topic 1: atomic structure and the periodic table Flashcards
structure of atom
- protons and neutrons in nucleus
- electrons in orbitals
rel charge proton
+1
rel mass proton
1
rel charge neutron
0
rel mass neutron
1
rel charge electron
-1
rel mass electron
1/1836
atomic number
- number of protons in nucleus of atom
- Z
mass number
total number of protons and neutrons in nucleus of atom (also known as nucleon number)
- symbol A
isotopes
same number of protons but different number of neutrons
properties of isotopes
- similar chemical properties but different physical properties
why do isotopes have similar chemical properties (2)
- same electron configuration
- same number of outer shell electrons so react similarly
relative isotopic mass
mass of one atom of an isotope relative to the mass of 1/12 of a carbon-12 atom
relative atomic mass
MEAN mass of an atom relative to the mass of 1/12 of a carbon-12 atom
chlorine ATOM mass spec
- 2 molecular ion peaks as exists as TWO ISOTOPES
-35 Cl and 37 Cl - peak heights ratio is 3:1 as abundance of 35Cl is 3* that of 37 Cl
diatomic chlorine molecule mass spec
-3 molecular ion peaks
- 35Cl+35Cl
-35Cl + 37Cl
-37Cl + 37Cl
RATIO of peaks: multiply probability of each; eg for 35, 35 3/4*3/4
one BROMINE atom mass spec
- 2 isootopes
- so 2 molecular ion peaks
-79Br and 81 Br - 1:1 abundance
diatomic bromine moleculemass spec
- 3 molecular ion peaks
- 79Br, 79Br
-79Br,81Br
-81Br,81Br
peak with highest m/z value…
molecular ion peak which gives info about MOLECULAR MASS
FIRST ionisation energy
amount of 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
first ionisation energy of calcium
Ca(g) -> Ca+(g) + e-
second ionisation energy
energy required to remove one mole of electrons from one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions
second IE calcium
Ca+(g) -> Ca2+(g) + e-
why do successive ionisation energies increase (generally)
- when an electron is removed, a positive ion is formed
- less electrons for same number of protons
- larger effective nuclear charge- STRONEGER ES ATTRACTION (decreasing p to e ratio)
- more energy required
shape of s orbital
spherical (draw a circle)
shape of p orbital
infinity sign (facing upwards)
what is an orbital
a region within an atom that can hold up to 2 electrons with opposite spins
IE across period
increases
IE down group
decreases
IE across period explanation
- increases
- nuclear charge increases
- atomic radius decreases as stronger attraction, so distance decreases
- CONSTANT shielding as electrons added to same shell
- more energy needed to remove an electron
beryllium to boron ionisation energy
DECREASE:
- boron electron in 2p
- - higher energy subshell
- more sheilding
- weaker attraction , smaller radius, less energy required
nitrogen to oxygen (same for phosphorus to sulphur)
DECREASE
- in oxygen , 2 electrons in 2p orbital
- in nitrogen , only 1 electron in 2p orbital
- repulsion in electrons means easier to remove
from one period to the next
LARGE DECREASE in IE
- increased distance between nucleus and outer shell e- as NEW SHELL
- more sheilding
- OUTWEIGHT increased nuclear charge
IE down group explanation
- DECREASES
- more protons, higher nuclear charge
- atomic radius INCREASES
- distance increases
- shielding increases
- factors outweighs increased nuclear charge
shell CLOSEST to nucleus
n=1 quantum shell
number of electrons that can be hold in each shell
2n^2
eg: in shell 4, 32 e-
no. of electrons per orbital
2
no. orbitals in s subshell
1 (2e-)
no. orbitals in p subshell
3 (6e-)
no. orbitals in d subshell
5 (10e-)
no. orbitals in f subshell
7 (14e-)
orbitals in same subshell are
equal in energy (degenerate)
how are subshells filled
in order of increasing energy
Chromium electron config
[Ar] 3d5 4s1
Copper electron config
[Ar] 3d10 4s1
s d p blocks
left, middle, right
random decrease in IE across period (eg Mg to Al, Be to B)
electron removed from HIGHER energy level subshell, so less IE
periodicity defintion
trends that repeatedly occur across a period
state how to find relative abundance of isotopes
measure number of particles for each isotope detected in a mass spectrometer
chlorine mass spec ratios
for 35,35: 0.752
for 35,37: 0.750.35 2
for 37,37: 0.250.25
9:6:1 ratio
mass spec deflection
- by electromagnets
- ions with higher mass are deflected LESS
- ions with smaller mass (or higher charge) deflected more
why does mass spec happen in a vacuum
to prevent collisions with air particles
meaning of the arrows in boxes
- 2 electrons with opposite spins in the same orbital
y might 2 elements react similarly (2)
- same number of outer shell electrons
- governs their chemical reactions
deductions from ionisation energy graphs
- big jumps between x and x
- therefore ELECTRON CONFIGURATION ….
why is there a bigger increase in 2nd and 3rd IE compared to 1st and 2nd? (group 2)
- 1 and 2 from same subshell
- similar shielding
- 3 from subshell CLOSER TO NUCLEUS
- less shielding
- weaker attraction so less energy required
why use logs for IE
- range too big
- numbers too large so y axis too large
why might x have a lower IE
- electron removed from higher energy subshell
- more shielded from nucleus
in mass spec, which is the molecular ion peak
the one with the highest m/z
why is ionisation energy always positive
- endothermic
- energy taken in by the reaction
orbitals can hold
up to 2 electrons with OPPOSITE SPINS
ion making 4s
empty 4s BEFORE 3d
big jump in successive ionisation energy indicates…
what group is in
- eg big jump between 2 and 3 means group 2. more nergy required to remove 3 as was in an electron shell closer to nucleus so less shielding so stronger attraction
what element has the largest first ionisation energy
helium
- first shell so no shielding
- more than hydrogen as has one more proton
why big decrease in ionisation energy from Ne to Na
- different periods
-Na electron in a 3s shell further from nucleus,
-more shielding
-weaker attraction so more energy required
decrease in IE from P to S
- S has 4 electrons in 3p and, with the 4th starting to doubly fill the first 3p orbital
- slight repulstion between the 2 negatively charged electrons so second electron is easier to remove
melting and boilung point across period3
Na- Al : metallic bonding. Increase as smaller ion with a higher charge on ion, stronger attraction to outer shell e-, more energy required
Si: peaks here. giant covalent, lots of energy required to break many strong covalent bonds
P4, (slight increase to S8) ,Cl2 (simple molecular): london forces increase with more e-
Ar: LOWEST, monatomic, very weak london forces
melting and boiling point of B and C
- similar to S8
- very high mp
-C IS HHIGHEST
HOW to find relative abundance of 2 isotopes (2)
- measure intensity of each isotope
- in a mass spectromoter
why mass spec under vaccum
prevents collisions with air molecules that could deflect the ions
atomic emmission spectra provide evidence for …
existence of quantum shells
SUCCESSIVE ionisation energies provide evidence for …
the existence of quantum shells AND THE GROUP OF THE ELEMENT
first ionisation energy for elements proves evidence for…
electron subshells
why is there not a big difference between ist IE of those next to each other
- electorns moved from SAME subshell
- same distance from nucleus etc
