Chapter 2 NotesChapter 2 Notes

Atomic StructureAtomic Structure

AtomsAtoms

Democritus – Ancient Greek Science Democritus – Ancient Greek Science dude, 1dude, 1stst proposed the idea of atoms, tiny proposed the idea of atoms, tiny indivisible particlesindivisible particles

Atomos – ancient Greek word for Atomos – ancient Greek word for indivisibleindivisible

John Dalton’s Atomic TheoryJohn Dalton’s Atomic Theory

1.1. All elements are composed of All elements are composed of submicroscopic particles called atomssubmicroscopic particles called atoms

2.2. Atoms of the same element are identical. Atoms of the same element are identical. Atoms of one element are different from Atoms of one element are different from atoms of another elementatoms of another element

3.3. Atoms of different elements can combine Atoms of different elements can combine in simple whole number ratios to form in simple whole number ratios to form compoundscompounds

Cont.Cont.

4. Chemical rxn’s occur when atoms are 4. Chemical rxn’s occur when atoms are separated, joined or rearranged. However, separated, joined or rearranged. However, atoms of one element are never changed atoms of one element are never changed into atoms of another element as the result into atoms of another element as the result of a chemical reaction.of a chemical reaction.

ATOMATOM- the smallest particle of an element - the smallest particle of an element that retains the properties of that elementthat retains the properties of that element

Electrons, Protons and NeutronsElectrons, Protons and Neutrons

ElectronsElectrons- are negatively charged particles- are negatively charged particles

– Discovered by Discovered by J.J. ThomsonJ.J. Thomson in 1897 by in 1897 by bending a charged beambending a charged beam

– Elektron (greek) shining beamElektron (greek) shining beam

– http://www.chem.uiuc.edu/clcwebsite/video/Cath.mov

ProtonsProtons

Positively charged particlePositively charged particle

Discovered 1886 – E. GoldsteinDiscovered 1886 – E. Goldstein

Discovered by Henry Mosley in 1911Discovered by Henry Mosley in 1911

Protos (greek) firstProtos (greek) first

NeutronNeutron

Subatomic particle with no chargeSubatomic particle with no charge

Discovered by Discovered by James ChadwickJames Chadwick in 1932 in 1932

SymbolSymbol ChargeCharge Mass Mass (AMU)(AMU)

ElectronElectron ee-- -1-1 1/18401/1840

ProtonProton pp++ +1+1 11

NeutronNeutron nn00 00 11

The Structure of the Nuclear AtomThe Structure of the Nuclear Atom

Nucleus – central core of the atom, Nucleus – central core of the atom, composed of protons and neutronscomposed of protons and neutrons

Discovered by Earnest Rutherford in 1911Discovered by Earnest Rutherford in 1911

Gold foil Experiment

Atomic NumberAtomic Number

The number of protons in the nucleus of an The number of protons in the nucleus of an atomatom

Neutral atoms – have equal # pNeutral atoms – have equal # p++ (+ charge) (+ charge) and eand e-- (- charge) (- charge)

Mass NumberMass Number

Number of pNumber of p++ and n and n0 0 in the nucleusin the nucleus

pp+ + + n + n00 = mass = mass

Isotopes of ElementsIsotopes of Elements

Isotopes: Atoms that have the same Isotopes: Atoms that have the same number of protons, but different numbers number of protons, but different numbers of neutronsof neutrons

Carbon – 12Carbon – 12

Carbon – 13Carbon – 13

Carbon - 14Carbon - 14

Atomic MassAtomic Mass

Atomic Mass Unit (amu) – 1/12 the mass Atomic Mass Unit (amu) – 1/12 the mass of a Carbon – 12 atomof a Carbon – 12 atom

Atomic Mass – The weighted average Atomic Mass – The weighted average mass of the isotopes in a naturally mass of the isotopes in a naturally occurring sampleoccurring sample

Calculating Atomic MassCalculating Atomic Mass

Ex. Magnesium: Ex. Magnesium: Magnesium – 24 78.70%Magnesium – 24 78.70%

Magnesium – 25 10.13%Magnesium – 25 10.13%

Magnesium – 26 11.17%Magnesium – 26 11.17%

Multiply the mass number by the percent and Multiply the mass number by the percent and add up the answers to get the average mass.add up the answers to get the average mass.