bohr models of ions. the purposes of the following notes are to help you: 1.learn to recognize the...
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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”
-1 “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) NaClSodium Chlorine →remove the “ine” from chlorine
→add the “ide” to Chlor___.
Becoming: Sodium Chloride
2) MgF2
Write the chemical name:
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
• Roman numerals are included in the names of these ionic compounds to show the charge of the metal ionmetal ion.
• Examples: I, II, III, IV, V,
Example 1:
• Write the name for• FeCl2
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
• FeCl3
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