Why does K(Potassium) have a valence electron of 1 and not 9?

[yh4747]

I thought the electrons in the last shell were the valence electrons. K has 19 electrons. If you start filling the shells, the first one would have 2, the second would have 8, the third shell can hold up to 18, so the remaining 9 would go in the third shell. So shouldn't K have 9 valence electrons?

Please clearly explain. Thanks.

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[DAT Destroyer]

I thought the electrons in the last shell were the valence electrons. K has 19 electrons. If you start filling the shells, the first one would have 2, the second would have 8, the third shell can hold up to 18, so the remaining 9 would go in the third shell. So shouldn't K have 9 valence electrons?

Please clearly explain. Thanks.

Draw out the electron configuration 1s22s22p63s23p64s1 The outer most energy level is n equals 4 and there is 1 electron in this level. All group 1 metals contain 1 valence electron. Consult any text book and review the Aufbau principle.

Hope this helps, good luck in your studies.