Chapter 6. Chemical Compounds

Transcription

1 Chapter 6 Chemical Compounds

2 Chemical Formula: Shows what is found in a molecular compound: Types of atoms Numbers of atoms

3 Chemical Formula: Monatomic elements are represented by their atomic symbols Example: Helium is represented by He

4 Chemical Formula: If more than one atom is present, the number of atoms is represented with a subscript Example: Diatomic form of Oxygen = O 2

5 Diatomic Molecules: Hydrogen H 2 Chlorine Cl 2 Fluorine F 2 Bromine Br 2 Oxygen O 2 Iodine I 2 Nitrogen N 2

6 Molecular Formula Shows the type of molecules and numbers present in a molecule of a compound Example: Molecular formula of water- H 2 O Notice there is no need for a subscript next to oxygen

7 Molecular Formula: The molecular formula for ethane is C 2 H 6 This formula tells us that ethane contains two carbon molecules, each of which has three hydrogens

8 Molecular Formula: Tells us the composition of a molecule Does not tell us about the structure of the molecule (does not show the arrangement of the atoms)

9 Molecular models: There are a variety of models that describe the arrangement of molecules: NH 3

10 Formula Unit: Used to represent an ionic compound Is the lowest whole number ratio in the compound

11 Formula Unit: Table Salt = NaCl Lowest whole number ratio = 1:1 One sodium to each chloride

12 Formula Unit There is no such thing as a molecule of sodium chloride Ionic compounds exist as a collection of positively and negatively charged ions arranged in repeating 3-D patterns

13 Law of definite proportions: In samples of any chemical compound, the masses of the elements are always in the same proportions

14 Example: Magnesium Sulfide: 100g sample: breaks down to 43.13g of magnesium and 56.87g of sulfur Ratio: 43.13/56.87 =.7584:1 (Mg:S) This proportion remains the same no matter how many grams of MgS you have

15 Chemical Bonding An electrostatic force of attraction between two atoms, ions, or molecules Opposite charges attract and like charges repel.

16 Chemical Bonding Atoms within the same group of the periodic table have the same number of valence electrons. Valence electrons determine the chemical properties of an element

17 Valence Electrons Valence electrons: are the electrons in the highest occupied energy level of an element s atoms.

18 Valence electrons How do you determine the number of valence electrons? The group number The electron configuration diagram

19 Valence electrons Valence electrons are usually the only electrons used in chemical bonds.

20 Octet Rule In forming compounds, atoms tend to achieve the electron configuration of a noble gas.

21 Octet Rule An octet is eight. Noble gases (except for He) have eight electrons in their highest energy level (ns 2 np 6 )

22 Why do Atoms Bond? Octet Rule: Atoms will lose, gain, or share electrons to achieve a stable octet. Stable Octet: 8 valence electrons or a noble gas configuration.

23 Valence electrons Electron dot structures are used to show the valence electrons. They are diagrams that show valence electrons as dots.

24 Electron Dot Structures Diagrams that show valence electrons as dots.

25 Electron Dot Structures H Ca Al C N O Cl Ar

26 Chapter 6.5 Molecular compounds

27 Binary molecular compounds: Composed of two non- metallic elements Ionic charges are not used to assign formulas or names

28 Binary molecular compounds: When two non- metallic elements combine, they can often combine in more than one way Example: Carbon and Oxygen

29 Binary molecular compounds: Two molecular compounds composed of only carbon and oxygen: Carbon dioxide CO 2 Carbon monoxide CO

30 Binary molecular compounds: Prefixes- tell how many atoms of each element are present in each molecule

31 Binary molecular compounds: PREFIX NUMBER MONO 1 DI 2 TRI 3 TETRA 4 PENTA 5 HEXA 6 HEPTA 7 OCTA 8 NONA 9 DECA 10

32 Binary molecular compounds: Carbon Monoxide prefix: mono = one Carbon Dioxide: prefix: di = two

33 Rules for writing molecular compounds: 1. Use the prefix to tell you the subscript of each element in the formula 2. Write the correct symbols for the two elements, with the appropriate subscripts

34 Example: Tetraiodine nonoxide tetra = four, so I 4 non or nona = nine, so O 9 Formula: I 4 O 9

35 Examples: Write the following molecular formulas: sulfur trioxide phosphorus pentafluoride

36 Examples: Answers: SO 3 PF 5