Chapter 19 – Molecules and Compounds

1. Chapter 19 – Molecules and Compounds 19.1 -- Bonding and Molecules • Atoms react /combine with other atoms to form molecules. Chemical bonds hold them together. • Electrons in atoms are found in energy levels in the electron cloud. Outermost region contains the valence electrons and is the valence shell.

2. Maximum # of valence electrons that an atom can have is 8, except for the 1st energy level that can only hold 2 electrons. • Stable atoms have 8 valence electrons. • When an atom has 8 valence electrons, it is said to have an octet of electrons. • In order to reach 8 electrons, atoms will lose, gain, or share electrons.

3. Atoms with fewer that 4 valence electrons will lose electrons. • Atoms with more than 4 will gain electrons. • Valence electrons are often represented using dot diagrams.

4. Elements in Group 1 have 1 valence electrons • Elements in Group 2 have 2 valence electrons • Elements in Group 13 have 3 valence electrons • Elements in Group 14 have 4 valence electrons • Elements in Group 15 have 5 valence electrons • Elements in Group 16 have 6 valence electrons • Elements in Group 17 have 7 valence electrons • Elements in Group 18 have 8 valence electrons

5. MUST DRAW DOT DIAGRAMS IN RED BOX

6. Types of chemical bonds: Ionic and covalent • Ionic bonds are formed when atoms lose or gain electrons. • Covalent bonds are formed when atoms share electrons. Covalently bonded atoms of the same type are diatomic molecules. Ex: o2 http://facstaff.gpc.edu/~pgore/PhysicalScience/Naming-chemical-compounds.html

7. 19.2 – Chemical Formulas • When atoms combine, they form compounds. All compounds are neutral. • A compound made of ions is called an ionic compound. • A covalent compound is a compound that consists of covalently bonded atoms.

8. The periodic table shows the charge of the ions of the elements based on the group. • An oxidation number indicates how many electrons are lost, gained, or shared when bonding occurs.

9. http://mskathypearson.tripod.com/id3.html

10. To write a chemical formula: • Write the symbol of the positive ion with its charge • Write the symbol of the negative ion with its charge • Criss-Cross the charges of each and use the numbers as the subscript • MUST DRAW

11. Ions with more than one element are called polyatomic ions. • Ex: Carbonate = CO3

12. To name compounds: • Write the name of the first element • Write the root name of the second element • Replace the ending with –ide

13. To name a compound that contains polyatomic ions: • Write the name of the positive ion first • Write the name of the negative ion second.

14. Greek prefixes are used in naming binary covalent compounds. • Ex: CO = Carbon Monoxide • The simplest whole electrons number ratios by which elements combine are written is called the empirical formula. • The actual number of atoms of each element in the compound is written is called the molecular formula.