Electronic Structure Noadswood Science, 2016

Monday, May 21, 2018 Electronic Structure To be able to represent the electron structure of atoms

Precise Learning The electrons in an atom occupy the lowest available energy levels (innermost available shells). The electronic structure of an atom can be represented by numbers or by a diagram. For example, the electronic structure of sodium is 2,8,1 or showing two electrons in the lowest energy level, eight in the second energy level and one in the third energy level (students should be able to represent the electronic structures of the first twenty elements of the periodic table in both forms) Students may answer questions in terms of either energy levels or shells.

Nucleus containing protons and neutrons Atomic Structure Atoms consist of a nucleus (containing protons and neutrons) which are orbited by electrons, within specific shells… Electrons Nucleus containing protons and neutrons

Electron Shells Electrons which orbit the nucleus of an atom occupy specific shells – the follow some specific rules: - Electrons always occupy shells (energy levels) The lowest energy levels are always filled up first Only a certain number of electrons are allowed in each shell (1st shell = 2; 2nd shell = 8; 3rd shell = 8) In most atoms the outer shell is not full, making them want to react

Electron Shells Electrons of an atom are arranged in shells… x x x x x The first shell only has 2 electrons at most The next two shells can contain up to 8 electrons in each x x x x x x x x x x x x The number of electrons in the outer shell affects the properties of the atom (i.e. it’s reactivity) x x Each shell must be filled up before electrons can be added to the next shell x x

Electron Shells – Potassium (K) 39 K x x x 19 19 protons 20 neutrons 19 electrons x x x Potassium (K) has 19 electrons – these are arranged as follows… 1st shell = 2 2nd shell = 8 3rd shell = 8 4th shell = 1 x x x x x x x x x x x x x

Electron Shells – Potassium (K) Potassium has 1 outer electron (found in group I) – meaning it is very reactive!

H B O Na Cl Ca Electron Shells Using the information note the number of protons, neutrons and electrons of the following elements, and draw their electron shell structures… 1 H 11 B 16 O 1 5 8 23 Na 35 Cl 40 Ca 11 17 20

H Electron Structure – 1 Hydrogen: - 1 1 1 proton 0 neutrons x 1 H 1

B Electron Structure – 2,3 Boron: - 11 5 5 protons 6 neutrons x x x x x 11 B 5

O Electron Structure – 2,6 Oxygen: - 16 8 8 protons 8 neutrons

Na Electron Structure – 2,8,1 Sodium: - 23 11 11 protons 12 neutrons x x x x x x x x 23 Na x x x 11

Cl Electron Structure – 2,8,7 Chlorine: - 35 17 17 protons 18 neutrons x x x x x x x x x x x x x 35 Cl x x x x 17

Ca Electron Structure – 2,8,8,2 Calcium: - 40 20 x 20 protons 20 neutrons 20 electrons x x x x x x x x x x x x x x x 40 Ca x x x x 20 x

Electrons Underlying Chemistry Electrons occupying shells around the nucleus is the ‘cause’ of all underlying chemistry When elements react their atoms join with other atoms forming compounds – this involves giving, taking, and sharing of electrons What link is there between the electron structure and the elements position within the periodic table?

Electron Structure There is a link between an atom's electronic structure and its position in the periodic table – an atom's electronic structure can be worked out from its place in the periodic table…

Electron Structure Atoms in group I have 1 electron in the out shell Atoms in group II have 2 electrons in the outer shell Atoms in group III have 3 electrons in the outer shell etc… Atoms in group VIII have a full outer shell

Building A Nucleus

Electron Structure

Remember Electrons are arranged in different shells around the nucleus The innermost shell - or lowest energy level - is filled first Each succeeding shell can only hold a certain number of electrons before it becomes full - the innermost shell can hold a maximum of two electrons, the second shell a maximum of eight, and so on... Energy Level (Shell) Maximum No. Electrons First 2 Second 8 Third Fourth 18

Lithium For example, work out the atomic structure of Lithium...

Lithium Lithium - 2nd period so it has 2 circles drawn around it and in group 1 so it has 1 electrons in the outer shell...

Lithium Lithium (Li) - 2,1 (three electrons (2 in shell 1 and 1 in shell 2))

Summary Electrons which orbit the nucleus of an atom occupy specific shells – the follow some specific rules: - Electrons always occupy shells (energy levels) The lowest energy levels are always filled up first Only a certain number of electrons are allowed in each shell (1st shell = 2; 2nd shell = 8; 3rd shell = 8; 4th shell = 18) In most atoms the outer shell is not full, making them want to react

Atomic Structure Anagrams

Practice Questions What is another name for an electron shell? What is the maximum number of electrons that can go in the first electron shell? What is the maximum number of electrons that can go in the second electron shell? What is the maximum number of electrons that can go in the third electron shell? Which shell fills with electrons first?

Answers An energy level 2 electrons 8 electrons The one closest to the nucleus (lowest energy level)