electronegativity电负性alevel化学

Induced dipole moment
▪Permanent Dipole-dipole force between two polar molecules; stronger force (ex: HCl)
▪ Hydrogen bond forms between the hydrogen end of one dipole and fluorine, oxygen, or nitrogen (that have at least one lone pair) end of another dipole; strongest force (ex: H2O)
A dipole is represented by a dipole arrow pointing towards the more negative end
Is it Polar?
▪HF ▪H2O ▪NH3 ▪CHF3 ▪CO2
Guide to Determination of Polarity of a Molecule
Note
▪fluorine is the most electronegative element
▪Carbon and hydrogen have similar electronegativities that are lower than those of most other non-metallic elements.
molecules
1) CH4
1) polar
2) HCl
2) polar
3) NaF
3) ionic
4) MgCl2 5) SO2 6) NH3 7) H2O 8) KCl
4) ionic 5) polar 6) polar 7) polar 8) ionic
9) CsF
9) ionic
10) Cl2
▪Examples:
▪H2O
HCl
▪NH3
Dipole
When there is unequal sharing of electrons a dipole exists Dipole is a molecule that has two poles or regions with opposite charges
charges cancel out or balance out)
▪Examples:
▪CO2BF3源自▪CCl4Asymmetrical Molecules
If a molecule has polar bonds (and there is no symmetry to cancel out + and – charges), the molecule is polar.
Hydrogen bond
IMF’s
▪ALL molecules have dispersion forces ▪All polar molecules have dipole-dipole forces and dispersion forces ▪Molecules that hydrogen bond have all 3
The patterns of electronegativity
▪ electronegativity __________ (incr✔ease or decrease) across a period from Group 1 to Group 17
▪ electronegativity __________ (increase or decrea✔se) down each group.
Intermolecular forces and melting/boiling point
H-Br
Polar bond
O=O Non-polar bond
▪Why is AlCl3 covalent bond instead of ionic bong?
Give the electronegativity difference and
determine the bond type in the following
Solubility of polar molecules
▪Like dissolves like
▪Polar substances will dissolve polar molecules (and ionic compounds)
▪Non-polar substances will dissolve non-polar molecules
Electronegativity
Note
▪The greater the value of the electronegativity,
▪the ______________(gre✔ater or weaker)
the power of an atom to attract the electrons in a covalent bond towards itself.
10) nonpolar
Showing Polarity of a Bond
Determining Polarity of Molecules
Symmetrical Molecules
Because of symmetry, molecules that have polar
bonds are overall a nonpolar molecules (+ and –
Intermolecular Forces
▪The force that exists between separate molecules. ▪This force attracts molecules to each other.
▪3 Types
▪London Dispersion force (van der Waal’s forces or temporary dipole-induced dipole forces) or induced dipole moment between molecules; only force in non-polar molecules; weakest force (caused by the motion of electrons) (ex: CH4)
Electronegativity
Polarity in molecules
Electronegativity
▪is the ability of a particular atom, which is covalently bonded to another atom, to attract the bond pair of electrons towards itself.