General Chemistry M. R. Naimi-Jamal Faculty of Chemistry Iran University of Science & Technology

فصل دوم: مقدمه ای بر نظریه اتمی‌

Contents Electrons and the Nuclear Atom Chemical Elements Atomic Masses The Mole

Protons, Neutrons, and Electrons Electricity –By the time of Benjamin Franklin ( ), two types of electric charge had been discovered –Franklin named them positive and negative because they appear as opposites and can repel one another Like charges repel, and unlike charges attract –Franklin noted that charge is balanced: negative and positive present in same amount

Protons, Neutrons, and Electrons Radioactivity: spontaneous emission of energy as atoms disintegrate –Henri Becquerel and Marie Curie Marie Curie’s concept that atoms disintegrate contradicts Dalton’s idea that atoms are indivisible. If atoms can break apart, there must be something smaller than an atom: “subatomic particles”

Protons, Neutrons, and Electrons Michael Faraday ( ) experimented with electrolysis (passing a current through a solution) Found that different quantities of different metals “plated” at the same current (related to mass of the atoms of those elements) As atoms are fundamental particles of elements, the fundamental particle of electricity was given the name “electron”

Behavior of charges

Cathode ray tube Julius Plücker 1859

Properties of cathode rays Joseph, J. Tomson 1897

آزمایش تامسون (محاسبه (e/m (aدر میدان مغناطیسی r شعاع حرکت دورانی b ) در میدان الکتریکی ومغناطیسی

Charge on the electron  From Robert Millikan showed ionized oil drops can be balanced against the pull of gravity by an electric field.

Milikan Experiment

آزمایش میلیکان  The charge is an integral multiple of the electronic charge, e. 1 e = –1.602 x C

پروتون آزمایش اشعه کانالی اوژن گلدشتاین :1886 مشاهده اشعه ای که در خلاف جهت اشعه کاتدی حرکت می کرد و به سبب عبور از کانالهای کاتد آن را اشعه کانالی نامید ویلهلم وین :1898 محاسبه مقدار q/m برای این اشعه و تفاوت زیاد آن با اشعه کاتدی : 1) سنگین تر بودن از الکترون 2) تغییر نوع اشعه با نوع ماده گازی درون لامپ

پروتون q/m = x 10 4 C/g q = + e= x C m= q/q/m= x

نوترون ) جیمز چادویک (1932 جایزه نوبل در 1935 nCBe  139 

مدل اتمی تامسون مدل کیک کشمشی

Radioactivity Radioactivity is the spontaneous emission of radiation from a substance.  X-rays and  -rays are high-energy light.   -particles are a stream of helium nuclei, He 2+.   -particles are a stream of high speed electrons that originate in the nucleus.

, , and  Rays

The nuclear atom Geiger and Rutherford 1909

The  -particle experiment  Most of the mass and all of the positive charge is concentrated in a small region called the nucleus.  There are as many electrons outside the nucleus as there are units of positive charge on the nucleus

Atomic Structure Ernest Rutherford called the tiny core of the atom (contains the protons and neutrons) the “nucleus” The nucleus contains all of the + charge and almost all of the mass of the atom (protons and neutrons) The electrons (-) surround the nucleus and occupy most of the volume of an atom # of electrons = # of protons

Ratherford Experiment

The nuclear atom Rutherford protons 1919 James Chadwick neutrons 1932

Atomic Diameter cm Nuclear diameter cm Nuclear Structure ParticleMassCharge kgamuCoulombs (e) Electron x –1.602 x –1 Proton x x Neutron x Å

Scale of Atoms Useful units:  1 amu (atomic mass unit) = x kg  1 pm (picometer) = 1 x m  1 Å (Angstrom) = 1 x m = 100 pm = 1 x cm  The heaviest atom has a mass of only 4.8 x g and a diameter of only 5 x m. Biggest atom is 240 amu and is 50 Å across. Typical C-C bond length 154 pm (1.54 Å) Molecular models are 1 Å /inch or about 0.4 Å /cm

Isotopes, atomic numbers and mass numbers  To represent a particular atom we use the symbolism: A= mass numberZ = atomic number

Measuring atomic masses

The Periodic table Alkali MetalsAlkaline EarthsTransition MetalsHalogensNoble Gases Lanthanides and Actinides Main Group

Periodic Table

The Periodic Table Read atomic masses. Read the ions formed by main group elements. Read the electron configuration. Learn trends in physical and chemical properties. We will discuss these in detail later.

The Mole Physically counting atoms is impossible. We must be able to relate measured mass to numbers of atoms. –buying nails by the pound. –using atoms by the gram

Avogadro’s number  The mole is an amount of substance that contains the same number of elementary entities as there are carbon-12 atoms in exactly 12 g of carbon-12. N A = x mol -1

Molar Mass The molar mass, M, is the mass of one mole of a substance. M (g/mol 12 C) = A (g/atom 12 C) x N A (atoms 12 C /mol 12 C)

Combining Several Factors in a Calculation—Molar Mass, the Avogadro Constant, Percent Abundance. Potassium-40 is one of the few naturally occurring radioactive isotopes of elements of low atomic number. Its percent natural abundance among K isotopes is 0.012%. How many 40 K atoms do you ingest by drinking one cup of whole milk containing 371 mg of K? Want atoms of 40 K, need atoms of K, Want atoms of K, need moles of K, Want moles of K, need mass and M(K). Example 2-9

Convert strategy to plan m K (mg) x (1g/1000mg)  m K (g) x 1/M K (mol/g)  n K (mol) Convert mass of K(mg K) into moles of K (mol K) Convert moles of K into atoms of 40 K n K (mol) x N A  atoms K x 0.012%  atoms 40 K n K = (371 mg K) x (10 -3 g/mg) x (1 mol K) / (39.10 g K) = 9.49 x mol K atoms 40 K = (9.49 x mol K) x (6.022 x atoms K/mol K) x (1.2 x K/K) = 6.9 x K atoms