Mrs. Howland Chemistry 10 Rev. November 2015

What is meant by the term “chemical bond”? What are the 3 main types of bonds? Why do atoms bond with each other to form compounds? How do atoms bond with each other to form compounds? What are the properties of compounds with differnet types of bonds? Which elements are likely to bond?

Chemical Bonds are the force of attraction between atoms or ions TYPES: Ionic Bonds Metallic Bonds Covalent Bonds Bonding forms molecules Determines nearly all of the chemical properties We’ll see that it’s all about the ELECTRONS!!

Outermost electrons in an atom The Periodic Table predicts how many electrons tend to be lost or gained for an atom (for Group A elements) Involved in chemical reactions (bonding)

Lewis Dot structures follow the OCTET rule. Bohr models show all electrons.

Atoms are most stable with a FULL valence (outermost) shell, and will bond with other atoms (REACT!) to fill their shells and become more stable

Remember! Electrons in the outermost shell are called Valence Electrons OCTET RULE: EIGHT (8) electrons in the outer energy shell makes an atom STABLE for Group A elements (NOT transition or inner transition metals) Atoms “want” to be stable, like the NOBLE GASES that already have a full octet! NOTE: Helium is considered ‘stable’ because it has a full inner shell (2 electrons)

The number of valence electrons for an element in the MAIN GROUPS is the same as its group number Don’t worry about these elements right now These elements all have 1 valence electron These elements all have 7 valence electron

HYDROGEN (1 valence electron) and HELIUM (2 valence electrons) do not follow the “octet” rule, because they have only 1 electron shell The innermost electron shell is considered FULL with only 2 electrons BOTH Helium and Neon are “stable” with complete valence shells. Note that the innermost electron shell is full with 2 electrons while other, external shells require 8

Lewis Dot Structures represent number of valence electrons for an atom Provides a means for modeling how an atom gains or loses electrons in a given compound A model that shows how bonds are formed within a compound Electrons are drawn as DOTS 0IA

Dots around chemical symbol symbolize valence electrons  Do you notice any patterns in Lewis Dot Structures above?

Lewis Dot shows VALENCE electrons, not total number of electrons: Bohr Model Lewis Dot

TRY THIS: OCa What group are the elements in? How many valence electrons?

TRY THIS: Li + F  ? What group are the elements in? How many valence electrons? How are they transferred? What are the resulting ionic charges?

TRY THIS: BeCl 2 (Be goes in the middle!) Cl Be Cl

Ionic bonds form when there is a transfer of electrons TRY THIS: Which elements are shown in the diagrams above? (HINT: Count # of valence electrons!)

Positively charged ions (Li+) are cations Negatively charged ions (F-) are anions

Crystalline structure BRITTLE A regular repeating arrangement of ions in the solid Ions are STRONGLY bonded RIGID High melting points- because of strong forces between ions! Conductive (aqueous solutions) Soluble in water, but not in nonpolar substances

Sodium atom Sodium ion Na (neutral) – e   Na + Na has 1 valence electron. When 1 electron is “given up” there result is a charge of p + 11 p + 11 e - 10 e

N/A You don’t have to worry about the Transition metals! (the B groups) The charges written in the ORANGE boxes indicate the charges commonly carried for the elements in each group. Examples: Na has a charge of 1+ and O has a charge of 2-

A. Number of valence electrons in aluminum 1) 1 e - 2) 2 e - 3) 3 e - B. Change in electrons for octet 1) lose 3e - 2) gain 3 e - 3) gain 5 e - C.Ionic charge of aluminum 1) 3- 2) 5- 3) 3 +

Metal + Nonmetal Metals form CATIONS Nonmetals form ANIONS Commonly form SALTS (NaCl, KCl)

Polyatomic ions have more than one atom Examples: F - (anion) OH - (polyatomic anion

KNOW THESE! NH 4 + ammoniumNO 3 - nitrate CN - cyanideSO 4 2- sulfate OH - hydoxideCO 3 2- carbonate O 2 2- peroxideClO 3 - chlorate C 2 H 3 O 2 - acetatePO 4 2- phosphate

Covalent bonds form when there is a sharing of electrons

Nonmetal + Nonmetal Gases, liquids, soft solids Flexible; break easily Do not conduct electricity (aqueous solutions) May be flammable Low melting/boiling points

Diatomic elements are so unstable that, when isolated from all other elements, one atom will combine with another atom (of the same element) in order to become stable Commonly exist as GASES at room temperature

KNOW THESE!

Metallic bonds are the forces that hold atoms together in metallic solids Valence electrons are weakly held onto by the metal atoms Electrons form a SEA of electrons ~ the electrons are free to move around the solid!

Shiny Ductile and malleable Conduct electricity All properties are due to the SEA of electrons!

COMPARE / CONTRAST: Ionic bonds, covalent bonds, metallic bond COMPARE / CONTRAST: Ionic compounds, covalent compounds