Page 12 - PRE-U STPM CHEMISTRY TERM 1
P. 12
Chemistry Term 1 STPM
Quantised energy levels 4 The single electron in the hydrogen atom can be located in any of
can be visualised as the the orbits (depending on its energy) but not in spaces between the
shelves in a book shelf.
The books can be on any orbits.
shelf, but not the space
n = 7
between the shelves. n = 6
CHAPTER n = 5
n = 4
2 Book n = 3
n = 2
Shelf
n = 1
+
5 Each orbit is also known as a principle shell and is represented by
an alphabet.
Orbit, n Principle shell
1 K
2 L
3 M
4 N
5 O
6 P
7 Q
6 When the electron is in the orbit closest to the nucleus (i.e. at orbit
In the ground state, the
electron is stable. n = 1), it is in its ground state and is stable. It will not lose energy as it
revolves round the nucleus. (This is in contradiction to the classical
law of physics which states that an electron revolving around a
positive nucleus must lose
Contradiction to classical
Physics energy continuously and Energy absorbed
will eventually fall into the
nucleus).
Nucleus
7 The electron can be excited
Excitation of the electron
to higher energy levels by
absorbing the required
energy. This is called the
excited state.
Energy released
8 The electron in the excited
Returning to the ground state state will ‘drop’ back to
lower levels by emitting the Nucleus
excess energy in the form of
electromagnetic radiations.
42
02 Chapter 2.indd 42 3/26/18 3:14 PM
