Flashcards in Module 2 Deck (68):
What is an isotope?
Isotopes are atoms of the same element with different numbers of neutrons and different masses
What is a positive ion?
What is an anion?
A negative ion
State the definition of relative atomic mass
The weighted mean mass of an atom or element relative to 1/12th the mass of an atom of carbon-12
State the definition of relative isotopic mass
The mass of an isotope relative to 1/12th of the mass of an atom of carbon-12
What does the weighted mean mass take account of?
The percentage abundance of each isotope
The relative isotopic mass of each isotope
What is a binary compound?
A compound which consists of two elements only
What is a polyatomic ion?
An ion which contains more than one element bonded together
What is Avogadro’s constant?
The number of particles in each mole of carbon-12
Assumptions for the calculations of water of crystallisation
All water has been lost
No further decomposition
How are standard solutions prepared?
Dissolve an exact mass of the solute in a solvent and make up the solution to an exact volume
How do you find concentration in gdm^-3?
m = n X M
n= concentration in Mol dm^-3
What is the molar gas volume?
The volume per mole of gas molecules at a stated temperature and pressure
How do you convert between the amount of moles of gas and the volume of the gas?
n = volume(dm-3) / 24
n = volume(cm-3) / 24000
Assumptions of an ideal gas
No intermolecular forces
Units for the equation
p = Pa
V = m^3
n = mol
R = 8.31 J mol -1 K -1
T = K
How do you calculate atom economy?
Sum of molar masses of desired products / sum of molar masses of all products
What kind of acid completely dissociates, releasing all of its hydrogen atoms into solution as H+ ions?
What does a base do?
Neutralises an acid to form a salt
What is an alkali?
A base that is dissolved in water releasing hydroxide ions (OH-) into the solution
Acid + alkali =
Salt + water
Uncertainty of a 100cm^3 volumetric flask
Uncertainty of a 250cm^3 volumetric flask
Tolerances of a 10cm^3 and a 25cm^3 pipette
Tolerances of a 50cm^3 burette
What must titres agree within to calculate the mean titre?
Work out the amount in mol of the solute in the solution for which you know both the concentration and volume
Use the equation to work out the amount in mol of the other solute
Work out the unknown information
Oxidation number of elements
Oxidation number of H in metal hydrides
Oxidation number of O in peroxides
Oxidation number of O bonded to F
What do Roman numerals represent?
The oxidation state of the element
What is oxidation?
Addition of oxygen
Loss of electrons
Increase in oxidation number
Metal + acid =
Salt + hydrogen
What is an atomic orbital?
A region around the nucleus that can hold up to two electrons, with opposite spin
What is the shape of an S orbital and how many electrons can it hold?
Up to 2 electrons
What is the shape of a P orbital and how many electrons can it hold?
Up to 6 electrons
How do orbitals fill?
In order of increasing energy
Why does the 4s sub-shell fill before the 3d sub-shell?
4s subshells are at a lower energy level than 3d
In what direction do ions attract oppositely charged ions?
Properties of ionic compounds
All solids at room temperature
Melting points are higher for lattices containing ions with greater ionic charge
Many dissolve in polar solvents. In a compound with large charges the ionic attraction may be too strong for water to be able to break down the lattice.
Only conducts electricity when melted or in aqueous solution.
What is covalent bonding
The strong electrostatic attraction between a shared pair of electrons and the nuclei of bonded atoms.
The overlap of atomic orbitals.
What is the attraction in a covalent bond?
Localised, it acts only between the shared pair of electrons and the nuclei of the two bonded atoms
What is a double covalent bond?
The electrostatic attraction is between two shared pairs of electrons and the nuclei of the bonding atoms
What is a dative covalent / coordinate bond?
A covalent bond in which the shared pair of electrons has been supplied by one of the bonding atoms only.
The shared pair was originally a lone pair of electrons on one of the bonded atoms.
How are average bond enthalpy and covalent bond strength related?
The larger the value of the average bond enthalpy, the stronger the covalent bond
Shape of a molecule with 4 bonded pairs and 0 lone pairs
Shape of a molecule with 3 bonded pairs and 1 lone pair
Shape of a molecule with 2 bonded pairs and 2 lone pairs
Shape of a molecule with 2 bonded pairs
Shape of a molecule with 3 bonded pairs
Shape of a molecule with 6 bonded pairs
Why do lone pairs repel more strongly than bonded pairs?
Lone pairs are slightly closer to the central atoms and occupy more space
What is electronegativity?
The attraction of a bonded atom for the pair of electrons in a covalent bond
Pauling electronegativity values
Electronegativity increases up and right of the periodic table
Across the periodic table nuclear charge increases and atomic radius decreases
Electronegativity difference for a covalent bond, polar covalent bond, and an ionic bond
What is a non polar bond?
The bonded electron pair and shared equally between the bonded atoms
When will a bond be non polar?
The bonded atoms are the same
The bonded atoms have the same or similar electronegativity
What is a polar bond?
The electron pair is shared unequally between the bonded atoms.
The atoms are different and have different electronegativity values.
How are induced dipole-dipole interactions formed?
Movement in electrons produced a changing dipole in a molecule
At any instant and instantaneous dipole will exist but it’s position constantly changing
The instantaneous dipole induces a dipole on a neighbouring molecule
The induced dipole induces further dipoles on neighbouring molecules, which then attract one another
How are induced dipole-dipole interactions affected when there are more electrons in each molecule?
The larger the induced and instantaneous dipoles
The greater the induced dipole-dipole interactions
The stronger the attractive forced between molecules
More energy is needed to over come intermolecular forces so boiling point increases
When will a molecule have permanent dipole-dipole interactions?
When the atoms have permanent dipoles
What is a simple molecular substance?
Simple molecules in the solid state.
The molecules are held in place by weak intermolecular forces but the atoms within each molecule are bonded together strongly by covalent bonds
Properties of simple molecular substances
Low meeting and boiling points
Non-polar simple molecular substances:
•Soluble in non-polar solvents
•Insoluble in polar solvents
Polar simple molecular substances:
•solubility depends on the strength of the dipole and can be hard to predict
Non-conductors of electricity
Where is a hydrogen bond found?
Between molecules containing:
•An electronegative atom with a lone pair of electrons
•A hydrogen atom attached to an electronegative atom