Ionic Bonds

Objective/Warm-Up SWBAT describe ionic bonds and write ionic formulas. Which element has more electronegativity? Na Cl Ca O Cs F

Valence electrons –An atom’s outermost electrons Valence shell –Outer shell which valence electrons occupy

Lewis dot structure (electron dot configuration) –Shows valence electrons as a series of dots surrounding an atomic symbol –Place one dot around at a time before you double up –Maximum of 8 dots (4 pairs of 2)

Paired valence electrons –Relatively stable –Resistant to change –Don’t form chemical bonds –Called non-bonding pairs

Unpaired valence electrons –Have a strong tendency to participate in chemical bonding

Atoms tend to form chemical bonds so that they each have 8 electrons (in pairs) in their valence shells (octet rule) –This is similar to electron configuration of a noble gas

The Octet Rule The octet rule says: –Atoms tend to gain or lose electrons in order to have _________ valence electrons. For example: –How many valence electrons does CHLORINE have? –How many more does it need to have 8? –What would happen if chlorine gained an eighth valence electron? eight

Ions and Lewis Dot Structures Find the number of valence electrons Following the octet rule, find how many electrons will be gained or lost for each atom to become an ion. Combine the ions to form compounds.

Practice Combine the following atoms to form ionic compounds (show Lewis dot structures). Na Cl Mg F 2 Na 2 O

Electrons occupy innermost shell first –Exposed electrons in outer shell responsible for bonding

Chemical bond –Force of attraction between atoms that holds them together

A.Ion An atom having a positive or negative charge

B.Cation –An ion where electrons are lost –Has a positive charge –Na 1+ → Na +

1.Electron dots for cations –Metals will have few valence electrons Ca

1.Electron dots for cations –Metals will have few valence electrons –These will come off Ca

1.Electron dots for cations –Metals will have few valence electrons –These will come off –Forming positive ions Ca 2+

C.Anion –An ion where electrons are gained –Ion has an overall negative charge –Cl 1- → Cl -

1.Electron dots for anions –Non-metals will have many valence electrons –They will gain electrons to fill outer shell P P

1.Electron dots for anions –Non-metals will have many valence electrons –They will gain electrons to fill outer shell –Forming negative ions P 3-

D.Ionization Energy –The amount of energy needed to remove an electron from an atom –The closer the electron is to the nucleus, the harder it is to remove

E.Ionic bond Transfer of electrons Formation of cations and anions Na + ClNa + + Cl -

E.Ionic bond Transfer of electrons Formation of cations and anions Opposite charges hold ions together NaCl

F.Ionic compounds 1.Are highly ordered compounds each anion actually attracts several cations These attract several more anions A network of ions forms crystals

F.Ionic compounds 2.Consist of elements found on opposite sides of the periodic table 3.Positive and negative charges must balance (Oxidation numbers) 4.When melted or dissolved, they carry an electrical charge

Criss-cross method Examples: Mg Cl Na S Al Br Ca N Ba P

K S Sr F Cs P Al O

Essential Questions- Ch.7-Bonding How do I distinguish between ionic, covalent, and metallic compounds? How are ionic and covalent compounds named? How do I write the formula for ionic and covalent compounds?

Objective/Warm-Up SWBAT write formulas for ionic compounds. What charges do the following elements have when they form ions? F Ca K N O

Monatomic vs. Polyatomic Ions

Practice

Objective/Warm-Up SWBAT write formulas for ionic compounds. What is an ionic bond? List at least 3 characteristics of an ionic bond.