Unit: Atomic Structures Mr. Nylen Pulaski Academy High School 2008 PACS 2008

The Modern Atom Atom – smallest indivisible particle of matter Each specific element is made up of the same type of atoms Every Hydrogen atom has the same number of subatomic particles Every Helium atom has the same number of subatomic particles PACS 2008

Atoms Hydrogen Atom Oxygen Atom Element (H) Element (Oxygen) Compounds (H2O) PACS 2008

Sub-Atomic Particles Atoms are made up of subatomic particles Protons Electrons Neutrons All atoms contain subatomic particles A group of atoms making up an element are all IDENTICAL PACS 2008

The main sub-atomic particles Charge Mass Symbol Location Proton 1 1 amu H+ , or + Nucleus Neutron Electron -1 0 amu e- , or - Outer shell PACS 2008

Atomic Mass Mass of the atom – made up mostly of mass of protons and neutrons Measured in Atomic Mass Units 1 amu = 1/12 the mass of a Carbon-12 atom (the standard for all relative atomic masses) PACS 2008

Atomic Mass (A) Since a proton = 1 amu, and a neutron = 1 amu (or u), atomic mass also represents the number of protons and neutrons in the nucleus Electrons have negligible weight and aren’t factored in to atomic mass PACS 2008

Atomic Number (Z) Represents the charge in the nucleus For atoms this means Z = the number of protons in the nucleus This is what makes an atom of an element different compared to other elements PACS 2008

Charting Atoms/Elements Symbol – Accepted letter or letters representing that atom (or element) Atomic Number – Directly proportional to number of protons in the nucleus Also represents charge in the nucleus Atomic Mass – Mass of the nucleus Remember, electrons are negligible Protons + Neutrons PACS 2008

Charting Atoms/Elements Number of Protons – Same as atomic number, or usually half of atomic mass Number of electrons Assuming atom or element has zero charge # Electrons equal the number of protons Number of neutrons All the mass of an atom is made up of protons + neutrons We know the number of protons so we can calculate the number of neutrons PACS 2008

Page 4-5 Work in small groups PACS 2008

Together Notes p. 6 and 7 PACS 2008

Isotopes Atoms of the same element (w/same # of protons and same charge) BUT different number of neutrons (therefore different atomic mass) Ex. The 3 naturally occurring isotopes of CARBON Carbon 12, Carbon 13, Carbon 14 PACS 2008

Carbon 12, 13, and 14 14 PACS 2008

Isotopes of Hydrogen Hydrogen usually has 1 proton, and atomic mass of 1 Isotopes of Hydrogen can have an atomic mass of 2 or 3 How many protons in these isotopes? How many neutrons? PACS 2008

Page 8, Weighted Atomic Mass Atomic mass shown in periodic table is a weighted average of the masses of the naturally occurring isotopes of the element. This is why hydrogen has a mass of 1.00074 PACS 2008

Weighted Atomic Mass You take an exam having three parts. The first multiple choice part is weighted 20%, the second part is weighted 40%, and the third part is weighted 40% A student scores the following Exam Score Weighted Percent Fraction of points earned Overall Score Part A - 80 20% Part B - 72 40% Part C - 94 PACS 2008

Weighted Atomic Mass An element has three isotopes (different number of neutrons). What is the weighted atomic mass of the element? Isotope % abundance in nature Fractional Abundance Product Carbon 12 98.9% 12 * (.989) = Carbon 13 1.05% 13 * (.0105) = Carbon 14 .05% 14 * (.0005) = Weighted Atomic Mass: PACS 2008

Weighted Atomic Mass (K) Isotope % abundance in nature Fractional Abundance Product K- 39 93.12% K- 40 6.88% Weighted Atomic Mass: PACS 2008

Lab – Isotopes of Pennium PACS 2008

Problem Set – Pg. 9 PACS 2008

Isotopes = neutrons Ions = electrons PACS 2008

Page 10 - Ions Atoms with a net charge. Formed when atoms gain or lose electrons (If an element loses a proton it isn’t the same element anymore!) Therefore the number of protons doesn’t equal the number of electrons PACS 2008

Ions - continued If we lose electrons, we become more positive (take away negative charge) If we gain electrons, we become more negative (adding negative charge) If we lose or gain protons, we completely change the atom or element! PACS 2008

Ions - SUMMARY Never change # of protons Charge comes from # electrons If electrons = protons, charge is 0 If electrons > protons, charge is negative If electrons < protons, charge is positive Neutrons are used to make up difference in atomic mass ONLY (they have no charge) PACS 2008

Classwork Finish table at bottom of page 10 PACS 2008

Lab - Page 11 - 14 PACS 2008

Homework Read section 3-2 in text Do p. 6-7 At. Structure notes PACS 2008

Ions – Counting neutrons… Bottom of page 10 PACS 2008

Isotope Lab PACS 2008

Pages 16 – 21 in Notes Answer questions in notes Work in computer lab Work quietly as there is a class next door PACS 2008

Models of the atom Dalton’s Indivisible Atom J.J. Thomson’s Plum Pudding Model Rutherford’s Solar System Model PACS 2008

Dalton’s Indivisible Atom Elements consist of tiny particles called “atoms” Atoms of different elements are different Compounds have constant composition because they contain a fixed ratio of atoms tiny, indivisible, indestructible particles PACS 2008

J.J. Thomson’s “Plum Pudding” Model Discovered e- in 1897 Also called chocolate chip cookie model How does this differ from what we know about the modern theory of the atom? PACS 2008

Rutherford’s Atom “Gold foil” experiment Region of dense charge in center of atom Electrons orbit around this “center” PACS 2008

Bohr’s Modern Theory Most accepted during mid/late 1900’s e- actually fill imaginary “shells” PACS 2008

Wave Mechanical Model Electrons aren’t in “shells”, but rather are in “regions of probability” PACS 2008

Posters Create a poster outlining one of the models of the atom we talked about Dalton J.J. Thomson Rutherford (gold foil experiment or atom) Bohr Wave Mechanical Sequential Development of the atom Poster should contain visuals as well as any other necessary information You will be graded as a group and you will present these to the class PACS 2008

Light as a Wave – Electromagnetic Radiation Visible light is energy that travels in the form of an electromagnetic wave We can use a sine wave drawing as a model of an electromagnetic wave. Wavelength = λ crest wavelength crest wavelength PACS 2008

Light as a Wave Wave frequency – The number of crests passing a point each second. Units = 1/seconds (Hertz, Hz) Wave speed = The speed of all electromagnetic waves in a vacuum is 3x108 m/s (This is the speed of light) c = f λ c = speed of light, f = frequency, λ = wavelength PACS 2008

Electromagnetic Spectrum PACS 2008

Spectra Looks like a rainbow All frequencies of visible light in one continuous band Produced by passing white light through a prism PACS 2008

Bright Line (Emission) Spectra Looks like bright colored lines on a colored background Only specific frequencies of visible light observed, called Spectral Lines Produced by adding energy (by putting in a flame or adding electricity) and viewing light through a prism Emission spectra is like a fingerprint for an element PACS 2008

Emission Spectra PACS 2008

Bohr Model of the Atom Applied Quantum Theory to the Atom Energy is absorbed and emitted by atoms in discrete amounts Electrons may only be located in specific orbits Electrons possess definite amounts of energy

Bohr Model Electrons arrange themselves in specified energy orbits around nucleus Electrons fill lower energy levels first Arrangement of electrons equals electron configuration

Principal Energy Levels K shell (holds 2 electrons) L shell (holds 8 electrons) M shell (holds 18 electrons) N shell (holds 36 electrons) If electrons absorb exactly the difference between 2 orbits, they will “jump up” This is an all or nothing proposition This jumping orbital change causes emission spectra

Lab – Spectral Lines PACS 2008

Quiz Models of the Atom PACS 2008

Ground State vs. Excited State The normal energy configuration of electrons Electrons occupy Lowest orbits first Very energetically stable Excited State Electrons absorb energy from external source Electrons jump to higher orbits Higher than normal orbits = excited state

Excited State Very unstable Electrons want to fall back to ground state Energy is released when electrons fall back In the form of electromagnetic radiation These can be in visible range (photons) Each jump represents EMR frequence of energy PACS 2008

Electron Configurations Add up # electrons Match to element on periodic table See if electron configuration matches that on periodic table (if so, it is in ground state) If no, then it is in excited state Example: 12Mg Ground = 2-8-2 Excited = 2-7-3, or 1-8-3, or 1-7-4 PACS 2008

Practice Zinc = atomic number 30 Electron configuration = 2-5-8 30 electrons Ground state = 2-8-18-2 Electron configuration = 2-5-8 15 electrons, atomic number 15 = Element Phosphorous Ground state = 2-8-5, so it must be excited Notice: Total number of electrons do not change from ground to excited state PACS 2008

More Practice Electron configuration 2-7 Number of electrons = Atomic Number must equal… Element must be… Ground state for element is… Does Ground state match 2-7… PACS 2008

Try the last 2 on your own PACS 2008

Quantum Mechanical Model of the Atom Incorporated findings that electrons behave like waves and particles Electrons do not move in definite, fixed orbits, they move in areas around the nucleus called orbitals Orbital = region of space around nucleus where an electron of a certain energy is MOST LIKELY to be found PACS 2008

Notes pg. 26 Use Text 3-3 as a guide Part 2: Type of radiation means Tv, microwaves, infrared, etc. For visible spectrum, list the 7 colors of the rainbow (which has the highest wavelength?) PACS 2008

Review Activity PACS 2008

Homework Pg. 28 in notes PACS 2008