topic 1: atomic structures Flashcards
3 subatomic particles
protons, neutrons and electrons
nucleus of atom
-most of the mass of an atom is concentrated in the nucleus, which is very small
-consists of protons and neutrons
-they are held together by a strong nuclear force (much stronger than electrostatic force)
where are electrons found?
-electrons orbit the nucleus in shells, the orbitals take up most of the volume of the atom
relative charges of subatomic particles
-protons: +1
-neutrons: 0
-electrons: -1
relative mass of subatomic particles
-protons: 1
-neutrons: 1
-electrons: 0
all atoms are neutral so… (equation)
the number of protons= the number of electrons
mass number (A)
-total number of protons and neutrons in the nucleus
atomic (proton) number (z)
-the number of protons in the nucleus (identifies the elements)
isotope
Atoms of the same element with the same number of protons but a different number of neutrons
Why do all isotopes have the same chemical properties?
They all have the same ELECTRONIC CONFIGURATION
history and the developing ideas of the atom: scientists and dates (ordered)
- atoms were solid spheres and each element is made from different spheres
- discovered the electron, which led to the discovery of the plum pudding model
-showed that atoms wasn’t solid and invisible
- ernest rutheford
-1909
-conducted the alpha scattering gold foil experiment
-to develop the nuclear model (a small positively charged nucleus, surrounded by a ‘cloud’ of negative electrons
-the atom was mostly empty space
gold foil experiment
-fired positively charged alpha particles at a very thin sheet of gold
-plum pudding model suggested: most alpha particles would be slight deflected by the positive ‘pudding’ (that made up most of the atom)
-actually: most alpha particles passed straight through (most of the atom is empty space) the gold foil, some deflected backwards (since they hit the small positive nucleus)
most alpha particles pass through empty space…
since most of the atom is mainly empty space
small number of alpha particles being slightly deflected backwards…
due to very strong by the small positive nucleus
- Niels Bohr
-1913
-adapted to ruthefords nuclear model, the ‘cloud’ of electrons could spiral down into the positive nucleus and cause the atom to collapse
-Bohr proposed putting electrons in fixed energy shells/ orbitals
-therefore when electrons move to a new shell electromagnetic radiation (with fixed energy/frequency) is emitted (electrons move down to lower energy, close to the nucleus) or absorbed (electrons move up to higher energy shells/ away from the nucleus).
what did scientists discover about electrons?
-electrons dont have the same energy in shells, so refined the model to include subshells
-not a perfect model but it is accurate and useful as it is simple and explains many experimental observations e.g. bonding and ionisation energy
relative atomic mass definition
the average mass of an atom of an element relative to one twelfth of the mass of an atom of carbon-12
what is the time of flight mass spectrometry?
-time of flight mass spectometry is a powerful analytical technique which gives the accurate determination of the relative isotopic mass and relative abundance of isotopes
-it can be used to identify the relative atomic mass (Ar) to identify elements and relative molecular mass (Mr)
stages of TOF
- ionisation (electron impact ionisation or electrospray ionisation)
- acceleration
- ion drift (in the flight tube)
- detection
what is ionisation in TOF and the 2 types?
-ionisation is where an atom becomes an ion and can happen 2 ways, depending on its mass: electron impact ionisation or electrospray ionisation
electron impact ionisation
-electron impact ionisation is for elements and substances with a LOW relative molecular mass
-the sample is vapourised, then high energy electrons are fired at the sample using an electron gun, one electron is knocked off each particle forming a positive (1+) ion
equation of electron impact ionisation
X(g) —> X+(g) + e-
electrospray ionisation
-electrospray ionisation is for substances with a HIGH relative molecular mass
-the sample is dissolved in a volatile solvent (e.g. water or methanol) and is injected through a hypodermic needle, with a high voltage, positive power supply, this produces a fine mist Aerosol. the particles are ionised by gaining a proton and becomes a 1+ ion, the solvent evaporates leaving the 1+ ions, which are attracted towards a negative plate where they are accelerated
equation of electrospray ionisation
X(g) + H+ —> (XH)+ (g)
acceleration in TOF
-the positive ions are accelerated using an ELECTRIC FIELD, to have the same kinetic energy,(the positively charged ions are attracted towards a negatively charged ion so all the ions accelerate at the same kinetic energy) but their velocity of each ion particle will differ as it depends on its mass:
-lighter ions will have a higher velocity
-heaving ions will have a lower velocity
Ion drift (in the flight tube)
-the positive ions travel through a hole in the negatively charged plate into the flight tube where they enter a region with no electric field , so they just drift through it towards the detector.
ions with different masses have a different time of flight:
-lighter ions will drift through faster than heavier ions and reach the detector in less time
-heavier ions will drift through slower than lighter ions and take long to reach the detector
detection in TOF
-the positive ions will hit the detector which is a negatively charged plate and generates a current, and gain an electron, causing a current to flow
-the size of the current is proportional to the abundance of those ions hitting the plate and gaining an electron
- the detector plate is connected to a computer, which produces the mass spectrum
mass spectrum definition
the mass spectrum of an element shows the mass: charge ratio and abundance of each ion that reaches the detector, given that all ions produced from electron impact and electrospray have a 1+ charge, the m:c ratio is the mass of each ion
-this can be used to work out the relative atomic mass of the element
time of flight formulas
-kinetic energy
-time of flight
-mass
1) KE=1/2mv²
2) t=d√m/2KE
3) t=d/v
4) mass= relative atomic mass (Ar) / 1000 x avogrado constant (6.022 x 10 23)
1.label electron configuration of atom 1S
2. what happens to the lowest energy subshells?
3. list order of subshells + explain the 4s
- 1 - shell number
s - sub shell
² - number of electrons - lower energy subshells always fill first
- 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 4d
-the 4s subshell has a lower energy than the 3d subshell so it fills up first
-electrons fill orbitals singularly before they start sharing
electron configuration exceptions in CHROMIUM
-expect the ending of electron configuration of chromium to be 4s², 3d4 , however it donates one of it’s 4s electrons to the 3d subshell, so the 3d subshell is more stable as it is half full, so it’s configuration is actually 1s2, 2s2, 2p6, 3p2, 3p6, 4S1, 3D5, this makes it more energetically stable
electron configuration exceptions in COPPER
-expect the ending of electron configuration of copper to be 4s2, 3d9, however it donates one of its s electrons to the 3d subshell so that the 3d subshell is more stable as it is now full, it’s configuration is actually: 1s2, 2p2, 2p6, 3s2, 3p6, 4S1, 3D10, this makes it more energetically stable
- first ionisation energy
- units for first ionisation energy
- equation for the first ionisation energy
-the enthalpy change (Energy change) when one electron is removed from one mole og gaseous atoms to form one mole of gaseous ions with a single positive charge (1+)
KJ mol-1
X (g) —> X+ (g) + e-
second ionisation energy + equation of the second ionisation energy
-the enthalpy change (energy change) when one electron is removed from one mole of gaseous atoms (1+ ions) to form one mole of gaseous ions with a double positive charge (2+)
X+(g) —> X2+ (g) + e-
factors affecting ionisation energy
-nuclear charge
-atomic radius (Size of the atom)
-shielding
nuclear charge affecting ionisation energy
-the higher the nuclear charge, the higher the first ionisation energy. the more protons in the nucleus, the greater the nuclear charge, there is a smaller atomic radius so there is a greater attraction of the outer electrons to the nucleus
atomic radius affecting ionisation energy
the smaller the atomic radius, the higher the first ionisation energy because the outer electron is more strongly attracted to the nucleus
shielding affecting ionisation energy
the more shielding (Shells), the lower the first ionisation energy - weaker attraction of the outer shell to the nucleus. inner shells repel the outer electrons making them easier to lose
trends in ionisation energy
-ionisation energy increases across a period
-ionisation energy decreases down a group
ionisation energy increases across a period
-HIGHER NUCLEAR CHARGE (higher proton number), so smaller atomic radius
-outer elecrons are more attracted to the nucleus - more energy is require to remove the outer electrons because of greater attraction between protons and electrons
-CONSTANT/ SIMILAIR SHIELDING because electrons are added to the same shell
ionisation energy decreases down a group
-LARGER ATOMIC RADIUS (increasing number of occupied energy levels down a group)
-INCREASED SHIELDING as more energy levels
-outer electrons is LESS ATTRACTED to the nucleus and therefore is easier to lose as it requires less energy
exceptions in ionisation energy trends between group 2 and 3
-small decrease in first ionisation energy
-move to a new energy levels (s —> p subshell) with higher energy
-further away from the nucleus and more shielding
exceptions in ionisation energy trends between group 5 and 6
-small decrease in first ionisation energy
-in group 5, p subshell has one electron in each orbital, no repulsion
-in group 6, p subshell has one orbital with 2 electrons in - the electrons in the same orbital repel eachother, so less energy is needed to remove the outer electron
successive ionisation energy definition
when you remove an electron following one after another , each from an ion that becomes increasingly positive
trends in successive ionisation energy
-successive ionisation energies increase between shells
-successive ionisation energies increases within each shell
successive ionisation energies increase between shells + example
-each time a new shell is broken into, there is a sudden rise in ionisation energy
-example: sodium which has one outer electron, there is a big jump in ionisation from the first to second, this is because the second electron is being removed from a shell that is much closer to the nucleus, meaning there is stronger attraction from the nucleus
successive ionisation energies increase within each shell + example
-each time an electron is removed, even if you havent broken into a new inner shell, the ionisation energy increases because you are removing an electron from an increasingly positive ion
-example: magnesium which has two outer electrons, the second ionisation energy is greater than the first, because ot os harder to remove an electron from an Mg2+ ion than an Mg+ atom because there is a stronger attraction
evidence for shell structure
-every time there is a sudden jump in ionisation energy, shows another shell has been entered
-drop in first ionisation energy between group 2 and group 3 shows evidence for subshells
