EL Flashcards
Mass number definition
No of protons and neutrons
Atomic number definition
Number of protons = number of electrons
Electrons relative mas - 1/2000
What is an isotope?
Same number of protons different number of neutrons
What is the empirical formula?
The simplest whole number ratio of atoms in a compound
Percentage yield =
actual yield / theoretical yield
x 100
Exceptions of electron configuration
Copper - 3d10 4s1
Chromium - 3d5 4s1
This means they’re more stable
Periods 2 and 3 metal periodic trends
Melting points increase across the period because bonds get stronger
This is because there’s an increasing number of delocalised electrons and a decreasing ionic radius
This results in a higher charge density which attracts the ions more strongly
Periods 2 and 3 giant covalent structures periodic trends (C and Si)
Have the highest melting points in their periods
Periods 2 and 3 simple molecular structures periodic trends
Their melting points depend upon the strength of the intermolecular forces between their molecules
Intermolecular forces are weak and easily broken so they have low melting points
The noble gases have the lowest melting points because they’re monoatomic with very weak intermolecular forces
More atoms in a molecule means stronger intermolecular forces
What is the first ionisation enthalpy?
The energy needed to remove 1 electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions
X(g) –> X+(g) + e-
The lower the ionisation enthalpy the easier it is to remove an outer electron and form an ion
What 3 things affect the size of ionisation enthalpies?
1) Atomic radius
2) Nuclear charge
3) Electron shielding
What is electron shielding?
The inner electrons shield the outer shell electrons from the attractive force of the nucleus. More inner shells results in more shielding
This means the ionisation enthalpy will be lower
What is atomic radius?
The further the outer shell electrons from the positive radius the less nuclear attraction
Ionisation enthalpy will be lower
What is nuclear charge?
The positive charge of the nucleus, caused by the number of protons
The more protons, the more the nucleus will attract outer electrons so ionisation enthalpy will be higher
First ionisation enthalpy trends with groups
Decrease down a group
Because there’s less nuclear attraction to the outer electrons
This shows that electrons are arranged in energy levels
Shielding increases which also decreases nuclear attraction
First ionisation enthalpy with periods
Increase across a period
Because of the increasing number of protons so stronger nuclear attraction
There’s little extra shielding as all outer-shell electrons are roughly at the same energy level
Why do s-block metals have low ionisation enthalpies?
Relatively low nuclear charges
So less nuclear attraction
P-block metals have higher nuclear charges because of the increase in protons across each period. So higher first ionisation enthalpy
Group 2 elements reaction with water
Form metal hydroxides and hydrogen
Ca(s) + 2H2O(l) –> Ca(OH)2(aq) + H2(g)
Reactivity trends down group 2
Increasingly more reactive because there’s less nuclear attraction so outermost electrons lost more easily
Group 2 elements burning in oxygen
Form solid white oxides
2Ca(s) + O2(g) –> 2CaO(s)
How do group 2 oxides and hydroxides form alkaline solutions?
Group 2 oxides react readily with water to form metal hydroxides which dissolve
The OH- ions make these solutions strongly alkaline
Mg oxide is an exception as it reacts slowly and the hydroxide isn’t fully soluble
The hydroxides get more soluble down the group so the oxides form more strongly alkaline solutions
How do group 2 metals neutralise acids?
Group 2 oxides and hydroxides are bases
Both neutralise dilute acids forming salts
MgO(s) + 2HCl(aq) –> H2O(l) + MgCl2(aq)
Mg(OH)2(s) + 2HCl(aq) –> 2H2O(l) + MgCl2(aq)
Solubility trends in group 2
Depend on the compound anion
If the compound contains singly charged negative ions (e.g. OH-) there’s an increase in solubility down the group
If the compound contains doubly charged negative ions (e.g. CO32- or SO42-) there’s a decrease in solubility down the group
What do group 2 carbonates thermally decompose to form?
Carbon dioxide and metal oxides
The volume of CO2 produced decreases down the group as the metal gets bigger so a smaller number of MCO3 moles are contained in the same mass
Thermal stability down group 2 carbonates
Thermal stability increases down the group
Carbonate ions are large anions which can be made unstable in the presence of a cation (such as group 2 metal ion)
The cation polarises the carbonate ion - the greater the distortion, the less stable the carbonate ion
The larger the cation the less distortion as lower charge density
So, the further down the group, cations get larger
Lower charge density
so less distortion and the more stable the carbonate anion
What is charge density?
The charge on the ion relative to its volume
Group two cations all have a charge of 2+ but the charge density decreases down the group
Acid + base –>
salt + water
Name the soluble salts
Nitrates
Sodium
Lithium
Potassium
Ammonium
Most chlorides, iodides and bromides (except for silver halides)
Sulfates
Name the insoluble salts
Most hydroxides except lithium, sodium, potassium, calcium, strontium, barium, and ammonium
Most carbonates except lithium, potassium, sodium and ammonium
Insoluble carbonates form coloured precipitates
Insoluble carbonate precipitates
Silver carbonate - yellow
Copper carbonate - blue-green
Iron (II) - off white
Barium, calcium, lead (II) and zinc - white
Making an insoluble salt
Use a precipitation reaction
Pick two solutions that contain the ion you need
Once the salt has precipitated filter from solution, wash and dry
Making soluble salts using an alkali
Use a titration to add exactly the right amount of alkali to just neutralise the acid
Repeat the titration, this time without indicator otherwise the salt will be contaminated
Evaporate off the water and crystallise the salt
Making soluble salts using a metal or insoluble base
To make chlorides use HCl, to make sulfates use H2SO4, to make nitrates use HNO3
Add the solid metal, metal oxide or hydroxide to the acid to neutralise acid. When all the acid has been neutralised no more solid will dissolve
Filter out excess metal to get salt solution
Crystillise to get pure solid crystals of the salt
Exam question on electron energy levels
E=hv
Order of electromagnetic spectrum in increasing frequency and decreasing wavelength
Radio
Micro
Infrared
Visible
UV
X-rays
Gamma rays
Absorption vs emission spectra
Absorption is dark lines on coloured background
Emission is coloured lines on dark background
Both line spectra with lines in the same position for a given element
Lines get closer together as frequency increases
