Atomic Structure Flashcards
Atoms made up of
Protons, neutrons and electrons
Electrons describe
-1 charge
Whizz around nucleus in orbitals. Orbiter take up volume of atom
Nucleus of atom describe
Most of mass of atom is concentrated in nucleus
Diameter of nucleus of rather titchy compared to whole atom
Nucleus where you find proteins and neutrons
Proton
1 mass
+1 charge
Neuton
1 mass
0 charge
Electron e-
1/2000 mass
-1 charge
What can you figure out from nuclear symbol
Number of protons, neutrons and electrons in an atom
What is the mass number?
Total number of protons and neutrons in nucleus
Elements made of
Atoms
What is the atomic (proton) number?
Number of protons in nucleus it identifies the element
All atoms of same element have same number of protons
What is sometimes left out?
The atomic number of the nuclear symbol because you don’t need it because the elements symbol tells you it’s value
Neutral atoms number of protons and electrons?
Which have no overall charge the number of electrons is the same as the number of protons
What is the number of neutrons?
The mass number minus the atomic number
Top minus bottom in nuclear symbol
How do atoms form ions?
By gaining or losing electrons
Negative ions have more
Electrons than protons
e.g. Br-
Negative charge means 1 more electron than there are protons
Br has 35 protons do Br- must have 36 electrons
Positive ions
Have fewer electrons than protons
E.g. Mg2+
2+ charge means 2 fewer electrons than there are protons Mg had 12 protons so Mg2+ must have 10 electrons
What are isotopes
Isotopes of an element are atoms with same number of protons but different number of neutrons
What do different mass numbers mean for isotopes?
Different number of neutrons
Atomic numbers for isotopes?
Are the same because both isotopes have 17 protons and 17 electrons
What does the periodic table give?
Atomic number of each element
Other number by elements symbol in periodic table isn’t mass number through its relative atomic mass
At the start of the 19th century, atom structure model?
John Dalton described atoms as solid spheres and said different spheres made up different elements
In 1897, atom structure model?
J.J Thomson discovered the electron. This showed stone weren’t solid and indivisible. Solid sphere idea of atomic structure had to be changed. New model known as “plum pudding model”
1909 atom structure model?
Ernest Rutherford and student Hand Geiger and Ernest Marsden conducted their famous gold foil experiment?
What did they do for the Gold foil experiment?
Fired positively charged alpha particles at a very thin sheet of gold.
What would the plum pudding model suggest should have happened in the gold foil experiment?
Most alpha particles would be slightly deflects by positive pudding that made up most if the atom
What were the results of the gold foil experiment?
Most particles passed straight through gold
Only small number deflected backwards
Results of gold foil experiment meant?
Plum pudding model couldn’t be right so Rutherford developed nuclear model of atom.
Ruthfords model of atom?
Tiny positively charged nucleus surrounded by cloud of negative electrons most of atom is empty space
What did scientists realise?
Electrons in a cloud around the nucleus of an atom as Rutherford described would quickly spiral down into buckets causing atom to collapse
Niels Bohr?
Proposed a new model of atom where electrons exist in shells or orbits of fixed energy. When electrons move between shells electromagnetic radiation with fixed energy or frequency is emitted or absorbed
What did the Bohr model do?
Fitted experimental observations of radiation emitted and absorbed by atoms
What did scientists later discover?
Not all electrons in a shell have the same energy meaning the Bohr model wasn’t quite right so they refined it to include sub-shells.
The refined Bohr effect?
Isn’t perfect
More accurate models exist today
Useful because it’s simple and explains many experimental observations like bonding and ionisation energy trends
Relative atomic mass Ar is?
Average mass of an atom of an element on the scale where an atom of carbon-12 is 12
Relative isotope mass?
Mass of an atom of an isotope of an element on a scale where an atom of carbon-12 is 12
Relative atomic mass describe?
Average not usually whole number
Relative isotope mass usually whole number
Relative molecular mass Mr is?
Average mass of a molecule on a scale where an atom of carbon-12 is 12
How to find relative molecular mass?
Just add up relative atomic mass values of all atoms in a molecule
Relative formula used instead of relative molecular mass when?
Ionic or giant covalent compounds
To five the relative formula mass?
Add up relative atomic masses of all atoms in formula unit
What can mass spectrometer?
Relative atomic mass, relative molecular mass, relative isotope abudance
Vaporisation and ionisation
Sample dissolved and pushed through small nozzle at high pressure. High voltage applied to it causing particles to lose an electron and turning sample to positive ions gas (electrospray ionisation)
Acceleration
Postive ions accelerated by electric field (positively charged particles needed) ions with lower mass/ charge ratio experience greater acceleration
Ion drift
When ions leave electric field they have constant speed and kinetic energy so enter region with no electric field so drift. Lower mass/charge ratio drift quicker.
Detection
Ions have lower mass/ charge ratio travel quicker in drift region they reach detector in less time than ions with high mass/ charge ratio. Detector detects charged particles and mass spectrum produced
Y axis of mass spectrum graph?
Abudance of ions often percentage for elements height of each peak gives relative isotope abundance
If sample is an element what will each line represent?
Different isotope of element
X units
Mass/charge
Can assume relative isotopic mass
How to calculate relative atomic mass?
Read % relative isotopic abundance from y acid snd relative isotopic mass multiply together to get total mass
Add totals
Divide by 100
If relative abundance given as non-percentage
Total abundance may not add up to 100 don’t panic divide by total relative abundance
How can mass spectrometry identify elements?
Different isotopes produce more than one line in mass spectrum because isotopes have different masses priding characteristic patterns like fingerprints to identify certain elements
How can mass spectrometry be used to identify molecules?
You can get a mass spectrum for a molecular sample
Molecular ion is formed in mass spectrometer when one electron removed from molecule
Can be used to help identify unknown compound
In currently accepted model of atom electrons have and do?
Have fixed energies
Move around the nucleus in certain regions called shells or energy levels
What is each shell given?
A number (principal quantum number)
What happens to principal quantum number and distance?
The further the shell is from the nucleus the higher its energy and the larger its principal quantum number
Experiment shows that not all electrons in a shell?
Have the same energy
How does the atomic model explain not all electrons in a shell having exactly the same energy?
Shells are divided into sub-shells that have slightly different energies. Sub-shells have different number of orbitals which can hold up to 2 electrons
Sub-shell s
Number of orbitals and maximum electrons?
1 orbital
2 electrons maximum
Sub-shell p
Number of orbitals and maximum electrons?
3 orbitals
6 electrons maximum
Sub-shell d
Number of orbitals and maximum electrons?
5 orbitals
10 maximum electrons
Sub-shell f
Number of orbitals and maximum electrons?
7 orbitals
14 electrons maximum
Shell 1 sub-shell and total number of electrons?
1s
2 electrons
Shell 2 sub-shell and total number of electrons?
2s 2p
8 electrons
Shell 3 sub-shell and total number of electrons?
3s 3p 3d
16 electrons
Shell 4 sub-shell and total number of electrons?
4s 4p 4d 4f
32 electrons
How do the two electrons in each orbitals spin?
In opposite directions
Three rules of electron configurations
1) Electrons fill up lower energy sub-shells first
2) electrons fill orbitals singly before they start sharing
3) for configuration of ions from s and p blocks of periodic table just add or remove electrons to it from highest energy occupied sub-shell
Exception to rule 1
4s sub-shell has lower energy level than 3d sub-shell even though principal quantum number is bigger. 4s sub-shell fills up first.
What do up and down arrows represent?
Electrons spinning in opposite directions
Sub-shell notation?
Main way of showing electron configuration
What else are sometimes used in electron configuration?
Noble gas symbols
Why are chromium and copper nightmares?
They donate one of their 4s electrons to the 3D sub-shell because they’re happier with more stable full or half-full d sub-shells
Chromium atom
1s2 2s2 2p6 3s2 3p6 3d5 4s1
Copper atom
1s2 2s2 2p6 3s2 3p6 3s2 3p6 3d10 4s1
Fe ion 26
1s2 2s2 2p6 3s2 3p6 3d6 4s2
Fe3+ 23
1s2 2s2 2p6 3s2 3p6 3d5
What determines chemical properties of an element?
The number of outer shell electrons
The s block elements have?
1 or 2 outer shell electrons that are easily lost to form positive ions with inert gas configuration
The elects in group 5, 6 and 7 in the p block can?
Gain 1,2 or 3 electrons to fork negative ions with an inert gas configuration
Group 4 and 7 can also share?
Electrons when form covalent bonds
Group 0 inert gases?
Completely filled s and p sub-shells and don’t need to bother gaining or losing or sharing electrons. Full sub-shells make them inert
What do d block metals (transition metals tend to do?
Lose S and d electrons to form positive ions
What has a atom or molecule being ionised?
When electrons have been removed
What’s the first ionisation energy?
The first ionisation energy is the energy needed to remove 1 electron from each atom in 1 mile of gaseous atoms to form 1 mole of gaseous 1+ ions
Ionisation energy equation example
O(g) -> O+(g) + e-
Ionisation energy= +1314
Important points about ionisation energy
Must use gas state symbol because ionisation energies are measured for gaseous atoms
Must refer to 1 mole of atoms as stated in definition rather than to single atom
Lower ionisation energy easier to form ion
Factors affecting ionisation energy?
Nuclear charge
Distance from nucleus
Shielding
Nuclear charge affects ionisation energy how?
More protons in nucleus the more positively charged the nucleus is and the stronger the attraction for electrons
Distance from nucleus affects ionisation energy how?
Attraction falls off very rapidly with distance. Electron close to nucleus will be much more strongly attracted than one further away
Shielding affects ionisation energy how?
As number of electrons between outer electrons and nucleus increases outer electrons feel less attraction towards nuclear charge. Lessening pull of nucleus by inner shells of electrons is called shielding
What does a high ionisation energy mean?
There’s a high attraction between the electron and the nucleus and so more energy is needed to remove the electron
How many electrons can you remove from an atom?
All of the electrons leaving only the nucleus
Define the second ionisation energy
The second ionisation energy is the energy needed to remove 1 electron from each ion in 1 mole of gaseous 1+ ions to form 1 mole of gaseous 2+ ions
Second ionisation for oxygen
O+(g)-> O2+(g)+ e-
What happens to ionisation energies in each shell?
They increase because electrons are removed from an increasingly positive ion-there’s less repulsion amongst the remaining electrons so held more strongly by the nucleus
When do big jumps in ionisation energy happen?
When a new shell is broken into an electron is being removed from a shell closer to the nucleus
What can successive ionisation energies graph tell you about an element?
Which group of the periodic table it belong to. Just count how many electrons are removed before the first big jump to find the group number
What can successive ionisation energies graph be used to predict?
The electron structure of elements working from right to left count how many points before each big jump to find out how many electrons are in each shell starting with the first
What happens to first ionisation energy going down a group of the periodic table?
Decrease
What will the first ionisation energy of elements across a period generally do?
Increase
What does the first ionisation energies of group 2 elements give evidence for?
That electrons shells do exist and that successive elements down the group have extra bigger shells
What happens if elements down group 2 have extra electron shells compared to the once above?
The extra inner shell will shield the outer electrons from attraction of the nucleus
Outer electrons are further away from the nucleus do nucleus attraction will be greatly reduced
What do these two factors mean for ionisation energy?
It will make it easier to remove outer shell electrons resulting in a lower ionisation energy
What happens as you move across a period?
The general trend is for ionisation energies to increase
Why does across a period make ionisation energies increase?
number of protons is increasing meaning strong nuclear attraction.
All electrons roughly equal energy level even if outer shell at different orbital types.
Therefore generally little shielding effect of extra distance to lessen attraction from nucleus
Where is aluminium’s outer electron?
In 3p orbital rather than 3s.
Two factors overriding effect of nuclear charge resulting in ionisation energy dropping slightly?
3p orbital slightly higher energy than 3s orbital do electron on average is further away from nucleus
3p orbital has additional shielding provided by 3s2 electrons
What does this pattern give evidence for?
The theory of electron sub-shells
What is the drop between group 5 and 6 due to?
Electron repulsion
What is identical in phosphorus and sulfur atoms?
Shielding of identical
Electron being removed from identical orbital
What makes first ionisation energy of sulfur lower than phosphorus?
In phosphus, electron being removed from singly-occupied orbitals.
Sulfur, electrons being removed from orbital containing two electrons. Repulsion between two electrons in orbitals means electrons are easier to remove from shared orbitals
What’s this evidence for?
Electronic structure model
