Atoms Bonding and the Periodic Table Chapter 5

Atoms, Bonding and the Periodic Table Chapter 5. 1 Page 176

Electron Energy Levels • Electrons exist around the nucleus in different energy levels. • Only a certain number of electrons can occupy a single energy level – – K (1) = 2 L (2) = 8 M (3) = 18 Formula : 2 n 2 - N (4) = 32 - O (5) = 50 - P (6) = 72 • The electrons found in the outermost energy level are called valence electrons.

Shell structure • • Carbon=C Sodium=Na Neon=Ne Chlorine=Cl e p p p e e Review: what is this element? How many protons and electrons do these elements have? Draw the electron shell structure for each.

Valence Electrons • Valence electrons are the electrons that have the highest energy level and held most loosely. • Valence electrons are the electrons primarily involved in forming bonds with other elements. • The number of valence electrons in an atom determines many properties of that element, including the ways in which the atom can bond with other atoms.

Valence Electrons and the Periodic Table • From left to right across the periods, as the atomic mass increases, so does the number of electrons. • Except for period 1, a given period ends when the number of valence electrons reaches 8. • The next period begins with atoms having valence electrons with higher energy. • Because the number of valence electrons increases from left to right across the periodic table, this means from top to bottom (in the groups) each element has the same number of valence electrons.

The Periodic Table • Atomic number = number of protons (and electrons) • Periods – (~number of electron energy levels) • Groups – (reactivity valence)

Electron Dot Diagrams • Each element has a specific number of valence electrons, ranging from 1 to 8. – An easy way to determine the number of valence electrons for the group A elements is to simply look at the group number. The group number also stands for the number of valence electrons (only group A elements!!!!) • A way of depicting the number of valence electrons is with an electron dot diagram (also known as a Lewis Dot Diagram). – Each dot in an electron dot diagram stands for one valence electron.

The Periodic Table • • • Metals (types) Non-metals Transition metals Noble Gases Matter state

Inert Gases - Group 18 • Inert gases are found in Group 18 (8 A) • Inert gases have eight valence electrons in their outer shell (except for Helium) • They are “happy atoms” and therefore do not react easily with other atoms

The Halogens - Group 17 (7 A) • The elements in Group 17 (7 A) – the Halogens (“salt forming”) all have seven valence electrons. • Gaining one more electron will make these atoms stable • They react easily with elements that have one valence electron

The Alkali Metals – Group 1 • Atoms of the alkali group (Group 1)have one valence electron • They have one electron to share or give in reacting with other atoms • This property makes alkali metals very reactive

Other Metals – Groups 2 -12 • Most of the metals in these groups have one, two or three valence electrons • Metals in Group 2 (Alkaline Earth metals) have two valence electrons and react with other atoms easily

Nonmetals • Nonmetals are in Groups 14 -17 (4 A-7 A) • Nonmetals usually react by gaining electrons from the atoms they combine with

Semimetals • Semimetals lie along a zigzag line in the periodic table • They will either lose or gain electrons as they combine with other atoms

Assignment • Do Cornell notes for Chapter 5, Section 1