Basic Atomic Structure Democritus Dalton Subatomic Particles Symbol Notation Isotopes Average Atomic Mass
Democritus ( BC) Before Democritus… Classification system: earth, wind, fire, water Named parts of matter “atomos.” (translation: not able to be cut) How did he come up with this? Later scientists realized that the atom consists of charged particles.
John Dalton’s Atomic Theory of Matter All elements are composed of tiny indivisible particles called atoms Atoms of the same element are identical, atoms of different elements are different and have different properties. Atoms of different elements can mix in whole number ratios to form compounds Chemical reactions cause atoms to separate, but not change into different atoms Which hold true?
Law of Constant Composition (Proust): In a given compound the relative numbers and kinds of atoms are constant. (postulate #3) Law of Conservation: matter can neither be created nor destroyed (postulate #4) NEW** Law of Multiple Proportions: If two elements A and B combine to form more than one compound, the masses of B that can combine with a given mass of A are in the ratio of small whole #’s. Water Vs. Hydrogen Peroxide 8.0g of O combines with 1.0g of H to form water 16g of O combines with 1.0g of H to form hydrogen peroxide What can you conclude about the ratios of hydrogen and oxygen in these two compounds?
Subatomic Particles
Three Kinds of Sub-Atomic Particles Protons: x C charge Neutrons: NO charge Electrons: x C charge Atoms have an equal # of protons and electrons so they have no NET electrical charge. For convenience, the charges are expressed as multiples rather than in coulombs. Protons have a +1 charge while electrons have a -1 charge.
Comparing Subatomic Particles The proton gives identity to an atom, the electron gives personality.
Ernest Rutherford: mation.php?ani=121&cat=Chemistry Conclusion: the nucleus is small and highy positive. Most of the atom is empty space.
Mass Number & Atomic Number Mass Number = Number of protons + neutrons Atomic Number = Number of protons
Complete the Table SymbolAtomic Number Mass Number Number of p + Number of n 0 Number of e Na S Ga 3+ 39
Isotopes Have the Same… Number of protons Atomic Number Number of electrons
Isotopes Have Different… Number of neutrons Mass Number Mass n0n0
Isotopes of Hydrogen Hydrogen-1 Hydrogen-2 Hydrogen-3 ProtiumDeuteriumTritium
The mass of an atom is EXTREMELY small! The heaviest known atom is 4x g. For convenience, (thank you)... we express the size of atoms in a derived unit, the a.m.u. (Atomic Mass Unit) Diameters of atoms fall between 1x m and 5x m, or pm, or 1-5Angstroms 1A= m (both pm and A are commonly used) How many atoms are in one penny? 24,000,000,000,000,000,000,000 or 2.4 x How many people live on this planet? 6,000,000,000 or 6 x 10 9
Atomic Mass Unit (amu) carbon-12 isotope used as standard 1 atom of carbon-12 = 12 amu carbon-12 has 12 particles with mass mass of proton = 1 amu mass of neutron = 1 amu 12 C 6
Average Atomic Mass Weighted average of all isotopes Seen as mass number on periodic table Units in amu
To Calculate Average Atomic Mass You Need… Number of Isotopes Mass of Isotopes Percent Relative Abundance
Calculating Average Atomic Mass Mass x Rel. Abundance Average Atomic Mass Isotope A Isotope B
AVERAGE ATOMIC MASS CALCULATING AVERAGE ATOMIC MASS Atomic Mass or Atomic Weight: a calculated percentage of existing isotopes according to abundance: mass isotope x % abundance (DECIMAL FORM) mass isotope x % abundance + mass isotope x % abundance
Find the Number of Neutrons: a) Oxygen-17 d)Bromine- 80 b) 32 S e) 207 Pb c) 108 Ag f) 25 Mg Write the symbols for each element with the correct atomic number and mass number in proper notation a) O-16, O-17, O-18 b) Cr-50, Cr-52, Cr-53
Element X has two natural isotopes... X-10 and X-11 X-10 weighs amu and is 19.91% abundant X-11 weighs amu and is 80.09% abundant What is the atomic mass? Naturally occurring chlorine is 75.78% 35Cl, which has an atomic mass of amu, and 24.22% 37Cl, which has an atomic mass of amu. Calculate the average atomic mass of chlorine.
Three isotopes of silicon occur in nature: 28Si (92.23%), which has a mass of amu; 29Si(4.68%), which has a mass of amu; and 30Si(3.09%), which has a mass of amu. Calculate the atomic weight of silicon. Boron has two isotopes, B-10 and B Which is more abundant? Silicon has 3 isotopes, Si-28,29,30 Which is more abundant?