3.1.1- Atomic Structure
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What letter is used to represent the atomic number of an atom?
Z
What does the atomic number tell us about an element?
atomic number = number of protons in an atom
What letter represents mass number?
A
How is the mass number calculated?
number of protons + number of neutrons
Define relative atomic mass
mean average mass of all atoms of an element (taking isotopes into account) relative to 1/12 mass of an atom of carbon12
What are isotopes of an element?
• different forms of the same element • have the same number of protons (and electrons) but a different number of neutrons • they still have the same chemical properties
What is the mass of a proton?
1
What is the charge of a proton?
+1
What is the mass of a neutron?
1
What is the charge of a neutron?
0 (no charge)
What is the mass of an electron?
0 (negligible)
What is the charge of an electron?
-1
define ionisation
process in which atoms lose or gain electrons and become ions - cations (+) - anions (-)
Define 1st ionisation energy
the energy required to remove one electron from one mole of gaseous atoms to form one mole of gaseous 1+ ions
1st ionisation energy general formula
M(g) = M+(g) + e-(g)
2nd ionisation energy general formula
M+(g) = M2+(g) + e-(g)
Trends in ionisation energies: - ionisation energy as more electrons are removed
• more electrons removed = successive ionisation energy increases -more significant jumps in ionisation energy where electrons are being removed from the next principle energy level ( as electrons are closer to the nucleus on nearer electron shells so are held more tightly)
Trends in ionisation energies: group 2 elements and 1st ionisation energy
• nuclear charge increases down group 2 but the 1st ionisation energy decreases • this means electrons are being removed from successively higher energy levels, which lie further from the nucleus and so are less attracted to the nucleus • outer electrons also ‘shielded’ from nuclear pull by inner shells
Trends in ionisation energies going along a period and ionisation energy (overall trend)
• as you go along a period (L-R), the 1st ionisation energy increases • this is because as you go along a period, the number of protons in the nucleus increases so the attraction between the nucleus and outer electrons increases • therefore amount of energy needed to remove an electron increases
Why are all ionisation energies endothermic?
• endothermic = positive energy changes and require energy • endothermic as energy is needed to overcome the electrostatic attraction between electron + nucleus
what is an electron shell known as?
principle energy level
Max number of electrons for sublevel S
2
Max number of electrons for sublevel P
6
Max number of electrons for sublevel D
10