substanta chimica speciala, nitrura de bor.
   Nanotubul este atasat la capatul unei pipete de sticla si acoperit cu un strat subtire de aur.Incarcatura ce trebuie introdusa in celula este atasata de stratul de aur cu ajutorul unor molecule speciale, cu rol de legatura ( molecule linker ). Odata introdus nanoacul in citoplasma sau nucleul unei celule, aceste legaturi se desfac eliberand incarcatura.

   Nanoacul care are un diametrul de numai 50 nanometri ( 1 nanometru = 1 milion parte dintr - un metru ) produce perturbari minime la nivelul membranei, atunci cand intra in celula si, pentru prima oara, introducerea substantelor straine in celula poate fi precis controlata si inregistrata.Cu ajutorul acestei tehnologii, afirma inventatorii, vor putea fi studiate cu mare precizie numeroase procese biofizice si biochimice la nivel celular. 

   








vineri, 10 mai 2013

QUALITATIVE CHEMICAL ANALYSIS


QUALITATIVE CHEMICAL ANALYSIS


QUALITATIVE CHEMICAL ANALYSIS - aims to identify elements and groups of elements that are found in an unknown substance. Isolate on all elements (ions) with similar properties using group reagents, after which the separation continues in each group to reach each cation in part that identifies with specific reagents.
Qualitative analysis begins with a series of preliminary tests in order to obtain information about analytes.
After you run these samples, the dissolution reaches a mixture of cations and anions that are subject to a systematic review.
In general any qualitative analysis of substances takes place in two stages, namely, preliminary analysis and the analysis itself.

PRELIMINARY ANALYSIS METHODS

Preliminary research done on the substance in the solid state.If it is in a state of solution, focuses on water bath to dryness and the residue research are obtained.Preliminary tests consist of the following operations:1 - heating tubules (closed tube)2 - heating coal3 - as pearls,4 - stain flame5 - behavior from H2SO46 - heating with alkali

Preliminary analysis should be performed in the above order.Information obtained in the preliminary analysis are particularly useful when reliable, but not always obtained conclusive indications for an item, especially when considering mixtures. In analyzes using mixtures containing flame of a gas burner.

Lamp Teclu - is formed in the combustion tube, for adjusting the flow rate of the air brake, DMIS gas pipe, a base, a screw for adjusting the flow rate of gas.
Photo    - 1 

Bunsen lamp - contains the same components, except the adjusting screw for the gas and air adjustment is provided with a sleeve. These bulbs are used in the various Laboratory (evaporation, boiling, roasting) allowing heating to temperatures of 1000-1200 degrees C. The flame is the combustion gas. It consists of three distinct areas:1 - the inner, colorless gas formed by combustion and unreacted still having a temperature somewhere from 350 - 400 degrees C.2 - the middle, bright interior and the surrounding region is made up of CO gas and incandescent particles of carbon, because the combustion is incomplete, insufficient oxygen.This area is about 520 degrees C.
3 - the outer, less bright because it is devoid of incandescent carbon particles, containing end-products of combustion to CO2 and water vapor having high temperature.

These three areas are distinguished not only by their temperature but 
by how different chemical action of substances.
Thus, in the outer region, where burning is complete and 
highest temperature, flame oxidant in nature. In this region substances oxidize. In the middle region due existence of incandescent carbon particles and CO flame Reducing. A chemical bring in this area is reduced.


Photo    - 2

Photo     - 3 


Photo     - 4












ANALIZA CHIMICA CALITATIVA


ANALIZA CHIMICA CALITATIVA


        ANALIZA CHIMICA CALITATIVA - are drept scop identificarea elementelor si a gruparilor de elemente care se gasesc intr-o substanta necunoscuta. Se izoleaza pe rand elementele ( ionii ) cu proprietati asemanatoare cu ajutorul reactivilor de grupa, dupa care, separarea, continua in fiecare grupa pana ajunge la fiecare cation in parte care se identifica cu ajutorul reactivilor specifici.
     Analiza calitativa incepe cu o serie de probe preliminare in vederea obtinerii unor informatii despre substanta de analizat.
     Dupa ce se executa aceste probe, prin dizolvare se ajunge la un amestec de cationi si anioni care se supun unei analize sistematice.
   
In general orice analiza calitativa a unei substante se desfasoara in doua etape si anume, analiza preliminara si analiza propriu- zisa.


           METODELE ANALIZEI PRELIMINARE

     Cercetarile preliminare se efectueaza asupra substantei in stare solida.
Daca aceasta este in stare de solutie, se concentreaza pe baia de apa pana la uscare iar cercetarile se fac pe reziduul obtinut.
Incercarile preliminare constau in urmatoarele operatii:

1 - incalzire in tubusor ( tub inchis ),
2 - incalzire pe carbune , 
3 - forma perlelor, 
4 - coloratia flacarii,
5 - comportarea fata de H2SO4
6 - incalzirea cu alcalii

    Analiza preliminara trebuie efectuata in ordinea de mai sus.
Indicatiile obtinute in analiza preliminara sunt deosebit de utile atunci cand sunt sigure, dar nu intodeauna indicatiile obtinute sunt concludente pentru un element, mai ales atunci cand se analizeaza amestecuri. In efectuarea analizelor ce contin amestecuri se foloseste flacara unui bec de gaz.

Becu Teclu este format dintr-un tub de combustie, disc pentru reglarea debitului de aer, tub de dmisie a gazului, un postament, un surub pentru reglarea debitului de gaz.

Imagini:




IMAGINEA 1   -  BECUL TECLU   

Becul Bunsen - contine aceleasi parti componente, mai putin surubul de reglare a debitului de gaz, iar pentru reglarea aerului este prevazut cu un manson. Aceste becuri servesc la cele mai diferite lucrari de laborator ( evaporare, fierbere, calcinare ) permitand o incalzire pana la temperaturi de 1000 - 1200 grade C. Flacara este un gaz in combustie. Ea este formata din trei zone distincte:

1- zona interioara, incolora, formata din gaze neintrate inca in combustie si care au o temperatura undeva la 350 - 400 grade C.
2 - zona mijlocie, luminoasa, care inconjoara regiunea interioara si care este formata din gaze de CO si particule incandescente de carbon, datorita faptului ca combustia este incompleta, cantitatea de oxigen fiind insuficienta .       
Aceasta zona are circa 520 grade C.
 3 - zona exterioara, mai putin luminoasa deoarece este lipsita de particulele de carbune incandescent, contine produsii finali ai arderii ca CO2 si vapori de apa ce au temperatura maxima.

      Aceste trei zone se deosebesc nu numai prin temperatura lor ci 

si prin modul actiunii chimice diferite asupra substantelor.

     Astfel, in regiunea exterioara, unde arderea este completa si 

temperatura cea mai inalta, flacara are caracter oxidant. In aceasta 

regiune substantele se oxideaza. In regiunea mijlocie, datorita 

existentei particulelor de carbon incadescent si a CO, flacara este 

reducatoare. O substanta chimica aduca in aceasta zona se reduce.
                                                              





















joi, 9 mai 2013

ATOMS and MOLECULES

ATOMS and MOLECULES

   
     
Any material is composed of very small particles (invisible) called atoms.They are so small they fit in the millions on top of a needle. Grouping of atoms forming molecules, the largest of its kind containing several thousand atoms.
  
    
The idea that any material is composed of small particles appeared since the time of Ancient Greece. Around the year 420 BCE philosopher Democritus concluded that matter is composed of smaller particles which in turn divide.
   
These particles are called nowadays atoms athome Greek word meaning indivisible.
   
But other philosophers had different theories. In the fourth century BCE Aristotle believed that every material is composed of four basic elements: - earth, air, fire, water, only diferite.Aceasta quantity theory has been widely accepted in the early seventeenth century. The objective was to create alchimieia, elixir, a drink that give eternal life of man.
    
Another objective was enriching by turning ordinary metals into gold.
Many alchemists boasted that they had solved these problems, but in reality none was successful.

                    
DALTON'S REVOLUTIONARY THEORY

        
Some scientists still remained of the opinion that matter is composed of atoms, but by the early 1800s there was no clear evidence to support these allegations scientifically.
       
An English chemist and writer named John Dalton performed experiments with gases, specifically investigated the combination of these. A determined such that hydrogen and oxygen combine in the same weight ratio to form apa.La reached similar results and other researchers, but Dalton was the first to understand their implications.
    
He concluded that materials are composed of atoms and the atoms of a substance are all the same weight division.If two primary substances combine atoms join together then always the same quantitative ratio (on weight).Dalton's theory explained the cause of the atoms in the same report combines quantitative and created a starting point for other researchers to examine the matter.

    
In conclusion matter is composed of atoms, ... right, but the atoms that compose?
   
The first indications of this appeared in the late 1800s, when researchers examined the passage of electricity through thin air through a glass tube. Tube issued from time to time in the light of the times when a high voltage was applied to two metal plates placed in gas, or otherwise electrodes. The light was produced by invisible radiation that start and stop the negative electron in the wall of the glass tube.
      
In 1890 British physicist JJ Thompson showed that these cathode rays, as it is called in that time, are actually particles of negative charge currents.
      
At that time it was assumed that electrons are ripped in some way the atoms, but it was not clear their organization within an atom.
     
Thompson's hypothesis was that atoms somehow resembles a pudding with raisins, more particles negatively charged electrons are embedded in a voluminous but lightweight material, spherical,.

     
Experiences developed and subsequently made to clarify the internal structure of the atom denied Thompson's theory.
RUTHERFORD MODEL

    In 1911, a colleague of Thompson, Ernest Rutherford, born in New Zeeland, but has worked in the UK, outlined a new atomic structure, which gave the answer to the phenomena observed in experiments. According to them, the middle atom nucleus or otherwise, is positive charge and is relatively hard. Electrons revolve around it: particles very small and light, carrying a negative charge.
    
Rutherford did not realize though that the atomic nucleus is composed of many particles:- Some positively charged- Other no load
  
The existence of positively charged particles (protons) was found around 1920.
  
Particles without electrical charge mentioned above were discovered around 1932 by Sir James Chadwick, which he called electrons.
 
This was completed model atom we can understand the behavior of matter.

          Elements

      
Elements are the substances submitted in each atom has the same number of protons. This indicates the number of protons atomic number of the element. There are a total number of 92 elements in nature.
      
Using special equipment, called particle accelerators can produce several other items that contain more protons.
  
Among the natural elements remind iron, mercury hydrogen.
     
In many substances, the atoms form groups called molecules.
     
Hydrogen gas is formed from molecules, each molecule is composed of two atoms of hydrogen.
     
And water is a composition, each water molecule contains two hydrogen atoms and an oxygen atom.
     
There are many molecules that contain a larger number of atoms: protein in living organisms are composed of molecules of sophisticated molecules and the number reaching thousands.
    
APPENDIX


nuclear accelerator  -1 

nuclear accelerator  - 2  


nuclear accelerator   - 3

Rutherford model pictures 


model   - 1 


model   - 2









miercuri, 8 mai 2013

ATOMI si MOLECULE

ATOMI si MOLECULE 

      
     Orice material este compus din particule foarte mici ( invizibile ) numite atomi.
Acestea sunt atat de mici incat incap cu milioanele pe varful unui ac. Gruparea mai multor atomi formeaza molecule, cele mai mari de acest gen contin mai multe mii de atomi.
     
    Ideea ca ,, orice material ,, este compus din particule mici a aparut inca din vremea Greciei Antice. In jurul anului 420 i.e.n. filosoful Democrit a ajuns la concluzia ca materia este compusa din particule mai mici care la randul lor se divid.
   Aceste particule se numesc in ziua de astazi atomi dupa cuvantul grecesc athomos care inseamna indivizibil.
   Alti filosofi aveau insa teorii diferite. In secolul IV i.e.n. Aristotel era de parere ca fiecare material se compune din patru elemente de baza: - pamant, aer, foc, apa, numai ca in cantitati diferite.Aceasta a fost o teorie acceptata pe larg la inceputul secolului XVII.       Obiectivul alchimieia fost crearea ,, elixirului vietii ,, , o bautura care sa dea viata eterna omului . 
    Un alt obiectiv a fost imbogatirea prin transformarea metalelor obisnuite in aur. Multi alchimisti s-au laudat ca au rezolvat aceste probleme, dar in realitate niciunul nu a avut succes.

                    TEORIA REVOLUTIONARA A LUI DALTON

        Cativa oameni de stiinta au ramas in continuare de parere ca materia se compune din atomi, insa pana la inceputul anilor 1800 nu a existat nici o dovada clar stintifica care sa sustina aceste presupuneri.
       Un chimist si scriitor englez, pe nume John Dalton, a realizat experiente cu gaze, mai precis a cercetat modul de combinare intre acestea. A determinat de exemplu ca hidrogenul si oxigenul se combina in acelasi raport de greutate spre a forma apa.La rezultate similare au ajuns si alti cercetatori, insa Dalton a fost primul care a inteles implicatiile acestora. 
    El a concluzionat ca materiile sunt compuse din atomi si ca atomii unei substante primare au toti aceeasi greutate.

Daca doua substante primare se combina intre ele atunci atomii se unesc intotdeauna in acelasi raport cantitativ (referitor la greutate ).
Teoria lui Dalton a explicat cauza din care atomii se combina in acelasi raport cantitativ si a creat un punct de plecare pentru alti cercetatori spre examinarea materiei.

    In concluzie materia se compune din atomi,...corect, dar atomii din ce se compun?
   Primele indicii in acest sens au aparut spre sfarsitul anilor 1800, cand cercetatorii au examinat trecerea electricitatii prin aerul rarefiat printr-un tub de sticla. Tubul a emis din cand in cand lumina in momentele in care s-a aplicat o tensiune inalta  cele doua placute de metal introduse in gaz, sau altfel spus electrozi. Aceasta luminozitate era produsa de radiatia invizibila care pornea de pe electronul negativ si se oprea in peretele tubului de sticla. 
      In anii 1890 fizicianul britanic J. J. Thompson a aratat ca aceste raze catodice, dupa cum se numeau in aceea vreme, sunt de fapt curenti de particule de sarcini negative.
      In aceea vreme s-a presupus ca electronii sunt smulsi intr-un mod oarecare din atomi, dar nu era deloc clara organizarea lor din interiorul atomului.
     Ipoteza lui Thompson era ca atomii seamana intr-un fel cu o budinca cu stafide, ,, mai multe particule cu sarcina negativa electronii, sunt incorporate intr-o materie voluminoasa dar usoara, de forma sferica ,,. 

     Experientele elaborate si realizate ulterior pentru clarificarea structurii interne  a atomului au infirmat teoria lui Thompson.


MODELUL RUTHERFORD

In 1911, un coleg al lui Thompson, Ernest Rutherford, nascut in Noua Zeenlanda, dar care a lucrat in Marea Britanie, a schitat o noua structura atomica, care a dat raspuns la fenomenele observate in experimente. In conformitate cu acestea, mijlocul atomului sau altfel spus nucleul, are sracina pozitiva si este relativ greu. In jurul lui se invart electronii: particule foarte mici si usoare, purtatoare de sarcina negativa. 
    Rutherford nu a realizat insa ca nucleul atomic se compune din mai multe particule:
- unele cu sarcina pozitiva 
- altele fara sarcina
  Existenta particulelor cu sarcina pozitiva ( protoni ) s-a dovedit in jurul anilor 1920.
  Particulele fara sarcina electrica, amintite mai sus au fost descoperite in jurul anului 1932 de Sir James Chadwick, care le-a denumit electroni.
 Prin aceasta s-a completat modelul de atom prin care putem intelege comportamentul materiei.

          Elemente

      Elementele sunt acele substante inscrise, in care fiecare atom are acelasi numar de protoni. Acest numar de protoni indica numarul atomic al elementului respectiv.Exista in totalitate un numar de 92 de elemente in natura.
      Prin intermediul echipamente speciale, numite acceleratoare de particule se pot produce alte cateva elemente care sa contina mai multi protoni.
  Printre elementele naturale amintim fierul, mercurul hidrogenul.
     In multe substante, atomii formeaza grupari numite molecule.
     Gazul de hidrogen este format tot din molecule, fiecare molecula fiind compusa din din doi atomi de hidrogen.
     Si apa este o compozitie, fiecare molecula de apa contine doi atomi de hidrogen si unul de oxigen.
     Exista numeroase molecule care contin un numar mult mai mare de atomi: proteinele din organismele vii sunt compuse din molecule din molecule sofisticate ajungandu-se si la numarul miilor.
     
ANEXE
accelerator nuclear  - 1  


accelerator nuclear   - 2


accelerator nuclear    - 3



accelerator nuclear   - 4



MODELUL NUCLEAR RUTHERFORD


modelul Rutherford   - 1


model Rutherford   - 2