Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

Where do elements come from?
The life cycle of stars:
Hydrogen is the most common element in the universe, stars produce He from H in nuclear fusion, this helps to
explain how heavy elements are formed from lighter ones
...

To fuse together they must come very close together- need very high temperatures and pressure to overcome the
EM repulsion
...

Lightweight stars:
They keep burning all the H till it runs out, then expands as a red giant- unstable- then outer gases drift into space
leaving a small core- white dwarf (100th the size of the original star)
Heavyweight stars:
Extremely high temp + pressure at the centre of heavyweight stars mean fusion reaction form elements heavier
than He up to Fe
...

Core centre is iron, which when fuses together does not release energy, absorbs
...


become very

Isotopes:
Atoms of the same element with different numbers of neutrons, causing the mass number to be different
...

Most elements exist naturally as a mixture of the elements’ isotopes
...

Mass spectrometry
Used to find the atomic mass of elements and compounds, and
their abundancies
...

Sample atoms/molecules given positively charged cations- ionised
(by firing electrons at the vaporised sample, knocks off an electron
giving a charge of +1)
1) Vaporisation- sample turned into a gas, electric heater
2) Ionisation- gas particles bombarded with high energy e- to
ionise them, e- knocked off, +ve ion
3) Acceleration- +ve ions accelerated by an electric field to same EK
4) Detection- time taken for +ve ion to reach detector, retention time, depends on mass and charge
Bombarding with electrons can make some molecules break up, which show up on the mass spectrum as a
fragmentation pattern
...
Speed is the same for all, 3 x 108 m/s
...
Atom’s e-s take in energy from EMR,
can move to higher energy levels, away from the nucleus, at higher energy levels, e-s = excited
...

ΔE = h * v
Electrons in the outer parts of atoms that interact in chemical reactions
...

Transition between energy levels produces line spectra:
Absorption spectra – dark lines
Energy related to V, so when EMR passed through gaseous element, e- absorb certain frequencies that correspond
to differences in energy levels
...

Emission spectra – bright lines
When the e- drop back down to lower energy levels, they give out certain frequencies of EMR
...

Each electron has a different arrangement of e-, so frequencies of radiation absorbed and emitted are different,
unique spectrums
...
e- and reactivity due to the stability of
the outer e-‘s
...
e-‘s move around the nucleus in shells, which are given
principle quantum numbers
...

Type of orbital
S
P
D
F

Number of orbitals
1
3
5
7

Max
...
e- in each orbital
have to ‘spin; in opp
...

Chromium:
To achieve a more stable arrangement of lower
energy, one of the 4s e- promoted into 3d e- to give
6 unpaired e- with lower repulsion (would be 4 else)
Copper:
One of the 4s e- promoted into the 3d orbital
In an ion:
4s e- are ionised before 3d as they are in a lower energy state when the 3d orbital has e- in it
...

The 3d orbitals have the lowest energy, but as we add electrons, repulsion within the orbital can push some of
them out into the higher energy 4s level
...
chemguide
...
uk/atoms/properties/3d4sproblem
...

Melting points and boiling points:
When an element is melted, or boiled, bonds between atoms/molecules break
...

Aluminium forms +3 ions
...
Balance between repulsion of +ve nuclei
and attraction to -ve electrons
...

Note: not all atoms need 8e- in outer-shell to be stable:
Less

More

Atoms can use d orbitals to expand the octet, so have more than 8e- in their ‘outer shell’
...

•
•
•

Electron pairs repel each other as much as they can, both -vely charged
Type of electron pair affects how much it repels other e- pairs; lone pairs repel more strongly than bonding
pairs due to higher density of the electron cloud
...


The shape depends on the type of e- pair surrounding central atom
...
g
...

n= g/RFM
Formulas
Formula unit, basic units and match formulae of substances
...
g
...
But in ionic
compounds the formula unit is a group of ions; e
...
in Ca(NO3)2 is a group of 3 ions, Ca2+ and 2* NO3-
...

Water of crystallisation
Crystals of some ionic lattices include water molecules
...
Crystals ‘hydrated’
...

Percentage yield
Can calculate theoretical yield but certain factors can reduce the amounts of products produced:
1
...

3
...

5
...
g
...
t
...
Non-metals gains e-s to form -vely charged
anions
...

Ionic bonding
Ions are only formed if a metal non-metal reaction has a favourable overall energy change
...
s
...
The cations and anions are held together by opp
...

Each ion attracts many others of the opposite charge, so ions build up into a giant lattice, making salts
...
solutions of salts can conduct electricity
...
They have lots
of practical application: water treatment, production coloured pigments- paints + dyes, identifying certain
metal ions in solution
...
e
...
testing SO4 add HCl and Barium chloride
...

Barium
sulfate
Lead
iodide

Colour
white
Bright
yellow

Flame test: (based on emission spectrum)
1
...

2
...
Record the colour seen
Li+
Na+
K+
Ca2+
Ba2+
Cu2+

Bright red (crimson)
Yellow
Lilac
Brick red
Apple green
Blue green

Ionic bonding
Ionic compounds, typically solids r
...
p
...

Electrostatic forces of attraction of opp
...

Attractions are strong so lots of energy needed to overcome and pull ions apart high mpt and bpt
Once melted, ions free to move, can conduct electricity
Metallic bonding
Metals have a lattice structure
•
•

Giant structure of metal cations in a sea of delocalised e-, free to move, so account for the flow of
electricity
Whole structure held together by the attraction of metal cations and the delocalised e-s  strong

Covalent networks
Carbon- diamond/graphite
Silicon dioxide- quartz
•
•
•

These are very strong and hard, covalent bonds between atoms in the network, which require huge
amounts of energy to break the intermolecular forces, giving them a very high mpt
...

Insoluble in water and don’t conduct electricity (except graphite which has 1 delocalised e- per
atom, which can carry charge)
...


Spectacular metals
Grp 1 – alkali metals, grp 2 – alkaline earth metals
Elements become more metallic down a group, e
...
they more readily form cations in ionic compoundsmore reactive
...
reactive with water and O2
...
E
...
magnesium oxide
...
Input energy
always needed to remove e- because the e- attracted to the nucleus
...

X(g)  X+(g) + e1st IE removes the most loosely held e-, thus the trend as you remove more e- is that it gets harder
...

IE and electron shells
There are some variations in the general trend for the IEs for an atom as you go across the period
...

•

•
•

Between Be & B, IE decreases
...

The s-subshell is lower in energy than the p-subshell, so
less energy is needed to remove the e- in the p orbital, due
to shielding by 2s e-s
...

F is harder to lose e- because the nuclear charge has
increased, but shielding

Going down the grp, IE decreases as the attraction between
nucleus and outermost e- decreases- due to more filled shells
of e- in-between nucleus and that e-, reduces attraction ‘experienced’- so easier to lose e-
...


Group 2 elements
•
•

These elements are all reactive, they form compounds containing ions with a +2 charge
...

o Mg reacts slowly when mixed with water and heated
o Ba reacts rapidly, producing a steady stream of hydrogen
M(s) + 2H2O  M(OH)2 (aq) + H2 (g)

Should be noted: grp 2 elements with water don’t react as vigorously as grp 1 metals do
...


Cations with a higher charge density – top grp 2- can distort or polarise the negative charge cloud around
the carbonate ion, making it less stable and easier to break up upon heating
...


Oxides and hydroxides
In water, grp 2 metal oxides and hydroxides form alkaline solutions, although they are not very soluble

---