# Bohr Models of Ions. The purposes of the following notes are to help you: 1.learn to recognize the difference between a Bohr model for an atom and a Bohr.

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Bohr Models of Ions

The purposes of the following notes are to help you: 1.learn to recognize the difference between a Bohr model for an atom and a Bohr model for an ion. 2.understand why ions form in the predicable way as seen on the periodic table.

Changing Protons, electrons and neutrons We know that if we change the number of neutrons in an atom, we create a new isotope. We also know that if we change the number of protons in an atom, we create a brand new element. But what happens if we change the number of electrons in an atom?

Changing the electrons: Because protons are positive and electrons are negative, an atom with equal numbers of protons and electrons is “electrically neutral.” Having a different number of protons and electrons will produce something that is no longer electrically neutral. It can no longer be called in atom. Now it will be called an ion.

Comparing protons and electrons (12 protons) + (12 electrons) =_________ (12 protons) + (11 electrons) =_________ (12 protons) + (13 electrons) =_________ “neutral Atom”0 +1 “Positive ion” “negative ion”

But why do elements form ions? To answer this we must look at the noble gases.

The Noble Gases He Ne Ar

Noble Gases are “cool.” Noble gases have the perfect number of electrons…that is they have a full outer shell or valence shell All the other atoms have not enough electrons or too many electrons. As a result, all of the other elements spend their time trying to imitate the “cool” noble gases by getting rid of or by chasing after extra electrons from other atoms. When atoms gain or lose electrons they become ions. Noble gases, since their valence shells are filled, don’t react with other elements and are said to be inert. Thus they will not form ions.

Example 1: Metals A) Lithium (Li) Lithium wants to give away 1 electron and look like Helium. If it does, it will turn into a Li +1 ion.

Example 1 Metals: B) Magnesium (Mg) Magnesium wants to lose two electrons and look like Neon. If it does it will turn into a Mg +2 ion.

Metal ions All metals need to lose one or more electrons to become “cool” which means they will always form Positive ions called cations. LEP

Example 2: Non-metals A)Fluorine (F) Fluorine wants to gain one electron to look like neon If it succeeds, it will turn into a F -1 ion

Example 2: Non-metals B) Phosphorus (P) Phosphorus wants to gain 3 electrons to look like Argon. When it does, it will become a P -3 ion.

Non-metals All non-metals need to pick up one or more electrons to be cool like the noble gases. Thus they always form negative ions called anions. GEN: Gain Electrons=Negative

Exercise: 1) Determine the type on ion that each of the following atoms wants to form a)Al → Al +3 (positive ion) b)Be c)O d)Br e)Na

Exercise: When a METAL meets a NON-METAL they form an Ionic Bond A)When Na meets F: Na wants to give away 1 electron and become Na +1. F wants to take away 1 electron and become F -1. They exchange electrons and are now “cool” and they have opposite charges and opposite charges cancel.

Exercise B) When Mg meets O

Exercise: C) When Mg meets F:

Exercise: D) When Al meets Cl:

Exercise: D) When K meets S:

Assignment: WB p63-64 Q# 1-14, 16 Quiz next class: Bohr models of atoms vs ions.

Ionic Compounds

Writing Ionic Compound Formulas: A)Binary Compound: a compound with only two types of elements in an ionic bond (metal and non-metal) Step 1: Metal is written first, non-metal is written second Step 2: Write the combining capacities (or charge) beside each ion as a superscript. Step 3: Flip flop the combining capacities for each element and remove the charges (signs +/-) from subscripts. Step 5: reduce the subscripts and remove any “ones”

Assignment: Text p 188 practice problems 1 and 2

Naming Ionic Compounds Step 1: Metal name stays the same and is written first Step 2: Non-metal name is written second and ends with “ide”

Write the chemical name: 1)NaCl Sodium Chlorine → remove the “ine” from chlorine → add the “ide” to Chlor___. Becoming: Sodium Chloride

2) MgF 2 Write the chemical name:

K +1 and S -2

Assignment: Text p 187 practice problems 1a-o

B) Elements with more than one combining capacity: How do you recognize these elements? Elements on the periodic table that have more than one charge metal ionRoman numerals are included in the names of these ionic compounds to show the charge of the metal ion. Examples: I, II, III, IV, V,

Example 1: Write the name for FeCl 2 1.Check for metal and nonmetal 2.Check for multiple combining capacity If yes: use roman numerals in name If no: no roman numerals in name 3.Reverse flip flop 4.Check nonmetal charge 5.Write name (metal (RN) non-metal-”ide”)

Example 2: Write the name for FeCl 3

Assignment: Text p 190 and 191 practice problems

C) Charged Groups of Atoms: AKA Polyatomic ions Groups of atoms that tend to stay together and carry an overall charge. How do you recognize them in a formula for a compound? Recognized by three or more capital letters in a formula of a compound Polyatomic ions are treated as a single ion See data booklet sheet

Formulas: If two or more polyatomic ions occur in a compound, then the chemical formula for the polyatomic ion is enclosed in parenthesis Naming: the names of polyatomic ions stay as they are seen in the data booklet. No changing of the ending is needed. C) Charged Groups of Atoms: AKA Polyatomic ions

Example 1: Write the formula and name for Ca +2 and OH -1

Assignment: Text p193 practice problems

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