# Chem. Lecture 7/19

 define accuracy
 accuracy = closest to the actual #; has the smallest error
 define precision
 precision = how consistent a set of measurements is
 equation for calculating error
 error = measured – accepted answer
 equation for percent error
 percent error =           error                              ___________   x 100                                accepted
 equation for converting Celsius to Kelvin
 Celsius → Kelvin   Kelvin = ºC + 273.15
 equation for converting Kelvin to Celsius
 Kelvin → Celsius   Celsius = ºKelvin – 273.15
 equation for converting Celsius to Fahrenheit
 Celsius → Fahrenheit   Fahrenheit = 9/5 x ºC + 32º
 equation for converting Fahrenheit to Celsius
 Fahrenheit → Celsius   Celsius = 5/9 (ºF – 32)
 What was Thales theory about matter?
 Thales (ancient Greek, “1st” to explore this concept) thought that everything was made up of water; that water was the basic element.
 What was Empedocoles theory about matter?
 Empedocoles agreed with Thales that water was an element, but believed it was one of 4 – earth, air, fire, and water (like the Last Airbender…haha). He believed that all things were comprised of combinations of these elements, that were effected by the forces of harmony and discord.
 What was Democratus’ theory about matter?
 Democratus, by observing grains of sand, theorized that matter is made up of tiny, indestructable particles, but that there is a minimum size (the atom) and that it cannot get any smaller
 What was Socrates’ theory about matter?
 Socrates agreed with Democratus that everything is made up of small, indestructable particles, but disagreed about the minimum size. He believed that there is no minimum size, that matter can continuously be broken down; the CONTINUOUS THEORY. This became the norm until after the “Dark Ages of Chem.”, and scientists began to reavaluate Democratus’ ATOM THEORY.
 Who brought back Democratus’ atom particle concept, and what was his theory?
 Boyle (English) in the 1660s theorized that gas made up of little particles with space in between them that could be pressed together. Essentially Boyle was the 1st to re-examine Democratus’ concept of an atom/particle after years of the Continuous Theory being the accepted scientific norm.
 Bernoulli (1730s, Italian) theorized that pressure is caused by particle/atom collisions
 What theory did Lavoisier disprove, and how did he do it?
 Before Lavoisier, many believed in the existance of “phlogiston”, an element of sorts that was present in everything, and was released when things burned. This theory was “confirmed” by comparing the weight of a block of metal to the weight of that same metal sample after being burned; in such experiments, the burned sample (“calx”) would weigh more – thus, they believed it had actually changed forms. Lavoisier, suspicious of this theory, revised the experiment. He covered both the samples with glass hoods before weighing them, and found that they ended up weighing the same. Therefore, the LAW OF THE CONSERVATION OF MASS was developed – matter is neither created nor destroyed.
 What was Dalton’s 1st law? What is accurate and inaccurate?
 Dalton’s 1st Law   1.) Each element is made from tiny, indestructable atoms (similar to Democratus!)   However, the truth is, atoms are NOT indestructable; they can in fact be destroyed. Also, an atom is not the smallest particle; smaller particles exist (protons, electrons, etc.)
 What is Dalton’s 2nd law? What is accurate and inaccurate?
 Dalton’s 2nd Law   2.) All atoms of an element are identicle.   FALSE! Not all atoms are identicle; isotopes exist.
 What is Dalton’s 3rd Law? What is accurate and inaccurate?
 Dalton’s 3rd Law 3.) Elements combine in fixed ratios to form compounds This is TRUE 🙂
 What is Dalton’s 4th Law? What is accurate and inaccurate?
 Dalton’s 4th Law   4.) In reactions, atoms are just rearranged, not created or destroyed.   This is partially true; for the most part, atoms cannot be created or destroyed….except in radioactivity and nuclear reactions
 Who experimented with the “cathode ray tube”?
 J.J Thompson
 Who discovered the electron?
 J.J Thomas discovered the electron
 What did the cathode ray tube experiment prove?
 J.J Thompson’s cathode ray tube experiment proved that negatively charged particles gravitate toward positively charged cathodes – and because the beam of light created in the tube was made up of particles/ atoms, he determined that all atoms have some negative charge (electrons!)
 What was Millikan’s model of the atom?
 Millikan (American) called his model of the atom the “PLUM PUDDING” model, with little “raisins” (electrons) randomly distributed in a bunch of “positive stuff” within the atom
 What did Rutherford want to know and how did he experiment to find an answer? What did he discover?
 Rutherford (New Zealander) wanted to know how big atoms are. To determine this, he devised the GOLD FOIL EXPERIMENT.   Flattened out a sheet of gold, reeeeally thin. Shot alpha particles (+ charge) of Helium at the sheet of gold, which had a curved screen behind it. The alpha particles produced light, which he expected to shine directly on the spot of the screen that it was aimed at. Instead, it deflected to cover almost the entire screen, and some of it reflected back.   The result of this experiment was the discovery that atoms have small, dense, positive nucleuii (nucleus) and are mostly empty space
 What did Rutherford’s model of the atom look like?
 Rutherford’s model of the atom   Small, dense, positively charged nucleus in the center – protons only in the nucleus   Outside of nucleus there is mostly empty space, with randomly scattered electrons (negative charge)
 What is a neutron’s charge?
 A neutron is neutral; it has a charge of 0.
 What is a proton’s charge?
 A proton has a positive charge; +1.
 What is an electron’s charge?
 An electron has a negative charge; -1.
 Who discovered the neutron?
 Where are protons located?
 Protons (positive charge) are located in the nucleus
 What does the atomic # of an element tell you?
 The atomic # of an element tells you the NUMBER OF PROTONS
 What does the mass # of an element on the periodic table tell you?
 The mass # of an element on the periodic table tells you the number of protons + neutrons within 1 atom of that element; the mass. mass number = # of protons + # of neutrons So, knowing the # of protons from the atomic #, the number of neutrons can be deduced. And because the number of electrons is always equal to the number of protons, it is easy to calculate the quantities of all 3 within 1 atom.
 The number of electrons is always equal to….
 The number of electrons always = to the number of protons
 The number of protons is always equal to…..
 The number of protons is always = to the number of electrons
 Define isotopes
 Isotopes are atoms with the same number of protons, but different numbers of neutrons. In other words, they have the same atomic # but different mass #s than you would find on the periodic table.
 What is atomic mass and how is it calculated?
 Average Atomic Mass is the sum of the abudance x isotopes. It is what is used to create the mass #s used on the periodic table. For example, 75% of Cl. atoms in the world have a mass of 35, and 25% have a mass of 37. (.75 x 35) + (.25 x 37) = 35.5 the atomic mass of Cl on the periodic table
 Define ion
 ion – an atom that has gained or lost 1 or more electrons
 Define cation
 Cation – A positive ion; it has lost electrons (lost some negative charge, therefore becoming positive)
 Define anions
 Anions – negative ions; gained electrons
 Compare atoms vs. molecules
 Atoms – smallest particle of an element that exists ; still has chem. properties of that element. ; Molecule – smallest particle of a compound that exists and still has chemical properties of that compound. Consists of more than 1 atom bonded together
 What happens to the protons and electrons of an atom when neutral?
 When neutral, atoms have equal numbers of protons and electrons
 What is a diatomic element?
 A diatomic element has more than 1 atom of the same type of element bonded together (therefore it is still an element; if they were different it would be a compound.)
 What are the 7 diatomic elements?
 Dr. Br I N Cl H O F ; Br = Bromine I = Iodine N = Nitrogen Cl = Chlorine H = Hydrogen O = oxygen F = Fluorine
 Who was the 1st to organize a periodic table of the elements, and how was it organized?
 Mendeleev was the 1st to attempt to organize a periodic table. He organized it by mass (the proton hadn’t been discovered yet.)
 Who organized the periodic table as it appears today?
 Mosely reorganized Mendeleev’s periodic table to account for the discovery of the protons. It is organized by atomic #.
 The horizontal rows on the periodic table are called….
 horizontal rows = periods
 The vertical columns on the periodic table are called…..
 vertical columns = groups
 What are the elements in group 1 on the periodic table called?
 Group 1 = Alkali metals
 What are the elements in group 2 of the periodic table called?
 Group 2 = Alkaline earth metals
 What are the elements in group 17 of the periodic table called?
 group 17 = Halogens (they make salts)
 What are the elements in group 18 of the periodic table called?
 group 18 = Noble gases ; (hardly interact with other elements; they’re too “noble” for the “commoners”)
 The left side of the periodic table (to the left of the little ‘staircase’) contains…
 Left side of the periodic table = metals
 The elements on the right side of the periodic table (to the right of the little “staircase”) are….
 The elements on the right side are non-metals
 The elements that lie upon the staircase on the periodic table are called….
 On the staircase = metalloids
 Groups 3 – 12 on the periodic table are….
 Groups 3-12 are the Transition Metals
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