AQA Chemistry 5.1.1.7 · Combined and Triple

Electronic structure

Electrons fill the lowest shell first: 2, then 8, then 8. Write the structure of any of the first twenty elements in numbers and as a diagram, and read its group and period from it.

Triple Science · Higher tier

Start here

An empty bus.

Electrons getting onto an atom behave like passengers with a strict rule about where to sit.

If you had to guess, do they fill the seats nearest the door first, or spread out to the back?

Shell filling

2, 8, 8, then start the fourth.

The first shell holds up to 2 electrons, the second up to 8, the third up to 8 for the first twenty elements. Write the structure as numbers, 2,8,1, or draw it. Choose an element, read its atomic number, then write its structure before you look at the diagram.

Sodium has atomic number 11, so 11 electrons in a neutral atom. Its electronic structure is:

Which is the electronic structure of sodium?

AQA writes the number form with commas (2,8,1); dots (2.8.1) are also accepted.

Group and period

The structure tells you where it sits.

Elements in the same group have the same number of electrons in their outer shell, which is why they have similar chemical properties. The period is the number of shells in use. This course numbers the groups 1 to 7 and 0: the noble gases have a full outer shell, 8 electrons, except helium with 2.

An element is 2,8,6. Which group?

Pick one.

Lithium is 2,1 and sodium is 2,8,1. Why are they chemically similar?

Pick one.

Group 0 has its own lesson: Group 0: the noble gases. Metals lose their outer electrons and non-metals gain electrons to reach a full outer shell; that is for the bonding lessons.

Think again · the third shell

“Potassium has 19 electrons, so it is 2,8,9.”

Your call

Choose

Potassium (atomic number 19). What is its electronic structure?

Sort

Group or period?

Which does each statement describe?

Tap a card, then tap the box it belongs in. Tap a placed card to take it back.

Command words in this lesson

Give: The electronic structure of an element, in numbers or as a diagram.
Explain: Why elements in a group are similar; how structure fixes group and period.
Identify: The group and period from a structure such as 2,8,6.

Key fact

Electrons fill the lowest shell first: 2, 8, 8. Group = electrons in the outer shell. Period = number of shells. Same group, same outer electrons, similar chemistry.

Key note · AQA 5.1.1.7 · Combined and Triple

Electronic structure

The electrons in an atom occupy the lowest available energy levels (innermost available shells). Shells hold 2, 8, 8 for the first twenty elements.
Structures can be written as numbers (sodium 2,8,1) or drawn as a diagram with electrons on concentric shells. Be able to do both for the first twenty elements.
Elements in the same group have the same number of electrons in their outer shell, which gives them similar chemical properties. The period is the number of shells.
The noble gases (Group 0) have a full outer shell: 8 electrons, except helium with 2. This course numbers the groups 1 to 7 and 0.
Potassium is 2,8,8,1, not 2,8,9: the third shell holds 8 before the fourth starts.

Photograph this card. Tomorrow, cover it and say each line first.

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Putting 9 in the third shell?

Shell capacities 2, 8, 8 apply to the first twenty elements, which is all this course asks for.