CH1: Atomic structure Flashcards
Relative mass and charge of subatomic particles?
PROTON : +1 1
NEUTRON : 0. 1
ELECTRON : -1. 1/1836
What is an ions?
- when atoms either gain/lose electrons causing them to be charged
What are isotopes?
Atoms of the same element with the same atomic number, but different number of neutrons (so different MASS number)
How are chemical properties of isotopes effected?
- not effected
Isotopes of same element show same chemical characteristics - because same electrons configuration on outer shells - determining chemistry of atom
How and why are physical properties different for isotopes ?
- isotopes have different number of neutrons
- leads to differences in mass, density, mp and BP
What is relative isotopic mass?
Mass of an atom of that isotope relative to 1/12 of a carbon-12 atom
E.g relative isotopic mass of oxygen is 15.99… but rounded to 16
What is mass spectrometry?
Used to identify different isotopes/find overall relative atomic mass of an element (Ar)
Relative atomic mass?
Mean mass of an atom relative to 1/12th of carbon 12 atom.
Relative molecular mass?
Mean mass of a molecule of a compound, relative to 1/12th of a carbon12 atom
Difference between relative molecular mass and Relative formula mass?
Relative formula mass is similar to Mr but used for compounds with GIANT STRUCTURES
How to calculate relative atomic mass?
Ar = (abundance x mass) + (abundance2 x mass2 ) / total abundance
How does Time Of Flight (TOF) Mass Spectrometry work?
- records time taken for ions of each isotope to reach detector
1) IONISATION : electrons are removed from atoms, leaving them with +1 charge
2) ACCELERATION- positive ions are accelerated towards negatively charged detection plate
3) DEFLECTION - ions are deflected by a magnetic field into a curved path - the radius of their path depends on CHARGE and MASS of ion - smaller mass/higher + charge = deflected most
Larger mass = deflected least
4) DETECTION- when + ions hit negative detection plate, they GAIN an electron , producing current/signal - GREATER the abundance , GREATER the current/intensity of signal
How is Ar calculated from mass spectrometer ?
(M/z (isotopic mass) x % abundance ) / total abundance
What is ionisation energy?
Amount of energy needed to remove one mole of electrons from one mole of GASEOUS atoms of an element to form one mole of gaseous ions
What is the first ionisation energy?
Energy required to remove one mole of electrons from one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions
Ca (g) → Ca+ (g) + e-
Trend in ionisation energy across a period?
INCREASES
- nuclear charge increases (increasing at action of valence electrons to nucleus)
—> DECREASES ATOMIC RADIUS
Outer electrons are more ATTRACTED to nucleus
(MORE ENERGY NEEDED ) - shielding is constant
Trend in ionisation energy down a group?
DECREASES
- shielding increases - decreased attraction between outer electrons and nucleus
- atomic radius increases - decreased attraction
(Overall VALENCE ELECTRONS ARE LESS ATTRACTED TO NUCLEUS , SO LESS ENERGY NEEDED)
Nuclear charge increases, but other 2 factors outweigh effects of nuclear charge
Why do successive ionisation energies increase?
- Removing an electron from an increasingly positive ion is more difficult than from a neutral atom
Ionisation energies increase as you remove an electron, because of :
- increased nuclear charge
- decreased shielding
When big jumps in ionisation energy —> means it is moving shell
What are the dips in the ionisation energy trend across PERIOD 2/3 between group 2 and 3?
DECREASE between BERYLLIUM AND BORON (group 2/3)
- as the outer electrons in boron is in 2p shell, which further from nucleus than 2s shell of beryllium
- 2p shell is higher in energy and s shell shields p shell - needs less energy to lose electron
DECREASE between MAGNESIUM and ALUMINIUM
- outer electron on aluminium is on 3p shell, which is further from nucleus than the 3s shell of magnesium
Why are there dips in the ionisation energy trend ACROSS A PERIOD 2/3 between group 5 and 6?
Decrease between NITROGEN AND OXYGEN (group 5 and 6)
- in oxygen , there are 2 electrons in the 2p orbital , so the repulsion between those electrons makes it easier to remove an electron
Decrease between PHOSPHOROUS AND SULFUR (group 5/6) P3
- spin pair repulsion in the 3p orbital of sulfur
How do electrons move from shell to shell?
ABSORB ENERGY - move up
EMIT ENERGY - move down
What is convergence?
When set of lines get closer tgt towards one end of line emission spectrum
Aufbau principle?
Electrons go into the orbital with lowest available energy level first
Hund’s rule?
Electrons only occupy orbitals on their own/ only pair up when no empty orbitals of same energy available
How does the electronic configuration of Cr and Cu differ from others?
Instead of having a pair of electrons in 4s shell - there is only 1
- the remaining electron is donated to 3d shell
Why does mass spectrometer need to be operated under a vacuum?
Prevent collisions with gas molecules that would deflect the ions
Periodicity meaning ? Trend in atomic radius across Period 2/3?
Trend of repeating properties
Atomic radius DECREASE from left to right in P2/3
- increase in positive charge - electrons pulled closer to nucleus : reducing ATOMIC RADIUS
Second ionisation energy?
Energy required to remove one mole of electrons from one mole of gaseous +1 ions to form one mole of +2 gaseous ions
