Chapter 3 History of the Atom

Element Symbols Rule 1 First letter is capitalized H Hydrogen C Carbon O Oxygen Rule 2 Second letter is lower case Cl Chlorine He Helium Ne Neon Rule 3 Some are Latin names Na Sodium (natrium) Fe Iron (ferrum) Rule 4 Some elements are named for places, scientists, greek gods… Eu Europium Am Americium

Period Group

Foundations of Atomic Theory Law of conservation of mass: Antoine Lavoisier Mass is neither created nor destroyed. HgO  Hg + O 433.2 g 401.2g + 32g

Dalton’s Atomic Theory (1808) All matter is made of indivisible and indestructible atoms. All atoms of the same element are identical in their physical and chemical properties. Atoms of different elements have different properties. Atoms of different elements combine in simple whole-number ratios to form compounds. Atoms cannot be subdivided, created, or destroyed when they are combined, separated, or rearranged in chemical reactions.

Changes to Dalton’s Theory Are atoms actually indivisible? Are all atoms identical? No, atoms are made of protons, neutrons, and electrons No, different electrons prodcues ions, different neutrons produces isotopes

The Atom the smallest unit of an element that retains that elements properties Made of protons, neutrons, and electrons Can you see inside an atom? How did they know it contains protons, neutrons and electrons? Scientists needed to experiment in order to learn of atoms and that they were made of protons, neutrons and electrons

Obscertainer Activity

Ob-scertainer Solutions #1 #2 #3 #4 #5 #6 #7 #8 #9 #10 #11 #12

Cathode Ray Tube When connected to electric current the remaining the gas forms a BEAM OF LIGHT. The beam always started at the NEGATIVE electrode and flowed to the POSITIVE electrode. The electrode is named by what type of particle it attracts Cathode: Negative (-) Anode: Positive (+)

Cathode Ray Tube Experiment

Cathode Ray Conclusions 1. The beam was attracted to a POSITIVE magnet. 2. The beam must be made of NEGATIVE particles.

JJ THOMSON DISCOVERED A NEGATIVE PARTICLE CALLED THE: ELECTRON!

Plum Pudding Model

Plum Pudding OR Chocolate Chip Cookie

Radioactivity Becquerel Curie discovered RADIATION uranium would expose photographic plates in the dark The properties of an element changed as it gave off radiation Curie Discovered radium and polonium The radioactive emissions of alpha, beta and gamma rays were identified.

(Uranium compound)

Types of Radioactive Decay Decay Type Symbol Charge Reaction Particle Strength Can be stopped by… Alpha Beta Gamma

Radioactive Decay

Ernest Rutherford’s Gold Foil Experiment Set up Gold Foil with a detection sheet around it. Set up radioactive source emitting alpha particles. ALPHA PARTICLES shot at gold foil.

Rutherford’s Gold Foil Experiment

MOST particles went through the gold foil Rutherford: It’s like shooting a cannon at a piece of tissue paper and having it bounce back at you! MOST particles went through the gold foil SOME particles BOUNCED back

Gold Foil Conclusions The atom is made up of mostly EMPTY SPACE The center of the atom contains a POSITIVE CHARGE Rutherford called this positive bundle of matter the NUCLEUS

Rutherford’s Model of the Atom NUCLEUS EMPTY SPACE – + If the atom is the size of Giants Stadium Then the nucleus is a marble on the 50 yard line

Other scientists later confirmed that the nucleus was made up of protons and neutrons

**DISCOVERED ENERGY LEVELS!! Niels Bohr – 1913 Developed a new diagram of the atom Electrons can only be at certain energies Electrons must gain a specific amount of energy to move to a higher level, called a quantum **DISCOVERED ENERGY LEVELS!!

Bohr’s Model of the Atom

SUBATOMIC PARTICLES

Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons X A Z Mass Number Element Symbol Atomic Number Isotopes: atoms of the same element (X) with different numbers of neutrons in their nuclei H 1 H (D) 2 H (T) 3 U 235 92 238

Isotopes

Do You Understand Isotopes? How many protons, neutrons, and electrons are in C 14 6 ? 6 protons, 8 (14 - 6) neutrons, 6 electrons How many protons, neutrons, and electrons are in C 11 6 ? 6 protons, 5 (11 - 6) neutrons, 6 electrons

Hyphen Notation The mass number is written with a hyphen after the name of the element. Element – Mass# Uranium – 235 Calcium – 40

cation – ion with a positive charge An ion is an atom, or group of atoms, that has a net positive or negative charge. cation – ion with a positive charge If a neutral atom loses one or more electrons it becomes a cation. Na 11 protons 11 electrons Na+ 11 protons 10 electrons anion – ion with a negative charge If a neutral atom gains one or more electrons it becomes an anion. Cl- 17 protons 18 electrons Cl 17 protons 17 electrons

Do You Understand Ions? Al How many protons and electrons are in ? 27 13 ? 3+ 13 protons, 14 neutrons, 10 (13 – 3) electrons How many protons and electrons are in Se 78 34 2- ? 34 protons, 44 neutrons, 36 (34 + 2) electrons

Average Atomic Mass

Relative Atomic Mass Atomic Mass Unit Carbon is the standard for all masses on the periodic table. Carbon: 6 p and 6 n = 12 amu Atomic Mass Unit Periodic table lists weighted average atomic masses of elements (like a GPA or final grade calculation)

Calculation AVERAGE Atomic Mass Steps: 1. Percent to a decimal 2. Multiply by mass 3. ADD IT UP! 75% 133Cs 20% 132Cs 5 % 134Cs