Understanding Ionic Compounds: The Octet Rule and Chemical Formulas
Dive into the fascinating world of ionic compounds and the Octet Rule! This guide explains how atoms achieve stability by gaining or losing electrons. Discover the role of cations and anions, and how to name them correctly when forming compounds. Explore the crossover method for writing chemical formulas and learn about polyatomic ions that act as single charged entities. With clear examples including sodium and chlorine, and aluminum and oxygen, you’ll gain a solid understanding of ionic bonding, electron configurations, and compound naming conventions.
Understanding Ionic Compounds: The Octet Rule and Chemical Formulas
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Presentation Transcript
Happy New Year!!! Remember the old year?
Remember??? • All atoms “want” to have stable electron configurations like the noble gases. • Most of the noble gases have 8 valence electrons (except Helium). • What’s the name of this rule that atoms want 8 valence electrons (usually)? • The Octet Rule!!!
Remember??? • Metals lose electrons to follow the octet rule. • What is the charge on a metal ion that has lost electrons? • Positive • What is the name for an ion with a positive charge? • Cation • Is the cation the “first name” or “last name” when naming a compound? • First name • How is the cation name different from the element’s name? • It’s the same
Remember??? • Non-metals gain electrons to follow the octet rule. • What is the charge on a non-metal ion that has gained electrons? • Negative • What is the name for an ion with a negative charge? • Anion • Is the anion the “first name” or “last name” when naming a compound? • Last name • How is the anion name different from the element’s name? • The ending is changed to “ide.”
Remember??? • To determine valence electrons, just use the group number.
Remember??? Chlorine needs to gain an electron Sodium needs to lose an electron • Ionic compounds form when metal and non-metal ions give and take electrons, are attracted, and stick together due to their opposite charges. The sodium and chlorine are oppositely charged and opposites attract!
Remember??? • Chemical Formulas • Symbols tell the elements in the compound • Subscripts tell the number of atoms of each element. • No subscript means that there is one atom of the element. • C2H6 6 hydrogen atoms 2 carbon atoms
Remember??? • In ionic compounds, the charges must balance out. • If calcium ionically bonds with fluorine, calcium is giving up 2 electrons but each fluorine atom only needs 1…so you have to have 2 fluorine atoms for every calcium atom. • Ca+2 + F-1 = CaF2
Remember??? • The easy way to determine chemical formulas for ionic compounds is the crossover method. • For Aluminum and Oxygen • Write the cation and anion and their charges. Al+3 O-2 • Cross the charges over and down (without the signs). Al+3 O-2 • You have the correct formula! Al2O3 2 Aluminum atoms each gave up 3 electrons for a total of 6 given 3 Oxygen atoms each took 2 electrons for a total of 6 taken • Remember to reduce subscripts if divisible by the same number • Ex. C2O4 reduces to CO2 • Lastly, remember you don’t need to write 1’s as subscripts since having the symbol means there is one atom.
Remember??? • Polyatomic ions • Polyatomic ions are groups of atoms that act together as one ion with one charge. • For example, the nitrate ion (NO3)-1 is made of a nitrogen atom along with 3 oxygen atoms that act together and have an overall charge of -1. • Hydroxide is (OH) -1 • Ammonium is (NH4) +1 • Dichromate is (Cr2O7) -2
Remember??? • When writing formulas with polyatomic ions, I recommend keeping the polyatomic ions in parentheses ‘til the end so that you don’t mistakenly change subscripts in the polyatomic ion. • Ammonium oxide • (NH4)+1 O-2 • Crossover: (NH4)+1 O-2 • Formula: (NH4)2O • Lastly, the name of a polyatomic ion does not change when in a compound.
