Molecules and Compounds Compounds Display Constant Composition
Compounds and Molecules
description
Transcript of Compounds and Molecules
Compounds and Molecules
4.1vid
What are compounds?
Two or more elements chemically combined to form new substances.
What are compounds?
Chemical Bonds – the attractive forces that hold different atoms or ions together
Bonds distinguish compounds from mixtures.
Chemical FormulaC12H22O11 can only be sugar
H20 can only be water
Parts to the Formulas
2H2O
Coefficient Subscript
Parts to the Formulas
Coefficient – gives the amount of molecules or moles
Subscript – tells the number of atoms or ions
Chemical StructureBond length
-the distance between two bonded atoms
Bond angle-the angle formed between two bonded atoms
Models of compounds
Ball and stick model-atoms are represented balls, bonds are represented by sticks.
O
H H
Bond length
Bond Angle
Models of compounds
Structural formulas-chemical symbols represent the atoms.
H HO
Models of compounds
Space-filling-show the space occupied by each atom represented in the compound. Hydrogen
Oxygen
Structure of Compounds Network Structures = strong solids
Molecules= weak solids, liquids, or gases
Ionic and Covalent Bonding
4.2
fun
Why Bond?Atoms bond so they can become stable!
They want to achieve a full outer energy level
They want 8 electrons.
1. Ionic bond
A bond formed by the attraction between oppositely charge ions.
The joining of a positive metal ion and a negative nonmetal ionNa+ + Cl- NaCl
Ionic bond Formed by transferring electrons
Now each ion will have 8 valence electrons
Na+ + Cl- NaCl
Ionic bond PropertiesThey form network structureshigh melting pointsGood conductors of electricity when dissolved or melted because of their ions
Metallic bond
Formed by the attraction between positively charged metal ions and the electrons around them.
Metallic bond
Held together by free flowing electrons
Hold metallic elements together
Covalent Bonds
Formed when atoms share one or more valence electrons
Formed between non-metals
May form single, double, or triple bonds
Covalent Properties
They are poor conductors of electricity (no ions)
Low melting points.form molecules
Polyatomic ion An ion made of two or more atoms
that are covalently bonded and that act like a single ion.
A molecule with a charge Examples: carbonate (CO3)-2
Nitrate (NO3)-1
Fun
Compound Names and Formulas
4.3
REMEMBER!!!!!!!! If it starts with metal it is an ionic
compound If it starts with a nonmetal it is a covalent
compound If the formula contains a parentheses
(polyatomic ion) it contains both ionic and covalent bonds
If it is just a metal it is metallic
Writing Ionic FormulasCalcium Fluoride Step 1 - Look up both positive and negative ions
Ca2+ F-1
Writing Ionic CompoundsStep 2Criss-cross numbers down, making subscripts
Ca2+ F-1
Ca1 F2
Writing Ionic Compounds
Step 3Combine your new compound.
Ca1 + F2 Ca1F2
Polyatomic ion
Al+3 (CO3)-2
Al2 (CO3)3
Al2(CO3)3
Aluminum Carbonate
Naming Ionic Compounds
Step one – Name the first ion in the formulaEx. CaCl2 – calcium
Na2(SO4) - sodium
Naming Ionic Compounds
Step two – Name the second ion Ex. CaCl2 –Calcium Chloride Na2(SO4)-sodium sulfate
PROBLEMEx. Fe2O3 and FeO are different compounds from different ions
Fe3+ O2- = Fe2O3
Fe2+ O2- = FeO
Solution-Roman Numerals
Same naming schemeAdd a Roman Numeral to
identify the charge of the metal ion.
Solution-Roman Numerals Fe2O3 = iron(III)Oxide
FeO = iron(II)OxideRemember!!!
R.N. is the charge, not the subscript of the metal.
Naming Covalent Compounds
Mono – 1 Di - 2 Tri - 3 Tetra - 4 Penta - 5
Hexa – 6Hepta - 7Octa - 8Nona - 9Deca - 10
Naming Covalent Compounds
Step 1Identify the number of atoms in the first elementEx. H2O two H atoms
Naming Covalent Compounds
Step 2Identify the number of atoms in the 2nd element.
Ex. H2O one O atom
Naming Covalent Compounds
Step 3Name the compound with the appropriate prefixes. Ex. H2O
dihydrogen monoxygen
Naming Covalent Compounds
Step 4 add an -ide ending to the second element
Ex. Dihydrogen monoxide
Empirical FormulaThe simplest chemical formula
of a compound.Different covalent compounds
can have same empirical formula
Ch. 4.4