1. Atomic structure and the Periodic Table Flashcards
atomic number
proton number
all isotopes have the same number of protons
equal to no of electrons if uncharged
mass number
total number of protons and neutrons in the nucleus
mass and charge of subatomic particles
proton 1, +1
electron 1/2000, -1
neutron 1, 0
What are isotopes?
Different atoms of the same element with the same proton number but different neutron number
What is the Relative Atomic Mass?
The weighted mean mass of an atom of an element compared to 1/12th of the mass of an atom of carbon-12
What is the Relative Isotopic Mass?
Relative mass of an atom of an isotope compared to 1/12th of the mass of an atom of carbon-12
What is the M+ peak?
Molecular ion peak. Shows the relative molecular mass.
What is the M+1 peak?
The peak that has +1 m/z than the molecular ion peak due to the existence of a carbon 13 isotope.
Name the subshells, their orbitals and how many electrons each can hold
S, p, d, f
1, 3, 5, 7
2, 6 , 10, 14
Which shape does the s orbital have?
Spherical.
Which shape does the p orbitals have?
Dumbell (8) shape. 3 orbitals. Px, Py and Pz.
What does spin pairing mean?
Electrons occupying the same orbital have different spins.
What are the different subshells from lowest energy to highest?
1s, 2s, 2p, 3s, 3p, 4s, 3d
What is the electron configuration of Chromium?
1s2, 2s2, 2p6, 3s2, 3p6, 4s1, 3d5
An electron is excited from the 4s to fill the 3d orbitals.
What is the electron configuration of Copper?
1s2, 2s2, 2p6, 3s2, 3p6, 4s1, 3d10
an electron is excited from 4s to fill the 3d subshell.
Which block is the one in red?
s block
Which block is the one in purple?
d block
Which block is the one in green?
p block
Which block is the one in purple?
f block.
How are line spectra formed? How are they used to identify an element?
- Electron is in ground state.
- Electron absorbs energy from surroundings and is excited (moves to a higher-energy shell)
- Electron moves back to ground state and releases energy in the form of electromagnetic radiation with a specific frequency.
- Emission spectra shows the frequency of light emitted.
This is unique for every element.
How do line spectra prove that electrons exist in quantum shells?
Defined lines in the emission spectra show energy levels are discrete, electrons jump without an inbetween stage. This proves electrons exist in shells and each shell has a fixed energy.
What is ionisation energy?
Energy required to remove 1 mole of electrons from 1 mole of gaseous atoms to form 1 mole of gaseous 1+ions
i.e. Na(g) > Na+(g) + e-
How does shielding affect ionisation energies?
The more electron shells between the positive nucleus and the negative outer electron that is being removed, the weaker the attraction and so less energy is needed.
How does nuclear charge affect ionisation energies?
The more protons in the nucleus, the bigger the positive charge and so the bigger the attraction between nucleus and electrons therefore more energy is needed to remove an electron.
How does atomic size affect ionisation energies?
The bigger the atom, the further away the outer electrons are from the nucleus and so the attractive force between them is less so its easier to remove electrons.
Why do ionisation energies decrease as you go down the group?
- Down a group the no of shells increases so atomic radius increases, the outer electrons are further from the nucleus (attractive force is weaker so energy required decreases)
- Extra inner shells shield outer electrons from nucleus (more shielding)
- Positive charge of nucleus increasing is overidden by shielding effect
Why does atomic radius decrease across a period?
- Increased nuclear charge (more protons) so more attractive force, pullling electrons closer to the nucleus
- Electrons are added to the same shell so shielding is similar.
Why does atomic radius increase down a group?
- More quantum shells, so more shielding.
- This offsets the fact that there’s an increasing nuclear charge.
Why does ionisation energy increase as we go across a period?
- Increasing number of protons increases attractive forces towards the nucleus.
- Shielding and size of the atom are similar.
Why is there a dip in Al?
Aluminium has its outer shell electron in a higher energy subshell, further away from the nucleus than magnesium.
Al - …3s2, 3p1
Mg - …3s2
Therefore the force of attraction of the electron with the nucleus is weaker and so less energy is needed.
Why is there a dip in S?
Both P and S have lectrons in 3p sub shell so shielding is the same.
However, sulfur has an orbital with two electrons while phosphorus doesn’t.
There’s repulsion between electrons in the same orbitals so less energy is needed to remove the electron
Why is there an increase from Na to Al?
- Increasing positive charge of ions
- Increaseing number of delocalised electrons.
- Therefore bonds are stronger and so more energy is needed to overcome them.
Why is there a peak in Si?
Giant covalent (macromolecular) structure. Many strong covalent bonds hold silicon together so a large amount of energy is required.
Why is there a decrease from Si to P?
P4 is a simple molecular formula so less energy is needed to overcome the intermolecular forces than in the giant covalent in Si.
Why is there an increase from P to S?
S8 larger simple molecular structure so london forces are stronger than in P4 so more energy is needed to overcome intermolecular forces.
Why is there a decrease from S to Cl?
Cl2 smaller molecular structure so decrease london forces so weaker intermolecular forces and so less energy is needed.
Why is there a decrease from Cl to Ar?
Ar exists as individual atoms so weaker forces of attraction.
difference between relative molecular mass and relative formula mass
molecular mass used when talking about simple molecules
formula mass used for ionic or giant covalent molecules
to work out add up atomic numbers
how to work out relative atomic mass from mass spectrum
isotopic mass x relative isotopic abundance
then divide by sum of isotopic abundances
how to predict mass spectra for diatomic molecules
- turn percentage abundances to decimal
- make a table showing possible combinations e:g Cl-35xCl35
2x2 table with abdundance x abundance - add up any that are the same
- divide all by the smallest to get whole number ratio, work out rmm of each and plot mass spectrum
orbital
region within an atom that holds upto 2 electrons with opposite spins
what does group number tell you
the number of electrons in the outer shell is the same for each group so have similar chemical properties
what does period number tell you?
the number of electron shells
number of electrons in each shell
4 shells
2, 8, 18, 32
periodicity
repeating trends in physical and chemical properties
