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Published byMargaret Randall Modified over 9 years ago
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Valence Electrons, Lewis Dot Structures, and Electronegativity
Ionic Bonding Valence Electrons, Lewis Dot Structures, and Electronegativity
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Valence Electrons valence electrons – the outermost electrons.
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6 protons = C = carbon Outer electrons = 4 e–available for bonding Inner electrons = 2 e– not available for bonding
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4 electrons in valence shell
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Lewis Dot Structures Lewis dot structures are a convenient way to show how many valence electrons an atom has. Example: Draw the Lewis dot structure for hydrogen. H
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Ne He Lewis Dot Structures dots = number of valence electrons.
The maximum number of dots is 8. Look for the number at the top of the column (e.g. 5A). Exception: Helium only has 2 dots. Ne He
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More Lewis Structure Practice
Draw the Lewis structure for oxygen. Draw the Lewis structure for magnesium. Draw the Lewis structure for chlorine. O Mg Cl
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Even More Lewis Structure Practice
Draw the Lewis structure for carbon. Draw the Lewis structure for potassium. Draw the Lewis structure for phosphorus. C K P
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Electronegativity electronegativity – how much an atom wants to keep hold of its electrons. ionization energy – the energy required to remove an electron from an atom.
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Lower electronegativity Greater electronegativity
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Metals
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Nonmetals
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Role Models: The Noble Gases
An atom’s electrons are at their most stable when they reorganize their electrons to more closely resemble the electron configuration of a noble gas. All atoms want to have stable electron configurations.
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Role Models: The Noble Gases
All atoms wish their electrons were like the noble gases’ electrons.
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Example: Beryllium and Oxygen
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The 2 valence e– Now beryllium’s matches that of helium 4 protons = Be = beryllium
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Now oxygen’s matches that of neon
The 6 valence e– 8 protons = O = oxygen
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Same Thing, but in Lewis Dot Structure
Be
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Semi-metals or metalloids Nonmetals Metals
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Three General Bonding Types
Metal with Nonmetal - form ionic compounds Metal with Metal - form metallic compounds Nonmetal with Nonmetal - form covalent compounds
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Metal with Nonmetal Bonding
Ionic compounds – the metal gives all of its valence e– to the nonmetal. Known as – Salts, ions
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Ions ion – an atom that gained or lost electrons to become more like a noble gas. + Metals lose electrons to become positively charged ions. We call them cations (cat-ions) the “t” looks like a “+”. [e.g. 2A +2] – Nonmetals gain electrons to become negatively charged ions. We call them anions (an-ions) “n” for negative “–”. [e.g. (8 – 6A) × -1 -2]
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Writing the Charges Na+ Cl– Mg2+ O2–
Write out the ion that sodium forms. Na+ Write out the ion that chlorine forms. Cl– Write out the ion that magnesium forms. Mg2+ Write out the ion that oxygen forms. O2–
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So where do the electrons go?
Usually atoms that become cations give their electrons to anions. Now both the cations and anions resemble noble gases, however now both have net charges. 2– 2+ O Be
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Basic Electrical Charge Laws
+ and – : Attract (pull together)
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Naming (aka nomenclature)
Metals keep their names unchanged. (e.g. sodium, aluminum, calcium) Transition metals have their charge shown as roman numerals in parenthesis after the name. Fe2+ iron (II) Cu1+ copper (I) Fe3+ iron (III) Cu2+ copper (II) Nonmetals have the last one or two syllables of their names altered with an –ide ending. fluorine fluoride nitrogen nitride chlorine chloride oxygen oxide
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Naming (aka nomenclature)
Metals keep their names unchanged. (e.g. sodium, aluminum, calcium) If there are more than one possible charge for a metal (the transition metals), the charge will be specified in roman numerals after the name Fe2+ iron (II) Cu1+ copper (I) Fe3+ iron (III) Cu2+ copper (II)
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Naming Continued Nonmetals have the last one or two syllables of their names altered with an –ide ending. Examples: carbon carbide fluorine fluoride nitrogen nitride chlorine chloride oxygen oxide bromine bromide sulfur sulfide iodine iodide phosphorus phosphide
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Naming Continued Now put the metal and nonmetal ion names together and you get the name for the ionic compound. Examples: LiF lithium fluoride NaCl sodium chloride KBr potassium bromide MgS magnesium sulfide CuI copper (I) iodide CuO copper (II) oxide FeN iron (III) nitride
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+ 6 – 6 Sodium Chloride – NaCl Na+ Cl– Na+ Cl– Cl– Na+ Cl– Na+ Na+ Cl–
Na+ Cl– Cl– Na+
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+ 12 – 12 – 6 + 6 Magnesium Chloride Mg2+ Cl– Mg2+ Cl– Cl– Cl– Cl– Cl–
– 12 – 6 Cl– Mg2+ Mg2+ Cl– + 6 Cl– Cl– Cl– Cl– Mg2+ Mg2+ Cl–
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Magnesium Chloride Mg2+ 6 x Cl– 12 x Mg6Cl12 6 1 12 2 = MgCl2
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MgCl2 Magnesium Chloride Empirical Formula
Formula Unit (f.u.) – the smallest amount of an ionic compound that still has the same ratio of ions as in the formula.
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Fe3+ O2– 2 x (+3) = +6 3 x (–2) = –6 criss-cross Fe2O3
Iron (III) Oxide Fe3+ O2– 2 x (+3) = +6 3 x (–2) = –6 criss-cross Fe2O3
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Sodium Cloride Na+ Cl– criss-cross Na1Cl1 NaCl
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Magnesium Sulfide Mg2+ S2– criss-cross 2 1 = Mg2S2 MgS
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Sodium Oxide Na+ O2– criss-cross Na2O
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Fe3+ O2– Fe2O3 REMEMBER Top right corner: Charge Bottom right corner:
How many atoms/ions
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Polyatomic Ions Poly – many Atomic – having to do with atoms
Polyatomic ions – ions made from multiple atoms List on p.257
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Polyatomic Ions (List on p.257)
Ion name Formula Acetate CH3COO– Ammonium NH4+ Carbonate CO32– Chromate CrO42– Cyanide CN– Dichromate Cr2O72– Hydroxide OH– Ion name Formula Nitrate NO3– Nitrite NO2– Permanganate MnO4– Peroxide O22– Phosphate PO43– Sulfate SO42– Sulfite SO32– Thiosulfate S2O32–
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Magnesium Nitrate Mg2+ NO3– criss-cross Mg (NO3)2 1 x Mg 2 x N 6 x O
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Mg2+ NO3– Mg (NO3)2 REMEMBER Top right corner: Charge
Bottom right corner: How many atoms/ions
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Sodium Chloride – NaCl Na+ Cl– Na+ Cl– Cl– Na+ Cl– Na+ Na+ Cl– Cl– Na+
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Sodium Chloride – NaCl
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Sodium Chloride – NaCl
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Sodium Chloride – NaCl
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Sodium Chloride – NaCl
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Sodium Chloride – NaCl
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Magnesium Chloride (MgCl2)
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Magnesium Chloride (MgCl2)
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Magnesium Chloride (MgCl2)
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Calcium Fluoride (CaF2)
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Calcium Fluoride (CaF2)
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Calcium Fluoride (CaF2)
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Calcium Fluoride (CaF2)
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Calcium Fluoride (CaF2)
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Calcium Fluoride (CaF2)
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He H B C N O Ne F Li Be P Al Si S Cl Ar Na Mg Br Kr K Ca I Xe
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4 e– in valence shell
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Ions ion – an atom that gained or lost electrons.
metal ions lose electrons to become more positively charged. (e.g. 2A +2) Nonmetal ions gain electrons to become more negatively charged. (e.g. 8 – 6A –2)
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Ions ion – an atom that gained or lost electrons.
metal ions lose electrons to become more positively charged. (e.g. 2A +2) Nonmetal ions gain electrons to become more negatively charged. (e.g. 8 – 6A –2)
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+ Metal ions = cations (cat-ions) the “t” looks like a “+”.
Ions - again ion – an atom that gained or lost electrons to become more like a noble gas. + Metal ions = cations (cat-ions) the “t” looks like a “+”. – Nonmetal ions = anions (an-ions). “–”
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