The Bohr Model & The Lewis Structure

1. The Bohr Model & The Lewis Structure

2. Remember Bohr? • Niels Bohr ( 1885 - 1962 ) – a Danish scientist • Studied at Cambridge • Worked in the Professor Rutherford’s lab • Published 115 times • Escaped the Nazi’s when they occupied Denmark • Won Nobel Prize in Physics in 1922 • Explained that colors make up a line spectrum

3. The Bohr Model • First, there are some errors in the Bohr Model • The model is simpler and relatively easy to understand • Shows that the electrons in atoms are in orbits of differing energy around the nucleus • Uses the term energy levels (or shells) to describe the orbits of differing energy • The higher the energy-level number, the farther away the electron is from the nucleus – the higher the energy

4. The Shell Count… Maximum # of Electrons Shell Number 1 2 2 8 3 18 4 32

5. Let’s Make a Bohr Model Take the element Nitrogen N The symbol is? The Atomic Number is? Which means the number of Protons and Electrons are? 7 7 Draw a circle for the Nucleus and identify how many protons Draw a circle to represent the second shell and place a max of eight electrons 7P 7P 7P Draw a circle to represent the first shell and place max of two electrons

6. Let’s Make a Bohr Model Take the element Neon Ne The symbol is? The Atomic Number is? Which means the number of Protons and Electrons are? 10 10 10P 10P 10P

7. Let’s Bring it All Together! 6 Tell me what group Oxygen is in? 2 Tell me what period Oxygen is in? 8 How many protons does Oxygen have? 8P 8P 8P

8. Do you see the trick? 6 Tell me what group Oxygen is in? 2 Tell me what period Oxygen is in? 8 How many protons does Oxygen have? What period? Does it match the number of shells? 8P What group? Does it match the number electrons in the outer shell?

9. Now you try… Take the element Carbon and draw the Bohr Model. Now check yourself… what period is Carbon? what group is Carbon? Do they match the number of shells and the number of electrons in the outer shell ?

10. Now you try… Take the element Calcium and draw the Bohr Model. Now check yourself… what period is Calcium? what group is Calcium? Do they match the number of shells and the number of electrons in the outer shell ?

11. Who is Gilbert Lewis? • Gilbert Newton Lewis (1875 – 1946) • Died in his laboratory in the University of California Berkeley at age 70 • Introduced the Lewis Dot Structure • Postulated the electron pair relationship of acids and bases known as the Lewis Theory • Set the standard for Chemical Thermodynamics • First to produce deuterium and isolated naturally occurring heavy water

12. What is the Lewis Dot Structure? • It depicts paired and unpaired valence electrons (those electrons in the outer shell) • Also called the electron-dot diagrams • Represents the covalent bonding of a molecule (or ion) • Covalent bonds are chemical bonding formed by the sharing of electrons in the outer most shell • The atoms in a Lewis Structure tend to share electrons so that each atom has eight electrons (the octet rule – that states an atom in a molecule will be stable or “happy” when there are eight electrons in the outer shell) • Lewis Structure displays the electrons of shells because these are the ones that participate in making chemical bonds

13. Lewis Structures • Write the element symbol. • Carbon is in the 4th group, so it has 4 valence electrons. • Starting at the right, draw 4 electrons, or dots, counter-clockwise around the element symbol. C

14. Lewis Structures • Check your work. • Using your periodic table, check that Carbon is in the 4th group. • You should have 4 total electrons, or dots, drawn in for Carbon. C

15. Now try yourself… K Mg Al Si P S Cl Ne