Bohr Models and Lewis Dot Diagrams Niels Bohr

Bohr Models and Lewis Dot Diagrams

Niels Bohr

Bohr Models… O Niels Bohr explained the structure of the atom in his “Bohr models”. His model of the atom resembles a solar system. He came up with this model in 1913. Here is a typical Bohr model, what can you figure out from it?

O Bohr models show the nucleus in the center with the # of Protons (p) and Neutrons (n) in it O Around the nucleus, it shows the electrons in shells or clouds O Each shell or cloud can only hold a certain # of electrons and then it is full. Draw this in your notebook. Identify the number of protons, neutrons and electrons. Protons: ___ Neutrons: ___ Electrons: ___

How many e- can each CLOUD hold? O 1 st cloud can hold 2 e. O 2 nd cloud can hold 8 e. O 3 rd cloud can hold 18 e. O 4 th cloud can hold 32 e. O 5 th cloud can hold 32 e. O 6 th cloud can hold 18 e. O 7 th cloud can hold 8 e-

How many do I need to know for the test? O 1 st cloud can hold 2 e. O 2 nd cloud can hold 8 e. O 3 rd cloud can hold 8 e. O You don’t need to know any higher orbits – you won’t be tested on higher elements. O You can depict any element in a Bohr model!

Which elements are these?

How do you know which atom? The number of protons determines the identify of the atom!!! Four protons is an atomic number of 4 which is Beryllium! 4 p+ 5 n 4 e-

So how do we draw a Bohr model of… say…Sodium? O Start with a nucleus, and put in how many protons and neutrons are in sodium (look at your periodic table) P: 11 N: 12 O Next place some orbits around it P: 11 N: 12

O Next figure out how many e- are in sodium (look at your periodic table). Place them in dots in the orbits Remember!! 2 max in 1 st orbit 8 max in 2 nd orbit 18 max in 3 rd orbit Sodium has 11 electrons !! they are the same as the protons P: 11 N: 12

Draw a Bohr Model for an Argon atom O How many neutrons and protons does it have? O How many electrons does it have?

With a partner draw a Bohr model of: Silicon Neon Magnesium

Valence Electrons 1. Valence electrons and stability O Which atoms did you draw which had its valence electron shell full? ____________ O Every element wants to have a full outer shell – because then it is ___________ and never has to react. O Every element wants to be like the _____________ because they have full valences and are stable!!

Secret way to tell how many Valence e- in each element… O Look at your periodic table O Locate the 1 vertical row, the 2 nd, then skip over to the 13 th, 14 th all the way to the 18 th. O The last digit of each vertical row number is the amount of valence electrons O Column 1 – all elements in that row have 1 valence e- ( 1 e- in the last shell), Column 2 – all elements in that row have 2 valence e-. O Column 13 - all elements in that row have 3 valence e- , so row 18 has a full valence e(except Helium which has a full outer orbit of 2 e-)

Lewis Dot Diagrams… O Gilbert Lewis used a different model than Bohr, and he only showed the valence e- in it. O His model is called the Lewis dot structure. He put dots around the symbols so that we can see just the valence electrons for the elements (so we can easily see which e- are going to react)

The red dots show you the VALENCE ELECTRONS in each element’s atoms

See the difference? ? . . . Lewis just shows the valence e P: 11 N: 12 Bohr model of Sodium Atom Na Lewis Structure of Sodium Atom

Lewis Dot Structures when two electrons are together we call them a lone pair, they won’t react and make an atomic bond The # of valence e- is … 8 8 e- is stable. when atoms have a full 8 valence orbit – we call it a stable octet

How to draw …

Try some … O Remember, up to 4 e-, you put separately on each side of the symbol, once you get to 5, you have to start pairing up. O 1) Magnesium Mg 3) Flourine F Bonding pair 2) Nitrogen N 4) Argon Ar Lone pair

Things to Kn. Ow… O Every element wants to have a full outer cloud– then they are stable – so… O if an element has it’s 1 st orbit full and stable – it will have 2 valence e. O if an element has it’s 2 nd , or 3 rd orbit full and stable – it will have 8 valence e- (we call that a Stable octet) O Everything wants to bind together to get a maximum of 8 valence e- shared between them – then they are stable!!

Lewis Dot Structures Draw the Lewis dot diagrams for the elements in the blank periodic table