Unit 3 Periodic Table and Valence electrons

Modern Periodic Table Elements are arranged by increasing atomic number. Recall that atomic number gives the number of protons in the nucleus of an atom.

Periods Horizontal rows on the periodic table are called periods. Elements in the same period have the same number of energy levels. Elements in the same period share NO similar chemical properties.

Groups / Families Vertical columns on the periodic Table are called groups. Groups are numbered 1-18 Elements in the same group have the same chemical properties because they have the same number of valence electrons. Valence Electrons – electrons in the highest energy level s and p orbitals only. They participate in bonding and ion formation Some groups have special names.

Groups/Families

Group 1 Metals Known as Alkali Metals Most active metals on periodic table React violently with water, and become more reactive down the group Only have 1 valence electron (because they all end in s1) They all form ions with a +1 charge.

Group 2 Metals Known as Alkaline Earth Metals Also extremely reactive, but not as much as Alkali Metals Contain 2 valence electrons (they end in s2) They all form ions with a +2 charge.

Group 1 are the alkali metals (but NOT H) Group 2 are the alkaline earth metals H

Groups 3-12 These groups are known as Transition Metals Not very reactive metals Generally have 2 valence electrons Some of their “d” orbital electrons jump around into “p” orbitals so many of these elements have more than one possible positive charge. Many form colorful ion solutions (bright vibrant colors)

The group B are called the transition elements These are called the inner transition elements, and they belong here

Group 17 Known as Halogens Extremely reactive nonmetals; reactivity increases up a group (Fluorine the most active) Have 7 valence electrons (e- configuration ends in s2p5) Most of these elements are toxic in their natural state Most are also diatomic in their natural state (F2, Br2, Cl2, I2) They all form ions with a (-1) charge.

Group 18 Known as Noble gases Unreactive nonmetals All have 8 valence electrons (e- configuration ends in s2p6), except Helium (which has 2 electrons) They do not form ions because they have a filled energy level!

Group 18 are the noble gases Group 17 is called the halogens

Valence electrons Valence electrons are electrons located in the outermost energy level. They are located only in the s and p sublevels These electrons are involved in chemical bonding.

Electron Configurations An element’s electron configuration shows how many valence electrons it has. Example: 1s22s22p63s23p64s23d104p4 Valence electrons = 6

Practice How many valence electrons do the following elements have? 1s22s22p63s23p64s23d104p6 1s22s22p63s23p2 1s22s2 8 valence electrons 4 Valence Electrons 2 valence electrons

Octet Rule Most elements want to have 8 valence electrons (exception He) Elements will gain or lose electrons in their valence shell in order to achieve an octet. This process forms Ions. Ions have the same electron configuration as their nearest noble gas.

Positive Ions Elements with less than 4 valence electrons lose their outermost “s” and “p” sublevel electrons . Loss of electrons always results in positive ions. Example Be: 1s22s2 has 2 valence electrons Be2+: 1s2 notice the ion has the same configuration as He Metals tend to form positive ions

Negative Ions Elements with more than 4 valence electrons gain electrons in their outermost “p” sublevel Gain of electrons always results in negative ions Example O: 1s22s22p4 has 6 valence electrons O2-: 1s22s22p6 now has 8 valence electrons just like Ne Non-Metals usually tend to form negative ions

Ion Formation Summary 1+ 2+ 3+ 3- 2- 1- Atoms gain or lose electrons to become more stable. They achieve the same electron configuration as the Noble Gases. 1+ 2+ 3+ 3- 2- 1-

Noble Gas Shorthand Electron Configurations Longhand Configuration S 16e- 1s2 2s2 2p6 3s2 3p4 Core Electrons Valence Electrons Shorthand Configuration S 16e- [Ne] 3s2 3p4

Noble Gas Shorthand Configuration Core e-: Go up one row and over to the Noble Gas. Valence e-: On the next row, fill in the # of e- in each sublevel.

Noble Gas Shorthand Notation Example - Germanium [Ar] 4s2 3d10 4p2