Unit 3Atomic Structure

Chemistry IMr. Patel

SWHS

Topic OutlineLearn Major IonsDefining the Atom (4.1)Subatomic Particles (4.2)Atomic Structure (4.2)Ions and Isotopes (4.3)Nuclear Chemistry (25.1)

Defining the AtomAtom – the smallest particle of an

element that retains its identityCan not see with naked eyeNanoscale (10-9 m)Seen with scanning

tunneling electronmicroscope

DemocritusDemocritus was a Greek to first

come up with idea of an atom.

His belief: atoms were indivisible and indestructible. = WRONG!

Atom comes from “atmos” - indivisible

Dalton’s Atomic Theory2000 yrs later, John Dalton used

scientific method to transform Democritus’s idea into a scientific theory

Dalton put his conclusions together into his Atomic Theory (4 parts)

Dalton’s Atomic Theory1. All elements are composted of tiny,

indivisible particles called atoms.

Dalton’s Atomic Theory2. Atoms of the same element are

identical. Atoms of different elements are different

Dalton’s Atomic Theory3. Atoms of different elements can

physically mix or chemically combine in whole number ratios.

Dalton’s Atomic Theory4. Chemical reactions occur when

atoms are separated, joined, or rearranged. Atoms of one element can never be changed into atoms of another element due to a chemical reaction.

The ElectronParticle with negative charge

Discovered by J.J. Thomson

Used cathode ray (electron) beam and a magnet/charged plate.

Millikan found the charge and mass

The Proton and NeutronAn atom is electrically nuetral

If there is a negative particle then there must be positive particle

Proton – particle with positive charge

Chadwick discovered neutron – neutral charge

Thomson’s Atomic ModelElectrons distributed in a sea of

positive chargePlum Pudding Model

Rutherford’s Atomic ModelPerformed Gold-Foil ExperimentBeam of Alpha particles with positive

charge shot at thin piece of gold foilAlpha particles should have easily passed

through with slight deflection due to positive charge spread throughout.

Results: Most particles went straight through with no deflection. Some were deflected at large angles.

Rutherford’s Atomic ModelThe nucleus is the central part of the

atom containing protons and neutronsPositive chargeMost of the mass

Electrons are located outside the nucleusNegative chargeMost of the volume

Atomic Number An element is defined only by the

number of protons it contains

Atomic Number – number of protons

Number of protons = number of electronFor a neutral element

Identify the number of Protons1. Zinc (Zn)

2. Iron (Fe)

3. Carbon (C)

4. Uranium (U)

1. 30

2. 26

3. 6

4. 92

Mass NumberNucleus contains most of the mass

Mass Number – total protons and neutrons

Number of neutron = Mass # – Atomic #

Identify # of Subatomic Particles1. Lithium

(MN = 7)

2. Nitrogen(MN = 14)

3. Fluorine(MN = 19)

**MN = Mass Number

1. 3 p+ , 3 e-, 4 n0

2. 7 p+ , 7 e-, 7 n0

3. 9 p+ , 9 e-, 10 n0

Differences in Particle NumberDifferent element: different number of

protons

Ions – same number of proton, different number of electrons

Isotope – same number of proton, different number of neutronsDifferent Mass Numbers

Two Notations for AtomsNuclear Notation

Write the element symbolOn left side, superscript = Mass NumberOn left side, subscript = Atomic Number

Isotope –Hyphen NotationWrite full name of elementOn right side, put a dashOn right side put Mass Number after dash

Hydrogen - 3

Ex: Three isotopes of oxygen are oxygen-16, oxygen-17, and oxygen-18. Write the

nuclear symbol for each.

Ex: Three isotopes of chromium are chromium-50, chromium-52, and chromium-53. How many neutrons are in each isotope?

Ex: Calculate the number of neutrons for 99

42Mo.

Atomic MassAtomic Mass Unit (amu) – one-twelfth of

the mass of the carbon-12 atom

Different isotopes have different amu (mass) and abundance (percentage of total)

Atomic Mass – weighted average mass of the naturally occurring atoms.Isotope MassIsotope Abundance

Atomic MassBecause abundance is considered, the

most abundant isotope is typically the one with a mass number closest to the atomic mass.

Example, Boron occurs as Boron-10 and Boron-11. Periodic Table tells us Born has atomic mass of 10.81 amu.Boron-11 must be more

abundant

Calculating Atomic MassConvert the Percent Abundance to

Relative Abundance (divide by 100)

Multiple atomic mass of each isotope by its relative abundance

Add the product (from step above) of each isotope to get overall atomic mass.

Ex: Calculate the atomic mass for bromine. The two isotopes of bromine have atomic masses and percent abundances of 72.92 amu (50.69%) and 80.92 amu

(49.31%).

Ex: Calculate the atomic mass for X. The four isotopes of X have atomic masses and percent abundances of 204 amu

(1.4%), 206 amu (24.1%), 207 amu (22.1%), and 208 amu (52.4%).

Ex: Calculate the atomic mass for H. The three isotopes of H have atomic masses and percent abundances of 27

amu (85%), 26 amu (10%), and 28 amu (5%).

Nuclear RadiationRadioactivity – nucleus emits particles

and rays (radiation)

Radioisotope – a nucleus that undergoes radioactive decay to become more stable

An unstable nucleus releases energy through radioactive decay.

Nuclear RadiationNuclear force – the force that holds

nuclear particles together Very strong at close distances

Of all nuclei known, only a fraction are stableDepends on proton to neutron ratioThis region of stable nuclei called band

of stability

Half LifeHalf Life – the time required for one-

half the sample to decayCan be very short

or very long

Symbol Element Radiation Half-Life Decay Product

U-238 Uranium-238 alpha 4,460,000,

000 years Th-234

Th-234 Thorium-234 beta 24.1 days Pa-234

Pa-234 Protactinium-234 beta 1.17

minutes U-234

U-234 Uranium-234 alpha 247,000

years Th-230

Th-230 Thorium-230 alpha 80,000

years Ra-226

Ra-226 Radium-226 alpha 1,602

years Rn-222

Rn-222 Radon-222 alpha 3.82 days Po-218

Po-218 Polonium-218 alpha 3.05

minutes Pb-214

Pb-214 Lead-214 beta 27 minutes Bi-214

Bi-214 Bismuth-214 beta 19.7

minutes Po-214

Po-214 Polonium-214 alpha

1 microseco

ndPb-210

Pb-210 Lead-210 beta 22.3 years Bi-210

Bi-210 Bismuth-210 beta 5.01 days Po-210

Po-210 Polonium-210 alpha 138.4 days Pb-206

Pb-206 Lead-206 none stable (none)

Ex: The original amount of sample was 100 g. The amount currently remaining is 25 g.

How many half-lives has gone by?

Ex: The original amount of sample was 100 g. The amount currently remaining is 25 g after 30 minutes. What is the half life?

Ex: The original amount of sample was 100 g. The amount currently remaining is 6.25 g. The half life

is 50 years. How much time has passed?

Types of RadiationAlpha Radiation (Helium Atom)

Low penetrating powerPaper shielding

Beta Radiation (Electron)Moderate penetrating powerMetal foil shielding

Gamma Radiation (Pure energy)Very high penetrating powerLead/concrete shielding

Nuclear Decay EquationsTransmutation – conversion from one element to

another through a nuclear reactionOnly occur by radioactive decayOnly when nucleus bombarded with a particle

Emissions – given offAlpha Emission, Beta Emission, Positron EmissionPositron = beta particle with a positive charge

Captures – taken inElectron Capture

Ex: Show a Beta Emission of Copper-66.

Ex: Show an Electron Capture of Nickel-59.

Ex: Show a Positron Emission of Boron-8.

Ex: Show an Alpha Emission of Thorium-232.