Topic 1 - Atomic Structure and the Periodic Table Flashcards
How much does an electron weigh?
1/1836
What is the definition of 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 definition of relative isotopic mass?
The mass of an atom of an isotope, compared to 1/12th of the mass of an atom of carbon-12
What are isotopes?
Atoms of the same element with different numbers of neutrons.
What are isotopes?
Atoms of the same element with different numbers of neutrons.
Why do isotopes have the same chemical properties?
They have the same configuration of electrons. Electrons determine the chemical properties
Why do isotopes have different physical properties?
They have different masses. Physical properties are determined by the mass of an element
What is the definition of relative molecular mass/formula mass?
The weighted mean mass of a molecule/formula unit, compared to 1/12th of the mass of an atom of carbon-12.
What is an orbital?
The area that an electron moves in. (Orbitals within the same subshell have the same energy.)
What is it called when electrons in the same orbitals spin in opposite directions?
Spin-pairing
What shape are s-orbitals?
Spherical
What shape are p-orbitals?
Dumbbell shaped
What are the two rules working out electron configurations?
- Electrons fill up the lowest energy subshells first.
- Electrons fill orbitals singly before they start pairing up.
In what order to subshells fill?
1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d10
Chromium (Cr) and copper (Cu) donate one of their 4e electrons to the 3d subshell. Explain why.
They’re more stable with a full or half-full d-subshell.
What is electromagnetic radiation?
Energy that’s transmitted as waves, with a spectrum of different frequencies. (As frequency increases, wavelength decreases)
How is an emission spectrum made?
- In their ground state, atoms gave their electrons in their lowest possible energy levels.
- Electrons absorb energy and move to higher energy levels, further from the nucleus.
- Electrons release energy by drilling Frim a higher energy level down to a lower energy level. (The energy levels all have certain fixed values - they’re discrete.)
- The frequencies of light emitted when the electrons drop down appear as coloured lines in a dark background.
What do the different sets of lines in emission spectrum represent?
Electrons moving to a different energy level
What are the four basic principles of electron shells?
- Electrons can only exist in fixed orbitals, or shells, and not anywhere in between.
- Each shell has a fixed energy.
- When an electron moves between shells electromagnetic radiation is emitted or absorbed.
- Because the energy of shells is fixed, the radiation will have a fixed frequency.
What is the definition of first ionisation energy?
The energy needed to remove 1 electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions.
Is ionising atoms endothermic or endothermic?
Endothermic
What is the equation for the first ionisation of oxygen?
O(g) —) O+(g) + e-
How does nuclear charge affect ionisation energy?
More protons in the nucleus, more positively charge, stronger attraction between nucleus and electrons
How does atomic radius affect ionisation energy?
Attraction reduces rapidly with distance. Electrons in shells closer to the nucleus more strongly attracted to nucleus.
How does shielding affect ionisation energy?
As number of shells between nucleus and outer electrons increases, outer electrons feel less attraction towards the nuclear charge.
What does a high ionisation energy mean?
There’s a strong attraction between the electron and the nucleus, so more energy is needed to overcome the attraction and remove the electron.
Why do first ionisation energies decrease down a group?
Extra electron shells so larger atomic radii so electrons are further away from the nucleus and more shielding, reduces their attraction and makes them easier to remove. Overrides increasing nuclear charge
What is the definition of the second ionisation energy?
The energy needed to remove 1 electron from each ion in 1 mole of gaseous 1+ ions to form 1 mole of gaseous 2+ ions
Why do successive ionisation energies increase?
Electrons are being removed from an increasingly positive ion and there’s less repulsion amongst the remaining electrons so they’re more strongly attracted to the nucleus
Why do successive ionisation energies increase?
Electrons are being removed from an increasingly positive ion and there’s less repulsion amongst the remaining electrons so they’re more strongly attracted to the nucleus
What do the big jumps in ionisation energy show?
A new shell is being broken into - and electrons is being removed from a shell closer to the nucleus
Why does atomic radius decrease across a period?
Number of protons increases, positive charge of the nucleus increases so electrons are pulled closer to the nucleus. Extra electrons gained across the period are added to the outer energy level so they don’t provide any extra shielding effect
Explain how the drop between first ionisation energies of atoms in group 2 and group 3 shows subshell structure.
Group 3’s outer electron is in a p orbital rather than an s. The p orbital has a slightly higher energy than the s orbital, so the electron is, on average, to be found further from the nucleus. The p orbital has additional shielding provided by the s electrons. Both these factors override the effect of the increased nuclear charge.
Explain why there is a drop in first ionisation energies between group 5 and 6 atoms.
Elements with singly filled or full subshells are more stable than those with partially filled subshells.
The shielding is the same and the electron is being removed from an identical orbital.
In group 5, the electron is being removed from a singly-occupied orbital but, in group 6, it is being removed from an orbital containing two electrons. The repulsion between two electrons in an orbital makes electrons easier to remove from shared orbitals
What are 4 pieces of evidence for electron shells?
- Emission spectra
- Successive ionisation energy
- Drop between first ionisation energies of group 2 and 3 atoms
- Drop between first ionisation energies of group 5 and 6 atoms
