Doc Brown's chemistry notes on atomic and electron structure

6. Which electron arrangements are stable and which are not and why? Considering electronically stable or unstable atoms or ions

• WHY ARE SOME ELECTRON ARRANGEMENTS ARE MORE STABLE THAN OTHERS?

• WHICH ELECTRON ARRANGEMENTS ARE THE MOST STABLE AND WHICH ELECTRON ARRANGEMENTS THE LEAST STABLE?

• HOW DO ELECTRON ARRANGEMENTS RELATE TO THE REACTIVITY OF CHEMICAL ELEMENTS?

• When an atom has its outer level full to the maximum number of electrons allowed, the atom is particularly stable electronically and very unreactive.

• The most electronically stable atoms have a full outer shell

  • This is the situation with the Noble Gases: He is [2], neon is [2,8] and argon is [2,8,8] etc.

  • There atoms are the most reluctant to lose, share or gain electrons in any sort of chemical interaction because they are so electronically stable.

  • For all elements most of their chemistry is about what outer electrons do or don't!

  • [2], [2,8] and [2,8,8] etc. are known as the 'stable Noble Gas arrangements', and the atoms of other elements try to attain this sort of electron structure when reacting to become more stable.

  • More details on Electron configuration notes for Advanced Level Chemistry Students

• The most reactive metals have just one outer electron.

  • These are the Group 1 Alkali Metals, lithium [2,1], sodium [2,8,1], potassium [2,8,8,1]

  • With one outer shell electron, they have one more electron than a stable Noble Gas electron structure.

  • So, they readily lose the outer electron when they chemically react to try to form (if possible) one of the stable Noble Gas electron arrangements – which is why atoms react in the first place!

  • When Group 1 Alkali Metal atoms lose an electron they form a positive ion because the positive proton number doesn't change, but with one negative electron lost, there is a surplus of one + charge e.g.

    • sodium atom ==> sodium ion

    • Na ==> Na⁺

    • is [2.8.1] ==> [2.8] electronically more stable

    • in fundamental particles [11p + 11e] ==> [11p + 10e]

    • IONS are atoms or group of atoms which carry an overall electrical charge i.e. not electrically neutral.

• The most reactive non–metals are just one electron short of a full outer shell.

  • These are the Group 7 Halogens, namely fluorine [2,7], chlorine [2,8,7] etc.

  • These atoms are one electron short of a stable full outer shell and seek an 8th outer electron to become electronically stable – yet again, this is why atoms react!

  • They readily gain an outer electron, when they chemically react, to form one of the stable Noble Gas electron arrangements either by sharing electrons (in a covalent bond) or by electron transfer forming a singly charged negative ion (ionic bonding) e.g.

    • chlorine atom ==> chloride ion

    • Cl ==> Cl^–

    • is [2.8.7] ==> [2.8.8] electronically more stable

    • in fundamental particles [17p + 17e] ==> [17p + 18e]

    • the positive proton number of Cl doesn't change but the chloride ion carries one extra negative electron to give the surplus charge of a single – on the ion.

• For more on electron structure and chemical changes and compound formation see ...

  • GCSE/IGCSE/AS notes on CHEMICAL BONDING

• and for more on metal and non–metal reactivity see

  • GCSE/IGCSE notes REACTIVITY SERIES of METALS

  • GCSE/IGCSE notes Group 1 ALKALI METALS

  • GCSE/IGCSE notes GROUP 7 HALOGENS

Quizzes - practice exam questions

• Some basic practice exam questions on atomic structure (at end of index page)

• GCSE level Foundation (easier) Atomic Structure multiple choice QUIZ

• GCSE level Higher (harder) Atomic Structure multiple choice QUIZ

• gap-fill worksheet on Atomic Structure

• matching pair quiz on Atomic and electronic structure 1. fundamental particles

• matching pair quiz on Atomic and electronic structure 2. periodic table