3.1.1 Atomic structure Flashcards
What is the relative mass, relative charge and location in the atom of a proton?
- 1.
- 1+.
- Nucleus.
What is the relative mass, relative charge and location in the atom of a neutron?
- 1.
- 0.
- Nucleus.
What is the relative mass, relative charge and location in the atom of an electron?
- 1/1840.
- -1.
- Energy levels.
What happens due to the extremely high density in the nucleus?
- Particles within are drawn together by extremely powerful forces.
- Overcome the repulsion protons have for each other.
What is the atomic number (Z)?
- No. protons in nucleus.
What is the mass number (A)?
- No. protons + neutrons in nucleus.
What are isotopes?
- Same element but have different mass number but same atomic number.
What are the three isotopes of hydrogen?
- Protium.
- Deuterium.
- Tritium.
Do isotopes have the same chemical and physical properties?
- Same chemical bc same electron arrangement.
- Diff physical bc diff masses.
What are the two isotopes of chlorine?
- Chlorine-35.
- Chlorine-37.
What are the two important isotopes of carbon?
- Carbon-12.
- Carbon-13.
What is the carbon-12 standard?
- Relative mass is measured against 1/12 of a carbon-12 atom.
What is the relative isotopic mass?
- Mass of single isotope of element relative to 1/12 mass of carbon-12
- Same as mass number for particular isotope of an element.
Where is the relative isotopic mass derived from?
- Mass spectroscopy where mass of individual isotopes can be determined.
What is the relative atom mass (Ar)?
- Average mass of an atom of an element relative to 1/12 of mass of carbon-12.
What are the 5 steps of mass spectroscopy?
- Ionisation.
- Acceleration.
- Ion drift.
- Ion detection.
- Data analysis.
What is mass spectroscopy used for (elements)?
- Determine information about elements and compounds.
- Determines relative isotopic masses and abundances.
- This is used to calculate Ar.
How does mass spectroscopy help to identify compounds?
- Identify unknown purified compounds by comparing mass spectrum to those in database.
- Gives relative molecular mass (Mr).
What are the two methods of ionisation for mass spectroscopy?
- Electron spray ionisation.
- Electron impact ionisation.
How is the process of electron impact ionisation carried out?
- Sample vapourised then bombarded w e-.
- E- gun –> hot wire that emits e-.
- E- knocks e- off particle leaving molecular ion/ M+ ion.
What is the equation for electron impact ionisation?
- X(g) –> X+(g) + e-.
What type of substances is electron impact ionisation used for?
- Elements + substances w lower molecular mass.
What type of substance is electrospray ionisation used for?
- Substances w higher molecular mass.
What type of technique is electrospray ionisation?
- Soft ionisation technique.
- Fragmentation is unlikely.
How is the process of electrospray ionisation carried out?
- Sample dissolved in polar, volatile solvent.
- Pumped through hypodermic needle to create charged droplets.
- Mononuclear ions (single +ive charge).
- Ionised by gaining proton.
What is the equation for electrospray ionisation?
- X(g) + H+ –> XH+(g).
What happens during acceleration during mass spectroscopy?
- Negative electrical field attracts ions + give constant KE.
- KE=1/2mv^2.
- All same KE so heavier particles travel slower than lighter particles.
What happens during ion drift during mass spectroscopy?
- Region where no electrical field –> flight tube.
- Ions separated based on diff velocities.
- Small travel fast through flight tube + arrive at detector first.
What happens during data analysis during mass spectroscopy?
- Flight times analysed + recorded by data analyser.
- Mass spectrum obtained as plot of relative abundance against mass to charge ratio (m/z).
What does a trace from a mass spectrum show (axis)?
- Series of peaks vertically which show relative abundance.
- Horizontal axis - mass to charge ratio.
- relative abundance - how many of each ion is present.
What can sometimes be seen on a trace from mass spectroscopy when electron impact ionisation has been used?
- Cause diff peaks due to fragmentation caused by impact.
What is really important to remember when calculating an Ar from a mass spectrum (esp electro spray ionisation)?
- Take an average from the abundance.
- Also element - take off a proton that was added during mass spec!!!
How to read a trace from mass spec of a molecular elememt?
- Some exist as diatomic molecules so divide by 2.
How to read a trace from mass spec of a compound?
- Last major peak is molecular ion.
- M/z value for this peak is Mr of the compound.
What is the largest peak on a mass spec trace called?
- Base peak.
- Most stable ion produced as molecules is broken up.
How are elements (and compounds) detected from mass spectra?
- m/z values entered into computer.
- Compared to database.
- This requires pure sample.
What is an energy level and what is it split into?
- E- shells.
- Split into sub-shells.
What happens to the distance between energy levels as you move away from the nucleus?
- Energy levels get closer together.
What is an energy level split into?
- Sub-shells.
What is a sub-shell made up of?
- Orbitals or a combination of orbitals.
What is an orbital?
- 3D space that can hold up to 2 e-.
What happens in an orbital to minimise repulsion?
- e- in same orbital spin in different directions.
What are the 4 types of orbitals?
- s, p, d and f.
How many s, p and d orbitals are there at each energy level?
- s –> 1.
- p –> 3.
- d –> 5.
What are important features of filling sub-shells?
- Distance between sub-shells decreases further away from nucleus –> causes overlap.
- e- fill sub-shells closer to the nucleus first.
What do the up and down arrows in e- configuration represent?
- Direction of spin of e- in orbitals.
What is the ground state?
- When e- are in their lowest possible energy levels.
Why do e- prefer not to be in orbitals together?
- Because this causes a repulsion between the e-.
What are the two elements which are exceptions to e- configuration?
- Copper + Chromium.
What happens when metals form ions?
- When the loose e- loose from outermost level except d-block elements.
How do you name a non-metal ion?
- Use atom as stem and ‘-ide’ on end.
What are the two ions that can be formed from hydrogen?
- H+ –> hydrogen ion.
- H- –> hydride ion.
What does isoelectronic mean?
- Particles which have the same e- configuration.
What will elements in the main groups usually form ions of?
- The nearest noble gas.
What is the process of ionisation?
- Process of removing e- from atoms and ions.
What is the definition of the first ionisation energy?
- Energy required to remove 1 mole of e- from 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions.
How is the first ionisation of sodium represented?
- Na(g) –> Na+(g) + e-.
How is the second ionisation of sodium represented?
- Na+(g) –> Na2+(g) + e-.
How is the third ionisation of sodium represented?
- Na2+(g) –> Na3+(g) + e-.
How does ionisation in plasma televisions happen?
- Electrical current runs through.
- +ively charged ions collide w e- causing them to release ultraviolet photons that react to release visible light.
What are the units for ionisation energy?
- Kj mol-1.
Is ionisation an endothermic or exothermic reaction?
- Endothermic as energy is required to remove an electron from attractive power of nucleus.
How are the existence of energy levels proven?
- Large gaps between successive ionisation energies.
- Correspond to removal of e- from energy levels closer to nucleus so more energy required to remove.
What is effective nuclear charge?
- General increase in successive ionisation energies caused by increase in ratio of protons to e- as e- are removed.
What can successive ionisation energies be used for?
- Can be used as indicator of the group the element belongs to.
What are the 3 trends in ionisation energies?
- Ionisation energy decreases down the group.
- Ionisation energy generally increases across the period.
- Within short periods (2+3) there is a zig-zag pattern.
Which elements cause a zig-zag in the ionisation energies?
- Group 3 –> boron + aluminium.
- Group 6 –> oxygen + sulphur.
What are the three factors that can be used to explain trends in ionisation energies?
- Atomic radius.
- Nuclear charge.
- Shielding by inner e-.
What is atomic radius and how does this vary down a group and across a period?
- How far the outer e- are from the attractive power of the nucleus.
- Increase down group.
- Decrease across period.
How does atomic radius affect ionisation energy?
- The further the outermost e- is from attractive power of nucleus, the less energy is required to ionise it.
What is nuclear charge and how does this affect ionisation energy?
- How many protons are attracting the outer e-.
- Greater nuclear charge leads to a stronger attraction to the outer e- so more energy is required to ionise it.
What is shielding and how does this affect ionisation energy?
- How many e- are between outer e- and attractive power of nucleus.
- More inner e- means more shielding + less energy is required to ionise outer e-.
What happens to ionisation energy down the group?
- Decreases.
- Atomic radius - increases so easier to loose outer e-.
- Shielding by inner e- - more shells so more shielding so easier to loose outer e-.
- Nuclear charge - increases so works against other 2 factors.
What happens to ionisation energy across the period?
- Increases.
- Atomic radius - decreases outer e- has more protons to attract.
- Shielding - constant due to same energy level.
- Nuclear charge - increases due to more protons.
Why is there a dip in ionisation energy at aluminium?
- 3p1 e- is further from the nucleus + has additional shielding from 3s2 so requires less energy for ionisation.
Why is there a dip in ionisation energy at sulphur?
- Due to paring of e- in p sub-shell.
- 3p4 means that 2 e- are paired in 1st p orbital.
- Repulsion between e- lowers ionisation energy required to move an e-.
What provides evidence that 2nd + 3rd energy levels are divided into 2 sub-shells?
- Atoms in group 3 + 6 w lower ionisation energies show that 1st sub-shell has 1 orbital and 2nd has 3 orbitals.
Why do group 1 elements have the lowest first ionisation energy in each period?
- Greatest atomic radius + lowest nuclear charge in each period.
Why do group 0 elements have the highest first ionisation energy in each period?
- Smallest atomic radius.
- highest nuclear charge in period.
What is the general pattern for ionisation energy down the group?
- Decreases.
- Atomic radius increases.
- Shielding by inner e- increases.
- Less energy required to remove e-.
What is the general pattern for ionisation energy across the period?
- Increases.
- Atomic radius decreases.
- Nuclear charge increases.
- Shielding by inner e- stays the same.
- More energy required to remove e-.
Why are there lower 1st ionisation energies than expected in group 3?
- Group 3 have s2p1 arrangement.
- Outer p1 further from nucleus.
- Inner s2 e- increase shielding so less energy required to ionise outer p1 e-.
Why are there lower 1st ionisation energies than expected in group 6?
- Group 6 have p4 arrangement.
- Repulsion between 2 e- in p orbitals leads to less energy being required to ionise the outer e-.
What are the patterns in 2nd ionisation energies?
- Shifted one to the left.
- Group 1 element would have lowest 1st ionisation but would have highest 2nd ionisation energy.
Why do group 1 elements have the highest 2nd ionisation energies?
- 2nd e- is being removed from an energy level closer to the nucleus.
