Chemical Bonds Why atoms combine

Objectives Describes how a compound differs from the elements that compose it Explain what a chemical formula represents and how to analyze chemical formulas State a reason why chemical bonding occurs

Introduction Most matter in form of compounds or mixture of compounds Some matter uncombined Compounds have properties different from their constituent elements

Formulas Chemical shorthand Symbol for element with subscript to tell how many atoms of each element are present in formula Parenthesis used to show groups of atom ing.htm ing.htm

Why do atoms combine? Chemically stable- atoms whose outer energy level is completely filled with electrons Achieve noble gas e- configuration Atoms gain, lose, or share e-

Octet Rule Atoms tend to combine in a way that results in them attaining the stable outer electron configuration of the noble gases. For most atoms this means 8 outer electrons

Drawing Bohr Models for Elements 1-20 Draw a circle and write the number of protons inside (neutrons may be included) Draw concentric circles around the nucleus: 1 st energy level max 2 e- 2 nd energy level max 8 e- 3 rd energy level max 8 e-* 4 th energy level max 2 e-* * Maximum for elements astr.gsu.edu/hbase/pertab/p erlewis.html#c2 astr.gsu.edu/hbase/pertab/p erlewis.html#c2 What element is represented below?

Lewis Dot Diagrams Symbol for the element surrounded by the atom’s outer (“s and p”) electrons /lessons/lesson38.htm /lessons/lesson38.htm

Chemical bond Force of attraction resulting from the transfer or sharing of electrons between atoms

Diatomic elements Elements that are found in pairs in their “free” or uncombined state ns/DiatomicList.html ns/DiatomicList.html

Questions What happens to properties of elements when they form compounds? Write the formulas for (a) a compound w/1 calcium and two fluorine atoms (b) a compound with 2 aluminum and 3 sulfur atoms Why do most elements tend to form compounds? The label on the box of washing soda states that it contains sodium carbonate (formula to be given in class) Name the elements present and in which ratio they are present.

To which group does the yellow character belong? ges/sodium.jpeg ges/sodium.jpeg

Sources ochemistry.htm ochemistry.htm