Atoms, Elements, Molecules and Compounds

Atoms, Elements, Molecules and Compounds A Systematic Study of Chemistry

Systematic Study of Matter Fundamental Particles (p+, no,e-) >>> Atoms Elements Molecules Compounds Reactions

Fundamental Particles • Protons • Defines Atomic Number (Element’s Position on Periodic Table) • Has Positive Charge • Atomic Mass = 1.000 amu* • Rest Mass = 1.672 x 10-27 Kg • Internal Energy Content = 1.503 x 10-10 J = 938 MeV ( a candle burns at ~350 Kj) • Discovery: In 1911 Ernest Rutherfordwho performed many experiments to explore radioactivity did an experiment in which he discovered that the atom must have a concentrated positive center charge that contains most of the atom's mass. He suggested that the nucleus contained a particle with a positive charge the proton. *amu: atomic mass unit (relative mass scale ~C-12)

Fundamental Particles • Neutrons • Composition is one proton + one electron (p+ + e- => no) • Has ‘neutral’ charge • Relative Atomic Mass = 1.000 amu • Atomic Rest Mass = 1.675 x 10-27 Kg • Internal Energy Content = 1.503 x 10-10J= 939 MeV ( a candle burns at ~350 Kj) – Same as proton. • Discovery: James Chadwick in 1932 after performing numerous experiments on elemental radioactive particles discovered the neutron as a nuclear particle consisting of 1 proton and 1 electron and having a neutral charge and a rest mass slightly larger than the proton.

Fundamental Particles • Electrons • Define electronic structure of electron cloud • Atomic mass = 1/1837th the mass of the proton • Atomic rest mass = 9.11 x 10-31 Kg • Internal Energy Content = 8.199 x 10-14J = 0.511 MeV* • Discovery: In 1896, the British physicist J. J. Thompson, with his colleaguesJohn Townsend and H. A. Wilson, performed experiments indicating that cathode rays (electron beams) really were unique particles having a specific charge and mass. *From ΔE = mc2 ; This is the energy ↔ mass conversion equivalence ≡ Mass Defect. That is, the calculated mass is greater than the true mass by an amount = Mass Defect.

Discovery of the Electron http://www.youtube.com/watch?v=IdTxGJjA4Jw

Atoms & Elements • The Atom: The smallest particle of matter having specific chemical and physical properties and cannot be broken down by ordinary chemical or physical means; i.e. heat, light or electricity. • Elements: A collection of atoms all having the same structure as well as the same chemical and physical properties. Elements cannot be broken down by ordinary chemical or physical means; i.e. heat, light or electricity.

Molecules and Compounds • Molecules: The smallest particle of matter consisting of two or more elements chemically combined and having characteristic chemical and physical properties. • Compounds: A collection of molecules all having similar structure as well as similar chemical and physical properties. Compounds ( and, molecules ) can be broken down into it’s component elements by physical and/or chemical means; i.e., heat, light and electricity.

Atoms • Basic Atomic Structure • 2 Parts: Nucleus & Electron Cloud

Atoms • Models of the Atom • Thompson ‘Plum Pudding’ Model • Rutherford ‘Shell’ Model • Bohr ‘Concentric Ring’ Model • Schrodinger ‘Quantum’ Model

Atoms • Number of Protons, Neutrons and Electrons from Periodic Table The Element Block Atomic Mass (A) Z X Atomic Number (Z) [ p+ + no ] A [ p+ ] Atomic Mass (A) – Atomic Number (Z) = Number of Neutrons For a ‘Neutral’ element, #protons = #electrons

Elements • Elements: A collection of atoms all having the same structure as well as the same chemical and physical properties. Elements cannot be broken down by ordinary chemical or physical means; i.e. heat, light or electricity. • There are 118 elements on the Periodic Chart • Elements are classified according to properties and arranged in order of increasing atomic number; i.e., number of protons in the nucleus.

The Periodic Law • The chemical and physical properties of the elements are a periodic function of their atomic number. • Elements are Classified in terms of • Groups or families of elements all having similar reactive properties • Block groups of elements in terms of Metals, Non-metals and Metalloids

Element Groups • Element groups are vertical columns containing structures with similar chemical and physical properties. These include: • Group IA – Alkali Metals: Li, Na, K, Rb, Cs, Fr • Group IIA – Alkali Earth Metals: Be, Mg, Ca, Sr, Ba, Ra • Group VIIA – Halogens: F, Cl, Br, I, At • Group VIIIA – Noble Gases: He, Ne, Ar, Kr, Xe, Rn • Groups IIIA – VIA • Nonmetal Main Group Elements • Metallic Main Group Elements • B-Group Transition and Inner Transition Metals

Classification of Elements

Elements - Variations in Atomic Structure • Nuclear Variations (Isotopes) = A set of elements all having the same atomic number but different atomic masses. • Electronic Variations (Ions) = Charged Particles. Elements tend to gain or lose electrons at the valence level by the ‘path of least resistance’ to achieve a noble gas configuration.

Elements – Isotopes • Isotopes are a mixture of the same element but not all having the same mass. • The mass variation is due to number of neutrons in the nucleus. • Isotopes of Hydrogen

Elements - Isotopes • Determining Weight Average Atomic Weight • Weight Averaging is the statistical average of a mixture of similar objects but having different weight values. • Wt. Avg. Atomic Wt. = Σ (Weight Avg. Contributions) (WtAvg Contribution = Isotopic Wt. x Fractional Abundance)

Elements – Isotopes • Problem Types • Determining the Wt Average Atomic Weight of a mixture of Isotopes WtAvg At. Wt (amu) = Σ(Isotopic Mass x Relative Abundance) • Determining the relative abundance (percent or fractional) of isotopes Simultaneous Equations for Wt. Avg. Atomic Wt. and Sum of Relative abundance = 1.000.

Elements - Isotopes • Isotopes of Oxygen

Elements - Isotopes • Problems – Isotopes Chlorine consists of the following isotopes, determine its weight average atomic weight.

Elements – Isotopes • Problems – Isotopes • The average atomic mass of Eu is 151.96 amu. There are only two naturally occurring isotopes of europium, If 151Eu with a mass of 151.0 amu and 153Eu with a mass of 153.0 amu. What is the natural abundance of each of the isotopes? • There are only two naturally occurring isotopes of copper, 63Cu and 65Cu. Calculate the natural abundance of each isotope.

Elements - Ions • Ions are charged particles • Types are Cations (+) and Anions (-) • Ions are formed from the gain or loss of electrons at the valence level during chemical process. • Cations >>> from loss of electrons (#p+ > #e-) • Anions >>> from gain of electrons (#p+< #e-) • The driving force of ion formation is the natural tendency of elements to gain or lose electrons by the path of least resistance.

Periodic Trends in Ion Formation Tend to Gain Electrons >> Anions (-) Tend to Lose Electrons >> Cations(+) Nonmetals & Main Group Metalics Metals

Atoms, Elements, Molecules and Compounds