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

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

Complete the following table in your notes Atomic # Mass # # of Protons # of Neutrons # of Electrons

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 – 6 C 12 – 6 C 13  Three isotopes for Oxygen are oxygen-16, oxygen-17, and oxygen-18, write the chemical symbol for all three – 8 O 16 – 8 O 17 – 8 O 18

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:  = 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 x 63 = x 65 = = 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? 

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

SUMMARY 1. The Atomic Number of an atom = number of protons in the nucleus. 2. The Atomic Mass of an atom = number of Protons + Neutrons in the nucleus. 3. The number of Protons = Number of Electrons. 4. Electrons orbit the nucleus in shells. 5. Each shell can only carry a set number of electrons.

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; N Nitrogen in 1 st shell 5 in 2 nd shell configuration = 2, = 7

ELECTRONIC CONFIGURATION Write the electronic configuration for the following elements; Ca O ClSi Na B 11 5 a)b)c) d)e)f) 2,8,8,22,8,1 2,8,72,8,42,3 2,6

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

DOT & CROSS DIAGRAMS Draw the Dot & Cross diagrams for the following elements; OCl a)b) O X X X X X X X X Cl X X X XX X X X X X X X X X X X X