1

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 5th Ed. Houghton Mifflin; 2005.

3

Mendeleev’s Periodic Table

Zumdahl, Steven S. Chemical Principles 5th Ed. Houghton Mifflin; 2005.

4

The Modern Periodic Table

www.collegeboard.com

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

1st Shell holds up to 2 electrons 2nd Shell holds up to 8 electrons 3rd Shell holds up to 18 electrons (8 for main

group elements) 4th 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 1st shell

8

More Examples

11p

12n6p

6n

Carbon

6 protons, 6 neutrons, 6 electrons

1st Shell: 2 electrons

2nd Shell: 4 electrons

Sodium

11 protons, 12 neutrons, 11 electrons

1st Shell: 2 electrons

2nd Shell: 8 electrons

3rd Shell: 1 electron

9

Valence ElectronsThe 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

11

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 TableIA

IIAIIIA

IVA VA

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

C12.011

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?

Isotope Atomic Mass % AbundanceCarbon-12 12 98.9

Carbon-13 13 1.1

Carbon-14 14 trace

26

Picture Credits

Zumdahl, Steven S. Chemical Principles 5th Ed. Houghton Mifflin; 2005

www.collegeboard.com