atomic structure Flashcards
group number
number of electrons in outer shell
isotopes
atoms same number of protons but different number of neutrons
why do isotopes have same chemical properties
same number of electrons
what do periods tell us
number of highest energy electron shell
how many electrons does S orbital hold
2 electrons
how many electrons does P orbital hold
6 electrons
how many electrons does the D orbital hold
10 electrons
where do electrons enter first
lowest energy orbital
what happens to atomic radius moving across a period (left to right)
decreases
due to increased attraction between nucleus and electrons
outer shell electrons are… and why
partially shielded from attraction of nucleus by electrons in inner shells
what happens to atomic radius moving down a group
increases
why does the atomic radius increase going down a group
less attraction between outer electrons and nucleus
(more shells = further away)
first ionisation energy
minimum energy required to remove one mole of electrons from one mole of gaseous atoms
first ionisation energy (definition 2)
the enthalpy change when one mole of gaseous atoms forms one mole of gaseous ions with a single positive charge
OR
the enthalpy change of X ➡️ X+➕ e-
why does the atomic radius DECREASE across a PERIOD
positive charge in nucleus increases
as number of protons increases
increases attraction between nucleus and electrons
what causes first ionisation energy to increase across a period
increased nuclear charge and decrease atomic radius
means outer electrons more attracted to nucleus
why does boron have a lower first ionisation energy than beryllium
2p orbital (boron outer subshell) has higher energy than 2s orbital
takes less energy to remove outer electron
why does ionisation energy increase from carbon to nitrogen but decrease at oxygen
each of nitrogen’s electrons are in separate 2p orbitals
oxygen has a pair of electrons in 2p orbital - electrons repel each other = required less energy to remove one of those electrons
first ionisation in period 3
general increase in first ionisation energy moving across a period (uduuduu)
each of nitrogen’s electrons are in separate orbitals
oxygen has a pair of (2) electrons in orbital - electrons repel each other = required less energy to remove one of those electrons
(looking at third electron shell as its period 3)
why does the first ionisation energy decrease going DOWN a GROUP (as well as nuclear charge increasing)
- atomic radius increases going down group = outer electrons more attracted further from nucleus
- number of electron shells increases going down group = more shielding between nucleus and outer electrons
↪️ means attraction between nucleus and outer electron decrease going down group
whats a successive ionisation energy
occurs when further electrons are removed
sequence of ionisation energies
more electrons are removed, each from an ion that is becoming increasingly positive
what does a sudden large increase in a graph indicate
a change in energy level
successive ionisation of oxygen trend
- increase in IE as we remove first six electrons
each time outer electron removed
remaining electrons pulled closer to nucleus
= greater attraction between electrons and nucleus
ionisation energy increases - big increase in I.E removing 7th electron
first 6 e- found in 2nd electron shell,
7th electron removed from FIRST electron shell
first electron shell = closer to nucleus (greater attraction)
electrons in first shell experience less shielding
identifying element using ionisation energy (for element in period 3)
(work out no. of electrons in outer shell)
1. see gradual increase in ionisation energy (e.g increase from 1st IE to 4th IE = 4 electrons in outer shell = group 4)
2. MASSIVE JUMP = this electron must have been removed from internal shell
group 4 period 3 = Silicon
why do atoms react
to achieve the electronic configuration of a noble gas
formula to find electrons in a shell
2n²
where n is the number of the shell
e.g shell 2 = 2(2²)
relative charge of proton
+1
relative charge of neutron
0
relative charge of electron
-1
relative mass of proton
1
relative mass of neutron
1
relative mass of electron
1/1840
define relative atomic mass (Ar)
the average mass of an atom of an element compared to one twelfth of an atom of carbon-12.
relative atomic mass formula
average mass of one atom of X ÷ 1/12 x the mass of one carbon-12 atom
how are ions formed
when an atom loses or gains electrons
no longer neutral and will have an overall charge
what is mass spectrometry used for
analytical technique used to identify different isotopes and find the overall relative atomic mass of an element
steps of mass spectrometry
- ionisation - electron gun fires high energy electrons at the sample, knocks an electron off (forming a +ve ion)
- acceleration - +ve charged ions accelerated towards a -ve charge detection plate
- separation - move along a drift chamber, all ions have same K.E so different masses have different velocities
- detection - +ve ions hit negative charge detection plate & gain an electron
size of current ∝ abundance
( greater current + greater abundance)
what does a plum pudding model show
sphere of positive charge with small negative charges distributed evenly
what does Rutherfords electron shell model show
atom consists of small dense central nucleus surrounded by orbiting electrons in electron shells
what is the max amount of electrons that orbitals can hold
2 electrons
what does the mass number tell us
protons and neutrons
what does the atomic number tell us
protons
successive ionisation energy across period 3
IE increases across a period
increased nuclear charge
decrease in atomic radius
electron in same energy level
(stronger attraction between nucleus and outer electrons)
Deviation 1 aluminium
first electron in p-orbital
further from nucleus
higher energy
deviation 1 sulfur
3ps
Pair of electrons
in the P orbital
rePel each other
general trend of period 3
number of protons increases
shielding stays the same
increased attraction between nucleus and outer electrons
overall trend = increases
