Atomic Structure Standard Atomic Notation Isotopes Isotopic Abundance

Learning Goals Students will be able to: understand standard atomic notation explain the relationship between the atomic number and the mass number of an element, and the difference between isotopes and radioisotopes of an element identify the scientists who contributed to the development of the modern Periodic Table

Success Criteria Students will be able to: writing radioactive decay equations determining the number of protons, neutrons and electrons in an atom. explaining the contributions of scientists who developed the modern Periodic Table Calculate average atomic abundance using isotopic abundance values

Atomic Theory and The Periodic Table Review the development of atomic theory: Read pages for Mendeleev and Döbereiner Read pages for Bohr and Rutherford Read page 27 for Soddy Review the information on the various groups within the periodic table. Read pages for basic Chemistry term and Information on the elements Read pages on the groups within the periodic table

Modern View of Atomic Structure The atom has 2 main regions a)Nucleus - protons and neutrons b)Electron cloud- region where you might find an electron Rutherford’s Gold Foil experiment (remember grade 9) proved that the atom has an extremely dense, heavy nucleus surrounded by mostly empty space (save for some very light electrons).

Rutherford’s Gold Foil Experiment The Gold Foil Experiment

The gold foil is only a few atoms thick. Most of the positively charged α -particles pass straight through the gold foil A few are deflected the tiny positively charged nuclei of the gold atoms

Density and the Atom Since most of the α -particles went through the gold atoms in the thin gold foil, it proved that the atom was mostly composed of empty space. Since alpha particles are positively charged (they are actually the nuclei of helium atoms), they must be deflected by a positively charged “nucleus”. Since so few of the α -particles were deflected, the nucleus must be very small This nucleus was determined to contain almost all of the atoms mass.

Size of an atom Atoms are small. Measured in picometers, meters Hydrogen atoms have a 32 pm radius IF the atom was the size of a stadium, the nucleus would be the size of a marble. Hence most of an atom is empty space – thus you are mostly made out of nothing. Radius of the nucleus near m. The density of the nucleus is near g/cm 3 A dice made of a nucleus would weigh 100,000,000 tonnes (this equals 1000 supertankers).

Subatomic particles Electron Proton Neutron NameSymbolCharge Relative mass Actual mass (g) e-e- p+p+ n0n /184 or ≈ x x

Standard Atomic Notation Contain the symbol of the element (X), the mass number (A) and the atomic number (Z) X mass number (A) atomic number (Z) element symbol 12

Standard Atomic Notation Remember from grade 9: 1) Symbol 1 or 2 letter - the first is always a capitol the symbols of many elements come from their latin roots (ex. Gold (Au = aurum)) 2) Atomic Number the number of protons in the nucleus (atom) 3) Mass Number the mass of the atom - since almost all of the mass comes from the nucleus; mass number = number of protons + number of neutrons

Standard Atomic Notation the area to the top right of the symbol is used for ionic charge the area to the bottom right of the symbol is used for number of atoms (ex. H 2 )

Standard Atomic Notation FIND THE NUMBER OF PROTONS, NEUTRONS AND ELECTRONS FOR AN ATOM 1) Protons = atomic number 2) Electrons = atomic number unless an ionic charge is indicated (remember a positive charge indicates that electrons were LOST) 3) Neutrons = atomic mass - atomic number (can you explain this?)  Find the number of protons, neutrons and electrons for the two atoms at left

Symbols  Find the  number of protons  number of neutrons  number of electrons  atomic number  mass number F

Symbols  Find  Find the  number  number of protons of neutrons of electrons  atomic  atomic number  mass  mass Number Br

Symbols n If an element has an atomic number of 34 and a mass number of 78 what is the  number of protons  number of neutrons  number of electrons  standard atomic notation 18

Symbols n If an element has 91 protons and 140 neutrons and an ionic charge of what is the  atomic number  mass number  number of electrons  complete symbol 19

Isotopes Soddy determined that atoms of the same element can have different numbers of neutrons This means that an element can have different mass numbers Soddy called these atoms isotopes. Carbon has 3 isotopes, only 1 is common.

Naming Isotopes Put the mass number after the name of the element carbon- 12 or C-12 carbon -14 or C-14 uranium-235 or U g (Tyler DeWitt _ Isotopes) g (Tyler DeWitt – Isotopes and Elements examples)

Isotopes and Atomic Mass For example magnesium has 3 naturally occurring isotopes with masses of 24, 25 and 26. What atomic mass should be placed in the periodic table? Scientists decided that the average weight of the atoms based on the abundance should be placed on the periodic table as the atomic mass. This explains why mass values have decimals. (Tyler DeWitt)

Determining Isotopic Abundance The Mass Spectrometer

Determining Isotopic Abundance of Magnesium

Determining Isotopic Abundance The Mass Spectrometer Mass Spectrometer scan of a protein found in a performance enhancing drug at the Olympics. Mass Spectrometer read-out of Magnesium isotopes.

Try these questions Calculate the relative atomic mass of gallium given that the relative abundance of its two isotopes are: 60.5% of Ga-69 and 39.5% of Ga-71. Iron has four isotopes; Fe-54 (5.82%); Fe-56 (91.66%); Fe- 57 (2.19%) and Fe-58 (0.33%). Determine the average atomic mass for natural iron. Magnesium has three isotopes % magnesium 24 with a mass of amu, 10.00% magnesium 25 with a mass of amu, and the rest magnesium 25 with a mass of amu. What is the atomic mass of magnesium? (note the more accurate data) If not told otherwise, the mass of the isotope is the mass number in amu (atomic mass units)