Atomic Structure Flashcards
what is the atomic number (Z)
the number of protons
what is the mass number (A)
protons+neutrons
atomic number
protons and electrons
How to calculate neutrons
mass - atomic
Quantity of proton
relative mass- 1
relative charge- +1
Quantity of neutron
mass- 1
charge- 0
Quantity of electron
mass-1/1836
charge- -1
to find ions on the periodic table
proton stays the same
electron number changes
if it is a positive ion- take away from proton number
if it is a negative ion- add to proton number
add or take away charge on ion
john dalton
-Elements are made up of tiny particles called atoms.
-Atoms cannot be divided, altered or destroyed by chemical means.
-Atoms of an element are all the same in terms of shape and size and atoms of different elements differ in size and shape.
-Elements are characterised by mass of their atoms so all the atoms of an element have identical weight. Different elements have atoms of different atomic weight.
-Atoms of different elements can combine together to form chemical compounds.
-When elements undergo chemical reactions, their atoms combine in simple, whole number ratios or more than one simple whole number ratios. Dalton noted that tin can combine with either one or two oxygen atoms which was in line with the percentages of masses observed for tin oxides. Similarly he used the same principle to explain that the different ratios of nitrogen to oxygen in various nitrogen oxides were simple multiples of each other.
Berzelius
-all atoms are spherical
-all atoms are the same size
-they have different weights
-joined together in fixed proportions- +ve and -ve charge
Thomson
-discovered electron
-plum pudding model - negative electrons embedded in a sphere of positive charge
- charge balances
Rutherford
-gold firing experiment
-fired alpha particles at sheet of gold foil, most passed through some where reflected back
-showed positive charge in centre of atom
-mass of atom is concentrated in the nucleus
-electrons move around nucleus like planets
Bohr
-most of mass in central nucleus that contains positive protons
-electrons in shells orbiting nucleus
-long way away from nucleus
-atoms with full shells are not very reactive
Chadwick
-neutrons
-this is found in nucleus alongside protons
-nuclear model
What does the Schrodinger equation stand for
equation to estimate the probability of finding an electron in a given volume of space also known as an atomic orbital
what do atoms also have
sub-levels: s,p,d and f
what do you use to find the Ar of a sample
time of flight mass spectrometry
what are the stages in ToF MS
-ionisation
-acceleration
-flight tube/ion drift
-detection
describe the process of electron impact ionisation
-for low mass sample/molecule
-sample vaporised to a gas
-high energy electrons are fired at sample from an electron gun
-this causes one outer shell electron to be knocked off
-turning the sample into an ion (1+)
-attracted to a negative plate
describe the process of electrospray ionisation
-for high mass
-the sample is dissolved in a volatile solvent
-injected into a hypodermic needle to give a fine mist
-needle has high voltage power supply
-particles are ionised by gaining a proton from the solvent
-producing XH^+ ions
-these are then accelerated to a negative plate
describe the process of acceleration
positive ion are accelerated using an electric field until they have the same kinetic energy
-KE= 1/2mv^2
velocity depends on the mass , lighter = faster
-v =square root 2KE/m
-velocity is inversely proportional to mass
-the ions begin to separate
Describe the process of the flight tube/ ion drift
-The time in the flight tube is determined by the mass of the ions
-therefore lighter particles will travel at a greater velocity
-time is therefore proportional and dependent on mass
-time=distance / velocity
-time = distance x the square root of mass/ 2xkinetic energy
Describe the process of detection
-+ve ions hit -ve plate (opposite charges attract)
-+ve ions discharged by gaining electrons via the plate
-generating a flow of electrons and hence an electric current (electric current is flow of electrons)
-size of current detected will give a measure of the number of ions
What does this data produce
Mass spectrometer graph
What does the graph show - time of flight
The relative abundance of the ions in the sample
What is on the x-axis - time flight graph
Mass/charge ratio
What is on the y-axis
Relative abundance / intensity
Why is the mass/charge ratio the mass of each ion
Each ion has a 1+ charge meaning that the mass is effectively 1
Ionic equation to show electron impact
X(g) = X^+ (g) + e^-
Ionic equation to show electrospray
X(g) + H^+ = XH^+ (g)
What happens to the isotopes via their chemical properties
They will not charge between isotopes
-this is bc they have the same electronic structure/ same outer shell of electrons
How are electrons arranged
Energy levels - sub-shells/ levels
What levels are there
-s
-p
-d
-f
How may electrons are in the s sub-shell
2
How many electrons are in the p sub-shell
6
How many electrons are in the d sub-shell
10
How many are in the f sub-shell
14
What is an atomic orbital
The probability that you will find an electron in a given volume of space
What is Aufbau principal
Electrons occupy the lowest- energy orbital first
Eg 4s sub-shell is lower in energy to 3d
What is hunds rule
Electrons prefer to occupy electron shells on their own so fill squares up before you pair them
Only pair them up first when no empty orbitals are available
What is Pauli exclusion principle
Orbitals have their own spins so represent them with single headed arrows
What happens when writing ions configuration
Lose from 4s before 3d so take out the electrons from 4s
What is the configuration rule
Look at periodic table to see
What can you use in short hand
The nearest available noble gas
What are two exceptions to the rule
Chromium - 1s2 2s2 2p6 3s2 3p6 4s1 3d5
Copper- 1s2 2s2 2p6 3s2 3p6 4s1 3d10
Why do Cr and Cu exceptions matter
The reduced e- e- repulsion makes up for the fact that one electron is at a slightly higher level
what is the definition of ionisation energy
the energy required/(enthalpy change when) to remove one mole of electrons from a mole of isolated gaseous atoms or ions
what is the general formula for the 1st ionisation energy
X(g)= X+(g) +E-
what is the general formula for the 2nd ionisation energy
X+(g)=X2+(g)+E-
what factors effect ionisation energies
-distance from the nucleus-further way less attraction to the nucleus
-nuclear charge-greater number of protons more energy required to ionise
-shielding-greater full shells means that less attraction from positive nucleus/protons
what is the trend for group ionisation energy
The ionisation energy down a group decreases due to the following factors:
-The number of protons in the atom is increased, so the nuclear charge increases
-But, the atomic radius of the atoms increases as you are adding more shells of electrons, making the atoms bigger
-So, the distance between the nucleus and outer electron increases as you descend the group
-The shielding by inner shell electrons increases as there are more shells of electrons
-These factors outweigh the increased nuclear charge, meaning it becomes easier to remove the outer electron as you descend a group
what is the trend for the ionisation energy of periods
The ionisation energy across a period generally increases due to the following factors:
-Across a period the nuclear charge increases
-This causes the atomic radius of the atoms to decrease, as the outer shell is pulled closer to the nucleus, so the distance between the nucleus and the outer electrons decreases
-The shielding by inner shell electrons remain reasonably constant as electrons are being added to the same shell
-It becomes harder to remove an electron as you move across a period; more energy is needed
-the addition of the proton causes this
why is there a dip between group 2 and 3 in period trends
-in this the group 3 element is in the p orbital which is of a higher energy than the s orbital of group 2 therefore it is easier to lose an electron
-they are also slightly shielded by the s orbital
why is there a dip between group 5 and 6 in period trends
-in this group 6 element there is a greater repulsion between the pair of electrons in say the 2p4 orbital compared to that of the 2p3 group 5 orbital
-this repulsion force causes the second electron to be lost easier
trend for group 2
-general decrease
-bc off factors in general group trends
-Be,Mg,Ca,Sr,Ba
trend for period 3
-general increase
-bc off factors in general period trends
-dip from Mg to Al- p = higher energy lost easier
-dip from P to S- extra electron repulsion so easier to lose
What must the answer contain if question asks for what is the formula of the ion that reaches the detector first
Give the answer as an ion
Be careful to add a H+
Eg C3H5O2N
C3H6O2N+
When given atom question that says deduce with proton and neutron addition
Add both protons and neutrons to give mass number
Only add protons to find symbol
If given ion and need to find mass in calc (also given avagad)
Ion/1000/6.022x10^23
Find mass of isotope if given mass / charge graph
Mass/charge ratio - 1
help for % abundance calcs for 3 elements
make the heaviest unknown isotope x to avoid -ve numbers
-keep in decimals as easier than working with large numbers
-express smaller in terms of x eg 100- % of known - x
why is the first IE of an element less than the second
-in the second - remove electrons from a positive ion
-more energy is required to remove one mole fo e- from one mole of positive ions
in abundance calcs
-when do u divide by 100 or the total abundance
-100 if % are given
-total abundance if just the abundance
why is second IE in Ca lower than K- or any other elements that have the same relationship - group 2/ group 1
-In Ca+ / group 2 the outer e- are further away from the nucleus than K+/group 1
-Ca+ experinces more sheilding
