Electronegativity And Polarity Flashcards
What is electronegativity?
The tendency of an atom in a covalent bond or molecule to attract molecules ina. Covalent bond to itself
WHEN DO you get electronegativity
When bonded atoms are different elements - nuclear charges are different the atoms may be different in sizes and the shared pair of electrons may be closer to ONE nucleus than another
Factors affecting electronegativity
Shielding- more shells decreases the electron negativity
Protons- more protons means a higher electron negativity
Atomic radius
Most electronegative elements?
F, N, O and CL
As you go down a group, what does the electronegativity co?
It DECREASES because the distance between the nucleus and the outer electrons increases and the shielding of inner she’ll electrons increases
What happens tp electronegativity as you go across the period
INCREASES as the umber of protons increases and the atomic radius decreases, because the electrons in the same she’ll are pu;;ed on ,pre
Non polar bonds
The bonded electron pair is SHARED EQUALLY between the bonded atoms
A bond will be non polar when..
- the bonded atoms are the same
-the bonded atoms have the same or similar electronegativity
- same elements- PURE COVALENT BODN
POALR BONDS
Bonded electrons are shared unusually between the bonded atoms
When bonded atoms are different- have different electronegativity values- pure covalent bonds
Between ionic and non polar covalent
Electronegativity differnences for non polar covalent, polar covalent and ionic ?
<0.4- non polar
0.4-1.8- polar
>1.8 - ionic
How is electronegativity measured
PAULING scale
Symmetry - covalent bonding
If polar bonds are arranged symmetrically partial charges/individual dipoles
CANCEL OUT AND ITS NON POLAR
INTERMOLELAR forces?
Weak interactions between dipoles of DIFFERNENT molecules
3 categories of intermolecular forces?
VAN DER WAAL?
- induced dipole dipole interactions
- permanent dipole dipole interactions
- hydorgen bonding
What are intermolecular forces responsible for?
Boiling and melting point
COVALENT BONDING - IDENTITIY OF CHEMICAL REACTIONS OF MOLCUELS
BONDING- intra molecular
Within molecules and structures
Ionic
Covalent
Metallic
Intermolecular- between molecules
Broken to melt/boil covalent substances
Permenant dipole dipole interactions
Between permenant dipoles in POLAR molecules
Stronger than induced dipole - dipole interactions = compounds have higher boiling points
Polar molecules have a permenant dipole
INDUCED DIPOLE DIPOLE FORCES
Occur between all simple covalent molecules and separate atoms in noble gases
In any molecule the electrons are moving constantly and randomly
As this appends, electron density can fluctuate + parts of the molecule has become more or less negative ie small temporary or transient dipoles form
These temporary dipoles can cause dipoles to form in neighbouring molecules
factors affecting induced dipole dipole interactions
More electrons ( main factor ) Shape
More electrons - effect on size of induced dipole, dipole interactions
- larger the instances adn induced dipoles
- greater the induced dipole-dipole interactions
- stronger the attractive forces between molecules
LARGER INDUCED DIPOLES = MORE ENERGY TO OVERCOME INTERMOLECULAR FORCES= INCREASES THE BOILING POINT
Shape - effect on size of induced dipole dipole interactions
The shape of the molecule can have an effect on size of the induced dipole dipole interactions forces
long chain alkanes have a larger surface area if contact between molecules for induced dipole , dipole interactions to form than compared to spherical branched alkalies
Strength of intermolecular forces ?
H bonding - 10-40
Permenant D_D= 3-25
INDUCED D_D= 1-10
Simple molecular substances
Made up of simple molecules
Small units containing definite number of atoms with a definite molecular formula e.g. Neon. Hydrogen. Water . Co2
Solid - form regular structure called a simple molecular lattice, atoms he’d in place by WEAK IMF, atoms within molecule - strong covalent bonds
Hydrogen bonding ?
Strong dipole- dipole interaction between an electronegative atom with lone pair of electrons e.g. Oxygen. , nitrogen or fluorine ( FON)
A hydorgen atom attatched to an electronegative atom e.g. H-O , H_N or H_F
Eg h-n ——–H -N
Are hydrogen bonds STrong?
STRONGEST IMF
Properties of water
Without h bonds = -75 BP and gas at room temp
High melting and boiling point
When water boils- H bods break completely
When ice lattice breaks- rigid arrangement of H bonds is broken
Solid ice- less dense than liquid water, water molecules in ice - further apart than water , 2 lone pairs + 2 h atoms - each h20 can from 4 H bonds . Form a tetrahedral lattice with mSNY holes - 180 bond angle about the H atom
