Atomic Structure Flashcards
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 a isotope
Atoms of the element with the same number of protons (same atomic number) but different number of neutrons (different mass number).
What is the relative mass of an electron?
1/1836
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 dissolved sample is forced through a fine needle that is connected to the positive terminal of a high voltage supply. The sample loses electrons, forming positive ions. (high voltage knocks electron off sample)
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
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 Mr from a mass spectrometer reading.
Mr = Total of (m/z x abundance) / total abundance
Why do isotopes have similar chemical properties?
They have the same number of electrons and this is what determines an isotope’s chemical properties.
Define 1st ionisation energy
The energy required to remove one mole of electrons from one mole of gaseous atoms and is measured in kj/mol
Define 2nd ionisation energy
The energy required to remove one mole of electrons from one mole of gaseous 1+ ions
Describe and explain the general trend of 1st ionisation energy among group 2 elements
As you go down the group, the number of electrons an element increases. Therefore the atoms have more electron shells. This means the distance between outer electron and the nucleus increases. Due to this and increased shielding, the electrostatic attraction between them decreases. making the electrons easier to remove.
Name the 4 sub levels 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?
Cr and Cu
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
What is the electron structure of 21Se+ (in terms of orbitals)?
1s2 2s2 2p6 3s2 3p6 4s1 3d1
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 relative atomic mass or molecular mass, or to identify the different isotopes of an element.
What happens in the ionisation stage of a Time of Flight (TOF) Mass Spectrometer?
Electrospray - sample dissolved into a volatile solvent. Passed through a hypodermic needle attached to positive terminal at high voltage
Atoms lose an electron and they leave needle as positively charged droplets
They evaporate until they are left as singular positive ions.
Electron gun: Sample vaporised and fired with high energy electrons. An electron is knocked off and positive ions form
What is relative atomic mass (Ar)?
Ratio of the mass of one atom of an element relative to 1/12th the mass of one carbon-12 atom
Why is an atom’s relative atomic mass measured relative to 1/12th the mass of a carbon-12 atom?
Atoms have a mass that is too small to measure by itself.
Easier to know their masses compared to each other - and the standard atom used is carbon-12 as its Ar is exactly 12 (no other atom has a whole number as their relative Ar).
