Dr. Streit Week 2 Notes
Dr. Streit Week 2 Notes CHEM 1030 - 003
Popular in Fundamentals Chemistry I
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This 4 page Class Notes was uploaded by Rachel Ferrell on Thursday January 28, 2016. The Class Notes belongs to CHEM 1030 - 003 at Auburn University taught by John D Gorden in Fall 2015. Since its upload, it has received 73 views. For similar materials see Fundamentals Chemistry I in Chemistry at Auburn University.
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Date Created: 01/28/16
Rachel Ferrell CHEM 1030 1/26/16 Chapter 2: Atoms and the Periodic Table Atoms First: • Atom= the smallest quantity of matter that still retains property of matter • Element= substance that cant be broken down into 2 or more simpler substances by any means o Ex. Gold, oxygen, helium • John Dalton→said atoms(which make up all matter) are tiny, indivisible particles o He was right in that they are tiny, but atom can be broken down into subatomic particles o The nature (charge), number, and arrangement of subatomic particles determine properties of the atom and whatever thing the atoms make up together Subatomic Particles and Atomic Structure: • Discovery of the Electron: • Radiation=the emission and transmission of energy in the form of waves • Cathode ray tube= is a glass tube with two metal plates inside labeled (+) and (-‐) o When exposed to voltage, (-‐) plate emits a radiation called a cathode ray, which moves toward the (+) plate o Cathode ray is not visible to the eye, but it emits a light when it moves across the tube • Columb’s Law= like charges repel each other, and opposite charges attract each other • Thomson o Used the cathode ray tube to suggest that the cathode rays were actually (-‐) charged particles called electrons (since the rays moved towards the (+) plate) o By varying the electric field and measuring the degree of deflection of the cathode rays, he ???? determined the charge-‐to-‐mass ratio of electrons= 1.76 X ???????? C/g § C= Coulomb= SI unit foe electric charge • Millikan o Determined the charge of an electron by examining the motion of tiny oil drops o Charge of 1 electron= -‐1.6022 X 10 -‐1C o Knowing this charge, he could use Thomson’s charge-‐to-‐mass ratio to determine the mass of an electron ▯▯▯▯▯▯ ▯▯.▯▯▯▯ ▯ ▯▯▯▯▯ ▯ -‐28 o Mass of an electron= ▯▯▯▯▯▯/▯▯▯▯ ▯▯.▯▯ ▯ ▯▯ ▯/▯ = 9.10 X 10g • Radiation • Rontgen o Discovered X-‐Rays (type of radioactive emission) o X-‐rays are not made from charged particles because they were not deflected from electric fields • Becquerel o Discovered radioactivity=spontaneous emission of radiation o Radioactive substances (like uranium) can produce 3 types of radiation: § Alpha(????) Rays= (+) charge, deflect away from positively charged plate § Beta (????) Rays= (-‐) charge, electrons, deflect away from negatively charged plate § Gamma (????) Rays= neutral charge, like X-‐rays because no charge • Nuclear Model of Atom • Rutherford o Before Rutherford, Thomson proposed plum-‐pudding model= electrons are just embedded with the positive protons in the nucleus→not true o Rutherford used ???? particles to prove the structure of the atom using gold foil o Majority of particles penetrated gold foil undeflected o Sometimes, ???? particles bounced back § This happened because sometimes the gold foil bounced off of the nucleus, which is positively charged like the ???? particles § Most of the time though it would hit the electron or electron shell and would go right through it o Proposed nuclear model: § Positive charge is concentrated in the nucleus § The rest is mostly empty space § Nucleus is most of the atoms mass and it is an extremely dense core of an atom § Protons= (+) § Electrons= (-‐) § Concluded that atom was made of a nucleus that accounted for most of its mass but occupied only a tiny amount of its volume • Chadwick o Discovered neutrons= electrically neutral; mass slightly greater than protons Atomic Number, Mass Number, and Isotopes: • All atoms can be identified by number of protons, neutrons • Atomic number= number of protons; defines an element o Since atoms are neutral, this is also number of electrons (-‐) o ▯????????→Z is the atomic number • Mass n▯mber= total number of protons and neutrons o ▯ ????→ A is the mass number o protons + neutrons = mass number • Most elements have more than 2 isotopes= atoms with the same atomic number but different mass numbers (therefore different number of neutrons) o Isotopes of same element→usually have similar chemical properties o Ex. Same types of compounds and similar reactivities Nuclear Stability: • Since the density of an atom is so high, some force is needed to hold the particles together so tightly • Since all protons in a nucleus are (+) charge, they repel each other → repulsion factor • However, the addition of neutrons can add short-‐range attraction between particles to compensate for the repulsion factor • Atomic Stability= Columb repulsion factor – short range attraction o Higher the density of the atom/element→stronger repulsion forces o Therefore, atoms with a higher density need more neutrons to stabilize the atom • Neutron-‐proton ratio o Shows how stable an atom is o Elements with a higher atomic number have a higher ratio (because of their higher density) o Patterns of Stability § More stable nucleus with 2,8,20,50,82,126 protons/neutrons § More stable with even numbers § All atoms with atomic number >83 are radioactive • This means the nucleus is unstable and will spontaneously decay by losing protons and neutrons through ???? radiation Average Atomic Mass: • Atomic mass= mass of an atom in atomic mass units (amu) o 1 amu = 1/12 mass of Carbon-‐12 atom • Average atomic mass= mass listed on the periodic table; represents average mass of naturally occurring mixture of the isotopes o How to calculate average atomic mass for multiple isotopes: § (???????????????????????????????????? ▯▯▯▯▯▯▯ ▯ )(???????????????? ▯▯▯▯▯▯▯ ▯) + (???????????????????????????????????? ▯▯▯▯▯▯▯ ▯ )(???????????????? ▯▯▯▯▯▯▯ ▯ ) = Av. Mass The Periodic Table: • =a chart in which elements with similar chemical and physical properties are grouped together • periods=horizontal rows; increasing atomic number • metals= good conductors of heat/electricity(most known elements are metals) • nonmetals=poor conductors of heat and electricity • metalloids=intermediate properties(fewest number of elements are metalloids) • group= vertical column (also referred to as families) o Group 1A→ Alkali Metals § Li, Na, K, Rb, Cs, Fr o Group 2A→Alkaline Earth Metals § Be, Mg, Ca, Sr, Ba, Ra o Group 6A→Chalcogens § O, S, Se, Te, Po o Group 7A→Halogens § F, Cl, Br, I, At o Group 8A→Noble Gases § He, Ne, Ar, Kr, Xe, Rn o Elements in middle→transition metals The Mole and the Molar Mass: • Mole= the amount of substance that contains as many atoms as there are atoms in 12 grams of Carbon-‐12 • Avagadro’s Number (???? )= 6.▯22 X 10 23 o Similar measurement as 1 dozen= 12 • Ex. Problem: ▯▯ o 30 mol Ca X ▯▯ ▯ ▯▯ ▯▯▯▯▯ ▯▯ = 1.807 X10 atoms Ca ▯ ▯▯▯ o 1.00 X 10 X ▯ ▯▯▯ = 1.66 X 10 mol Ca ▯.▯▯▯ ▯ ▯▯▯▯▯▯▯▯▯ ▯▯ • molar mass= the amount of mass in grams of 1 mol of the substance o mass of 1 mol→same as atomic mass for each element o usually expressed as g/mol o Ex. Problem § 25 g C x = 2.082 mol C ▯▯.▯▯ ▯ ▯ • Interconverting Mass, moles, and number of atoms o Molar mass is a conversion factor from mass to moles, and vice versa o Ex. Problem ▯ ▯▯▯ ▯ ▯.▯▯▯ ▯ ▯▯▯▯▯▯▯▯▯ ▯ 22 § 0.515 g C ▯▯.▯▯ ▯ ▯ x ▯ ▯▯▯ ▯ = 2.58 x 10 atoms C Chapter 3: Quantum Theory and Electronic Structure of Atoms: Units of Energy: • Joule= the SI unit for energy o the amount of energy possessed by a 2 kg mass moving at the speed of 1 meter/second § 1 kg x m s = 1 J o can also be defined as the amount of energy exerted when a force of 1 Newton(N) is applied over the distance of 1 meter § 1 Nxm = 1 J o also is often is expressed in kJ (1 kJ = 1000J) Nature of Light: • electromagnetic spectrum= continuum of radiant energy o visible light is only a small portion • Properties of Waves: o All forms of electromagnetic radiation travel in waves o Characterized by: § Wavelength(????)= distance between identical points on succeeding waves § Frequency (v) = number of waves that pass through a point in 1 second § Amplitude= vertical distance from midline of a wave to the top peak of bottom of a trough 8 8 o Speed of Light(c)= 2.99792458 x 10 m/s OR 3.00 x 10 m/s o Speed, wavelength, and frequency are related in the equation: § C= ???? × ????
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