2.4 The Electronic Structure of an Atom

Electron Arrangement in an Atom
■ Structure of atom

	►	Atoms are made up of a nucleus and electrons.
	►	These electrons move around the nucleus of the atom.
	►	Electrons are arranged in these shells.
	►	This video contains information about electron arrangement in an atom.

■ Electron arrangement [electron configuration]

	►	The way in which electrons are distributed in the shells of an atom.
	►	The animation below shows the electron arrangement of atom.

■ Valence electrons

	►	Definition : The electrons in the outermost shell.
	►	Elements with the same number of valence electron have the same chemical properties.
	►	Example of electron configuration and valence electrons.
		Symbol Proton number Number of electrons Electron configuration Valence elektrons $\begin{array}{c}1\\ 1\end{array}H$ 1 1 1 1 $\begin{array}{c}16\\ 8\end{array}O$ 8 8 2.6 6 $\begin{array}{c}12\\ 6\end{array}C$ 6 6 2.4 4 $\begin{array}{c}40\\ 20\end{array}\mathrm{Ca}$ 20 20 2.8.8.2 2

✍ Worked-example 2.4(a)
Complete the following table:

Element Symbol Proton number Electron number Electron configuration Valence electrons Helium $\begin{array}{c}4\\ 2\end{array}\mathrm{He}$ 2 2 2 2 Nitrogen $\begin{array}{c}14\\ 7\end{array}N$ 7 7 2.5 5 Neon $\begin{array}{c}20\\ 10\end{array}\mathrm{Ne}$ 10 10 2.8 8 Sodium $\begin{array}{c}23\\ 11\end{array}\mathrm{Na}$ 11 11 2.8.1 1 Aluminium $\begin{array}{c}27\\ 13\end{array}\mathrm{Al}$ 13 13 2.8.3 3 Argon $\begin{array}{c}40\\ 18\end{array}\mathrm{Ar}$ 18 18 2.8.8 8 Potassium $\begin{array}{c}39\\ 19\end{array}K$ 19 19 2.8.8.1 1

← 2.3 Isotopes and Their Importance

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