ATOMIC STRUCTURE More free powerpoints at www.worldofteaching.com S.MORRIS 2006

~ The Hellenic Market Fire Water Earth Air Original concept of element: Four element theory AIR combined to form all other materials by combining WATER in different proportions. EARTH AIR Fire Water Earth Air ~

The Greeks History of the Atom Not the history of atom, but the idea of the atom In 400 B.C the Greeks tried to understand matter (chemicals) and broke them down into earth, wind, fire, and air. ~ ~

(greek for indivisible) Democritus develops the idea of atoms 460 BC he pounded up materials in his pestle and mortar until he had reduced them to smaller and smaller particles which he called ATOMA (greek for indivisible) No experiments to support idea Continuous vs. discontinuous theory of matter Democritus’s model of atom No protons, electrons, or neutrons Solid and INDESTRUCTABLE

Four Element Theory Plato was an atomist Thought all matter was composed of 4 elements: Earth (cool, heavy) Water (wet) Fire (hot) Air (light) Ether (close to heaven) ‘MATTER’ FIRE EARTH AIR WATER Hot Wet Cold Dry THE SCEPTICAL CHYMIST (1661) “The Greeks believed that earth, air, fire, and water were the fundamental elements that made up everything else. Writing in 1661, Robert Boyle (1627-1691) argued against this idea, paving the way for modern ideas of the elements. He defined an element accurately as a substance that could not be broken down into simpler substances.” Eyewitness Science “Chemistry” , Dr. Ann Newmark, DK Publishing, Inc., 1993, pg 18 Plato was Aristotle's student. It was Aristotle that suggested qualities of "hot, dry. cold, wet". Aristotle Added the idea of “qualities” – heat, cold, dryness, moisture Hot + dry made fire; hot + wet made air, and so on. Blend these “elements” in different proportions to get all substances

Who Was Right? Greek society was slave based Beneath famous to work with hands did not experiment Greeks settled disagreements by argument Aristotle was more famous He won! His ideas carried through middle ages. Alchemists change lead to gold California WEB

Alchemy After that chemistry was ruled by alchemy. They believed that that could take any cheap metals and turn them into gold. Alchemists were almost like magicians. elixirs, physical immortality

Contributions of alchemists: Information about elements - the elements mercury, sulfur, and antimony were discovered - properties of some elements Develop lab apparatus / procedures / experimental techniques - alchemists learned how to prepare acids. - developed several alloys - new glassware

HISTORY OF THE ATOM ATOMS John Dalton 1808 suggested that all matter was made up of tiny spheres that were able to bounce around with perfect elasticity and called them ATOMS

HISTORY OF THE ATOM ELECTRON Joseph John Thompson 1898 found that atoms could sometimes eject a far smaller negative particle which he called an ELECTRON

HISTORY OF THE ATOM PLUM PUDDING MODEL 1904 Thompson develops the idea that an atom was made up of electrons scattered unevenly within an elastic sphere surrounded by a soup of positive charge to balance the electron's charge like plums surrounded by pudding. PLUM PUDDING MODEL

HISTORY OF THE ATOM Ernest Rutherford 1910 oversaw Geiger and Marsden carrying out his famous experiment. they fired Helium nuclei at a piece of gold foil which was only a few atoms thick. they found that although most of them passed through. About 1 in 10,000 hit

HISTORY OF THE ATOM gold foil helium nuclei helium nuclei They found that while most of the helium nuclei passed through the foil, a small number were deflected and, to their surprise, some helium nuclei bounced straight back.

HISTORY OF THE ATOM However, this was not the end of the story. Rutherford’s new evidence allowed him to propose a more detailed model with a central nucleus. He suggested that the positive charge was all in a central nucleus. With this holding the electrons in place by electrical attraction However, this was not the end of the story.

HISTORY OF THE ATOM Niels Bohr 1913 studied under Rutherford at the Victoria University in Manchester. Bohr refined Rutherford's idea by adding that the electrons were in orbits. Rather like planets orbiting the sun. With each orbit only able to contain a set number of electrons.

Bohr’s Atom electrons in orbits nucleus

HELIUM ATOM + - + - Shell proton neutron electron What do these particles consist of?

ATOMIC STRUCTURE Particle Charge Mass proton + ve charge 1 neutron No charge 1 electron -ve charge nil

number of electrons = number of protons ATOMIC STRUCTURE He 2 Atomic number the number of protons in an atom 4 Atomic mass the number of protons and neutrons in an atom number of electrons = number of protons

Complete the following table in your notes Atomic # Mass # # of Protons # of Neutrons # of Electrons 9 10 14 15 47 22 55 25

“POP QUIZ”! Define the following terms on a separate sheet of paper Atomic number Ion Molecule Atom Valence Electrons

How’d You Do? The number of protons in the nucleus of an atom of an element An atom or group of atoms that has a positive or negative charge due to a gain or loss of electrons A neutral chemically bonded group of atoms that act as a unit The smallest particle of an element that retains the properties of that element An electron that is in the highest energy level

Isotopes Atoms that have the same number of protons but different numbers of neutrons Different mass numbers Chemically alike because they have identical numbers for the characteristic chemical behavior of each element Ex: Three known isotopes for H Hydrogen (no neutrons, mass # of 1) Deuterium (one neutron, mass # of 2) Tritium (two neutrons, mass # of 3)

Your turn… Two of the isotopes for Carbon are Carbon-12 and Carbon-13, write the chemical symbol for both 126C 136C Three isotopes for Oxygen are oxygen-16, oxygen-17, and oxygen-18, write the chemical symbol for all three 168O 178O 188O

Calculating Average Atomic Mass of Isotopes In nature, isotopes occur in various percentages In order to figure out the average mass of each element the percent abundance and mass of each isotope need to be considered We can calculate average atomic mass in much the same way as we calculate your grade in this class…

What are the different categories that you are graded on in this class? Classwork: 79% Practice: 7% Final: 14% What would your semester grade be if you received an 80% for classwork, 50% for practice, and 72% on your final? 0.80 x 79 = 63.2 0.50 x 7 = 3.5 0.72 x 14 = 10.1 Add all answers together to get % semester grade: 63.2 + 3.5 + 10.1 = 76.8 % (a C)

Now lets try with an element! Copper has two isotopes: copper-63 and copper-65. The relative abundances of these isotopes are 69.2% and 30.8% respectively. Calculate the average atomic mass of copper. 0.692 x 63 = 43.60 0.308 x 65 = 20.02 43.6 + 20.02 = 63.62

One more example… Uranium has three naturally occurring isotopes with the following percent abundances: U-234 (0.0058%), U-235 (0.71%), and U-238 (99.23%). What do you expect the average atomic mass to be and why? What is the average atomic mass? 237.85

ATOMIC STRUCTURE Electrons are arranged in Energy Levels or Shells around the nucleus of an atom. first shell a maximum of 2 electrons second shell a maximum of 8 electrons third shell a maximum of 8 electrons

SUMMARY The Atomic Number of an atom = number of protons in the nucleus. The Atomic Mass of an atom = number of Protons + Neutrons in the nucleus. The number of Protons = Number of Electrons. Electrons orbit the nucleus in shells. Each shell can only carry a set number of electrons.

1. Electronic Configuration ATOMIC STRUCTURE There are two ways to represent the atomic structure of an element or compound; 1. Electronic Configuration 2. Dot & Cross Diagrams

ELECTRONIC CONFIGURATION With electronic configuration elements are represented numerically by the number of electrons in their shells and number of shells. For example; Nitrogen configuration = 2 , 5 7 2 in 1st shell 5 in 2nd shell N 2 + 5 = 7 14

ELECTRONIC CONFIGURATION Write the electronic configuration for the following elements; 20 11 8 Na O Ca a) b) c) 16 23 40 2,8,8,2 2,8,1 2,6 17 14 5 Cl Si B d) e) f) 11 35 28 2,8,7 2,8,4 2,3

N DOT & CROSS DIAGRAMS Nitrogen With Dot & Cross diagrams elements and compounds are represented by Dots or Crosses to show electrons, and circles to show the shells. For example; X Nitrogen N 7 X X N X X 14 X X

DOT & CROSS DIAGRAMS O Cl Draw the Dot & Cross diagrams for the following elements; X 8 17 O Cl a) b) X 35 X 16 X X X X X Cl X X X X X X X O X X X X X X X X X X