CHEMISTRY The Molecular Science Chapter two Slides prepared by S. Michael Condren Department of Chemistry Christian Brothers University to Accompany CHEMISTRY The Molecular Science by John W. Moore, Conrad Stanitski, & Peter C. Jurs

Chapter 2 Elements & Atoms

Atomic Structure Electrical charges of the same type repel one another, and charges of the opposite type attract one another.

Radioactivity

Alpha Radiation composed of 2 protons and 2 neutrons thus, helium-4 nucleus +2 charge mass of 4 amu creates element with atomic number 2 lower

Beta Radiation composed of a high energy electron which was ejected from the nucleus “neutron” converted to “proton” very little mass -1 charge creates element with atomic number 1 higher

Gamma Radiation nucleus has energy levels energy released from nucleus as the nucleus changes from higher to lower energy levels no mass no charge

Structure of the Atom electrons –found in electron cloud –relative charge of -1 –relative mass of amu protons –found in nucleus –relative charge of +1 –relative mass of amu neutrons –found in nucleus –neutral charge –relative mass of amu

Millikan’s Experiment

Rutherford’s Experiment

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

Ions charged single atom charged cluster of atoms

Ions cations –positive ions anions –negative ions ionic compounds –combination of cations and anions –zero net charge

Metric Prefixes

Relative size of atom and atomic nucleus

Scanning Tunneling Microscope

Measurement and Units length - meter volume - liter mass - gram

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

Isotopes atoms of the same element which differ in the number of neutrons in the nucleus designated by mass number

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

Isotopes of Hydrogen H-2 or D, 2 H, deuterium 1 proton and 1 neutron in nucleus

Isotopes of Hydrogen H-3 or T, 3 H, tritium 1 proton and 2 neutrons in nucleus

Mass Number, A integer representing the approximate mass of an atom equal to the sum of the number of protons and neutrons in the nucleus

Nuclear Notation X-A C-12 X A C 12 Z X A 6 C 12

Masses of Atoms Carbon-12 Scale Masses of the atoms are compared to the mass of C-12 isotope having a mass of

Mass Spectrometer

Atomic Masses and Isotopic Abundances natural atomic masses = sum[(atomic mass of isotope)  (fractional isotopic abundance)]

The Mole a unit of measurement, quantity of matter present Avogadro’s Number  particles Latin for “pile”

Molar Mass Sum atomic masses represented by formula atomic masses  gaw molar mass  MM

Example How many grams of Cu are there in 5.67 mol Cu? #g Cu = (5.67 mol)(63.546g/mol) = 360. g Atomic mass of Cu

Example Calculate the number of boron atoms in 1.000g sample of the element. #B atoms = (1.000g)(1mol / 10.81g)  (6.022  atoms/mol) =  B atoms

Example How many moles of silicon, S, are in 30.5g of S? #mol Si = (30.5g)(1 mol/32.06g) = mol Si

Example What is the molar mass of methanol, CH 3 OH? MM = 1(gaw) C + (3 + 1)(gaw) H + 1(gaw) O = 1(12.011) C + 4( ) H + 1( ) O = g/mol

Example How many moles of carbon dioxide molecules are there in 6.45g of carbon dioxide? MM = 1(gaw) C + 2(gaw) O = g/mol #mol CO 2 = (6.45g)(1 mol/44.01g) = mol

Development of Periodic Table Newlands - English 1864 – Law of Octaves – every 8th element has similar properties

Development of Periodic Table Mendeleev Russian Periodic Law allowed him to predict properties of unknown elements

Mendeleev’s Periodic Table the elements are arranged according to increasing atomic weights Missing elements: 44, 68, 72, & 100 amu

Predicted Properties of Ekasilicon

Modern Periodic Table Moseley, Henry Gwyn Jeffreys 1887–1915, English physicist. studied the relations among spectra of different elements. concluded that the atomic number is equal to the charge on the nucleus based on the x-ray spectra emitted by the element. explained discrepancies in Mendeleev’s Periodic Law.

Modern Periodic Table the elements are arranged according to increasing atomic numbers

Periodic Table of the Elements

Organization of Periodic Table period – horizontal row group – vertical column

Family Names Group IAalkali metals Group IIAalkaline earth metals Group VIIAhalogens Group VIIIAnoble gases transition metals inner transition metals lanthanum seriesrare earths actinium seriestrans-uranium series

Types of Elements metals nonmetals metalloids – semimetals