Atomic Structure
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Give the definition of Atomic Number (Z)
The number of protons in the atom nucleus
Give the definition of Mass Number (A)
The number of protons and neutrons in an atom nucleus
Give the definition of an isotope
Atoms of the element with the same atomic number but a different mass number
What is the relative mass of a neutron?
1
What is the relative mass of a proton?
1
What are the relative charges of a proton, neutron and electron?
+1, 0, -1 respectively
Electrospray ionisation is the first step of mass spectrometry. What does it involve?
A volatile sample (X) is dissolved in a solvent and then is forced through a fine needle that is positively charged and connected to a high voltage supply. The sample gains a H+ ion, forming XH+
What happens in the acceleration area of a mass spectrometer?
Negatively charged plates attracts and accelerates ions to the same kinetic energy. The lighter ions accelerate more as they are lighter.
What is the role of an ion detector in a mass spectrometer?
When positive ions his the ion detector, they pick up an electron, causing a current to flow. A flight time can also be detected The abundance of the ion is proportional to the current produced
You are reading a graph giving mass spectrometer readings. There are two vertical lines, one with a m/z of 10, and another with an m/z of 12. What does this mean?
There are two isotope of this element, with the relative isotopic masses of 10 and 12.
Give an equation to work out relative atomic mass in mass spectrometry.
RAM = Σ(isotopic mass x relative abundance)/total abundance
Why do isotopes have similar chemical properties?
They have similar chemical properties as only the number of neutrons is different. The number of electrons is the same, and it’s the electrons which are involved in chemical reactions and so determine the properties
Define 1st ionisation energy
The energy required to remove one mole of electrons from one mole of gaseous atoms, under standard conditions
Define 2nd ionisation energy
The energy required to remove one mole of electrons from one mole of gaseous 1+ ions to form 1 mole of gaseous 2+ ions
Describe and explain the general trend of 1st ionisation energy among group 2 elements
There is a general decrease down the group. This is because as you go down the group, the number of electrons an element has increases. This means they have more shells and so there is more shielding, thus the nuclear charge holding the electrons in place is weakened, making the electrons easier to remove.
Name the 4 sub levels (we’ve been taught) and the number of orbitals each one has
s - 1, p - 3, d - 5, f - 7 (x2 for no. of electrons)
Two elements are anomalous when it comes to their electron structure. Which elements are they?
Chromium and Copper
What is the correct electron structure for Cu (in terms of orbitals)?
1s2 2s2 2p6 3s2 3p6 4s1 3d10
What is the electron structure of Cr (in terms of orbitals)?
1s2 2s2 2p6 3s2 3p6 4s1 3d5
Describe and explain the general trend in 1st ionisation energy across a period
There is generally an increase as you go along the period. This is because there is an increased nuclear charge and so the atoms gets smaller. Therefore there isa stronger attraction from nucleus to electron in outer shell.
Generally there is an increase in the 1st ionisation energy across a period. However, the energy decreases as you go from group 2 to group 3. Why?
The electron lost from group 3 is from the p orbital, while the one lost from group 2 is from the s orbital. The p orbital is higher energy and better protected by shielding than the s orbital, so it requires less energy to remove
What does a mass spectrometer do, and what can you use it for?
Separates atoms and molecules according to their charge and masses Allows you to identify a sample by measuring its atomic mass or molecular weight