3. Bonding in Compounds Flashcards
What are the 3 types of bonding found in compounds?
IONIC
POLAR COVALENT
NON-POLAR COVALENT
What is an ionic bond?
An Ionic bond is the electrostatic attraction between a positive and a negative ion.
How do metals and non metals gain a stable octet?
metals LOSE electrons to get a NOBLE GAS electron arrangement while non-metals GAIN electrons.
Explain ionic compounds
Ionic compounds tend to form from METALS and NON-METALS.
Ionic compounds have HIGH melting and boiling points.
Ionic compounds therefore are always SOLID at room temperature.
Why do ionic compounds not conduct when solid?
THE IONS ARE NOT FREE TO MOVE. They only conduct when MOLTEN or in SOLUTION.
Where can ionic bonding not be found?
Ionic bonding cannot be found in elements. Elements are made of atoms.
What are the 2 types of covalent compound?
molecular and network.
What is an example of a covalent network?
Silicon Dioxide SiO2.
Explain the structure of silicon dioxide
Each Si bonds to 4 O and each O bonds to 2 Si.
So the ratio is 2:4 so 1:2 and the formula is SiO2.
It’s a network so very high m.pt. and b.pt and very very hard and covalent bonds are very strong. SiO2 is sand, so used also in sand-paper.
Why do covalent networks have high melting points?
Covalent network compounds have very HIGH melting points because it takes a lot of energy to break the very strong covalent bonds.
Why are covalent networks very hard?
Covalent network compounds are very hard because it takes a lot of energy to break the very strong covalent bonds.
How do atoms form covalent bonds?
by SHARING electrons
If the electrons are shared equally i.e. sit in the MIDDLE of the bond what do we call it?
we call the bond a Non-polar Covalent Bond.
What is a non-polar covalent/pure covalent bond?
If the electrons are shared equally i.e. sit in the MIDDLE of the bond
What is a polar covalent bond?
Bonds in which the electrons are unequally shared are called Polar Covalent Bonds.
Bonds in which the electrons are unequally shared are called what?
Polar Covalent Bonds.
Explain Hydrogen Flouride?
H+ —- F-
The shared pair of electrons sit closer to the F than the H. The is why the F has a slightly negative charge δ-. This unequal sharing makes the polar bond. Sometimes also called a permanent dipole
Why are Polar Covalent bonds existing?
This unequal sharing is due to a property called ELECTRONEGATIVITY.
What is ELECTRONEGATIVITY?
Electronegativity is measure of the attraction that an atom has for the shared pair of electrons in a covalent bond.
Explain the trends in ELECTRONEGATIVITY.
Electronegativity INCREASES across a PERIOD.
Electronegativity DECREASES down a GROUP.
Explain why the electronegativity values increase across a period
- As the atomic number goes up there are more protons added to the nucleus, so the nuclear charge goes up.
- This stronger pull from the nucleus pulls the electrons in tighter
- (so the atom and it’s covalent radius get smaller).
- So the electronegativity must be higher due to the higher pull from the nucleus.
Explain why the electronegativity values decrease down a group
- As you go down the group you add extra shells of electrons, which makes the atoms bigger.
- The atomic number also gets bigger so they also have a larger nuclear charge.
- However the extra shells of electrons shield the outer electrons from the pull of the nucleus.
- As it’s the outer electrons that are involved in bonding this means the electronegativity must decrease as they are now pulled in as tightly.
Why can’t polar covalent bonding exist in an element?
- As we are talking about elements all the atoms present must be the same.
- So the electronegativity values are the same so the bonding electrons must be equally shared, so the bond must be non-polar.
- You can’t get polar bonds in an element.
Can polar covalent bonds exist in an element?
No.
How do you determine if a compound has more ionic or covalent character?
Compounds with the greatest difference in electronegativities between the atoms will have more IONIC character.
Compounds with very little difference in the electronegativity values will be more COVALENT.
What is the exception that has polar-covalent bonds?
TiCl4
How do you determine the polarity from a structure?
If the distribution of polarity is equal across the whole molecule it is non-polar.
If the distribution is unequal (like in water) it will be polar.
Explain the polarity and structure of Ammonia
It is polar.
N is negative, the 3 Hs are positive
Explain the polarity and structure of carbon dioxide
It is non polar.
C is positive
2 O’s are double bonded and are negative
Explain the polarity and structure of Chloroform
Polar
C+ in centre
Cl- x 3 branching out
H on top
Explain the polarity and structure of carbon tetrachloride
Non-Polar
C + in centre
Cl- x 4
Explain the polarity and structure of hydrogen sulphide
Polar.
- S in centre
H+ x 2
If a molecule is polar we say that it has a?
PERMANENT DIPOLE.
