Atomic Structure History of Atomic Theory (Review)

Model of an Atom (Review)

Think, Pair, ShareThink about what you already know about the history of atomic theory and write it on a piece of paper. Hint: How did Dalton, Thomson, and Rutherford contribute to development of the atomic model?

Pair up with one or two of your class members and discuss the similarities and differences between each of your answers and come up with a solution that you all agree on.

Share with the whole class!

Dalton’s Atomic Model Postulate 1: All matter is made up of small particles called atoms.

Postulate 2: An element consists of an atom of one type only.

Postulate 3: Compounds consist of atoms of more than one element.

Postulate 4: Atoms can not be created or destroyed in a chemical reaction.

Thomson’s ”Plum-Pudding” ModelNegatively charged particles submerged in a positive region like a plum-pudding (raisins are negative particles and pudding is the positive region in the analogy).

Rutherford’s scattering experiment

Source of 𝛂 - particles

Detector

Gold-Foil

𝛂 - particle is He2+ ion

Scattering Experiment PHet Simulation

https://phet.colorado.edu/sims/html/rutherford-scattering/latest/rutherford-scattering_en.html

Description of an Atom• An atom has protons (+ve), neutrons (no charge), and electrons (-ve)

• Protons and neutrons are located in the nucleus while electrons surround the nucleus in electron orbitals

Charge, Mass and Location

Subatomic Particle

Charge Mass Location

Proton +1 ~1 Nucleus Neutron 0 ~1 NucleusElectron -1 1/1836 Electron cloud

Isotopes and IonsWhat is an Isotope?

§ An atom of an element with a different number of neutrons.

§ Since it has a different number of neutrons, it has a different mass!

What is an Ion?

§ An atom of an element with a different charge due to gaining or loosing of electron(s).

Properties of Isotopes - DiffusionIs density of two isotopes different from each other?

YES!!

Density = mass/volume

Therefore species with different mass will have a different density!

Properties of Isotopes - DiffusionHow does rate of diffusion of H2 differ from the rate of diffusion of D2?

H2 atomic mass = 2

D2 atomic mass = 4

Rate of diffusion = 𝟏√𝑴

𝑅𝑒𝑙𝑎𝑡𝑖𝑣𝑒𝑟𝑎𝑡𝑒𝑠𝑜𝑓𝑑𝑖𝑓𝑓𝑢𝑠𝑖𝑜𝑛 = 5√6÷ 5

√8= √8√6= 1.4

Hydrogen diffuses 1.4 times faster than Deuterium.

Nuclear Symbol Notation (AZE)

ZEAMass Number

Atomic Number

Element Symbol

QuestionsElement Atomic Mass Atomic Number # Protons # Neutrons # Electrons

lithium 6.94 3 =Atomic #=3 =mass – Atomic#=4 =#Protons=3

carbon 12.011 6 6 6 3

chlorine 35.45 17 17 18 17

Li+ 6.94 3 3 4 2

S2- 32.06 16 16 16 18

+

32S2-16

AZE

Isotopes – Percent Abundance • Percent abundance refers to prevalence of each of an element’s isotope in nature.

Calculating average atomic mass

Mass Number Exact Weight % Abundance12 12.000000 98.9013 13.003355 1.10

Calculate the average atomic mass for carbon

𝐴𝑣𝑒𝑟𝑎𝑔𝑒𝐴𝑡𝑜𝑚𝑖𝑐𝑀𝑎𝑠𝑠 = (12.000000×EF.EG5GG

) + (13.003355×5.5G5GG

) = 12.011amu

Exercise • Calculate the average atomic mass for nitrogen

Mass Number Exact Weight % Abundance14 14.003074 99.6315 15.000108 0.37

𝐴𝑣𝑒𝑟𝑎𝑔𝑒𝐴𝑡𝑜𝑚𝑖𝑐𝑀𝑎𝑠𝑠 = (14.003074×EE.MN5GG

) + (15.000108×G.NP5GG

) = 14.007amu

Exercise

Mass Number Exact Weight % Abundance28 27.976927 92.2329 28.976495 4.6730 29.973770 3.10

Calculate the average atomic mass for Silicon

𝐴𝐴𝑀 = (27.976927×E6.6N5GG

) + (28.976495×8.MP5GG

) +(29.973770×N.5G5GG

) = 28.086amu

Homework

Atoms, Ions and Isotopes worksheet.

Isotopes and Relative Atomic Abundance Worksheet.