Bonding Flashcards
What is ionic bonding
Strong electrostatic forces of attraction between oppositely charged ions held in a lattice
Between MgO and NaCl which one is stronger/has a higher melting point
MgO is stronger/has a higher melting point than NaCl because when the ions are smaller and or have higher charges they have higher melting points and are stronger.
The ions involved in MgO are Mg2+ and O2+ where as in NaCl it is Na+ and Cl-
What effect does going down a group have on ionic radii
It increases because the ions have more shells of electrons
Why are positive ions smaller than negative ions
Positive ions are smaller because it has one less shell of electrons and the ratio of protons to electrons has increased so there is a greater net force on remaining electrons holding them more closely
Why do ionically bonded substances have high melting and boilling points
Requires alot of energy to break the strong electrostatic forces of attraction between opposites charged ions
Do ionic compounds conduct electricity? Why?
Yes, When molten/in solution as the ions are free to move and carry charge through the strcture
(they also tend to dissolve in water
What is molecular covalent bonding
A shared pair of electrons that has Weak van der waals forces of attraction between molecules
Can molecular covalent molecules conduct electricity? why?
No- all electrons used in bonding and aren’t free to move
Do molecular covalent substances have a high/low melting and boiling point? why?
Low- Weak van der Waals forces of attraction between molecules that don’t take much energy to overcome
Why do macromolecular covalent bonds have high MP and BP
Requires lots of energy to overcome the many strong covalent bonds
Why do metallic compounds have high MP and BP
Strong forces of attraction between metal ions and negatively charged sea of delocalised electrons
Do macromolecular covalent bonds conduct electricity
Most don’t as all electrons are used in bonding
Why do metallic compounds conduct electricity
The delocalised electrons move throughout the metal and to carry charge
Define electronegativity
The ability of an atom to attract the pair of electrons in a covalent bond to itself
Examples of molecular covalent substances
Iodine
Ice
CO2
Water
Methane
What effects electronegativity (3)
The number of protons in the nucleus;
The distance from the nucleus;
The amount of screening by inner electrons
Why exactly does the electronegativity increase?
Electronegativiity incrases across a period-Number of protons increases and atomic nucleus decreases because the eletrons in the same shell are pulled in more
It decreases down a group bcause the distance between the nucleaus and the outershell increases and the shielding of inner shell elctrons increases
How do you get a non polar bond
Both bonding elements have the same electronegativities
How do you get a polar bond
Bonding atoms have different electronegatuvities
Define metallic bonding
The electrostatic force of attraction between the positive metal ions and the delocalised electrons
What conditions are required for hydrogen bonding to occur?
- Partial charge on H and F/N/O
- Hydrogen attracted to the lone pair of O/N/F
- Large Electrobegativity diff
why is ice less dense than liquid water
Ice is less dense than water because the hydrogen bond orientation in ice causes the molecules to push farther apart, lowering the density.
When is a dative/co-ordinate covalent bond formed
When an electron deficient atom/ion accepts a lone pair of electrons from an atom/ion with a lone pair of electrons
what does the electron pair repulsion theory state
that electron pairs will take up positions as far away from each other as possible to minimise the repulsive forces between them
Which experiences the most repulsion?
(Lone pair-Lone pair
Lone pair-Bond pair
Bond pair-Bond pair)
Lp-Lp strongest repulsion
Lp-Bp repulsion middle
Bp-Bp repulsion weakest
Why are negative ions bigger than the corresponding atom
It has more electrons than the correspondng atom but the same number of protons so the pull of the nucelus is shared over more electrons and the attraction per electron is less making the ion bigger
what are the main factors affecting the strength of Metallic bonding
Number of protons( the more protons the stronger the bond)
Number of delocalised electrons(more delocalised= stronger)
Size of ion(the smaller the ion the stronger the bond)
Fact
A compound comtainning a small electronegatvity diff will be covalent
A compound containing elelmts of very diff electrongatvity and hence a very agre electronagtivity diff (>1.7) will be ionic
When does a dipole dipole occur
When the elements in the bond have diff electronegativities around 0.3 to 1.7
Symmetrical molecules
A symmetrical molecule (all bonds identical and NO lone pairs) will not be polar even if individual bonds wothin the molecule are polar
Why are symmetrica; molecules non polar
The individual dipoles on the bonds cancel out due to symmetrical shape of the molecule
What is the main factor affecting size of Van der Waals forces
The more electrons there are in the molecule the more VDW forces
Poperties of Dipole Dipole
Occur between polar molecules
Stronger than VDW
Assymetrical
Hydrogen bonding
A hydrogen attacthed to the three most electronegative compounds NFO and must have an available pair of lone electrons
U draw the line from the h bond to the lone pair
which atoms are the most electronegative
F N O CL
What is a polar molecule
When there is an electronegatibity diff between two or more atoms in a molecule
How can the shape of a molecule have an effect on the size of VDW forces
Long staright chains have a large surface area so they have stronger VDW whilst chains with kinks have a lower surface area
What are common compounds with dipole dipole
C-Cl C-Br C-F H-CL C=O
What are the 4 types of Crystals
Macromolecular
Giant Ionic
Molecular
Metallic
What are the ionic formulas for Sulfate Hydroxide Nitrate Carbonate and Ammonium
SO4^2-
OH-
NO3^-
CO3^-2
NH4^+
Why do simple covalent compunds have a low mp and bp
You only need to overcome the intermolcular forces
