Chapter 3 VocabularyAtomic mass- mass of an atom expressed in atomic mass units Atomic mass unit- symbolized by u Atomic number- the number of protons in the nucleus of each atom of that element Atomic structure- the identity and arrangement of smaller particles within atoms Avogadro’s number- the number of particles in exactly one mole of a pure substance Isotopes- atoms of the same element that have different masses Law of multiple proportions- If two or more different compounds are composed of the same two elements, the masses of the second element combined with a certain mass of the first element can be expressed as ratios. Mass number- the total number of protons and neutrons in the nucleus of an isotope Molar mass- the mass in grams of one mole of a pure substance Mole- the amount of a substance that contains the same number of particles Neutrons- electrically neutral, subatomic particles found in atomic nuclei Nuclear forces- short-range proton-neutron, proton-proton, and neutron-neutron forces hold the nuclear particles together Nucleus- the positively charged, dense central portion of the atom that contains nearly all of its mass but takes up only an insignificant fraction of its volume Nuclide- general term for any isotope of any element Protons- subatomic particles that have a positive charge equal in magnitude to the negative charge of an electron and are present in atomic nuclei
Chapter 3 Cheat Sheet Dalton’s Atomic Theory 1. All matter is composed of extremely small particles called atoms. 2. Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties. 3. Atoms cannot be subdivided, created, or destroyed. (Law of Conservation of Mass)4. Atoms of different elements can combine in simple whole-number ratios to form chemical compounds. 5. In chemical reactions, atoms are combined, separated, or rearranged Law of Conservation of Mass – Matter can neither be created nor destroyed A + B AB Mass of A + Mass of B = Mass of AB Law of Definite Proportions – Atoms of different elements combine in simple whole-number ratios to form chemical compounds. Hydrogen + Oxygen Water 2H2 + O2 2H2O Hydrogen : Oxygen H2O = 2:1 Law of Multiple Proportions – SO2 versus SO3 The oxygen mass ratio for one mass of sulfur in these two compounds is 2:3 SO2 = For 32 g of sulfur there are 32 g of oxygen. SO3 = For 32 g of sulfur there are 48 g of oxygen. 32 g Oxygen : 48 g Oxygen 2:3 Cathode Ray Tube- Thomson’s Results: - Ray is produced by all metals tested - Ray contains matter - Ray is negatively charged - Atom is neutral in charge and, therefore must contain both positive and negative particles Cathode Ray Beam – Is it energy or matter? - Paddle wheel move toward the anode (+) - Beam contains matter - Beam contains a negative charge Mass to Charge Ratio – Electromagnetic properties exploited - Both magnetic and electric fields deflect beam - Setting electric and magnetic fields so they cancel each other - Charge- to mass ratio determined Oil-Drop Experiment- Robert A. Millikan (1909) -Drop surface acquires negative charge from xray excited air molecules -Downward pull of gravity countered by upward push of electric repulsive force - Mass of electron Gold Foil Experiment – Geiger &Marsden (1908-1900) -Alpha (+ charged) particle cannon - Gold foil target - Film detector - Expectation -Particles will bounce off gold foil -Results - Most particles passed straight through the foil - A small portion pass through but were deflected -A few particles bounced off the foil back toward the cannon Rutherford’s Interpretation: Most of the atom consists of space occupied by little or no mass (particles pass straight through) * A dense region of positive charge contains most of the atom’s mass (deflected particles hit or pass close to this region) * The low mass region contains the negatively charged electrons Ruther ford’s Atom: Atom contains two regions -Low density region where electrons (- charge) reside occupies most of atom’s volume (nucleus) - Neutral particles (neutrons) discovered in 1932 also reside in the nucleus Electron Cloud: Electrons circle the nucleus -Negative charge of electrons attracts them to the positively charged nucleus - Some unknown force keeps electrons from crashing into the nucleus Nucleus: Home to bother protons and neutrons - Nucleus is a dense region of positive charge - At close approach distances, proton-neutron, proton-proton and neutron-neutron attraction holds the particles together. The force of attraction is referred to as either Nuclear force or strong force Elements: Y Yttrium V Vanadium Se Selenium Cd Cadmium As Arsenic Pu Plutonium Sr Strontium Bi Bismuth Np Neptunium Ga Gallium Sb Antimony Calculating Atomic Mass Using Isotopic Abundance: Example 1: Carbon Carbon has 2 natural isotopes, nuclide 12C and nuclide 13C. The mass and natural abundnace of these two nuclides are, respectively, 12.0000u at 98.892% and 13.00338u at 1.108%. The atomic weight of carbon is calculated as follows: C atomic wt. = (12Cmass)x(%12Cabundance/100)+(13Cmass)x(%13Cabundance/100) C atomic wt. = (12.0000 u)x(98.892/100)+(13.00338u)x(1.108/100) * C atomic wt. = 12.0111u Miscellaneous Notes: -JJ Thomson the plum pudding model Hydrogen atoms: -Protium 1 e, 1p * Deuterium 1e, 1p, 1n * Tritium 1e, 1p, 2n -Mass # of atoms = #p + #n -Avogadro’s Number (6.022x1023) = 1 mol = mass number