6-1 Notes Chemical Bonds and Compounds

Compounds have different properties from the elements that make them. O xygen and H ydrogen are both colorless, odorless gases until they combine to make WATER!!!! *** Think about the 26 letters in the alphabet that make thousands of words! Compound- substance made of two or more different elements. The atoms within the compounds are held together by chemical bonds. Bonds help determine the properties of a compound and how the atoms are arranged.

Uses chemical symbols to represent atoms of the elements and their ratios in a chemical compound. How to Write Chemical Formulas: 1.Find the symbols for the element on the periodic table and write them side by side. 2.Determine the valence (outer shell) electrons for each element (Lewis Dot). 3.Determine what ratio of each element is necessary to have a complete outer shell of 8 valence electrons for both elements. 4.Write the formula using subscripts to show the ratio.

Example: carbon dioxide 1.CO 2.C- 4 valence electrons O- 6 valence electrons 3. Since carbon has 4 and oxygen needs to 2 more to make 8, carbon will be left with 2 when one oxygen combines. One more oxygen can also bond with the two remaining electrons in carbon and make CO 2

1. calcium chloride 2. magnesium oxide 3. sodium chloride 4. aluminum oxide 5. magnesium chloride

6.2 Covalent Bonding 1

Non metals tend to have high ionization numbers. Prevents a transfer of electrons In order to bond, they have to SHARE electrons! 2

Sharing Electrons A covalent bond is a chemical bond in which two atoms SHARE a pair of valence electrons 3

Molecules of Elements A molecule is a neutral group of atoms that are joined together by one or more covalent bonds. The attraction between the shared electrons and the protons in each nucleus holds the atoms together in a covalent bond. 4

Nonpolar Covalent Bonds Occur between atoms with similar electronegativities Bonds where electrons spend roughly equal time with both atoms 5

Polar Covalent Bonds Occur between atoms with different electronegativities Electrons spend more time with the atom with higher electronegativity 6

6.3 Metallic Bonding

A metallic bond is the attraction between a metal cation and the shared electrons that surround it.

Metallic Bonding Metal atoms achieve stable configurations by losing electrons. The valence electrons are free to move among the atoms. In affect the metal atoms become cations surrounded by a pool or shared electrons.

The cations in a metal form a lattice that is held in place by strong metallic bonds between the cations and the surrounding valence electrons

Metallic Bonds in some metals are stronger than others. The more valence electrons the stronger the bond will be.

Periodic Trend Alkali metals only have one valence electron – This makes the bonds weak. Sodium for example has a low melting point and can be cut by a knife.

Transition metals have more valence electrons – Therefore harder – Higher melting point – Example- Tungsten used in light bulbs

Explaining Properties of Metals The mobility of electrons within a metal lattice explains some of the properties of metals. – Electric currents are carried by the free flow of loose electrons in the metal – Metal ions shift position to keep metals from breaking when struck with a hammer.

– Electric currents are carried by the free flow of loose electrons in the metal – Metal ions shift position to keep metals from breaking when struck with a hammer. – Metals can be drawn into thin wires without breaking