2- Bonding and structure Flashcards
How are ions formed?
When electrons are transferred from one aton to another.
What is the definition of an ionic bond?
electrostatic attraction between two oppositely chargen ions
Why are ions in a lattice arranged in a repeating pattern?
So positive charges cancel out negative
Describe the two things that affect the strength of an ionic bond
ion charges- Greater charge on an ion, the stronger the ionic bond
Ionic Radii- Smaller ions are packed closer together and eletrostatic attraction is weaker with distance so these smaller ions will have stronger ionic bonding
How come the overall charge lattice in ionic bonds are eletrically neutral?
Each ion is attracted to the oppositely charged ions around it.
What are isoeletric ions?
Ions that have the same electron configuration.
What is the pattern in ionic radii with positive and negative charges?
Ionic radii increases with increasing negative charge but decreases with increasing positive charge.
What is the M.P and B.P of ionic compunds like and why?
They are solids at room temperature because it requires a lot of energy to obvercome the strong electroststic force of attraction between oppositely charged ions. So, high temperatures are required to melt and boil and is even higher for ions with a higher ionic charge due to stronger attraction between the ions.
State the 3 talking points when talking ab the properties of ionic compounds.
m.p and b.p
eletrical conductivity
solubility
Describe the solubility of ionic compounds
Very soluble in polar solvents like water as the slighlty positive polar molecule surrounds the anion and slightly positive polar molecule surrounds cation.
Describe the eletrical conductivity of ionic componds
Must be in molten or aqueous state to carry eeltrical charge as ions and electrons must be free moving.
Solubility of an ionic compound depends on…
-Relative strength of eletostatic forces of attraction
- attraction between polar molecule
Decribe the evidence for the existence ions
Electrolysis as cations are attracted to anion and anions attracted to cation
What is covalent bonding?
Eletrostatic attraction between 2 nuclei
What are the three types of covalent bond and number of electrons in each?
Single-2
Double-4
Triple-6
What is dative covalent bonding?
When some molecules have a lone pair of electrons which can be donated to form a bond with an electreon deficient atom ao both electrons are from the same atom.
What is bond energy and its units?
The energy required to break one mole of a covalent bond
Kj mol-1
What is bond length?
Internuclear distance of two covalently bonded atoms
Rules to consider when deterining the shape and bond angles of a molecule
-Electron pairs repel eachother as they have the same charge
-Lone pair electrons repel eachother more than bonded pairs
-Repulsion between pairs of double bonds is greater
-Most stable shape is adopted to minimize repulsion forces
Name all the different structures and their bond angles
Pyrimidal-107
Bent-104.5
Triognal Planar-120
Linear-180
Tetrahedral-109.5
Triognal Bipyramidal-120 and 90
Octahedral-90
What three things have to occur for a substance to dissolve?
Bonds in substance break
Bonds in solvent break break
New bonds form between substance and solvent
When does a polar covalent bond form?
When then the elements in the bond have different electronegativites
Why does a polar covalent bond produce a charge seperation (dipole)?
Because there is an unequal distribution of electrons in the bond and it produces a charge seperation
Why is it that some molecules with individual bonds within the molecule that are polar are non polar molecules?
This is because the individual dipoles on the bond ‘cancel out’ due to the symmetrical shape of the molecule. There is no net dipole movement so the molecule is non polar
Explain the effect of charged rod on polar/ non-polar liquids
If the liquid is polar, the jet of liquid will be attracted to the electrostatic force of the rod. Dipoles in the polar molecules will align negative ends attracted to positive rod or vice versa. The stronger the dipole the more deflection of the jet. Non polar liquids will not be deflected and attracted to the charged rod
Where do london forces occur?
Between all molecules and substances and noble gases but not in ionic substances
What are London forces also called
Instantaneous, induced dipole-dipole
What is the main fator affecting the size of London forces?
The amount of electrons, the more electrons there are in the molecule, the higher the chance that temporary dipoles will form this makes london forces stronger between the molecules.
Why do temporary dipoles occur in molecules?
In any molecule electrons are moving constantly and randomly. As this happens, the electron density can fluctuate and parts of the molecule become more or less negative causing small temporary or transient dipoles to form
Explain why I2 is a solid whereas Cl2 is a gas?
Down group 7 there is an increasing no. of electrons in the bigger molecules causing an increase in the size of the London forces between molecules. Higher b.p in I2 more energy required to break bonds to change state
Descibe how the shape of the molecule can have an effect on the size of the London forces?
Long straight chain alkanes have a larger surface area of contact between molecules for london forces to form, compared to spherical shaped branched alkanes and so have stronger London forces
When do permannet dipole dipole forces occur, examples of molecules and properties
Permanent dipole-dipole forces occurs between polar molecules
It is stronger than London forces and so the compounds have higher boiling points •Polar molecules have a permanent dipole. (commonly compounds with C-Cl, C-F, C-Br H-Cl, C=O bonds)
Polar molecules are asymmetrical and have a bond where there is a significant difference in electronegativity between the atoms.
Describe when and how hydrogen bonding occurs and why is there a 180 degree angle around the hydrogen
It occurs in compounds that have a hydrogen atom attached to one of the three most electronegative atoms of nitrogen, oxygen and fluorine, which must have an available lone pair of electrons. e.g. a –O-H -N-H F- H bond. There is a large electronegativity difference between the H and the O,N,F.
there are two pairs of electrons around the H atom involved in the hydrogen bond. These pairs of electrons repel to a position of minimum repulsion, as far apart as possible.
Why are metals malleable?
Metals are malleable because the positive ions in the lattice are all identical. So the planes of ions can slide easily over one another. The attractive forces in the lattice are the same whichever ions are adjacent
The three main factors that affect the strength of metallic bonding are:
- Number of protons/ Strength of nuclear attraction. The more protons the stronger the bond
- Number of delocalised electrons per atom (the outer shell electrons are delocalised) The more delocalised electrons the stronger the bond
- Size of ion. The smaller the ion, the stronger the bond.
