6.1 How Compounds Form (pg 210) Compounds: a pure substance made up of 2 or more elements that are chemically combined. Ex: H 2 O made of the elements.

6.1 How Compounds Form (pg 210)

• Compounds: a pure substance made up of 2 or more elements that are chemically combined.

• Ex: H2O made of the elements hydrogen and oxygen

• There are 2 types of compounds: ionic and molecular compounds.

Ionic compounds:• form when metallic and non-metallic elements combine

chemically.• pure substance• have high melting points (ex, NaCl’s melting point is 800oC)• form crystals, which are very regular arrangements of

particles• dissolve in water to form solutions that conduct electricity• solids at room temperature

Ionic compounds, con’t• While combining, each atom changes into an ion. Ions form

when one or more electrons move from a metal atom over to a non-metal atom.

• Ex: NaCl

• sodium atom loses an electron by giving it to a chlorine atom• produces a positive sodium ion and a negative chlorine ion• positive and negative ions attract each other, called an ionic

bond

Molecular compounds:• form when non-metallic elements combine chemically• pure substance• atoms share electrons to form molecules• can be solid, liquid or gas at room temperature• usually good insulators but poor conductors of electricity• have relatively low boiling points

6.2 Names and Formulas of Compounds

• Every compound has a chemical name and formula.

• The chemical formula identifies which elements, and how much of each, are in a compound.

• Ex, sodium chloride’s formula is NaCl.

Ion Charges

• Each of the elements that commonly form ionic compounds has an entry in the periodic table showing what ion charge it can have.

Ion Charges, con’t

• The ion notation contains the symbol for the element and a superscript number and + or – sign at the top right.

• Ex, lithium ion, Li 1+

Ion Charges, con’t

• The name of non-metal ions is formed by taking the element name and changing the ending so that it includes the suffix “_ide”.

• Ex, the ion O2- is called oxide.

Naming Simple Ionic Compounds

• Name the metal ion first, keeping the element name.

• Name the non-metal ion second, changing the ending to “_ide”

• Ex, NaCl, sodium chloride.

Writing Formulas for Simple Ionic Compounds

• Identify the ions and their charges in the compound name.

• Ex magnesium chloride; Mg2+ Cl1-

• Determine the number of each ion needed to balance the charges.

• Note the ratio of positive to negative ions, and write the formula, MgCl2

• Reduce, if necessary, Mg2+ O2- MgO

MOLECULAR COMPOUNDS

• Ionic compounds can only bond to non-metals in so many ways. Ex for every Ca we can only bond 2 F to it. Molecular compounds do not work that way. Molecular compounds can have various numbers of atoms bonded together to create various molecules.

• Ex. NO, NO2, N2O2, etc.

Naming Molecular Compounds

• For naming molecular compounds of 2 elements, Greek prefixes are used to indicate how many atoms of each element are present in a compound.

Number of Atoms

Prefix

1 mono

2 di

3 tri

4 tetra

5 penta

6 hexa

7 hepta

8 octa

9 nona

10 deca

Naming Molecular Comp, con’t

• Examine the formula; 2 non-metals• Name the first element using the prefix.

(prefix mono is not used for the first atom)• Name the second element using the prefix

and ending with _ide. (monooxide, drop the o, tetraoxide, drop the a)

• Ex. N2O, dinitrogen monoxide• Practice page 226 #1-5

Writing Formulas for Molecular Compounds

• Working backwards is easier, using the prefix to indicate the number of atoms of each type of element.

Writing Formulas for Molecular Compounds; con’t

• Identify the first element, write symbol

• Identify the second element, write symbol

• Write subscripts using the prefix (if no prefix is given for the first element, there is one atom).

• Ex. Carbon tetrachloride; CCl4

• Practice Pg 227 #1-5

6.3 Hazards and Benefits of Compounds

Elements and Compounds in the Environment:

• Some chemicals are safe to handle but can cause long-term environmental damage.

• Other chemicals are toxic, even in tiny amounts, although the effects of exposure can take years to become apparent.

Mercury

• An element that is present in the environment naturally; at low levels

• High concentrations cause mercury poisoning, which effects the nervous system and muscles, reproductive problems and birth defects

Mercury, con’t

• Burning coal for energy increase mercury levels in the environment

• Falls to the ground with precipitation and contaminates the water

• Bacteria in the water changes mercury into methylmercury; even more toxic substance

• Animals that eat other animals have the highest conc. of mercury in their bodies

• Until the 1980s, paper mills used chlorine beach to make white paper

• Mercury was used to make chlorine and the disposal was not careful; large amounts of mercury leaked into the environment

• Tonnes of mercury were released into the water system each year, contaminating the environment and slowly poisoning the people

• Mercury lasts a long time in the environment

Mercury, con’t

• Studies are ongoing on the health effects on local people affected by mercury spills

• Science has an important role to play in our society

• Science can be used to assess the impact of technologies on society and the environment

• Science helps to monitor ongoing practices and to improve methods of handling matter

Mercury, Science and Society

Other Chemicals and the environment, page 234

• CFCs effect on the ozone layer

• Benzene, a regulated substance

• Homework: pg 236 #1-5

Compounds in the Environment Assignment

• Topics to discuss:

• Introduce compound (background info)

• How is it being released into the environment?

• Effects on human health and environment

• What are we (government) doing to stop/reduce its release?