Chemical Bonding How it all comes together!

Transcription

1 Chemical Bonding How it all comes together! Ionic Bonding Atoms like to become ions with noble gas electron configuration Ionic bonding is when ions of opposite charge are attracted to each other Electrons are TRANSFERRED between atoms There can be no extra or unused electrons Introductory Examples Lithium has 1 valence electrons It wants to get rid of this electron to get to a more stable energy state Fluorine has 7 valence electrons It wants to fill this empty spot with an electron to get to a more stable energy state Lithium and fluorine make a perfect pair If they meet, the electron lithium wants to get rid of will fill the spot fluorine wants to fill Together, they will be LiF-lithium fluoride 1

2 Not Always 1:1 Say we have calcium (wants to get rid of 2 electrons) and fluorine (wants to get one more electron Calcium will give one of its electrons to one fluorine atom and the other electron to another fluorine atom This compound is CaF 2 because one calcium atom can complete 2 fluorine atoms Essentially, we are looking for the lowest common multiple of each charge Criss-cross Method Once we understand why elements form compounds in specific ratios, we can look at shorter ways of determining the ratios Ionic compounds are always between a metal and a non-metal The metal comes first in naming and in the formula Write the symbol for the metal with its charge in superscript (ignore the sign) Write the symbol for the non-metal with its charge in superscript (ignore the sign) Switch the numbers and make them subscripts Reduce to lowest terms, if applicable Naming Ionic Compounds When naming BASIC ionic compounds: Write the metal first (don t change its name!) Write the non-metal second BUT CHANGE its ending to IDE Examples: sodium + chlorine yields sodium chloride calcium + oxygen yields calcium oxide ***it is incredibly important that you end these compounds in IDE*** 2

3 Multi-Valent Ionic Compounds Some elements have more than one energy state that is stable We call these multi-valent elements They can take on more than one charge in ion form To communicate which ion we are using, we need to include it in the name To do so, we use ROMAN NUMERALS Multi-Valent Ionic Compounds Iron is stable with a charge of +3 OR +2 Each ion forms a very different compound so it is important that we communicate which one we are dealing with If iron (III) combines with oxygen, we call it iron III oxide (Fe 2 O 3 ) If iron (II) combines with oxygen, we call it iron II oxide (FeO) Note how the roman number only communicate the CHARGE ON IRON and NOT the quantity of iron ions involved. Polyatomic Ions Polyatomic Ions are exactly what the name states: ions that have multiple atoms making them up Common examples are: nitrate (NO 3- ), phosphite (PO 3 3- ) and ammonium (NH 4+ ) These polyatomic ions are always together as a unit, they change in the same ratio If we have 2 (PO 3 3- ), it would be (PO 3 3- ) 2 I recommend ALWAYS WRITING BRACKETS around polyatomic ions before writing any formulae!!! 3

4 Polyatomic Ions and Bonding Examples Calcium and cyanide: Ca +2 (CN) -1 Criss-cross OUTSIDE of brackets Ca(CN) 2 Aluminum and carbonate: Al 3+ (CO 3) 2- Criss-cross OUTSIDE of brackets Al 2(CO 3) 3 Combos All individual rules apply when coming special cases If you have a multivalent metal combining with a polyatomic negative ion, you need to include the roman numeral and maintain the polyatomic ion by using brackets Covalent Bonding (after worksheet) Covalent bonding is much stronger than ionic bonding In covalent bonding, the atoms SHARE their electrons instead of transferring them Depending on the atom, they can share 1, 2, 3, or even 4 of their electrons! There are more complex examples that go beyond our curriculum** The electrons essentially split their time between atoms, making each atom believe it has a complete valence shell We have looked at this with Bohr diagrams, but Lewis diagram are much more easily utilized 4

5 Covalent Bonding Chlorine in its diatomic form Cl 2 (draw on board) Each chlorine has one spot to fill, they will share one of their electrons with the other Shared electrons are designated with a line Shared electrons Example: carbon tetrachloride CCl 4 1 Carbon, 4 Chlorine (draw) Covalent Bonding (double bonds) There are cases when atoms with share more than one electron Carbon dioxide CO 2 (draw) When 2 electrons are shared from between 2 atoms, two lines are used (double bond) When 3 electrons are shared between 2 atoms, 3 lines are used (triple bond) 5

6 Naming When naming covalent compounds, use the prefixes provided in your data booklets and add them to the beginning of each element ONLY FOR THE FIRST element can the MONO be omitted EX: H 2O>>dihydrogen monoxide N 2O 4>>dinitrogen tetraoxide CO>> carbon monoxide Chemical Formulae From a name, you can simply use the prefixes and the element name to write the compound name Examples Sulfur hexafluoride >> SF 6 Tetraphosphorus decaoxide >>P 4O 10 Dinitrogran monoxide >>N 2O 6