Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Topic 3 The Atom Section 1 Early Theories of the Atom There are two Views of Matter The Continuous view: matter can be broken down indefinitely Ex: How many times can a piece of chalk be split in half? ½ to ¼ Indefinitely? to 1/8th to 1/16th etc. There are two Views of Matter But what if there is a smallest part that can’t be divided further? The Discontinuous view: Matter can be broken down into simple building blocks. (an indivisible atomos)? Video atoms the building blocks Draw a microscopic view of a speck of chalk from the continuous perspective Draw a microscopic view of a speck of chalk from the discontinuous perspective 3.1 Atomic Theory If no one’s ever seen an atom, how do we know it exists? It’s a “theory” Theory: a mental picture (or concept) created to help understand a given phenomenon. History of atomic theory Democritus (400bc)– an ancient Greek philosopher – – – – Called them “atomos” Greek for “indivisible” His was the “philosophical atom” Philosophers are thinkers He used reason, not evidence. Check out the Democritus clip 4 min Dalton – an English school teacher (1800’s) His was the Ultimate particle model of the atom Next is John He was the first to use symbols to represent atoms Draw a molecule using the Dalton symbols for atoms from below John Dalton (1800’s) Ultimate particle model If all matter is made of indivisible particles (atoms) how can we answer the following? >What makes atoms of an element the same? Atoms of an element have same weight. (ex: all C atoms weigh 12) John Dalton (1800’s) Ultimate particle model If all matter is made of indivisible particles (atoms) how can we answer the following? >How do the atoms of elements differ? (eg. H vs He?) Atoms of different elements have different weights. John Dalton (1800’s) Ultimate particle model If all matter is made of indivisible particles (atoms) how can we answer the following? >How do different compounds form? Atoms combine in simple whole number ratios. John Dalton (1800’s) Ultimate particle model If all matter is made of indivisible particles (atoms) how can we answer the following? >What happens to the atoms during a chemical reaction? atoms separate and recombine in a different arrangement John Dalton (1800’s) Ultimate particle model What evidence do we have to support this theory? Law of conservation of mass Dalton atomic theory 2 min video How could weight (mass) be used to prove that atoms exist? How should the mass of chemicals change during reactions? video LaVoisier – 1600’s heated Tin in closed container – Mass remain unchanged after heating Interpretation?: same old atoms rearranged into a new formula; new ratios, but still same mass Particle diagram Regents question: Water reacts according to this equation: 2H2 + O2 2 H2O –Key: Reactants H= –O = Products Notice Leftover oxygen molecule Draw the products consistent with the law of conservation of mass Question: If 4 grams of hydrogen reacts with 32 grams of oxygen What mass of water is formed? 36 grams Why? Mass must be conserved! How can the composition of a compound be used to prove that atoms exist? Will atoms always combine in the same ratio to form a compound? Law of definite composition (constant composition) Atoms of a substance always combine in the same proportions by mass Ex: water 11 % H to 89% O always If water is H2O, how can this be explained? 11:88? H weighs1 O weighs16 What is a 2:16 ratio? H weighs1 To consider: How does the law of conservation of mass provide evidence for the theory of the atom? How does the atomic theory explain the law of definite composition (law of definite proportions) Subatomic particles Cathode ray tube -CRT video Electron JJ Thomson (1900) Cathode ray tube “CRT” Streams of particles from the negative “cathode” Particles were smaller than any known atom Came from any element tested. Where did they come from? Inside the atom! He Called them electrons Old time TV, computer monitor Thomson’s model of the atom We now know that the atom contains tiny negative particles: “electrons” We also know that the atom is neutral (its negative and positive balance each other. Draw a picture of Thomson's atom - A positive sphere with negative charge electrons embedded in it: Draw your own model here: A positive atom with tiny negative electrons embedded in it. “Plum Pudding” atom model Negative Electrons dispersed like raisins, in a positive matrix (pudding) Separating radiation particles Radiation can be of three kinds of particles: Alpha particles : mass of 4 with +2 charge Beta particles: mass of an electron (almost 0) with -1 charge Gamma rays: Like x-rays. No mass or Charge (neutral) Separating radiation particles How do you know that beta particles are negative? (hint: which way are they deflected?) Why aren’t alpha particles deflected as much as betas? (How do their masses compare?) Rutherford gold foil experiment He Shot alpha (+) radiation at thin gold foil 2 min Rutherford video Results: – Most alpha particles passed undeflected – Few alphas were deflected from original path Results of foil experiment if Plum Pudding model had been correct. What Actually Happened video Rutherford empty space atom model Interpretation: Atom is mostly empty space (didn’t stop most alphas) Atoms have a small dense positive nucleus (a few +’s were deflected) Electrons orbit around outside nucleus “like planets” Subatomic Particles Protons: Ernst Rutherford (1870’s) found positive (anode) rays in the Cathode Ray Tube Neutrons H= atomic #1 (has 1 proton) … but weighs 1 He = atomic #2 (has 2 protons) ….but weighs 4 How can we explain this difference? 0 neutrons 2 neutrons Neutrons: Chadwick (1930’s) found neutral particle in radiation. Explains the added weight in atoms Learning check: 1. Which model of the atom was the simplest? What were its characteristics? 2. How did Thomson surmise that electrons were subatomic particles? How did he know they were negatively charged? 3. Why did most of the alpha particles pass through the gold foil undeflected? Why did a few get deflected? 4. Why can’t two atoms pass through one another if there’s so much empty space? (Hint: what do like charges do when near each other?) 67 John Dalton was an English scientist who proposed that atoms were hard, indivisible spheres. In the modern model, the atom has a different internal structure. a Identify one experiment that led scientists to develop the modern model of the atom. [1] b Describe this experiment. [1] c State one conclusion about the internal structure of the atom, based on this experiment. [1] Section 3.2a The Charge Cloud Model The Charge Cloud Model video The atom consists of a Positive Nucleus with… Protons (+1 charge mass =1 amu) with neutrons (0 charge, mass = 1 amu) and Electrons (-1 charge, 0 mass) circling rapidly outside The “nuclear charge” Identifies the element : a.k.a. Atomic number = the number of protons: All atoms of an element have the same number of protons Boron has a +5 nuclear charge Boron is atomic number 5 The Mass Number – is the weight of the nucleus = # protons + # neutrons (electrons = 0 mass so they aren’t counted) The boron-10 nucleus has a mass of 10 5 protons + 5 neutrons The Mass Number – is the weight of the nucleus = # protons + # neutrons (electrons = 0 mass so they aren’t counted) C-12: Carbon atom with 6 p+ and 6 no is the mass standard = 12.000 atomic mass units Mass number is NOT on the periodic table (the table # is an average) Isotopes • Are atoms of the same element (same atomic number) but different mass number • Carbon -12 (12C) has 6 p and 6 n • Carbon -14 (14C) has 6 p and 8 n Isotopes Isotopes have the same nuclear charge (protons) but different a different number of neutrons Representing isotopes Write the name of the isotope, and the mass number in hyphen notation ex: Sodium-23 Is the sodium with 11 protons and 12 neutrons so it weighs 23 amu’s Representing isotopes The symbol shows the mass number and atomic number in nuclear symbol form Top: mass number 23 11 Na Bottom: Atomic number Isotopes? Which of the following represent isotopes of the same element? Which element? Each has a different mass # due to a different Neutron # 234 92 X 234 93 X 235 92 X 238 92 –Neptunium -234 Atomic # 92 all atoms of Uranium X Counting Protons, Neutrons, and Electrons Protons: Atomic Number (from periodic table) Electrons: If it’s an “atom”, the protons and electrons must be the SAME so that it is has a net charge of zero (equal numbers of + and -) (“ions” have diff. # of protons and electrons) Neutrons: Mass Number (not on table) minus the number of protons (mass number is protons and neutrons because the mass of electrons is negligible) = 18 n0 –Can you explain this? What gives atoms their characteristic properties? +4 8u +2 nucleus 5u nucleus +3 6u +4 9u nucleus +2 nucleus 6u nucleus +2 5u nucleus +3 8u nucleus +3 7u nucleus +4 nucleus 7u Its not how much they weigh. +4 7u nucleus +2 4u nucleus +3 6u nucleus –Can you explain this? What gives atoms their characteristic properties? 8u 9u 5u 6u 6u 5u 8u 7u 7u 7u 4u The nuclear charge (the number of protons) 6u Learning Check – Counting Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms. 12C 6 - ________ 13C 6 14C 6 6 #p+ _______ _______ _______ #no _______ _______ _______ #e- _______ _______ _______ Learning Check An atom has 14 protons and 20 neutrons. A. Its atomic number is 1) 14 2) 16 3) 34 B. Its mass number is 1) 14 2) 16 3) 34 C. The element is 1) Si 2) Ca 3) Se D. Another isotope of this element is 1) 34X 2) 34X 3) 36X 16 14 14 3.2b AVERAGE ATOMIC MASS 11B 10B Because of the existence of isotopes, the mass of a collection of atoms has an average value. Boron is 20% 10B and 80% 11B. 11B is 80 out of 100 atoms of Boron. 10B is only 20 / 100 10 11 11 11 11 11 10 11 11 11 3.2b AVERAGE ATOMIC MASS 11B 10B Calculate the average mass of these 10 atoms: For boron atomic weight = 20% (10 u) + 80% (11 u) = = 20/100 (10) + 80/100 (11) = 2.0 + 8.8 10 11 Notice that the atomic mass (average) comes out to be closer to the isotope of highest abundance (80% of the way between 10 and 11) = 10.8 u 11 11 11 11 10 11 11 11 11B 3.2b AVERAGE ATOMIC MASS 10B “Formula” Atomic mass = ( % abundance ) (mass) 100 Do you recognize the summation symbol? Try some: calculate the atomic mass 1) 6Li = 7.5% abundant and 7Li = 92.5% masses: Li – 6 = 6.015, Li-7 = 7.016 2) 28Si (27.98) = 92.23% 29Si (28.98) = 4.67%, 30Si (29.97) = 3.10% 3.3a The Periodic Table Dmitri Mendeleev (1834 - 1907) Dmitri Mendeleev was a Russian chemist, who, in 1870, looked for a way to organize the elements. He wrote the known properties of elements on blank playing cards. Explosive gas 1 H He placed element cards in order of increasing mass and looked for patterns. Inert gas 4 Notice the formulas of the compounds formed with F and O. He HF H2O Active metal 7 Li LiF Li2O Active metal 9 semimetal 11 Be B BeF2 BeO BF3 B2O3 nonmetal 12 unreactive gas 14 Explosive gas 16 active gas 18 Inert gas 20 C N O F Ne CF4 CO2 NF3 N2O3 OF2 O2 F2 F2O Active metal 23 Active metal 24 metal 27 semimetal 28 nonmetal 31 nonmetal 32 Active gas 35 Inert gas 40 Na Mg Al Si P S Cl Ar MgF2 MgO AlF3 Al2O3 SiF4 SiO2 PF3 P2O3 SF2 SO ClF Cl2O NaF Na2O Active metal 39 After fluorine, he noticed that sodium was similar to lithium, and the pattern repeated. K After chlorine, he noticed that potassium was similar to sodium, etc. KF K2O Hydrogen starts the table since it’s the smallest, and the noble gases, once discovered took their place at the end of the line. TED Link Notice how elements line up into columns with similar properties? Also, notice how the properties repeat each row? That’s “periodic”! Mendeleev’s Table –Video clip Organized first table based on increasing mass (but…. allowed elements to group by similar properties) Found that properties of elements repeated periodically (in a regular pattern) Put elements in vertical groups with similar properties Left spaces for elements that weren’t yet discovered –Eka-silicon - aka germanium Mass dilemma: mass sometimes decreases Henry Moseley (1913) Did X-ray studies Found that the positive nuclear charge increased by one for each element called it “atomic number” Modern Periodic Law: “Properties of the elements are periodic functions of their atomic numbers” Ie. Properties of atoms depend on number of protons Mass dilemma: mass sometimes decreases Modern table: Organized into groups (vertical columns) of elements with similar properties have same # of outer shell electrons Organized into periods (horizontal rows) – properties change systematically from metals to nonmetals to inert (unreactive) gases Properties are similar Group 1 Group 2 Etc. Period 1 Period 2 Period 3 Etc. Metals Properties change systematically To Non- Metals Regions of the Periodic Table Nonmetals Metals Noble gases are a special group of stable unreactive elements on the extreme right Noble Gases Metals on the left side and middle Non-Metals on the right side H Nonmetals Metals Noble Gases Hydrogen is actually a nonmetal, but starts the table since it is the smallest. Its is more at home on the right side of the table with the other non-metals H Nonmetals Metals Si Ge As Sb Te Po Noble Gases Metalloids are elements that lie along the border. They can behave like either metals or nonmetals depending on how you find them. B Types of elements Metals Solids (one liquid) Shiny Luster Malleable Ductile Good conductors of Heat and electricity Nonmetals Solids and gases (one liquid) Metalloids Noble gases Solids Gases Semiconductors Properties of both M & NM Inert or Unreactive Dull Luster Brittle Poor conductors Good insulators video Learning check: 1. State the modern periodic law: “Properties of elements are a periodic function of …. 2. What are “groups” on the periodic table? How are the members related to one another? 3. What are the periods on the periodic table? how do the properties change across a period (what pattern)? 4. What are the 3 + 1 types of elements? Where is each located on the table? How do their properties differ? 3.3b Families of the Periodic Table Nonmetals H Noble Gases Alkali metals Alkaline earth metals Metals Group 1 and 2 (S block) alkali metals and alkaline earth metals –2 video –clips Group 1 Alkali Metals and 2 Alkaline earth metals –Both groups very reactive –Found in nature only in compounds –Obtained from breakdown of salts Families of the Periodic Table Nonmetals H Transitional metals Rare earth elements Noble Gases Alkali metals Alkaline earth metals Metals Transitional metals Transition Element video Actinide video Lanthide video –Rare Earth metals Transitional Metals - d block • • • • • • Group 3 to 12 Less reactive than s-block metals Generally similar properties Many form colored ions Some found in elemental state in nature (ex Au) Transition from group 2 to group 13 • Includes rare earth elements of the f block Found in certain rare minerals Group 13 to 16 Nonmetals –Video –clip semimetals –Video –clip poor metals Groups 13 to 16 • Nonmetals at top change to metals at bottom • Properties change going down the groups • Nonmetals are gases and brittle solids • Reactivity increases toward oxygen • “poor” Metals are fairly unreactive • Aluminum, tin, lead Families of the Periodic Table Nonmetals H Transitional metals Rare earth elements Noble Gases Alkali metals Alkaline earth metals Metals Metaloids –Video –clip Metaloids (Semimetals) • Along stepped line • B, Si, Ge, As, Sb, Te, Po • Properties of both metals and nonmetals • Ex: computer “semiconductors” made of silicon Families of the Periodic Table Nonmetals H Rare earth elements Noble Gases Transitional metals Halogens Alkali metals Alkaline earth metals Metals Group 17 Halogens –Video –clip Group 17: The Halogens ( “salt makers” ) F, Cl, Br, I • Highly reactive nonmetals • Found in nature only in compounds • F gas - most active nonmetal (reactive) • Gas to liquid to solid –due to increasing intermolecular (sticky) forces Group 18 Noble gases Video clip Group 18: The Noble (Inert) Gases He, Ne, Ar, Kr, Xe, Rn • “Neon” signs • Very Unreactive because they have full electron shells Learning check: 1. What families of elements are so reactive that they are only found in nature combined in compounds? 2. Where are the transitional elements located? What kind of elements are they? Other traits? 3. Which groups on the table contain both metals and nonmetals? Explain 4. Which halogen is most reactive? What trend occurs in melting and boiling points for elements in group 17? Why does this trend occur? 5. List the 7 semimetals (metalloids): Why are they named as such? 6. What elements exist as diatomic molecules when in their pure, uncombined state? 6 An element that is malleable and a good conductor of heat and electricity could have an atomic number of (1) 16 (2) 18 (3) 29 (4) 35 –Hint: It’s a metal 3 In which list are the elements arranged in order of increasing atomic mass? (1) Cl, Ar, K (2) Fe, Co, Ni (3) Te, I, Xe (4) F, Ne, Na –Hint: mass usually increases left to right and top to bottom –(4) But there are at least 3 exceptions! 37 Which list of elements contains two metalloids? (1) Si, Ge, Po, Pb (2) As, Bi, Br, Kr (3) Si, P, S, Cl (4) Po, Sb, I, Xe –Tricky! Along the stepped line, doesn’t include Al or At In the 1920s, paint used to inscribe the numbers on watch dials was composed of a luminescent (glow-in-the-dark) mixture. The powdered-paint base was a mixture of radium salts and zinc sulfide. As the paint was mixed, the powdered base became airborne and drifted throughout the workroom causing the contents of the workroom, including the painters’ clothes and bodies, to glow in the dark. The paint is luminescent because radiation from the radium salts strikes a scintillator. A scintillator is a material that emits visible light in response to ionizing radiation. In watch dial paint, zinc sulfide acts as the scintillator. Radium present in the radium salts decomposes spontaneously, emitting alpha particles. These particles can cause damage to the body when they enter human tissue. Alpha particles are especially harmful to the blood, liver, lungs, and spleen because they can alter genetic information in the cells. Radium can be deposited in the bones because it substitutes for calcium. 72 Why does radium substitute for calcium in bones? [1] –Need a hint? Where is Ra located relative to calcium on the per. Table?