# Chapter 3

Chapter 3 ATOMS: THE BUILDING BLOCKS OF MATTER Section 1 FROM PHILOSOPHICAL IDEA TO SCIENTIFIC THEORY Foundations of Atomic Theory Particle Theory of Matter Democritus in 400 B.C. Stated that natures basic particle was the ___________ (indivisible in Greek).

Aristotle Believed all matter was ______________ (could be divided forever), and did not believe in atoms. Neither had experimental evidence to support their claims. Fast Forward to the18th century Three laws discovered due to improved instrumentation and carefully observed chemical reactions 1. Law of conservation of mass Mass is neither _______________ nor ___________ during an ordinary chemical reaction or physical change.

massreactants = massproducts % composition = part X 100% total Practice (law of conservation of mass) If 40 g of X reacts with 35 g of Y, what is the mass of the product XY? If 3.5 g of X reacts with 10.5 g of Y to form the compound XY, what is the percent by mass of X in the compound? Fast Forward to the18th century Three laws discovered due to improved instrumentation and carefully observed chemical reactions

2. Law of definite proportions A chemical compound contains the same ____________ in exactly the same ________________ by mass regardless of the size of the sample or source of the compound. Example: Table salt will always consist of 39.34 % Na and 60.66% Cl. percent by mass (%) = mass of element X 100% mass of compound Practice (law of definite proportions) 1.) 5 g of hydrogen reacts completely with 38 g of fluorine. What is the percent by mass of hydrogen in the compound that is formed?

2.) If 13 g of X reacts with 45 g of Y to form the compound XY, what is the percent by mass of the elements in the compound? 3.) Two unknown compounds are tested. Compound 1 contains 32.6 g of hydrogen and 167.4 g of Carbon. Compound 2 contains 8.0 g of hydrogen and 24.0 g of carbon. Are the compounds the same? Fast Forward to the18th century Three laws discovered due to improved instrumentation and carefully observed chemical reactions 3. Law of multiple proportions If 2 or more compounds are composed of the same two elements, the _________ of the masses of the second element combined with a certain mass of the first

element is always a __________ of small whole numbers. Example: Carbon and Oxygen can combine to form CO 2 or CO. Daltons Atomic Theory John Daltonproposed _______________________ Accounted for all three laws: conservation of mass, definite proportions, and multiple proportions. Daltons All Atomic Theory consists of the following statements:

matter is composed of ____________. Atoms of a given element are _____________ in size, mass, and all other properties. Atoms _______________ be subdivided, created, or destroyed. Atoms of different elements combine in simple ___________________________ to form chemical compounds. In

______________________, atoms are separated, combined, Modern Atomic Theory Advances in instrumentation have allowed some aspects of Daltons theory to be proven incorrect. Example: The thoughts that atoms are not divisible into smaller particles and have the exact same mass are incorrect. The two most important aspects of Daltons theory still hold true All matter is composed of atoms.

Atoms of any one element differ in properties than atoms of another element. Section 2 THE STRUCTURE OF AN ATOM JJ Thomson, 1900 Discovered the charge to mass ratio for the _______________ Concluded that the electron has a very large charge-to-mass ratio

Conducted Cathode-ray experiments to prove that atoms are ______________ and composed of ______________. Proposed ____________________ model for the atom (not a solid mass). http://www.youtube.com/watch?v=2xKZRpAs WL8 Discovery of the Electron Scientific advances allowed for the discovery of smaller particles that made up atoms. Electric current was passed through gases via a cathode ray tube.

Milikan and the oil drop experiment Measured __________ of droplets Applied charge to droplets through x-rays. Applied electric voltage to top and bottom plates Measured the amount of voltage it took to keep the oil droplets suspended. Was able to measure the ______________ of a single electron! http://www.youtube.com/watch?v=EV1owO1H2dA Ernest Rutherford

Discovered the __________________ of an atom with his gold-foil experiment. http://www.youtube.com/watch?v=XBqHkraf8iE Concluded that the volume of the nucleus was very ______________ compared to the total volume of the atom. Sizes of Atoms Expressed 1 in picometers (pm).

pm = 1*10-12 m = 0.000000000001m Section 3 COUNTING ATOMS Atomic Number The number of ____________ in each atom of a given element Unique to each element and does not change Used to _______________ elements. # Protons = # Electrons for ___________ atoms of an element Practice 1. How many protons and electrons are in each neutral atom? Radon, Rn

Titanium, Ti 2. A neutral atom of an element contains 50 electrons. Which element is it? 3. An atom of an element contains 14 protons. Which element is it? Isotopes and Mass Number The amount of protons and electrons are constant in all neutral atoms of an element, but the number of ______________ can vary Isotopes atoms of the same element that have different numbers of ________________

Example: Hydrogen atoms have three different isotopes. Protium1 proton/0 neutrons (accounts for 99.985% of all hydrogen atoms). Deuterium1 proton/1 neutrons (0.015%) Tritium1 proton/2 neutrons (radioactive, and can be produced artificially) Most elements contain mixtures of isotopes. Tin (Sn) has 10 stable isotopes, the most of any element.

Mass Number--The number of ___________ and ______________ that make up the nucleus of an isotope. Since electrons are so small, their mass is considered insignificant. Designating Isotopes Isotopes are usually identified by their _____________________. Two Methods: Hyphen notationhas hyphen after name of element, followed by the mass number.

Example: Tritium is hydrogen-3 since it has 2 neutrons and 1 proton. Example: Uranium-235 Nuclear symbol Mass number written as superscript Atomic number written as subscript Followed

by element symbol In both methods The number of neutrons is found by subtracting the atomic number from the mass number. Example: (Mass 235 Uranium-235 or 235 U

92 #) (Atomic #) = (# of neutrons) (protons + neutrons) 92 protons= 143 neutrons Notation Practice 1. Give the number of protons, electrons, and neutrons in each of the following atoms. a) 108 47

Ag b) 40 20 Ca 2. Name each isotope and write it in nuclear symbol and hyphen notation. a) atomic number 26; mass number 56 b) atomic number 29; mass number 64 3. How many protons, electrons, and neutrons are in each of the following isotopes? a) hydrogen-3

b) silicon-29 Relative Atomic Masses Because the masses of subatomic particles are extremely small and hard to work with, scientists created a new unit _______________________(amu) based on a standard of carbon-12 that has a mass of 12 amu Neutron Proton 1.007276 amu Electron

1.008665 amu 0.0005486 amu Important to note that the masses are slightly different between protons and neutrons. Average Atomic Mass Avg. atomic mass the __________________ of the masses of the isotopes of that element Avg. atomic mass = (mass x abundance)isotope1 + (mass x abundance)isotope2 +

To find abundance divide the percentage by 100 (all abundances must be _________________) Atomic mass can help you determine which isotopes of that element is the most ______________ Atomic Mass Practice 1. Boron has two naturally occurring isotopes: boron-10 (abundance 19.8%, mass 10.013 amu) and boron-11 (abundance 80.2%, mass 11.009 amu). Calculate the atomic mass of boron. 2. Calculate the average atomic mass of lithium, which occurs as two isotopes

that have the following atomic masses and abundances in nature: 6.017 amu, 7.30% and 7.018 amu, 92.70%. 3. Nitrogen has two naturally occurring isotopes, N-14 and N-15. Its atomic mass is 14.007. Which isotope is more abundant? Explain. Relating Mass to Number of Atoms The Mole (mol) Since atoms are so tiny, we count them in groups Same as 1 dozen = 12 donuts

Mole = SI unit for ______________ of substance. Avogadros number The number of ______________ in exactly 1 mol of a pure substance. 6.022 1023 atoms = 1 mol of any substance. 6.022

1023 molecules = 1 mol of any substance. Practice How many atoms are in 5.76 moles of a pure substance? How many moles are in 8.56 1026 atoms? Molar Mass The mass (in grams) of 1 mol of a pure substance. Units are _____________

Equal to the _________ of the atomic masses of each element of a compound. Example: K2CO3 2(39.10 g/mol) + 3(16.00 g/mol) = 138.21 C

O K g/mol) + 1(12.01 g/mol Examples Find the molar masses of the following compounds: SrCO3 C13H18O2 Sn2(SO4)4 REMEMBER! Grams Molar Mass

Moles Avogadros Number Molecules Atoms Mass must always be converted to moles before being converted to atoms Atoms must always be converted to moles before converting to mass Gram/Mole Conversions Use molar mass to convert moles to grams and vice versa.

Practice: Convert 7.00 g of He to moles. Convert 5.21 mol of NaCl to milligrams. Convert 5.67 mol of Xe to grams. Convert 65.4 g of K2CO3 to mol.

More Practice How many atoms are in 4.56 g of Na2CO3? What is the mass of 5.67 1032 atoms of NaOH? Chapter 3 Vocabulary Law of Conservation of Mass Law of Definite Proportions

Law of Multiple Proportions Mass Number Atom Nuclide Nuclear Forces

Atomic Mass Unit Atomic Number Average Atomic Mass Isotope