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Chemical BondingHow 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
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 CaF2 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***
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 (Fe2O3)
� 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 (NO3-), phosphite (PO3
3-) and ammonium (NH4+)
� These polyatomic ions are always together as a unit, they change in the same
ratio
� If we have 2 (PO33-), it would be (PO3
3-)2
� I recommend ALWAYS WRITING BRACKETS around polyatomic ions before writing any
formulae!!!
Polyatomic Ions and Bonding
� Examples
� Calcium and cyanide: Ca+2 (CN)-1
� Criss-cross OUTSIDE of brackets
� Ca(CN)2
� Aluminum and carbonate: Al3+ (CO3)2-
� Criss-cross OUTSIDE of brackets
� Al2(CO3)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
Covalent Bonding
� Chlorine in its diatomic form
� Cl2
� (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
� CCl4
� 1 Carbon, 4 Chlorine
� (draw)
Covalent Bonding (double bonds)
� There are cases when atoms with share more than one electron
� Carbon dioxide
� CO2
� (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)
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:
� H2O>>dihydrogen monoxide
� N2O4>>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 >> SF6
� Tetraphosphorus decaoxide >>P4O10
� Dinitrogran monoxide >>N2O