#### Transcript Chapter 3 - Atoms: the building blocks of matter

Chapter 3 - Atoms: the building blocks of matter Taken from Modern Chemistry written by Davis, Metcalfe, Williams & Castka Section 3.1 – The Atom: from philosophical idea to scientific theory HW – Notes on section 3.1 pgs 65-67 Objectives Students will be able to : • Explain the laws of Conservation of mass Definite proportion Multiple proportion • Summarize the 5 essential points of Dalton’s atomic theory • Explain the relationship between the 5 essential points and the above mentioned laws Section 3.1 – The Atom: from philosophical idea to scientific theory Foundations of Atomic Theory As early as 400 B.C.E. particle theory of matter was supported – the particle was called an atom based on the Greek for “indivisible”. Supported by Democritus Aristotle did not believe this theory and his opinion lasted for 2 000 years. Felt all matter was continuous. Section 3.1 – The Atom: from philosophical idea to scientific theory Foundations of Atomic Theory (continued) By 1700s accepted idea that an element could not be broken down further. Back The transformation of substance or substances into one or more new substances was known as a chemical reaction. By the 1790s there was a new emphasis on quantitative analysis of chemical reactions Section 3.1 – The Atom: from philosophical idea to scientific theory Foundations of Atomic Theory (continued) This work lead to the discovery of several laws. . . Law of Conservation of matter which states that mass is neither destroyed or created during ordinary chemical or physical reactions. Back Antoine Lavoisier Section 3.1 – The Atom: from philosophical idea to scientific theory Foundations of Atomic Theory (continued) The law of definite proportions, sometimes called Proust's Law, states that a chemical compound always contains exactly the same proportion of elements by mass. Book example: salt is always 39.34% Na (sodium) and 60.66% Cl (Chlorine) by mass Joseph Proust Section 3.1 – The Atom: from philosophical idea to scientific theory Foundations of Atomic Theory (continued) The law of multiple proportions, statement that when two elements combine with each other to form more than one compound, the weights of one element that combine with a fixed weight of the other are in a ratio of small whole numbers. Back You Tube Help Rethink value of video Section 3.1 – The Atom: from philosophical idea to scientific theory Dalton’s Atomic Theory 1.All matter is made of extremely small particles called atoms. Relationship 2.All atoms of the same element are identical in size, mass & other properties. Relationship 3.Atoms cannot be subdivided, created or destroyed. Relationship 4.Atoms of different elements combine in WHOLE-number ratios to form compounds. 5.In chemical reactions atoms are combined, separated or rearranged. Relationship Section 3.1 – The Atom: from philosophical idea to scientific theory Modern Atomic Theory Dalton turned idea’s (of ancient Greeks) into scientific theory Today we know that atoms can be divided, but the law of conservation of matter holds true still. Section 3.1 – The Atom: from philosophical idea to scientific theory Quiz Break Section 3.2 – The Structure of the Atom Objectives HW – Notes on section 3.2 pgs 70-74 Students will be able to : • Summarize the observed properties of cathode rays that led to the discovery of the electron. • Summarize the experiment carried out by Rutherford and his co-workers that led to the discovery of the nucleus. • List the properties of protons, neutron and electrons •Define atom. Section 3.2 – The Structure of the Atom Discovery of the Electron 1st discovery of a subatomic particle resulted from investigations into the relationship between electricity and matter. Section 3.2 – The Structure of the Atom Discovery of the Electron - Cathode Rays and Electrons Hypothesized that the glow was caused by a stream of particles which they called a cathode ray. Tested and found that 1. An object placed between the cathode ray and the opposite end casts a shadow. 2. A paddle wheel placed on rails rolled toward the anode from the cathode. Section 3.2 – The Structure of the Atom Discovery of the Electron - Cathode Rays and Electrons (continued) This supported the idea of a cathode ray. . . Further testing found that 1. Cathode rays were deflected by a magnetic field. 2. Deflected away from negatively charged objects. Thompson hypothesized that the ray was a particle, a negative one – later named electrons. Section 3.2 – The Structure of the Atom Charge and Mass of the electrons Thompson’s work showed that the electron has a very large charge for its tiny mass R. A. Millikan (right) showed the mass to be 9.109 x 10-31 kg Section 3.2 – The Structure of the Atom Charge and Mass of the electrons – (continued) Based on that information two more inferences were made about atomic structure. 1. Atoms are electrically neutral so there must be positively charged particles to balance out the negative electron. 2. Because electrons have so much less mass than atoms, atoms must contain other particles which account for most of their mass. Section 3.2 – The Structure of the Atom Discovery of the Atomic Nucleus Ernest Rutherford & associates bombarded a thin gold foil with alpha particles (+ charge & 4 x mass of H atom) Expected most particles to pass through with slight deflection – shocked to find that 1 in 8 000 were redirected back toward source. Section 3.2 – The Structure of the Atom Discovery of the Atomic Nucleus – (continued) Rutherford reasoned that the bounce back was from a densely packed bundle with a positively bundle he called the nucleus. If the nucleus were the size of a marble the atom would be the size of a football field Section 3.2 – The Structure of the Atom Composition of the Atomic Nucleus Except for the simplest type of hydrogen all atomic nuclei are made of two types of particles, protons and neutrons. Protons have a (+) charge which balances out the charge of the electrons. Mass = 1.673 x 10-27 kg Neutrons have a no charge and a mass = 1.675 x 10-27 kg Section 3.2 – The Structure of the Atom Composition of the Atomic Nucleus – (continued) Nuclei of atoms of different elements differ in the # of protons they contain and therefore in the amount of positive charge. Section 3.2 – The Structure of the Atom Properties Summarized Particle Symbols 0 Relative electric charge Mass number Relative Mass (amu*) Actual mass (kg) Electron e-,-1 e -1 0 0.000 5486 9.109 x 10-31 Proton p+, 11 H +1 1 1.007 276 1.673 x 10-27 Neutron no, 0 n 0 1 1.008 665 1.675 x 10-27 1 * 1 amu (atomic mass unit) = 1.660 540 x 10-27 kg Section 3.2 – The Structure of the Atom Composition of the Atomic Nucleus - Forces in the Nucleus Like forces generally repel one another however when two protons are extremely close there is a strong attractions These short-range proton-neutron, proton-proton, and neutron-neutron forces hold the particles together and a referred to as nuclear forces. Section 3.2 – The Structure of the Atom The sizes of Atoms Atomic radii range from 40 to 270 pm (picometers) Where as the nuclei of atoms have a much smaller radii About 0.001 pm Section 3.3(A) – Counting Atoms Objectives HW – Notes on section 3.3 pgs 75-80 Students will be able to : • Explain what isotopes are. • Define atomic number and mass number, and describe how they apply to isotopes. • Given the identity nuclide, determine its number of protons, neutrons and electrons. Section 3.3(A) – Counting Atoms Atomic Number The atomic number of an element is the number of protons in the nucleus of each atom of that element Section 3.3(A) – Counting Atoms Isotopes Isotopes are atoms of the same element that have different masses. All hydrogen contain the same number of protons but may contain different number of neutrons. Section 3.3(A) – Counting Atoms Mass Number The mass number is the total number of protons and neutrons in the nucleus of an isotope. Mass Number 1 2 3 Section 3.3(A) – Counting Atoms Isotopes - pogil Section 3.3(A) – Counting Atoms Isotopes – Pennium Lab Section 3.3(A) – Counting Atoms Designating Isotopes Nuclide is a general term for any isotope of any element. Nuclear Symbol a b S = element’s symbol S Bromine has a = protons + neutrons b = protons 80 Protons = ______ 35 Neutrons = _______ Br Electrons = ________ Practice Practice Key Section 3.3(A) – Counting Atoms Relative Atomic Masses The standard used by scientist to govern units of atomic mass is the carbon-12 nuclide. One atomic mass unit , or amu is exactly 1/12th the mass of a carbon-12 atom, or 1.660 540 x 10-27 kg Although isotopes may have different masses, they do not differ significantly in their chemical behavior. Section 3.3(A) – Counting Atoms Average Atomic Masses of Elements Average atomic mass is the weighted average of the atomic masses of the naturally occurring elements. Example with marbles (100 total) 25 marbles x 2.00 g = 50 g 75 marbles x 3.00 g = 225 g Adding the masses gives 50 g + 225 g = 275 g Divide this by the total number of marbles and you get an average marble mass of 2.75 g Section 3.3(A) – Counting Atoms Average Atomic Masses of Elements –(continued) Average atomic mass How are the masses on the periodic table determined? (KEY) Section 3.3(B) – Counting Atoms Objectives HW – Notes on section 3.3 pgs 80-85 Students will be able to : •Define mole in terms of Avogadro’s number, and define molar mass. •Solve problems involving mass in grams, amount in moles and number of atoms of an element. Section 3.3(B) – Counting Atoms Relating Mass to Numbers of Atoms - the Mole A mole (abbreviated mol)is the amount of a substance that contains as many particles as there are atoms in exactly 12 g of carbon-12. Section 3.3(B) – Counting Atoms Relating Mass to Numbers of Atoms – Avogadro’s number The number of particles in a mole has been experimentally determined in a number of ways. Avogadro’s number 6.011 1367 x 1023 – is the number of particles in exactly one mole of a pure substance. For ours (and most purposes) Avogadro’s number is rounded to 6.022 x 1023 Section 3.3(B) – Counting Atoms Relating Mass to Numbers of Atoms – Molar Mass The alternative definition of mole is the amount of substance that contains avogadro’s number of particles. The mass of one mole of a pure substance is called the molar mass of that substance. Usually written in units of g/mol. Section 3.3(B) – Counting Atoms Relating Mass to Numbers of Atoms – Gram/Mole Conversions Amount of element in moles There are 3 mole equalities. They are: 1 mol = 6.02 x 1023 particles 1 mol = g-formula-mass (periodic table) 1 mol = 22.4 L for a gas at STP* * STP = 0° C & 1 atm Pressure Mass of element in grams Number of atoms of element Section 3.3(B) – Counting Atoms Relating Mass to Numbers of Atoms – Conversions There are 3 mole equalities. They are: 1 mol = 6.02 x 1023 particles 1 mol = g-formula-mass (periodic table) 1 mol = 22.4 L for a gas at STP* These become. . . 1 mol [-------------] [-------------] 6.02 x 1023 particles or 6.02 x 1023 particles 1 mol [-------------] [-------------] [----] [----] 1 mol g-formula-mass (periodic table) g-formula-mass (periodic table) 1 mol 22.4 L or OR 1 mol 22.4 L 1 mol Reference Sheet There are 3 mole equalities. They are: 1 mol = 6.02 x 1023 particles 1 mol = g-formula-mass (periodic table) 1 mol = 22.4 L for a gas at STP* These become. . . 1 mol [-------------] [-------------] 6.02 x 1023 particles or 6.02 x 1023 particles 1 mol [-------------] [-------------] [----] [----] 1 mol g-formula-mass (periodic table) g-formula-mass (periodic table) 1 mol 22.4 L or OR 1 mol 22.4 L 1 mol Section 3.3(A) – Counting Atoms Relating Mass to Numbers of Atoms – What does it mean? g-formula-mass (periodic table) For a single element it is simply the atomic mass found on the periodic chart Section 3.3(A) – Counting Atoms Relating Mass to Numbers of Atoms – Examples g-formula-mass (periodic table) N Ca Ag Ba Section 3.3(A) – Counting Atoms Relating Mass to Numbers of Atoms – What does it mean? g-formula-mass (periodic table) For a COMPOUND you will need to calculate using atomic mass found on the periodic chart Section 3.3(B) – Counting Atoms Relating Mass to Numbers of Atoms – EXAMPLE g-formula-mass (periodic table) COMPOUNDS Table Salt NaCl Water H2O Sugar (glucose) C6H12O6 Section 3.3(B) – Counting Atoms Relating Mass to Numbers of Atoms – EXAMPLE g-formula-mass (periodic table) COMPOUNDS inorganic salt (soil fertilizer) (NH4)2SO4 Section 3.3(B) – Counting Atoms Relating Mass to Numbers of Atoms – MOLE PRACTICES Practice 1 Practice 2 Practice 2 (Key) Section 3.3(B) – Counting Atoms Relating Mass to Numbers of Atoms – FUN WITH MOLES Given : 2.860 m ceiling height 9.630 m room depth 10.620 m room width Atmosphere composition: 1 000 L = 1 m3 Nitrogen - 78.084% Oxygen - 20.95% How many mols of O2 and N2 are present in this room? Section 3.3(B) – Counting Atoms Relating Mass to Numbers of Atoms – FUN WITH MOLES Atmosphere composition: Nitrogen - 78.084% Oxygen - 20.95% Average lung volumes in healthy adults[7] Volume Inspiratory reserve volume Tidal volume Expiratory reserve volume Residual volume Value (litres) In men In women 3.3 1.9 0.5 0.5 1.0 0.7 1.2 1.1 How many particles of O2 and N2 are taken in with each breath? Section 3.3(B) – Counting Atoms Relating Mass to Numbers of Atoms – suggestions 1. Relax 2. Look for things you recognize 3. Estimate size of final answer (with this comes do I remember using any of these before) 4. Set up and work out 5. Double check with estimate and your sig figs Section 3.3(B) – Counting Atoms Relating Mass to Numbers of Atoms – MORE MOLE PRACTICES Practice 3 TAKE-HOME QUIZ Practice 4 Practice 3 (KEY) TAKE-HOME QUIZ (KEY) Practice 4 (KEY) Section 3.3(B) – Counting Atoms Relating Mass to Numbers of Atoms – Q - #4 100 atoms Ar 1x Want to get to Mols... 102 atoms Ar 1 mol 1 x 102 atoms Ar ------------------------- X ------------------------6.02 x 1023 particles 1 0.166 x 10-21 particles , which is equal to 1.66 x 10-1 x 10-21 Or more properly written as 1.66 x 10-22 mols Ar