Chapter 3: Atoms and Moles Sections 1 and 2

Atomic Theory Atomic Theory states that atoms are the building blocks of matter.

Law of Definite Proportions Law of Definite Proportions: states that two samples of a given compound are made of the same elements in exactly the same proportions by mass regardless of the sizes or sources of the sample. EX: H 2 O, 50mL or 1000mL its still composed of 2 hydrogens and 1 oxygen. EX: NaCl, it does not matter how much is present because every sodium chloride (table salt) compound is made up of 60.66% chlorine and 39.34% sodium.

Law of Conservation of Mass Law of Conservation of Mass: states that the mass of the reactants in a reaction equals the mass of the products in the same reaction. EX: 2H 2 + O 2  2H 2 O Mass of H = 1g there are 4H’s so 4 x 1g = 4g Mass of O = 16g there are 2O’s so 2 x 16g = 32g Reactants = Reactants = 36g On the products side there are 4H’s and 2O’s (4 x 1g) + (2 x 16) = 36g Products = 36g

Law of Multiple Proportions Law of Multiple Proportions: states that if there are two or more different compounds that are composed of the same two elements, the ratio of the masses of the second element (which combines with a given mass of the first element) is always a ratio of small whole numbers.

Law of Multiple Proportions Name of Compound FormulaMass O (g) Mass N (g) O(g) / N(g) Whole # Ratio of O Nitrogen Monoxide NO16.0g14.01g 16.0g O 14.01g N =1.14gO 1gN 1.14g O 2.28g O = 1:2 Ratio of O Nitrogen Dioxide NO g14.01g 32.0g O 14.01g N =2.28g O 1g N 1.14g O 2.28g O = 1:2 Ratio of O

Dalton’s Atomic Theory Dalton (1808) English School Teacher Combined the information from the Greek term atom, law of definite proportion, law of conservation of mass, and law of multiple proportions to develop the ATOMIC THEORY.

Dalton’s Atomic Theory 1. All matter is composed of extremely small particles called atoms which cannot be subdivided, created or destroyed. Today we know an atom can be broken down into electron, protons and neutrons. 2. Atoms of a given element are identical in their physical and chemical properties. 3. Atoms of different elements differ in their physical and chemical properties. 4. Atoms of different elements combine in simple, whole-number ratios to form compounds. Today we understand that one element can form a compound like O 2 5. In chemical reactions, atom are combined, separated, or rearranged but never created, destroyed or changed.

Structure of an Atom Chapter 3 Section 2

Subatomic Particles Electron Proton Neutron

Discovery of The Electron J.J. Thompson Discovered when studying electricity Used a device called a cathode ray tube Vacuumed sealed Sent electricity through two metal electrodes on both sides of tube Anode-positive terminalCathode-negative terminal Produced glowing beam that traveled cathode  anode b/c electrons (which is what electricity travels on) are negative. OPPOSITES ATTRACT, therefore the negative electrons are attracted to Positive anode. The electrons are repelled by the negative cathode.

J.J. Thomson and The Electron J.J. Thomson’s experiment proved that the cathode ray had mass and a negative charge. Electrons are negatively charged subatomic particles found in the electron cloud or orbitals of an atom. Charge: -1 Relative Mass: 0, although does Symbol: e - have mass. Plum pudding model

Rutherford’s Discovery of Nucleus Rutherford was a former student of J.J. Thomson. Rutherford performed the GOLD FOIL EXPERIMENT

Rutherford’s Gold Foil Experiment Alpha particles- positively charged particles These particles were shot at the piece of gold foil suspended in the middle of the detecting screen. Most alpha particles shot at the foil passed straight through it, small number of alpha particles were deflected. Rutherford Quoted, “ It was almost as if you fired a 15-inch shell into a piece of tissue paper and it came back and hit you.”

Rutherford’s Discovery The atom has a tiny positively charged nucleus in the center. The nucleus is very dense Nucleus: a very dense positively charged species found in the center of an atom. What else besides positively charged Protons can be found within the nucleus?

Protons Protons: positively charged particles found in the nucleus in the center of an atom. The charge of a proton is equal in magnitude but opposite in charge of an electron. Charge: +1 Symbol: p + Relevant Mass: 1 Protons = Atomic Number Protons = Electrons in neutral atom… any element or individual atom

Neutrons Discovered by Chadwick Neutrons: neutral particles found in the nucleus Neutrons and protons have equal masses. Charge: 0 Symbol: n 0 Relative Mass: 1

Atomic Number = Protons Atomic Number: the number of protons that an atom has. Protons = Electrons in neutral ATOMS… atoms are found on the periodic table; single. On our periodic tables the atomic number is directly above the symbol. Short hand notation: mass number on top, atomic number on bottom

Mass Number Mass Number: is equal to the total number of particles of the nucleus-that is the total number of protons and neutrons. Mass # = Protons (atomic number) + Neutrons Mass # - atomic number (protons) = Neutrons How many neutrons are in a Carbon Atom?

Practice Problems How many protons and electrons are in an atom of sodium whose atomic number is 11? An atom has 13 protons and 14 neutrons. What is its mass number? Calculate the mass number for an atom that has 45 neutrons and 35 electrons.

Answers Proton number = electron number in a neutral atom…meaning any atom found on the periodic table that’s not bonded. Answer = 11 electrons Protons + neutrons = mass number = 27 Protons = electrons therefore… Electrons + Neutrons = mass number = 80

Problem…even harder An atom of an element has 54 protons. Some of the element’s atoms have 77 neutrons, while other atoms have 79 neutrons. What are the atomic numbers and mass numbers of the two types of atoms of this element?

Answer…to even harder Q First know that 54 protons = atomic number. So atomic number is 54 for both atoms because THE ATOMIC NUMBER NEVER EVER EVER EVER CHANGES. Atomic Number (protons) + Neutrons = Mass # = 131g = 133g The mass number of the atoms are 131g and 133g

Different Elements Can Have Same Mass Number Atomic Number: identifies the element ALWAYS Isotopes: atoms of the same element that have different number of neutrons. All isotopes have the same atomic number but differ in number of Neutrons. Why can’t isotopes have different number of protons?

Practice Problems…again Chlorine has two stable isotopes, chlorine-35 and chlorine-37. The atomic number of chlorine is 17. Calculate the numbers of protons, electrons, and neutrons each isotope has. Calculate the numbers of protons, electrons, and neutrons for each of the following isotopes of calcium:

Answer #1…Again Chlorine- 35 Protons = 17 Electrons = 17 Neutrons = 18 Chlorine- 37 Protons = 17 Electrons = 17 Neutrons = 20

Answer #2…Again Calcium - 42 Protons = 20 Electrons = 20 Neutrons = 22 Calcium – 44 Protons = 20 Electrons = 20 Neutrons = 24