Electronic structure and the periodic table

Properties of the nucleus and electrons

How are electrons arranged? Electrons are not evenly spread but exist in layers called shells. The arrangement of electrons in these shells is often called the electron configuration. 1st shell 2nd shell 3rd shell

How many electrons per shell? Each shell has a maximum number of electrons that it can hold. Electrons will fill the shells nearest the nucleus first. 1st shell holds a maximum of 2 electrons 2nd shell holds a maximum of 8 electrons 3rd shell holds a maximum of 8 electrons

Calculating electron configurations

Summary: the atom so far The nucleus is: Dense – it contains nearly all the mass of the atom in a tiny space. Made up of protons and neutrons. Positively charged because of the protons. Electrons are: Thinly spread around the outside of the atom. Very small and light. Negatively charged. Found orbiting the nucleus in layers called shells. Able to be lost or gained in chemical reactions.

Which element am I?

I am made up of 7 electrons.

Answer: Nitrogen

I am made up of 12 electrons

Answer: Magnesium

I have 2 electrons in my first shell and 3 electrons in my second shell.

Answer: I am Boron

I have 2 electrons in my first shell, 8 in my second shell and 7 in my third shell.

Answer: I am Chlorine

I have two shells. In my second shell I have 6 electrons.

I am oxygen

I have 3 shells. In my outer shell I have 3 electrons.

Answer: I am Aluminium

Electron shells Electrons are arranged in shells around an atom’s nucleus. Each shell has a maximum number of electrons that it can hold. Electrons will fill the shells nearest the nucleus first. 2nd shell holds a maximum of 8 electrons 1st shell holds a maximum of 2 electrons 3rd shell holds a maximum of 8 electrons This electron arrangement is written as 2,8,8

What’s the electron arrangement?