FAIR USE STATEMENT: Please feel free to edit and use this presentation in your classroom. Please do not remove the credit line on the title page or republish the file in whole or in part as your own. Please do not distribute the file to individuals or at conferences or workshops. I am more than willing to share the presentation with anyone that contacts me at The images used in the presentation are not original and the presentation is distributed freely but only for classroom instruction. Please feel free to edit and use this presentation in your classroom. Please do not remove the credit line on the title page or republish the file in whole or in part as your own. Please do not distribute the file to individuals or at conferences or workshops. I am more than willing to share the presentation with anyone that contacts me at The images used in the presentation are not original and the presentation is distributed freely but only for classroom instruction. Rhonda Alexander

Atomic Structure & Periodicity

Chapter 3 - Atoms Democritus – a Greek philosopher 400 BC * ‘Atomos’ – atoms are indivisible. * ‘Atomos’ – atoms are indivisible. A – notTomos - cutting

Dalton’s Atomic Theory John Dalton – English school teacher John Dalton – English school teacher He proposed an explanation for several laws He proposed an explanation for several laws All matter is composed of small particles called Atoms Atoms of a given element are identical in size, mass, & other properties Atoms cannot be subdivided, created, or destroyed Atoms combine in simple whole-number ratios In a rxn, atoms are combined, separated, or rearranged

Law of Conservation of Mass (Energy) Matter is neither created nor destroyed. Matter is neither created nor destroyed. It only changes form. It only changes form. If 5 g of element A combines with 10 g of element B to form AB. How many grams of AB are formed? If 5 g of element A combines with 10 g of element B to form AB. How many grams of AB are formed?

Law of Definite Proportion A chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or the source of the compound A chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or the source of the compound Table salt – NaCl % Na & % Cl

Law of Multiple Proportions Two or more different compounds are composed of the same two elements, the masses of the 2 nd element combine with a certain mass of the 1 st element can be expressed as ratios of small whole numbers. Two or more different compounds are composed of the same two elements, the masses of the 2 nd element combine with a certain mass of the 1 st element can be expressed as ratios of small whole numbers. Water vs. Peroxide H 2 O H 2 O 2

Water vs. Hydrogen Peroxide

Cathode Ray tube 6. ***Sir Joseph John Thomson – 1897 *** Electrons are composed of negatively charged subatomic particles. Discovery of the Electron 1.Different gases glow with different colors if a current is passedthrough the tube. 2.Glass directly opposite the cathode glows. 3.An object placed in between will cast a shadow. 4.A paddle wheel will roll along on its rails from cathode toward the anode. 5. Rays are deflected away from a negative electrode.

Cathode Ray tube

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Development of Atomic Models

Robert A. Millikan 1909 American physicist showed that the mass of the electron is X 10 –31 kg American physicist showed that the mass of the electron is X 10 –31 kg Confirmed the electrons carry a negative charge and its mass. Brought about more questions about the atomic structure. 1.Atoms are neutral 2.Atoms have mass

Robert Millikan: Oil Droplet Experiment Not in handout

Rutherford Experiment: Nuclear Atom Not in handout

Recording of Rutherford

Discovery of the Atomic Nucleus Ernest Rutherford – 1911 Gold Foil Experiment ‘As if you had fired a 15 – inch shell at a piece of tissue paper And it came back to hit you.’

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IN NUCLEUS Protons - + charge p + Nuetrons – neutral n o Isotopes – atoms of the same element w/ different masses. In The early 20 th century, Rutherford showed that most of an atom’s mass is concentrated in a small positively charged region called the nucleus. Electron cloud - 90% probability of finding the electron within this space Electron: - charge ( e - )

Bohr Model After Rutherford’s discovery, Bohr proposed that electrons travel in definite orbits around the nucleus 90 % probability of finding the electron within this space

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Structure of the Atom Atom – is the smallest particle of an element that retains the chemical properties of the element Atom – is the smallest particle of an element that retains the chemical properties of the element Atom has 2 regions: Nucleus – protons & neutrons Electron Cloud - Electrons

Weighing and Counting Atoms Atomic number (Z) – number of protons in a nucleus Mass Number – total number of protons & neutrons in a nucleus Atomic Mass Units – amu 1/12 the mass of C-12 Charge = p + - e - Mass # = p + + n o Atomic Mass – Weighted average mass of all the isotopes of the element

Examples of PEN Atomic number = number of protons If atom is neutral, then the number of protons must equal number of electrons. Carbon Mass Number – Atomic Number = # of Neutrons 12 6 C12 - 6= 6 neutrons 1.Hydrogen2. Sodium3. Oxygen 4. Copper5. Gold

Isotopes Isotopes of Hydrogen include Isotopes of Hydrogen include Hydrogen -1 Hydrogen -1 Hydrogen – 2, Duterium Hydrogen – 2, Duterium Hydrogen – 3, tritium Hydrogen – 3, tritium They have the same number of protons but different numbers of neutrons and a different mass number They have the same number of protons but different numbers of neutrons and a different mass number

isotopes Not in handout

Average Atomic Mass – is the weighted average of the atomic masses of the naturally occurring isotopes of an element. Weighted Average of Isotopes Weighted Average of Isotopes Copper– %, Copper %, Calculate the average atomic mass. Copper– %, Copper %, Calculate the average atomic mass. (63 x.6917) + ( 65 x.3083) = = Carbon %, Carbon %