Topic 1 Atomic Structure & the Periodic Table Flashcards
(43 cards)
Relative Atomic Mass
The weighted mean mass of an atom of an element relative to 1/12 the mass of an atom of carbon 12.
Relative Isotopic Mass
The mean mass of an atom of an isotope relative to 1/12 of the mass of an atom of carbon 12.
Formula for RAM
Sum of (Mass of isotope x abundance of isotope) / total abundance of all isotopes.
Periodicity
Regularly repeating patterns across different periods/with increasing atomic number, e.g., in chemical , physical and/or atomic properties.
Describe the trend in melting point across period 3.
Increases: Na to Mg to Al. Metallic bonding: ionic radius decreases, protons & e- increase and attraction between the ions & e- increases.
Big jump to Si– giant molecular, lots of strong covalent bonds.
Big drop down to P4, slight rise to S8 and decreasing thereafter to Cl2 & Ar. All simple covalent molecules except Ar which is monoatomic with weak intermolecular forces.
d-block element
The last electron to fill an orbital does so in the d-subshell.
s-block & p-block elements
The highest-energy electron is found in an s-/p-orbital respectively.
Why don’t the d-block elements fit the same definition structure as p-block and s-block elements?
The 4s orbital e- has more energy than the 3d orbital e-.
Orbital
A region within an atom that can hold up to 2 e- with opposite spins.
In what order are e- lost?
e- further from the nucleus are lost first.
Filling of subshells
Singly first, then doubling up, so that e- in each orbital have opposite spins.
What determines the chemical properties of an element?
The number of electrons in the outer shell.
What’s so special about Cu and Cr?
They only fill the 4s1 orbital, not 4s2 like all the other elements in their period. This pattern is repeated periodically for Mo & Ag too!
Filling diagram
1s
2s 2p
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d 5f
6s 6p 6d
7s etc.
Graph of 1st IE against atomic number for periods 1 & 2
Big jump from H to He then a huge drop down below H to Li.
1st IE increases from Li to Ne: the shielding remains the same, but the number of protons increases, so the attraction between the nucleus & outer electrons increases.
What are the exceptions to the trend in increasing 1st IE across period 2?
B & O.
B: less energy to remove the e- as it’s alone in the p-orbital, which has more energy than an s-orbital and is shielded by e- in the full s-subshell. A similar trend applies to Al concerning 3p.
O: 2p4, the 2 e- in the same orbital repel, so less energy is needed to remove one. Similar applies to S.
Why does He have the highest 1st IE?
No shielding. Smallest atomic radius.
What does the big jumps on a 1st IE graph of an element indicate?
A shell change. e- are removed from a shell closer to the nucleus that experiences less shielding.
Why do successive IEs increase for an element?
The number of protons is the same, but the e- get closer to the nucleus.
Isotopes of the same elements have identical chemical properties. Why?
They have identical electronic configurations.
What is the difference between mass number & relative isotopic mass?
Mass number is always a whole number as it’s the sum of protons & neutrons in the nucleus) whereas relative isotopic mass is relative to the 1/12 the mass of an atom of carbon-12, so not likely to be an integer.
Describe the mass spectrum of chlorine.
2 peaks at 35 & 37 with relative heights of 3:1. 3 peaks at 70, 72 & 74 with relative heights 9:6:1. Peak heights won’t be exactly 9:6:1 (as relative isotopic masses are not integers).
What is the M + 1 peak?
In organic compounds, there is always a small % of the carbon-13 isotope present. the peak is only present/significant in molecules with large masses where the % of C-13 becomes significant.
Molecular ion peak
The peak with the highest m/z ratio in the mass spectrum, the M peak.
