Electrons, energy levels and atomic orbitals
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Define the terms 'shell', 'sub-shell', and 'orbital' in the context of atomic structure.
A shell is a region around the nucleus with a specific energy level (principal quantum number, n). A sub-shell is a group of orbitals within a shell that have the same energy level (s, p, d). An orbital is a region of space within a sub-shell that can hold a maximum of two electrons.
What are the number of orbitals in s, p, and d sub-shells, and how many electrons can each sub-shell hold?
An s sub-shell has 1 orbital and can hold 2 electrons. A p sub-shell has 3 orbitals and can hold 6 electrons. A d sub-shell has 5 orbitals and can hold 10 electrons.
Describe the order of increasing energy of the sub-shells within the first three shells, and the 4s and 4p sub-shells.
The order of increasing energy is: 1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p. Note that the 4s sub-shell fills before the 3d sub-shell due to lower energy.
Write the full electronic configuration for an atom of chlorine (Cl), given its atomic number is 17.
The electronic configuration for chlorine (Z=17) is 1s²2s²2p⁶3s²3p⁵. This notation indicates the number of electrons in each subshell.
Explain why electrons fill the 4s sub-shell before the 3d sub-shell.
Although the 3d subshell belongs to the n=3 shell and the 4s belongs to the n=4 shell, the 4s subshell is at a slightly lower energy level than the 3d subshell. Therefore, the 4s subshell is filled before the 3d.
Use the 'electrons in boxes' notation to show the electronic configuration of iron (Fe), given its atomic number is 26.
Fe: [Ar] 4s² 3d⁶. This shorthand notation uses the preceding noble gas (Argon) to represent the filled inner shells, followed by the filling of the valence shell.
Sketch the shapes of an s orbital and a p orbital.
An s orbital is spherical and centred around the nucleus. A p orbital has a dumbbell shape, with two lobes along one axis (x, y, or z).
Define a free radical and provide an example.
A free radical is a species with one or more unpaired electrons. Free radicals are highly reactive due to their tendency to pair their unpaired electrons.
What is ionisation energy and what state must the atom be in?
Ionisation energy is the energy required to remove one mole of electrons from one mole of gaseous atoms or ions. Each atom or ion described will be in the ground state
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