Chem Topic 1 Flashcards
What are the relative masses and charges of subatomic particles
Mass: Charge
Proton 1 1
Neutron 1 0
Electron 1/1840 -1
What do the atomic number and mass number of an element signify?
atomic number = proton/electron
mass number= proton + neutron
Define isotope
same element with the same number of protons different number of neutrons
How do the chemical and physical properties of isotopes compare?
Same chemical properties due to electron arrangement.
different physical properties due to masses
Define; relative atomic mass and relative molecular mass
relative atomic mass: average mass of one of its atom where carbon 12=12
molecular average mass of a molecule on a scale where carbon 12=12
Write a general equation to show how you would calculate relative atomic mass when given % abundance
∑(mass x abundance) / 100
Write a general equation to show how you would calculate relative atomic mass when given relative abundance
∑(mass x abundance) / ∑abundance
What are the 6 stages of a TOF mass spectrometer?
Ionisation, acceleration, ion drift, detection, mass spectrum, data analysis
Describe the two types of ionisation and write two different equations to represent the ionisation of chlorine
Electron impact:
The sample is vaporised
Then high energy electrons are fired at it/electron gun
This usually knocks off one electron from each particle forming a 1+ ion.
Cl(g) à Cl+(g) + e-
Electrospray ionisation
The sample is dissolved in a volatile solvent
Then injected through a positively charged capillary needle
Each molecule/particle gains a proton/H+
Cl(g) + H+ à ClH+(g)
Explain why it is necessary to ionize molecules when measuring their mass in a TOF mass spectrometer.
So they can be accelerated and detected
Explain how ions are accelerated, detected and have their abundance determined in a time of flight (TOF) mass spectrometer.
The ions are accelerated using an electric field so they have the same kinetic energy. They separate in the ion drift region as the lighter ions have a higher velocity. They are detected by a negative plate. Electrons pass from the plate to the positive ions. This creates a current. The size of the current is proportional to the abundance of the ion.
What does Avogadro’s constant represent?
6.022x1023 = the number of particles in one mole
Calculate the mass in Kg of one Na+ ion
23/1000 = 0.023
0.023/6.022x1023 = 3.819x10-26
On mass spectra of molecules what is the molecular ion? What is the m+1 ion?
The molecular ion represents the molecule’s Mr (for electron impact ionisation). The m+1 ion is the Mr+1 and is created by the natural occurrence of 13C
If you were given a mass spectrum for a molecule that was ionised via electrospray ionisation, how would you deduce its Mr?
Find the molecular ion peak value and subtract 1 (as the ion has gained a proton during ionisation)
describe Thomson’s and Rutherford’s model of the atom
Thomson’s model = plum pudding, positively charged sphere with negative electrons randomly arranged
Rutherford’s model = positively charged nucleus with negative electrons around the outside
Write the full electron configuration of krypton
1s22s22p63s23p64s23d104p6
Give the electron configuration of O2- and Ni2+ . What do you need to remember for electron configuration of transition metal ions?
1s22s22p6
1s22s22p63s23p63d8
For transition metal ions, the 4s electrons are removed before 3d
How do electrons fill p and d orbitals?
Electrons go into separate orbitals (boxes) to start with and then start to pair up
What are the names of the 4 blocks of the periodic table? How do they relate to electron structure?
Groups 1&2 = s block, between groups 2 & 3 = d block, groups 3-group 0 = p block
Define first ionisation energy
The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of positively charged gaseous ions
Write an equation for the first ionisation energy of oxygen (remember gas state symbol)
O(g) à O+(g) + e-
What is the general trend of first ionisation energy as you go down a group? Explain your answer
As you go down a group the first ionisation energy decreases. This is because the outer electrons become further from the nucleus and experience more shielding. This means it requires less energy to remove an outer electron because there is greater attraction between the nucleus and outer electrons.
What is the general trend of first ionisation energy as you go across a period? Explain your answer
As you go across a period the first ionisation energy generally increases. This is because the nuclear charge increases as there are more protons, but the shielding remains the same. This means there is a greater attraction between the nucleus and outer electron.
What are the 2 exceptions to the general trend of first ionisation energy in period 3? Explain each of them
For aluminium, the electron is removed from the 3p subshell which is at a higher energy than the 3s subshell so it is easier to remove.
In sulfur, two of the 3p electrons are paired. There is some repulsion between paired electrons in the same sub-level. This reduces the force of their attraction to the nucleus, so less energy is needed to remove one of these paired electrons than is needed to remove an unpaired electron from phosphorus.
Write equations for the second and third ionisation energies of oxygen
O+(g) à O2+(g) + e-
O2+(g) à O3+(g) + e-
What do the ‘big jumps’ in the successive ionisation energies of an element signify?
‘Big jumps’ in successive ionisation energy mean that the electron has been removed from a lower energy level (shell). This will tell you what group the element is in.
Atomic number and mass number
