Chapter #3 Atoms: The Building Blocks of Matter Chapter 3 ATOMS: West Valley High School General Chemistry Mr. Mata Chapter #3 Atoms: The Building Blocks of Matter

Standard 2a To compare and contrast the atomic number and atomic mass.

Essential Question Describe how atomic theory developed to give us our modern view of the atom.

3-1 Early Atomic Theory Atoms – smallest particle of matter. Democritus (400 B.C) stated world was made of atoms. (atomos = “indivisible”). Antoine Lavoisier (1800’s) discovered mass didn’t change after chemical rxn. Proposed “matter can be changed, but it cannot be created or destroyed “ (Law of Conservation of Mass).

Dalton’s Atomic Theory All matter composed of atoms. Atoms of same element identical in size, mass, properties; atoms of diff elements diff. in size, mass, properties. Atoms can’t be subdivided, created, destroyed. Atoms of different elements combine in whole-number ratios to form chemical compounds. In chemical reactions, atoms are combined, separated, or rearranged.

Modern Atomic Theory All matter is composed of atoms. Atoms of any one element differ in properties from atoms of another element. Element’s average mass unique to element. Atoms cannot be subdivided, created, or destroyed in ordinary chemical rxns. Changes CAN occur in nuclear rxns!

Atomic Structure Atom- smallest particle of element that retains chemical properties of element. Nucleus- positively charged, dense central portion of the atom; contains nearly all mass (~ 99.7%).

Subatomic Particles Electrons e- Negative charged particles. Found in electron clouds. Thomson (1897) Protons p+ Positively charged particles. Found in the nucleus. Rutherford (1918) Neutrons N No charge. Found in the nucleus. Chadwick (1932)

The Atomic Scale Most of the mass of the atom is in the nucleus (protons and neutrons) Electrons are found outside of the nucleus (the electron cloud). Most volume of atom=empty space.

Famous Scientists Scientist Experiment Name Conclusion JJ Thomson Cathode Ray Electron (-) Robert Millikan Oil Drop Mass of a single electron. Ernest Rutherford ______________ James Chadwick Gold foil _______________ Beryllium Detection Proton (+) _____________ Neutron (0)

Discovery of the Electron J.J. Thomson (1897) used a cathode ray tube to deduce the presence of a negatively charged particle. Discovered the – electron particle.

(1906)Thomson awarded the Nobel Prize in chemistry for discovery of the electron. The atom could be broken down into smaller particles.

Thomson’s Atomic Model Thomson believed electrons were like plums in a + charged “pudding”. He called it the “plum pudding” model.

Rutherford’s Gold Foil Experiment Alpha particles are helium nuclei. Particles fired at a thin sheet of gold foil. Particle hits on screen (film) are detected.

Rutherford’s Findings Most particles passed right through screen. Few particles deflected. VERY FEW were greatly deflected. Conclusions: The nucleus is small. The nucleus is dense. The nucleus is + charged.

Section 3-3 Atomic number: number of protons in the nucleus of atom. # p(+) = # e(-) 6 C Carbon 12.011

Atomic Mass number of protons & neutrons in the nucleus. Atomic Mass=protons + neutrons Atomic Mass C = 12.011 Mass number = rounded atomic mass Mass Number C = 12

235 92 Nuclear Symbols Mass number (p+ + n) Atomic Mass (p+ + n) Element symbol Atomic number (# of p+) U 235 92

Hyphen Notation Sodium-23 (23 is the atomic mass) Sooo… 23- 11 (atomic #) = 12 for the # of neutrons. Atomic number of 11 is the # of protons (11) and electrons(11).

Molar Relationships 1 mole = 6.02 x 1023 atoms, molecules, or particles Molar mass = mass of 1 mole of substance(Hint: Add up atomic masses) Ex: Find the molar mass of: H2O = (H=1(2), 0=16), 18 grams CO2 = (C=12, O=16(2)), 44 grams H2SO4=(H=1(2),S=32,O=16(4)), 98 g

Molar Masses Find molar masses: NaCl = 58 grams = 1 mole CaCl2 = 110 grams = 1 mole Fe(OH)2 = 90 grams = 1 mole H3PO4 = 98 grams = 1 mole C6H12O6 = 180 grams = 1 mole

Calculations: Converting moles to grams Given # of mole X ? g (look at periodic table)= g 1 mole How many grams of lithium are in 3.50 moles of lithium? 3.50 mole Li X 7 g = 24.5 g Li 1 mol

Your turn… How many grams of carbon are in 8.25 moles of carbon? 8.25 mole C X 12 g = 99.0 g C 1 mol

Your turn… How many grams of uranium are in 21.5 moles of uranium? 21.5 mole U X 238 g = 5117 g U 1 mol

Calculations: Converting grams to moles Given # of g X 1 mol = mol g (look at periodic table) How many moles of lithium are in 18.2 grams of lithium? 18.2 g Li X 1 mol Li = 2.6 mol Li 7 g

Your turn… How many moles of gold are in 150 grams of gold? 150 g Au X 1 mol Au = 0.8 mol Au 197 g

Your turn… How many moles of H2O are in 120 grams of water? 120 g H2O X 1 mol H2O= 6.7 mol H2O 18 g

I didn’t discover it. Its just named after me! Avogadro’s Number Number of particles in exactly one mole of a pure substance. 6.02 x 1023 is called “Avogadro’s Number”. Named in honor of the Italian chemist Amadeo Avogadro (1776-1855). I didn’t discover it. Its just named after me!

Important Skill To find electrons, protons, and neutrons for an element: 40 Ca  atomic mass (#p + #n) 20  atomic number (#p = #e) # electrons = 20 (atomic number) # protons = 20 (atomic number) # neutrons = 20 (atomic mass–atomic #) 40 – 20 = 20 neutrons

Chapter 3 SUTW Prompt Describe the contributions of Thomson, Millikan, & Rutherford to our understanding of the atom. Complete an 11-13 sentence paragraph using the SUTW paragraph format. Hilite using green, yellow, and pink. Due Date: Monday, September 11, 2017 (beginning of class).