View
1.375
Download
0
Category
Preview:
DESCRIPTION
Its all u need about electronegaativity of elements.....
Citation preview
ElectronegativityElectronegativity
+ – 0 0
H Cl H H
The basic units: ionic vs. covalentThe basic units: ionic vs. covalent• Ionic compounds form repeating units.• Covalent compounds form distinct molecules.• Consider adding to NaCl(s) vs. H2O(s):
HO
H Cl Na
Na Cl
Cl
Cl
Na
Na H
O H
HO H
• NaCl: atoms of Cl and Na can add individually forming a compound with million of atoms.
• H2O: O and H cannot add individually, instead molecules of H2O form the basic unit.
Holding it togetherHolding it togetherQ: Consider a glass of water. Why do
molecules of water stay together?A: there must be attractive forces.
Intramolecular forces occur between atoms
Intermolecular forces occur between molecules
• We do not consider intermolecular forces in ionic bonding because there are no molecules.
• We will see that the type of intramolecular bond determines the type of intermolecular force.
Intramolecular forces are
much stronger
I’m not stealing, I’m sharing unequallyI’m not stealing, I’m sharing unequally• We described ionic bonds as stealing electrons• In fact, all bonds share – equally or unequally.• Note how bonding electrons spend their time:
• Point: the bonding electrons are shared in each compound, but are not always shared equally.
• The greek symbol indicates “partial charge”.
H2 HCl LiCl
+ –0 0 + –
covalent (non-polar) polar covalent ionic
H H H Cl [Li]+[ Cl ]–
ElectronegativityElectronegativity• Recall that electronegativity is “a number that
describes the relative ability of an atom, when bonded, to attract electrons”.
• The periodic table has electronegativity values.• We can determine the nature of a bond based on EN (electronegativity difference).
EN = higher EN – lower ENNBr3: EN = 3.0 – 2.8 = 0.2 (for all 3 bonds).
• Basically: a EN below 0.5 = covalent, 0.5 - 1.7 = polar covalent, above 1.7 = ionic
• Determine the EN and bond type for these: HCl, CrO, Br2, H2O, CH4, KCl
Electronegativity AnswersElectronegativity Answers
HCl: 3.0 – 2.1 = 0.9 polar covalent
CrO: 3.5 – 1.6 = 1.9 ionic
Br2: 2.8 – 2.8 = 0 covalent
H2O: 3.5 – 2.1 = 1.4 polar covalent
CH4: 2.5 – 2.1 = 0.4 covalent
KCl: 3.0 – 0.8 = 2.2 ionic
Electronegativity & physical properties Electronegativity & physical properties • Electronegativity can help to explain properties
of compounds like those in the lab.
+ –
+ –
+ –
+ –• Lets look at HCl: partial charges keep molecules together.
• The situation is similar in NaCl, but the attraction is even greater (EN = 2.1 vs. 0.9 for HCl).
• Which would have a higher melting/boiling point?NaCl because of its greater EN.
• For each, pick the one with the lower boiling point a) CaCl2, CaF2 b) KCl, LiBr c) H2O, H2S
– +
+ –
CaCl2 would have a lower melting/boiling point:
CaCl2 = 3.0 – 1.0 = 2.0CaF2 = 4.0 – 1.0 = 3.0
LiBr would have a lower melting/boiling point:KCl = 3.0 – 0.8 = 2.2LiBr = 2.8 – 1.0 = 1.8
H2S would have a lower melting/boiling point:H2O= 3.5 – 2.1 = 1.4H2S = 2.5 – 2.1 = 0.4
Note: other factors such as atomic size
within molecules also affects melting and boiling points.
EN is an important factor but not the only factor. It is
most useful when comparing atoms and molecules of
similar size.
CaCl2 would have a lower melting/boiling point:
CaCl2 = 3.0 – 1.0 = 2.0CaF2 = 4.0 – 1.0 = 3.0
LiBr would have a lower melting/boiling point:KCl = 3.0 – 0.8 = 2.2LiBr = 2.8 – 1.0 = 1.8
H2S would have a lower melting/boiling point:H2O= 3.5 – 2.1 = 1.4H2S = 2.5 – 2.1 = 0.4
Note: other factors such as atomic size
within molecules also affects melting and boiling points.
EN is an important factor but not the only factor. It is
most useful when comparing atoms and molecules of
similar size.
Why oil and water don’t mixWhy oil and water don’t mix• Lets take a look at why oil and water don’t
mix (oil is non-polar, water is polar)
+
–+ +
–+
+
–+
+
–+ +
–+
+
–+
+
–+
+ – +
+
–+
The partial charges on water attract, pushing the oil (with no partial
charge) out of the way.
Chemical Symbols of Common Elements
Prepare a chart in your notes …
Complete for elements:1-20, 26, 28-30, 35, 47, 50, 53, 79, 80, 82, 92Use the chart on left to complete the two last columns (only listed elements will have anything for these columns).
Z Name Symbol *Latin *Mnemonic
1 Hydrogen H2 Helium He
Element Latin nameCopper CuprumGold AurumIron FerrumLead PlumbumMercury HydrargyrumPotassium KaliumSilver ArgentumSodium NatriumTin Stannum
Mnemonics• Mnemonics are ways to help you remember• Used by A students and experts• They are often rhymes or visual connections• E.g. “Thirty days has September, April, June
and November, all the rest have 31”• Or using your knuckles to remember months• Iron (Fe) …• Iron strong opposite is feeble Fe• A bad mnemonic for Cu is a copper cup (any
metal can be made into a cup)• A good mnemonic is a cup full of pennies• It may seem like more to know, but it works
Best Mnemonics
Sodium (Na)Salt? Bad for BP (Na, don’t want it)North Atlantic salt water
Potassium (K)Potatoes covered in ketchupKoala (or kangaroo) eating bananasPutting Special K into rolling paper
Best Mnemonics
Iron (Fe)Ironing with FeetFrench for iron is FerIron = strong = giant = Fe-Fi-Fo-Fum
Copper (Cu)Cu (see you) at copperfieldsCop drinking out of a cupA cup filled with pennies
Best Mnemonics
Silver (Ag)Almost goldAging = grey hair = silver
Tin (Sn)“Tin is Sin”
Gold (Au)Always united (wedding ring)Gold = shiny = auraleaves changing gold colour = Autumn
Best Mnemonics
Mercury (Hg)
thermometer = hug to stay warm
Huge globe (Hg), Hot gas, High gravity
Lead (Pb)
Peanut butter coming out of a pencil
Pellets and buckshot
Plumber uses lead pipes
For more lessons, visit www.chalkbored.com
Recommended