Chapter 2 Atoms and Elements Dr. S. M. Condren.

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Presentation transcript:

Chapter 2 Atoms and Elements Dr. S. M. Condren

Dalton’s Atomic Theory Postulates proposed in 1803 know for first exam Dr. S. M. Condren

Dalton’s Atomic Theory Postulate 1 An element is composed of tiny particles called atoms. All atoms of a given element show the same chemical properties. Dr. S. M. Condren

Dalton’s Atomic Theory Postulate 2 Atoms of different elements have different properties. Dr. S. M. Condren

Dalton’s Atomic Theory Postulate 3 Compounds are formed when atoms of two or more elements combine. In a given compound, the relative number of atoms of each kind are definite and constant. Dr. S. M. Condren

Dalton’s Atomic Theory Postulate 4 In an ordinary chemical reaction, no atom of any element disappears or is changed into an atom of another element. Chemical reactions involve changing the way in which the atoms are joined together. Dr. S. M. Condren

Structure of the Atom protons Composed of: protons neutrons electrons found in nucleus relative charge of +1 relative mass of 1.0073 amu Dr. S. M. Condren

Structure of the Atom neutrons Composed of: protons neutrons electrons found in nucleus neutral charge relative mass of 1.0087 amu Dr. S. M. Condren

Structure of the Atom electrons Composed of: protons neutrons found in electron cloud relative charge of -1 relative mass of 0.00055 amu Dr. S. M. Condren

ATOM COMPOSITION The atom is mostly empty space protons and neutrons in the nucleus. the number of electrons is equal to the number of protons in a neutral atom. electrons in space around the nucleus. extremely small. One teaspoon of water has 3 times as many atoms as the Atlantic Ocean has teaspoons of water. Dr. S. M. Condren

Radioactivity Alpha – helium-4 nucleus Ra226  Rn222 + He4(a) Beta – high energy electron U239  Np239 + b-1 Gamma – energy resulting from transitions from one nuclear energy level to another Ni60*  Ni60 + g Dr. S. M. Condren

Penetrations of Radioactive Emissions Dr. S. M. Condren

Isotopes & Their Uses 9943Tc Emits gamma rays Heart scans with radioactive technetium-99. 9943Tc Emits gamma rays Dr. S. M. Condren

The modern view of the atom was developed by Ernest Rutherford (1871-1937). Dr. S. M. Condren

Rutherford’s Model of the Atom atom is composed mainly of vacant space all the positive charge and most of the mass is in a small area called the nucleus electrons are in the electron cloud surrounding the nucleus Dr. S. M. Condren

Nucleus If nucleus is 1” The atom would be 1.5 miles in diameter Dr. S. M. Condren

Ions Ion cations anions ionic compounds electrostatically charged atom or group of atoms cations positive ions anions negative ions ionic compounds combination of cations and anions zero net charge Dr. S. M. Condren

Atomic number, Z the number of protons in the nucleus the number of electrons in a neutral atom the integer on the periodic table for each element 13 Atomic number Al Atom symbol 26.981 Atomic weight Dr. S. M. Condren

Dr. S. M. Condren

Imaging Dr. S. M. Condren

Which best represents the poles? Dr. S. M. Condren

Quantum Corral http://www.almaden.ibm.com/vis/stm/corral.html Dr. S. M. Condren

Mass Number, A C atom with 6 protons and 6 neutrons is the mass standard = 12 atomic mass units (u) Mass Number (A) = # protons + # neutrons A boron atom can have A = 5 p + 5 n = 10 u Dr. S. M. Condren

Isotopes atoms of the same element which differ in the number of neutrons in the nucleus designated by mass number Dr. S. M. Condren

Isotopes of Hydrogen H-1, 1H, protium 1 proton and no neutrons in nucleus only isotope of any element containing no neutrons in the nucleus most common isotope of hydrogen Dr. S. M. Condren

Isotopes of Hydrogen H-2 or D, 2H, deuterium 1 proton and 1 neutron in nucleus Dr. S. M. Condren

Isotopes of Hydrogen H-3 or T, 3H, tritium 1 proton and 2 neutrons in nucleus radioactive electron antineutrino Dr. S. M. Condren

The radioactive isotope 14C has how many neutrons? 6, 8, other Dr. S. M. Condren

protons, neutrons, electrons The identity of an element is determined by the number of which particle? protons, neutrons, electrons Dr. S. M. Condren

Mass Spectrometer a simulation is available at http://www.colby.edu/chemistry/OChem/DEMOS/MassSpec.html Dr. S. M. Condren

Mass spectrum of C6H5Br Dr. S. M. Condren

Atomic Masses and Isotopic Abundances natural atomic masses = SUM[(atomic mass of isotope) *(fractional isotopic abundance)] Dr. S. M. Condren

Example: Chlorine has two isotopes, Cl-35 and Cl-37, which have masses of 34.96885 and 36.96590 amu, respectively. The natural atomic mass of chlorine is 35.453 amu. What are the percent abundances of the two isotopes? let x = fraction Cl-35 y = fraction Cl-37 x + y = 1 y = 1 - x (AW Cl-35)(fraction Cl-35) + (AW Cl-37)(fraction Cl-37) = 35.453 Thus: 34.96885*x + 36.96590*y = 35.453 34.96885*x + 36.96590*(1-x) = 35.453 x = 0.75757 <=> 75.757% Cl-35 Thus 24.243% Cl-37 Dr. S. M. Condren

Molar Mass-Molecular Weight Sum atomic masses represented by formula atomic masses => gaw molar mass => MM Dr. S. M. Condren

Example What is the molar mass of ethanol, C2H5O1H1? MM = 2(gaw)C + (5 + 1)(gaw)H + 1(gaw)O = 2(12.011)C + 6(1.00794)H + 1(15.9994)O = 24.022 + 6.04764 + 15.9994 = 46.069 g/mol Significant figures rule for multiplication Significant figures rule for addition Sequence – multiplication then addition, apply significant figure rules in proper sequence Dr. S. M. Condren

The Mole a unit of measurement, quantity of matter present Avogadro’s Number 6.022 x 1023 particles Latin for “pile” Dr. S. M. Condren

One Mole of each Substance Clockwise from top left: 1-Octanol, C8H17OH; Mercury(II) iodide, HgI2; Methanol, CH3OH; and Sulfur, S8. Dr. S. M. Condren

Example How many moles of carbon dioxide molecules are there in 10.00g of carbon dioxide? MM = 1(gaw)C + 2(gaw)O = 44.01 g/mol #mol CO2 = (10.00g) / / (1 mol/44.01g) = 0.2272 mol Dr. S. M. Condren

Mendeleev’s Periodic Table Missing elements: 44, 68, 72, & 100 amu Dr. S. M. Condren

Properties of Ekasilicon Dr. S. M. Condren

Modern Periodic Table the elements are arranged according to increasing atomic numbers Dr. S. M. Condren

Periodic Table of the Elements Dr. S. M. Condren

Organization of Periodic Table period - horizontal row group - vertical column Family Names Group IA alkali metals Group IIA alkaline earth metals Group VIIA halogens Group VIIIA noble gases transition metals inner transition metals lanthanum series rare earths actinium series trans-uranium series Dr. S. M. Condren

Dr. S. M. Condren

ELEMENTS THAT EXIST AS MOLECULES Allotropes of C Dr. S. M. Condren

Dr. S. M. Condren

ELEMENTS THAT EXIST AS DIATOMIC MOLECULES Dr. S. M. Condren

AS POLYATOMIC MOLECULES ELEMENTS THAT EXIST AS POLYATOMIC MOLECULES S8 sulfur molecules White P4 and polymeric red phosphorus Dr. S. M. Condren