CHEMICAL BONDING What is it? Mod.H U.3 L.3

Identify the elements in these compounds Identify the elements in these compounds. Predict whether the elements are similar to each other. Why? C6H12O6 C2H5OH C6H8O6 C6H8O7

Carbon, hydrogen, oxygen. They are similar C6H12O6 (glucose - a sugar) C2H5OH (ethyl alcohol – an alcohol) C6H8O6 (vitamin C – found in citrus fruits) C6H8O7 (citric acid - found in citrus fruits)

Chemical Bonding is: The joining of atoms, or The re-arrangement of atoms - to form new substances

Examples: A silver spoon tarnishes. The silver reacts with sulfur in the air to make silver sulfide, or tarnish. 2 Ag + S Ag2S

An iron bar rusts. The iron reacts with oxygen in the air to make rust An iron bar rusts. The iron reacts with oxygen in the air to make rust. 4 Fe + 3 O2 2 Fe2O3

Methane combines with oxygen in the air to make carbon dioxide and water vapor. CH4 + 2O2 CO2 + 2 H2O

An antacid (calcium hydroxide) neutralizes stomach acid (hydrochloric acid): Ca(OH)2 + 2HCl CaCl2 + 2H2O

Sugar breaks down when fermented to give: C6H12O62 C2H5OH + 2 CO2 (glucose) (ethyl alcohol)

Carbon burns in air(oxygen) to give carbon dioxide C + O2 CO2

Chemical Bonds The force of attraction that holds atoms together (electromagnetic / electrostatic)

How are bonds formed? Bonds are formed by the outer shell or valence electrons of an atom. * Review Lewis models of atoms!

For sodium? (Na) For calcium? (Ca) For chlorine? (Cl) For Carbon? (C) What are the valences? For sodium? (Na) For calcium? (Ca) For chlorine? (Cl) For Carbon? (C)

Valences for transition metals Either 1, 2 or both, sometimes 3! Iron Fe shows all 3 valences! Fe(I), Fe(II), & Fe (III)

Valences for nonmetals Subtract 10 from the group number (in your book / P. table) C = 14-10=4 O = ? Cl = ? N = ?

The Octet Rule Atoms will form bonds with other atoms to get a full outer shell (8). Is most stable Noble gases already have 8! So are unreactive or inert.

H and Li need only 2 valence electrons to complete the k-shell Exceptions! H and Li need only 2 valence electrons to complete the k-shell (also He?)

Organizing electrons When bonding, atoms will attain the stable octet state by either: Losing (an) electron(s) Gaining (an) electron(s), or Sharing electrons

The farther away from the nucleus an electron is, the more energy it has, and the less strongly it is pulled to the nucleus. So, it’s easier to lose it !

So….. How are bonds formed?

1. Atoms Lose an electron: form positive ion - cation

2. Gain an electron – form a negative ion - anion

Na+Cl- crystal structure (cubic)

3. Share electrons

HOMEWORK! QUIZ!!

Physical Sc Ch 13 http://www.visionlearning.com/library/module_viewer.php?mid=55 http://www.nyu.edu/pages/mathmol/textbook/bonding.html http://www.nyu.edu/pages/mathmol/textbook/middle_home.html

Section 13-2 Types of Chemical Bonds Copy and View this very important link at home! http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/atomic/