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W3+4: Chemical Principles (9/9)

by: Olivia Lange

W3+4: Chemical Principles (9/9) sch 100 01

Marketplace > Seton Hill University > Chemistry > sch 100 01 > W3 4 Chemical Principles 9 9
Olivia Lange
Seton Hill University

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week 3's notes (only one class occurred) and week 4's notes (pre-exam notes)
Chemical Principles
Professor Flowers
Class Notes
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This 6 page Class Notes was uploaded by Olivia Lange on Monday October 3, 2016. The Class Notes belongs to sch 100 01 at Seton Hill University taught by Professor Flowers in Fall 2016. Since its upload, it has received 6 views. For similar materials see Chemical Principles in Chemistry at Seton Hill University.

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Date Created: 10/03/16
2.1 Atomic Theory ● The smallest particle that an element can be divided into and still be identifiable  is an atom. From the Greek word atomos, meaning “indivisible”. ● Chemistry is founded on four assumptions which together make up Atomic  Theory: ○ All matter is composed of atoms. ○ The atoms of a given element differ from the atoms of all other  elements. ○ Chemical compounds consist of atoms combined in specific ratios. Only whole atoms can combine. ○ Chemical reactions change only the way atoms are combined in  compounds. ● Atoms are composed of tiny subatomic particles. ○ Protons carry a positive electrical charge. ○ Neutrons have a mass similar to that of a proton, but are  electrically neutral. ○ Electrons have a mass that is only 1/1836 that of a proton and  carry a negative electrical charge ■ Electrons are so much lighter than protons and  neutrons that their mass is usually ignored. ● The masses of atoms and subatomic particles are expressed on a relative mass  scale. ● The basis for the scale is an atom of carbon that contains 6 protons and 6  neurons. This carbon atom is assigned a mass of exactly 12 atomic mass units (amu),  or daltons. ● The protons and neutrons are packed closely together in a dense core called the  nucleus. ● Electrons move about rapidly through a large volume of space surrounding the  nucleus. ● Page 44 visual ● The structure of the atom is determined by interplay of different forces. ● Opposite electrical charges attract each other, like charges repel each other. ● Protons and neutrons in the nucleus are held together by the nuclear strong  force. ○ Electrons repel eachother, protons repel eachother, protons and  electrons attract e/o 2.2 Elements and Atomic Number ● Atomic Number (Z): ○ Number of protons in atom of a given element ○ All atoms of a particular element have the same number of  protons in the nucleus ● Atoms are neutral (in general) ○ The number of positively charged protons and the number of  negatively charged electrons are the same in each atom. ● Mass Number (Atomic Mass) (A): ○  is the sum of the protons and neutrons in an atom. Worked Examples: ● 1.) Phosphorous has atomic number Z= 15 Mass Number A = 31 ● Find protons...15 neutrons...31­15=16 electrons….15 ● 2.) New atom has 28 protons and Mass Number A = 60 ● Fine electrons….28 Neutrons….60­28= 32  x….look for #28 atomic number on  periodic table...x=Nickel 2.2 Elements and Atomic Number continued... ● Isotopes are atoms with identical atomic numbers but different mass numbers. ● Protium, deuterium, and tritium are three isotopes of hydrogen. ● A specific isotope is represented by showing its mass number (A) as a  superscript and its atomic number (Z) as a subscript in front of the atomic symbol. ● The isotopes of most elements do not have given/distinct names. ● The mass number (A) is given after the name of the element. ● The isotope used in nuclear reactors is usually referred to as uranium­235, or U­ 235. ● Most naturally­occurring elements are mixtures of isotopes. 2.3 ● Atomic weight is the weighted average mass of an element’s atoms. ○ The individual masses of the naturally occurring isotopes and the  percentage of each must be known. ○ Atomic weight is calculated as the sum of the masses of the  individual isotopes for that element. ○ Atomic weight= E [(greek sigma/isotope abundance) x (isotope  mass)] ○ The greek symbol E (sigma) indicates the summing of terms. Worked Example 2.3 Gallium:  Ga­69 occurs 60.4% of time, mass is 68.927 amu Ga­71 occurs 39.6% of time, mass is 70.9248 amu (.604)(68.927)+(.396)(70.9248)= 41.6319+28.0862= 69.7181 Use 3 Sig Figs = 69.7 amu Isotope Element X: (top)194/(bottom)78X Find the...atomic number, mass number, number of protons, electrons, neutrons Atomic #: Z= 78 (Atomic Mass)A= 194  p= 78 n= 194­78=116 e­ =78 Go to #78 on periodic table…. Element X= Pt, Platinum 2.4 The Periodic Table ● Only 10 elements ● 1829­ Johann Do:bereiner ● Observed several triads ● 1869­ Dimitri Mendeleev ○ Organized elements by mass, then into columns based on  chemical behavior ○ Produced the forerunner of the periodic table ● Boxes for atomic mass, symbol, atomic mass  ● The vertical groups on the periodic table have similar chemical properties and  are divided into categories ● Main groups ○ Two groups on far left (1­2) ○ Six on far right (13­18) ● Transition Metal Groups ○ Elements in these groups are numbered 3 through 12. ● Inner Transition Metals ● Lanthanides ○ The 14 elements following lanthanum. ● Actinides ○ The 14 elements following actinium. Be sure to know where these are grouped on the Table: ­ Metals ­ Nonmetals ­ Metalloids ● Elements in a given group have similar chemical properties ● Chlorine, bromine, iodine, and other elements in group 7A behave similarly ● All seven Periods do not contain the same # of elements in them: ○ First has 2 elements ○ Second and third ­ 8 elements ○ Fourth and fifth ­ 18 elements ○ Sixth and seventh ­ 32 elements ○ The 14 Lanthanides and 14 Actinides are pulled out and shown  below the others. ● Groups are numbered in two ways, both shown (in Figure 2.2 in the book) ○ Main group elements ­ 1A through 8A ○ Transition metal elements ­ 1B through 8B ○ All 18 groups are numbered sequentially from 1 to 18 ○ The inner transition metal elements are not numbered. 2.5 Some Characteristics of Different Groups ● Graph of atomic radius versus atomic number ● Shows a periodic rise­and­fall pattern ● Maxima occur for group 1A elements ● Minima occur for group 7A elements ● More shells = larger radius Grouped elements show remarkable similarities, both physical and chemical properties. ● Group 1A ­ Alkali Metals (Alkali means basic in terms of Ph) ○ Lithium (Li), sodium (Na), Potassium (K), Rubidium (Rb), Cesium  (Cs), and francium (Fr) ○ Shiny soft metals with low melting points ○ React w/ water to form products that are highly alkaline ○ High reactivity, it is never found pure in nature ● Different metals can change a flame’s color (ex: fireworks) ● Group 2A ­ Alkaline Earth Metals ○ Beryllium (Ba), Magnesium (Mg), Calcium (Ca), Strontium (Sr),  Barium (Ba), & Radium (Ra) ○ Lustrous silvery metals ○ Less reactive than neighbor 1A ○ Never found in nature in pure state Non­metals/right side of table:  ● Group 7A ­ Halogens ○ Fluorine F Chlorine Cl Bromine Br Iodine I and Astatine At ○ Colorful and corrosive non­metals ○ Found in nature only in combination with other elements ■ Sodium in table salt (NaCl) ○ Group name, halogen, is taken from the Greek word “hals”,  meaning salt ● Group 8A ­ Noble Gases ○ Helium H Neon Ne Argon Ar Krypton Kr Xenon Xe and Radon Rn ○ Colorless gases ○ Labeled “noble” gases because of lack of chemical reactivity ○ Helium, neon, and argon don’t combine with any other elements ○ Krypton and xenon combine with very few 2.6 Electronic Structure of Atoms ● Properties of the elements are determined by the arrangement of electrons in  their atoms ● Understood using quantum mechanical model ● Developed by Erwin Schro:dinger ● Quantum Mechanical Model: Talk about Electrons: ○ Electrons have particle­like and wave­like properties ○ Quantized = categorized ○ Behavior of electrons can be described using an equation called a wave function. ○ Not perfectly free to move, restricted to certain energy values, or  quantized. ● A ramp changes in height continuously so it is not quantized. ● Stairs are quantized because of their fixed amount in height change. ● A ramp is not quantized, but stairs are. This analogy is to help you focused on  the fact that each “level up” will be it’s own movement and the same length of the last  one. ● Energy values available to electrons in an atom can change only in steps ● Wave functions also provide an electron with an “address” within an atom,  composed of shell, subshell, and orbital. ● Electrons in an atom are grouped around the nucleus into shells ● Fill inner shells first! ● The farther a shell is from the nucleus: ○ The larger it is ○ The more electrons it can hold ○ The higher the energies of those electrons ● First shell (closest to center, the nucleus) can hold a maximum of 2 electrons ● Second shell holds max. of 8 ● Third shell holds max. of 18 Subshells ● Within the shells, electrons are further grouped into subshells ○ Four different types ○ Identified as s, p, d, and f in order of increasing energy ● First shell       ­ s ● Second shell  ­ s and p ● Third shell      ­ s, p, and d ● Fourth shell   ­ s, p, d, and f ● The number of subshells is equal to the shell number ● A specific subshell is symbolized by writing the number of the shell, followed by  subshell’s letter (example: 1s, 2p, 3s) Orbitals ● Within each subshell, electrons are grouped into orbitals, regions of space within  an atom where the specific electrons are most likely to be found. ● An s subshell has 1 orbital, a p has 3 orbitals, a d has 5, an f has 7 orbitals. ● Each orbital holds two electrons which differ in a property known as spin. Shell # 1 2 3 4 Subshell designation s s,p s,p,d s,p,d,f # of orbitals 1 1,3 1,3,5 1,3,5,7 ● Different orbitals have different shapes and orientations. Orbitals in s subshells  are spherical, while orbitals in p subshells are roughly dumbbell shaped. ● Any orbital can hold a maximum of 2 electrons with opposite spin. ● First shell has one 1s orbital and holds 2 electrons. ● Second shell holds 8 electrons ○ 2 in a 2s orbital ○ 6 in three 2p orbitals ● Third shell holds 18 electrons ○ 2 in a 3s orb ○ 6 in 3 3p orbs ○ 10 in 5 3d orbs ● Fourth shell holds 32 electrons ○ 2 in a 4s orbitals ○ 6 in 3 4p orbs ○ 10 in 5 4d orbs ○ 14 in 7 4f orbs ● See table 2.2 in your book for overall electron distribution. Worked Example: How many electrons? 1st and 2nd shells filled (go to 3rd shell) has 4 electrons in third shell. It’s  Silicon with 14 electrons.


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