Unit 1-2 Flashcards
What is an orbital?
Region of space where there is a 95% chance of finding an electron
S,P,D and F
What is an orbit/shell/energy level?
The path of an electron around the nucleus
What shape are s and d orbitals respectively?
Spherical and dumbbell shaped
What is a charge cloud?
The orbital can be regarded as a spread of charge since the electron is likely to be anywhere in the orbital
Note: Greatest electron density is at the center
Orbitals can hold 2 electrons each. How many orbitals do each sub-shell have?
s sub-shell has 1 s-orbital
p sub-shell has 3 p-orbitals
d sub-shell has 5 d-orbitals
f sub-shell has 7 f-orbitals
What is exceptional about the 4s sub-shell?
It has a lower energy level than the 3d sub-shell and is filled first
What is an excited state?
Atoms with one or more excited electrons are in this state
What is the Aufbau principle?
Electrons in ground state occupy orbitals in order of orbital levels with the lowest being filled first
Note: 4s has a lower energy level than 3d and is filled first
What is the The Pauli exclusion principle?
Each orbital can hold 2 electrons which must have opposite spins
2 parallel spins is not allowed
What is Hund’s rule?
Each orbital of the same energy level must be occupied singly with parallel spin before pairing can take place
Why are chromium and copper exceptional in terms of electronic configuration
Its more stable to have a ½ full or full 3d sub-shell than to have a full 4s sub-shell and a 3d sub-shell with an empty orbital
As a result only 1 electron is given to the 4s sub-shell
Cr (Z = 24): [Ar]18 4s^1 3d^5
Cu (Z = 29) [Ar]18 4s^1 3d^10
Why are noble gases used for noble gas cores?
Only works using noble gases due to their full outer shells
What is the molar first ionisation energy (1st I.E)?
Energy required to remove one mole of electrons from 1 mole of gaseous atoms to form one mole of gaseous positively charged ions
What factors effect the ionisation energy of an atom?
How close the electron is to the nucleus
Weaker attraction force therefore less effective nuclear charge
Shielding
Filled inner shells weaken the attraction force, more shielding results in less effective nuclear charge
Spin pair repulsion
Paired e- are slightly easier to remove because they are repelled by their pair
What is nuclear charge?
Total positive charge of all the protons in a nucleus of an atom
What is effective nuclear charge?
The nuclear charge an outer shell electron experiences
What happens to the 1st I.E across the periodic table?
Generally increases across a row due to more protons for the same shielding, therefore increase in nuclear charge
Slight decreases occur to due shielding and spin pair repulsion
Note: Noble gases have the highest 1st I.E for their period
What happens to the 1st I.E down the periodic table?
Generally decreases down a group due to less effective nuclear charge from an increase in shielding
Note: Alkali metals have the lowest 1st I.E for their period
What is the trend for successive ionisation energies?
Increases by the 1st I.E for every successive ionisation until a new sub-shell or shell is reached, where I.E will increase slightly or significantly respectively
Note: Large increases in I.E are used to find the group of an unknown element; silicon’s 5th I.E requires far more energy than the first 4 as there’s less shielding in a new shell. Silicon is therefore in group 4
What is radioactive decay?
Protons, neutrons and electrons flying out when the original unstable nucleus divides
What happens to DNA if it is ionised by radioactive decay?
the instructions on how to live become confused, cells may turn cancerous and multiply uncontrollably
What are the qualities of alpha (α) radiation? (7)
- Slow
- Positively charged particles (2+)
- Mass of 4 and 2 units of positive charge (Helium nucleus)
- Powerful ionising effect
- Absorbed by thin paper
- Can’t enter or escape the body
- Slightly attracted towards the negative side of an electrical field
What are the qualities of beta (β) radiation? (8)
- Fast (velocities near the speed of light)
- Negatively charged electron
- Negligible mass
- Stopped by aluminium
- Can enter to skin to ionise cells
- 1/20 as ionising as alpha because of small mass and great kinetic energy
- Formed when a neutron changes to be a proton
- Highly attracted towards the positive side of an electrical field
What are the qualities of gamma (γ) radiation? (10)
- Speed of light
- Electromagnetic radiations
- Negligible mass
- Very penetrating
- Only stopped by thick lead
- Not very ionising
- Atoms gain a lot of energy upon absorbing, causing emission of other particles, which can be dangerous if it happens in a bodily cell
- Emitted in conjunction with alpha or beta
- Used as a means of removing excess energy from an excited nucleus
- Unaffected by electrical field
What is the consequence of radioactive decay?
Atomic number number can change to form now elements (alpha and beta)
Mass number can change to form isotopes (alpha)
What is half life?
Time taken for a radioactive sample to half in mass or radioactivity
Notes: Inversely proportional to rate of decay
Cannot be sped up or slowed down
What is positron emission?
Positron decay is opposite to beta decay (a positron is emitted)
1. Proton becomes a neutron due to something breaking down in the nucleus
2. Emits a positron and an electron neutrino which zoom off into space
3. Atomic number decreases by one
What is electron capture?
Unlike all other decays as an electron enters the nucleus
1. An electron from the closest energy level falls into the nucleus
Causes a proton to become a neutron
2. A neutrino is emitted
3. An electron falls to the empty energy level and so on
Causes a cascade of falling electrons
4. Atomic number decreases by one
What is radio-dating?
All living organisms absorb carbon. Carbon-14 starts to decay with a half life of 5570 years, however much is left can be used to calculate the age of the organism
How can radioactivity be used to monitor the content of tins/determine thickness of sheets?
The radioactive source and a radioactive detector are placed on either side of the body, radiation detected is inversely proportional to thickness/content
Alpha and beta are used respectively
How can radioactivity be used for the detection of leaks?
Sodium-24 is placed in the water, if the radiation detected increases in a specific area there is a leak
What is radiotherapy?
High energy gamma rays kill cancer cells
Cobalt-60 is used
What are medical tracers?
Labels a molecule (preferably taken by the tissue) to be studied
Technetium -99m is used
What is meant by “quanta”?
Each quantum has a certain inconsistent energy depending on frequency and is given by Planck’s equation, where h is equal to Planck’s constant
E=hf
Note: Energy and frequency are proportional
What is promotion?
Electrons gain one quantum of energy and jump to a higher energy level specific to the energy gained before falling back down instantaneously.
What is demotion?
Electrons fall from a high energy level to a lower energy level or the ground-state. One quantum of energy specific to the distance between energy levels is emitted.
Note: The energy emitted is in the form of light
What is the Lyman series?
Represents any electron falling into the first energy level (n=1)
What is the Balmer series?
Represents any electron falling to n=2
Note: Contains the wavelengths of visible light
What is the Paschen series?
Represents any electron falling to n=3
In the Balmer series, what colour does each energy level falling to n=2 represent?
n=2→n=3: Red
n=2→n=4: Blue
n=2→n=5: Indigo
n=2→n=6: Violet
What energy level sign represents ionization?
n=1→n=∞
What is the convergence limit?
Where the lines blur together in each series because energy levels grow closer as they increase
What does the frequency of convergence limit correspond to?
Ionization energy
E=hf
What is absorption?
Photons of certain energy may be absorbed when white light shines through gaseous atoms
Note: This causes promotion
What is an absorption spectrum?
A spectrometer produces dark lines against a bright background.
The dark lines correspond to absorbed photons of light.
What is an emission spectrum?
A spectrometer produces bright lines against a dark background.
The bright lines correspond to emitted photons of light.
What is the relation between frequency and wavelength?
c=fλ
Inversely proportional
What is the relation between frequency and energy?
E=hf
Proportional
