number of protons (Z / proton number)
Number of protons and number of neutrons
Atoms with the same numer of protons but a different number of neutrons.
- Different isotopes of the same element react chemically in the same way
- Vary in mass number due to the different amount of neutrons
An instrument used to measure the relative atomic mass (RAM) on a scale based on the mass of an atom of Carbon-12 which has a RAM of 12
Ionisation (Mass Spec)
A beam of electrons, fired from an electron gun, knocks an electron from an atom to create positive ions
Norally only one electron is removed creating a 1+ charge, but occasionally two electrons are removed creating a 2+ charge
Acceleration (Mass Spec)
The postive ions are attracted towards negitivly charged plates and accelerated to a high speed
The lighter the ion, the faster they go
Deflection (Mass Spec)
The beam of ions moves into a magnetic field, at right angles to it's direction of travel. The magnetic field deflcts the ions.
The amount of deflection depends upon the m/z vaue of the atoms, the charge mass ratio. As the charge, in most cases is 1, the deflection depends solely upon the mass number.
- 2+ ions are deflected twice as much
Detection (Mass Spec)
Ions hit the detector, accept electrons, lose their charge and create a current which is proportional to the abundance of each ion.
Mass Spectrum (Mass Spec)
A graph showing the relative abundance (y-axis) and mass/charge value (x-axis) produced by the mass spectrometer
Working out RAM (Mass Spec)
Relative atomic mass:
(m/z value x % abundance) + (m/z value x % abundance)
watch out for 2+ ions, as they may obscure your result
Applications of Mass Spec
Used on space probes, eg. Viking Martian, to identify the elements in rock samples on other planets/moons/comets in space.
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5d6
- Two electrons in the same orbital have opposite spins
- Represented by an arrow pointing up or down, depending on direction of spin
The energy required to remove one mole of electrons from a mole of atoms in the gaseous state.
measured in Kj/mol
Sucessive Ionisation Energies
The first IE needs the leas energy to remove
The secnds needs more energy than the first beacuase it is being removed from a 1+ ion
and so on..
Relative Atomic Mass
The average mass of one atom of an element
1/12th mas of one atom of Carbon-12
Relative Molecular Mass
average mass of one molecule
1/12 the mass of one atom of Carbon-12
The number of atoms in 12 g of Carbon-12
6.022x10^23 or mole
Moles = mass in g / RAM
V is proportional to T
or using a constant (k):
- V= kT
Gay-Lussac's Law (constant volume law)
PV/T = constant for a fixed mass of gas.
(as PV= k and V/T = k)
Ideal Gas Equation
PV = nRT
The simplest ratio of the atoms of each element present in a compound
To find empirical formula:
- Find the masses of each element
- Find the moles using moles = mass / ram
- convert moles into whole number ratio
The actual number of atoms of each element present in a compound.
To find molecular formula from empirical formula:
- units of empirical formua: relative molecular mass / relative mass of empirical formula
- times the empirical formula by the units
eg. CHv2 has a relative molecular mass of 12 and relative mass of 24
24 / 12 = 2
2 x 2 = 4 so molecular mass = Cv2Hv4
Concentration= number of moles / volume in dm^3
NB- if given in cm^3 divide by 1000
Atom economy = (mass of disired product / total mass of reactants ) x100
Used to determin how much of the reactants will be wasted and if the experiment is useful, cost effective and sustainable.
Percentage yield = (the number of moles of a specified product / theoretical maximum number of grams of the product) x100
- Between a metal and a non-metal
- Electrons are transfered from metals to non-metals
- Positive and negative ions are formed
- Electrostatic forces hold the ions together
Properies of ionicly bonded compounds
- Soild at room temperatures
- Giant structures
- High meltin temperatures
- Conduct electricity when molten or disolved in water
- Shatter easily
- A bond between a pair of non-metal atoms
- Share the outer shell electrons
- Two atoms share one pair of electrons
Occasionaly double covelent bonds are formed, when two atoms share two pairs of electrons. Called a double bond.
A single atom provides both the electrons in the shared pair. This can be called a dative covalent bond
- The atom that accepts the pair is an atom that doesn't have a filled outer level of electrons, this atom is deficient
- The atom doning the electrons has a pair of electrons that is not involved in a bondm called a lone pair
The power of an atom to attract the electron density in a covelent bond towards itself. It depends upon:
- thenuclear charge
- the distance between the nucleus and the outer shell electrons
- the shielding of the nuclear charge by the electrons in the inner shells
A lattice of positive ions in a sea of outer electrons.
- Giant structures
- Malleable and ductile
- High melting points- strong bonds
Forces that act between molecules.
- van der Waals
- Hydrogen bonding
An intermolecular force that results from the attraction between molecules with permenent dipoles.
- 2nd weakest intermolecuar force
van der Waals forces
All atoms and molecules have positive or negative charges, even if neutral overall. These charges produce a very weak electrostatic attractions.
- The distribution of the charge changes every second
- In addition to other forces
The weakest intermolecular force
When a hydrogen atom is bonded to a very electronegative atom:
The strongest intermolecular force
A saturated hydroarbon containing no double bonds.
An orgainic compound containing one or more double bond.