Module 2 Flashcards
Isotope definition
Atoms of the same element with different numbers of neutrons and different masses
Cations
Positive ions
Anions
Negative ions
Relative isotopic mass
Is the mass of an isotope relative to 1/12 th of the mass of an atom of carbon-12
Relative atomic mass
The weighted mean mass of an atom of an element relative to 1/12 of the mass of an atom of carbon-12
Mass to charge ratio (m/z) equation
Relative mass of ion / relative charge of ion
Relative atomic mass equation
(Abundance x mass) (abundance x mass) … / 100
Avogadros constant
6l02x10^23, the number of particles in each mole of carbon-12
Mol equation
Mol= mass/ mr
Molecular formula definition
The number of atoms of each element in a molecule
Empirical formula
The simplest whole number ratio of atoms of each element in a compound
mol equation ( from c and v )
Mol= conc x vol
Standard solution
A solution of known concentration. They are made by dissolving an exact mass of the solute in a solvent and making up the solution to an exact volume
Mol equation at rtp
Mol= vol (dm3) / 24
Ideal gas equation
pV= nRT
Value for the gas constant
8.314 j mol k
How to convert from cm3 to m3
X10^-6
How to convert from c to k
+ 273
Percentage yield
Actual yield / theoretical yield x 100
Theoretical yield
The maximum possible amount of product
Why isn’t the theoretical yield always reached
The reaction may not have been completely reacted
Side reactions may have taken place
Purification of the product may result in loss of some product
Actual yield
Obtained from a reaction is usually lower then the theoretical yield
Limiting reagent
The reactant that’s not in excess and when it’s completely used up first it stops the reaction
Atom economy
Sum of mr of desired product / sum of mr of all products X 100
Oxidation number for element s
0
Oxidation number of H in hydrides (eg NaH, CaH2)
-1
Oxidation number of O in peroxides
-1
Oxidation number of O bonded to F
+ 2
Reduction in terms of e-
Gain of electrons
Oxidation in terms of e-
Loss of electrons
Reduction in terms of oxidation number
Decrease in oxidation number
Oxidation in terms of oxidation number
Increase in oxidation number
Metal + acid——>
Salt hydrogen
How many electrons can an orbital hold
1 or 2 electrons no more
S-orbital shape
Sphere
P- orbital shape
Dumbbell
How many orbital in p
3
How many orbitals are in d and f
D- 5
F- 7
Why does the 4s sub shell fill before the 3d sub shell
It has a lower energy level
Ionic bonding definition
The electrostatic attraction between positive and negative ions
Ionic bond boiling and melting points
Almost all ionic compounds are solids at rtp. Most ionic compounds have high melting and boiling pts
Solubility in an ionic bond
Many ionic compounds dissolve in polar solvents such as water. Water breaks down the lattice and surround each ion in solution. If the compound is made up of ions with large charges the ionic attraction may be too strong so this compound will then not be very soluble
Electrical conductivity in ionic bond
In the solid state an ionic compound doesn’t conduct electricity. But once melted or dissolved it will
Covalent bonding
The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms. Occur in non-metallic compounds
Are covalent bonds localised
Yes, the attraction is solely between the nuclei and shared electrons , this can result in a small unit called a molecule
Double covalent bond
The electrostatic attraction between 2 shared pairs of electrons and the nuclei of the bonding atoksn
Dative cove lent bonds ( or coordinate bonds )
A covalent bond in which the shared pair of electrons has been supplied by one of the bonding atoms only
How to measure covalent bond strength
Average bond enthalpy. The larger the value of the average bond enthalpy the stronger the covalent bond
4 bonding pairs and 0 lone pairs , shape + bond angle
Tetrahedral , 109.5
3 bonding pairs and 1 lone pair , shape and bond angle
Pyramidal , 107
2 bonding pairs and 2 lone pairs, shape and bond angle
Non-linear , 104.5
2 bonding regions , shape and angle
Liner , 180
3 bonding regions, shape and region
Trigonal planar , 120
6 bonding regions, shape and angle
Octahedral , 90
Electronegativity definition
The attraction of a bonded atom for the pair of electrons in a covalent bond
How is electronegativity measured
The Pauling scale
Which element is the most electronegative
F
How are electrons shared in non-polar bonds
The electron pair will be shared equally . This is a pure covalent bond
How are electrons shared in polar bonds
The electron pair is shared unequally between the bonded atoms. Eg the bonded electrons in HCl will be closer to the Cl
Intermolecular forces , definition and 3 main categories
They are the weak interactions between dipoles of different molecules.
Induced dipole-dipole interactions ( London forces )
Permanent dipole-dipole interactions
Hydrogen bonding
Induced dipole- dipole interactions strength
They are weak intermolecular forces that exist between all molecules, polar or non-polar. The larger the number of electrons mean larger induced dipoles, more energy is then needed to overcome the intermolecular forces, increasing the boiling point
How are London forces formed
-Movement of electrons produces a changing dipole in a molecule
-at any instant, an instantaneous dipole will exist but it’s position is constantly shifting
-the instantaneous dipole induced a dipole on a neighbouring molecule
-the induced dipole induced further dipoles on neighbouring molecules, which then attracts one another
Properties of simple molecular substances
Low melting point and boiling point
Solubility- the solubility of non-polar substances is easier to predict, simple molecular substances tend to be insoluble in polar solvents
Electrical conductivity- there are no mobile charged particles in simple molecular structures so there is nothing to complete an electrical circuit
Hydrogen bonds
A special type of permanent dipole-dipole interaction found between molecules containing and O, N , F
Anomalous properties of water
Ice is less dense than water
Water has a relatively high melting and boiling point
Relatively high surface tension
Viscosity
Why is ice less dense than water
Hydrogen bonds hold the water molecules apart in an open lattice structure. The water molecules in ice are further apart than in water, so solid ice is less dense than liquid water and floats
Why does water have a relatively high melting and boiling point
Hydrogen bonds are extra forces over and above London forces . An appreciable amount of energy is needed to break the hydrogen bonds in water. Without hydrogen bonds water would have a boiling point of -75c
