Valance Electrons

Unit 2 Chemistry

Valence Electrons

Valence electrons are the electrons in the outer energy level of an atom.

These are the electrons that are transferred or shared when atoms bond together.

What does it mean to be reactive?

We will be describing elements according to their reactivity.

Elements that are reactive bond easily with other elements to make compounds.

Some elements are only found in nature bonded with other elements.

What makes an element reactive? An incomplete valence electron level. All atoms (except H and He) want to have 8 electrons

in their very outermost energy level (This is called the octet rule.)

Atoms bond until this level is complete. Atoms with less than 4 valence electrons lose them during bonding. Atoms with 6, 7, or 8 valence electrons gain electrons during bonding.

Elements that have either gained or lost electrons are called ions.

Positively charged: Cations Any atom that loses electrons to form

compounds are called cations. Cations have a positive charge.

Naming cations: Use the element name followed by the word “ion”.

Cation formula systematic name common name

Fe2+ iron(II) ion ferrous ion  

Fe3+ iron(III) ion ferric ion  

Cu1+ copper(I) ion cuprous ion  

Cu2+ copper(II) ion cupric ion  

Hg1+ mercury(I) ion mercurous ion

 

Hg2+ mercury(II) ion mercuric ion  

Pb2+ lead(II) ion plumbous ion

 

Pb4+ lead(IV) ion plumbic ion  

Sn2+ tin(II) ion stannous ion  

Sn4+ tin(IV) ion stannic ion  

 

Table: Metal cations with more than one common charged form

Elements that have either gained or lost electrons are called ions.

Negatively charged: Anions Atoms that gain electrons to form

compounds are called anions. Anions have a negative charge.

Naming Anions: Drop the last few letters of the element name and add “ide”.

Electron Orbitals

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Bohr’s Model of the Atom

Slide 9 Fig. 10-6, p. 269

Electrons orbit the nucleus at a fixed distance.

Each orbit is associated with a definite energy level.

Bohr Model

Energy levels are quantized

Electrons travel in orbits around the nucleus

The farther the electron is from the nucleus the more energy it has.

Bohr Diagrams

These are simple diagrams that show the number of electrons in each orbital of an element.

The symbol of the element is placed in the nucleus, and electrons are then placed in each orbital.

Let’s do a couple of examples.- Si, N

These diagrams are a combination of a Bohr Diagram and a Rutherford Diagram.

The main difference between this diagram and the Bohr diagram is the inclusion of the # of protons and # of neutrons in the nucleus.

Bohr-Rutherford Diagrams

How To Draw Bohr-Rutherford Diagrams:

Draw the nucleus as a solid circle. Put the number of protons (atomic number)

in the nucleus with the number of neutrons (atomic mass – atomic number) under it.

Place the number of electrons (same as protons) in orbits around the nucleus by drawing circles around the nucleus.

Remember, 1st shell – 2 electrons, 2nd shell – 8 electrons, 3rd shell – 8 electrons, 4th shell – 18 electrons.

How To Draw Bohr-Rutherford Diagrams:

Assignment

Which Atom is Which Intro. to chemistry