Notes P.1-2

January 22, 2014

Objectives

• You will be able to: – Define metallic, ionic, and covalent bonds and

explain their characteristics– State if two atoms will form a covalent or ionic

bond– Write ionic formula units

Overview of bonding

• Chemical bond: mutual electrical attraction between the nuclei and valence electrons of different atoms that binds those atoms together.

• Why do atoms bond?– Most atoms are more stable when they are

bonded than they were as individual atoms

Types of chemical bonds:

• Metallic – sea of electrons– Occur between: between metals

• Ionic – steal electrons– Occur between: metal—nonmetal

• Covalent – share electrons– Occur between: nonmetal—nonmetal

• Covalent or Ionic? – Determined by electronegativity difference

Remember: Metallic Character

METALS(IN YELLOW)

NONMETALS(IN GREEN)

Practice• Label as ionic, covalent, or metallic:

NaFCaBr2 H2SAl2O3

CuNO3

• Ionic• Ionic• Covalent• Ionic• Metallic• Covalent

METALLIC BONDING–Results from the attraction of nuclei

to a “sea of electrons”

Sea of Electrons

METALLIC BONDING

–Why an “electron sea”?• Vacant p and d orbitals in metal's outer

energy levels overlap, and allow outer electrons to move freely throughout the metal–Valence electrons do not belong to any

one atom

METALLIC BONDING–Common properties of metals: • High melting/boiling points• Conduct heat and electricity• Have luster (shiny) • Ductile/malleable

– All thanks to the electron sea!

IONIC BONDING• Results from the electrical attraction between

cations and anions

• Cation: +• Anion: -

The resulting ions come together due to electrical attraction (opposites attract)

IONIC BONDINGCommon Properties: • Solid crystals at room temperature• Very high melting/boiling points• (Most) Can dissolve in water • Conduct electricity when melted or

dissolved

Ionic Formula Units

• The net (total) charge on the compound must equal zero• Positive and negative cancel out

Hint: Use the criss-cross method

Ionic Formula Units

EXAMPLES: • Na and Cl • Na and O • Ca and O • Ca and Cl • Al and O

Ionic Formula Units

EXAMPLES: • Na and Cl Na+ + Cl- NaCl• Na and O Na+ + O2- Na2O • Ca and O • Ca and Cl • Al and O

Na and O

Na2O means that: Two sodium cations are needed to balance one oxygen anion.

Positive and negative charges must cancel each other out

EXAMPLES: Total + Total - Net

• Na+ and Cl- NaCl 1 1 0• Na+ and O2- Na2O 2 2 0• Ca2+ and O2- CaO 2 2 0• Ca2+ and Cl- CaCl2 2 2 0

• Al3+ and O2- Al2O3 6 6 0

Crystal Lattice

• A network of alternating cations and anions

Ionic compounds• The formula for ionic

compounds does not show the exact number of atoms that are bonded together.

• The formula tells the smallest whole number ratio of atoms that bond.

COVALENT BONDING• Results from the sharing of electron pairs

between two atoms (each has a full valence shell)

• A covalent compound is called a molecule

Each has a full octet

COVALENT BONDING• Common properties of covalent

compounds:• Low melting/boiling points • Many are liquids or gases at room

temp• Non-conductors of heat and

electricity

Can you…?

– Define metallic, ionic, and covalent bonds and explain their characteristics?

– State if two atoms will form a covalent or ionic bond?

– Write ionic formula units?

– Homework 6A, Due Friday– Lab on Friday