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2 The Early Periodic Table First developed by Dmitri Mendeleev Attempted to place elements with similar properties near each other. Organized according to combining capacity and atomic mass Zumdahl, Steven S. Chemical Principles 5 th Ed. Houghton Mifflin; 2005.

3 Mendeleev’s Periodic Table Zumdahl, Steven S. Chemical Principles 5 th Ed. Houghton Mifflin; 2005.

4 The Modern Periodic Table

5 The Modern Periodic Table Atomic Number increases as you go from left to right Organized according to atomic number and electron arrangement (configuration)

6 Electron Arrangement Electrons are arranged in energy levels or shells around the nucleus of the atom There are 7 energy levels Each shell holds a set number of electrons  1 st Shell holds up to 2 electrons  2 nd Shell holds up to 8 electrons  3 rd Shell holds up to 18 electrons (8 for main group elements)  4 th Shell holds up to 32 electrons (8 for main group elements)

7 Electron Dot Diagrams Shells are represented by circles and electrons are represented by dots. 2p 2n Example: Helium Nucleus: 2 protons, 2 neutrons 2 electrons in 1 st shell

8 More Examples 11p 12n 6p 6n Carbon 6 protons, 6 neutrons, 6 electrons 1 st Shell: 2 electrons 2 nd Shell: 4 electrons Sodium 11 protons, 12 neutrons, 11 electrons 1 st Shell: 2 electrons 2 nd Shell: 8 electrons 3 rd Shell: 1 electron

9 Valence Electrons The electrons in the outermost electron shell. 2p 2n 6p 6n 11p 12n Helium 2 Valence Electrons Carbon 4 Valence Electrons Sodium 1 Valence Electron

10 Example Draw electron dot diagrams and determine the number of valence electrons in the following elements: Lithium Beryllium Sodium Magnesium

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12 Trends in Valence Electrons Periodic table shows you how many valence electrons the Main Group Elements have  Group 1A has 1 valence electron  Group 2A has 2 valence electrons  Group 3A has 3 valence electrons  Etc.

13 Periodic Table IA IIA IIIA IVAVA VIA VIIA VIIIA

14 Ions Positively or negatively charged atoms  Positively charged = cation  Negatively charged = anion Formed by gaining or losing electrons  Why do atoms gain or lose electrons? To achieve a stable electron configuration

15 Octet Rule Main Group elements will gain, lose, or share electrons to get eight valence electrons.  8 valence electrons = stable configuration Metals lose electrons Non-metals gain electrons

16 Example 11p 12n Sodium Atom 1 Valence Electron Charge = 11 + (-11) =0 11p 12n Sodium Ion 8 Valence Electrons Charge = 11 + (-10) = 1

17 What happened? A sodium atom lost an electron and became a sodium ion (Na + )  Is it a cation or anion? A Cation!

18 Anion Example 9p 10n Fluorine Atom 7 Valence Electrons Charge = 9 + (-9) =0 9p 10n Fluorine Ion 8 Valence Electrons Charge = 9 + (-10) =-1

19 Example

20 Another Cation 12p 12n 12p 12n Magnesium Atom 2 Valence Electrons Charge = 12 + (-12) =0 Magnesium Ion 8 Valence Electrons Charge = 12 + (-10) =2

21 Another Anion 8p 8n 8p 8n Oxygen Atom 6 Valence Electrons Charge = 8 + (-8) =0 Oxygen Ion 8 Valence Electrons Charge = 8 + (-10) =-2

22 Average Atomic Mass 6 C Atomic number Average atomic mass (amu) Why an average atomic mass?

23 Isotopes Isotopes are atoms of the same element that differ in the number of _________________.  Same number of protons  Same number of electrons  Similar chemical behavior  Different number of neutrons  Different atomic mass  Different isotopes are NOT equally abundant (some are more rare)

24 Isotope Notation

25 What is the average atomic mass of carbon? IsotopeAtomic Mass% Abundance Carbon Carbon Carbon-1414trace

26 Picture Credits Zumdahl, Steven S. Chemical Principles 5th Ed. Houghton Mifflin;