ATOMIC STRUCTURE

Where are protons, neutrons and electrons found in the atom?

• protons in the nucleus

• neutrons in the nucleus

• electrons in orbitals

What is the relative mass of protons, neutrons and electrons?

• protons= 1

• neutrons= 1

• electrons= 1/1840 or 0

What is the relative charge of protons, neutrons and electrons?

• protons= +1

• neutrons= 0

• electrons= -1

What is the atomic number?

• Z

• the number of protons in the nucleus

What is the mass number?

• A

• the total number of protons and neutrons in the atom

What are isotopes?

atoms with the same number of protons but different numbers of neutrons

What are chemical and physical properties like for isotopes of the same atom?

• similar chemical properties as they have the same electronic structure

• varying physical properties as they have different masses

What is a mass spectrometer used for?

to determine all the isotopes present in a sample of an element, to identify elements

Why does the time of flight mass spectrometer need to be in a vacuum?

to prevent air particles from ionising

What’re the 4 steps in the time of flight mass spectrometer?

1. ionisation

2. acceleration

3. flight tube

4. detection

What’re the 2 methods of ionisation?

• electron impact

• electrospray

When is electron impact ionisation used?

for elements and substances with low formula mass, as electron impact can cause larger organic molecules to fragment

What occurs in electron impact ionisation?

• a vaporised sample is injected at low pressure

• an electron gun fires high energy electrons at the sample

• this knocks out an outer electron

• forming positive ions with different charges

When is electrospray ionisation used?

with larger organic molecules as fragmentation does not occur

What occurs in electrospray ionisation?

• sample is dissolved in a volatile, polar solvent

• injected through a fine needle giving a fine mist or aerosol

• the tip of needle has high voltage

• at the tip of the needle the sample molecule gains a proton from solvent forming MH+

• M(g) + H+ → MH+(g)

• solvent evaporates away while the MH+ ions move towards a negative plate

What occurs during acceleration?

• positive ions are accelerated by an electric field to a constant kinetic energy

• as all particles have the same kinetic energy, the velocity of each particle depends on its mass

• lighter particles have a faster velocity and heavier particles have a slower velocity

What occurs in the flight tube?

• positive ions with smaller m/z values will have the same kinetic energy as those with larger m/z and will move faster

• heavier particles take longer to move through the drift carea

• the ions are distinguished by different flight times

• t = d/v

What occurs in detection?

• ions reach the detector and generate a small current, which is fed into a computer for analysis

• current is produced by electrons transferring from the detector to the positive ions

• size of the current is proportional to the abundance of the species

What does the mass spectrometer measure?

• mass/ charge ratio

• abundance

How would you calculate the relative atomic mass?

sum of isotopic mass x relative abundance/ total relative abundance

What would happen if a molecule is put through a mass spectrometer with an electron impact ionisation stage?

• breaks up and gives a series of peaks caused by fragments

• peak with the largest m/z is equal to the Mr

• peak is called the parent peak

What would happen if a molecule is put through a mass spectrometer after electrospray ionisation?

• fragmentation will not occur

• one peak equal to the mass of the MH+ ion

• subtract 1 to get the Mr

What is the A-level model of electronic structure?

• principle energy levels numbered 1,2,3,4

• sub energy levels labelled s, p, d, f

• orbitals hold up to 2 electrons of opposite spin

How many electrons can the s orbital hold?

2

How many electrons can the p orbital hold?

6

How many electrons can the d orbital hold?

10

How many electrons can the f orbital hold?

14

How would you write oxygens electronic structure?

1s2 2s2 2p4

How would you write calciums electronic structure?

1s2 2s2 2p6 3s2 3p6 4s2

What do orbitals represent?

• the probabilities of finding an electron at any point within certain spatial distributions around the nucleus

• each orbital has its own 3 dimensional space

What is the shape of s sublevels?

spherical

What is the shape of p sublevels?

figure of 8 shaped

What’re spin diagrams?

What would a spin diagram for fluorine be?

What’re the different blocks of the periodic table?

• s block

• p block

• d block

What is the s block of the periodic table?

contain elements with their outer electron filling an s-subshell

What is the p block of the periodic table?

contains elements with their outer electron filling a p-subshell

What is the d block of the periodic table?

contains elements with their outer electron filling a d subshell

How are positive ions formed?

when electrons are lost from the outermost shell

How are negative ions formed?

when electrons are gained

What is the electronic structure of chromium?

1s2 2s2 2p6 3s2 3p6 4s1 3d5

What is the electronic structure of copper?

1s2 2s2 2p6 3s2 3p6 4s1 3d10

What is the definition of the first ionisation energy?

the enthalpy change when one mole of gaseous atoms forms one mole of gaseous ions with a single positive charge

What is the equation for the first ionisation energy?

H(g) → H+(g) + e-

What is the equation for the second ionisation energy?

the enthalpy change when one mole of gaseous ions with a single positive charge forms one mole of gaseous ions with a double positive charge

What is the equation for the second ionisation energy?

Ti+(g) → Ti2+ + e-

What’re the factors which affect ionisation energy?

1. the attraction of the nucleus

2. the distance of the electrons from the nucleus

3. shielding of the attraction of the nucleus

How does the attraction of the nucleus affect ionisation energy?

the more protons in the nucleus the greater the attraction

How does the distance of the electrons from the nucleus affect ionisation energy?

the bigger the atom, the further the outer electrons are from the nucleus and the weaker the attraction to the nucleus

How does shielding of the attraction of the nucleus affect ionisation energy?

an electron in an outershell is repelled by electrons in complete inner shells, weakening the attraction of the nucleus

Why are second ionisation energies always larger than the first ionisation energy?

as when the first electron is removed a positive ion is formed, which increases the attraction on the remaining electrons so the energy required to remove the next electron is larger

Why has helium got the largest ionisation energy?

its first electron is in the first shell closest to the nucleus and has no shielding effects from inner shells, so has a larger ionisation energy than hydrogen as it has one more proton

Why do first ionisation energies decrease down a group?

as one goes down a group, the outer electrons are found in shells further from the nucleus and are more shielded so the attraction of the nucleus becomes smaller

Why is there a general increase in the first ionisation energy across a period?

as one goes across a period, the electrons are being added to the same shell which has the same distance from the nucleus and the same shielding effect. the number of protons increases, making the effective attraction of the nucleus greater

Why has sodium got a lower first ionisation energy than neon?

sodium will have its outer electron in a 3s shell further from the nucleus and is more shielded, so sodiums outer electron is easier to remove and has a lower ionisation energy

Why is there a small drop from magnesium to alumium?

alumium is starting to fill a 3p sub shell wheras magnesium has its outer electrons in the 3s subshell. the electrons in the 3p subshell are slightly easier to remove because the 3p electrons are higher in energy and are also slightly shielded by the 3s electrons

Why is ther a small drop from phosphorus to sulfur?

with sulfur there are 4 electrons in the 3p subshell and the 4th is starting to fill the firs 3p orbital. when the second electron is added to a 3p orbital there is a slight repulsion between the 2 negatively charged electrons which makes the second electron easier to remove

What happens if a graph of second ionisation energies is plotted?

• similar pattern to the first ionisation energy graph

• all elements will have shifted to the left

• group 1 elements are now the peaks of the graph