bonding of the chemical kind. bonding and properties u compounds are formed by fixed ratios of atoms...
TRANSCRIPT
Bonding and Properties Compounds are formed by fixed ratios of
atoms forming chemical bonds (Dalton) When elements form chemical bonds,
their chemical and physical properties are changed
The properties of the resulting compounds depend on the elements making up the compound and the kind of bonds formed.
Forming Bonds In order to react (form a bond),
atoms must collide. When collisions occur, the valence
electrons touch first. Valence electrons (outside shell)
determine the type and number of bonds.
Octet Rule Every atom “strives” to have eight
electrons in its valence shell. Atoms or ions are more stable (less
reactive) with eight valence electrons because of symmetry
A full valence shell can be had by:
Octet Rule Stealing enough of someone else’s
electrons to make eight valence electrons – nonmetals take from metals
Giving away all valence electrons to expose a full shell underneath – metals give to nonmetals
These both happen in ionic bonding.
Octet rule and Bonding Sharing electrons. Shared
electrons “count” for both atoms – happens between nonmetals.
Shared electrons make a covalent bond (2e- per bond)
Ionic Bonding When metals lose valence
electrons, a positive ion called a cation is formed.
Metals usually lose all their valence electrons.
The resulting positive charge is equal to the number of electrons lost.
Ionic Bonding When nonmetals gain extra
valence electrons, a negative ion called an anion is formed.
Nonmetals gain enough electrons to fill their valence shell.
The negative charge that results is equal to the number of electrons gained.
Ionic Bonding Ionic bonds are formed by the electrostatic
attraction between oppositely charged ions.Na+ + Cl- NaCl
Compounds containing ionic bonds are called salts.
Salts are composed of a metal (+) and a nonmetal (-).
Ionic compounds form a crystal lattice. Ionic bonds are broken when the salt is
dissolved in water or melted.
Properties of Ionic Compounds
High melting point• This is because the ionic bonds must
be broken in order to melt the salt. Molten salts conduct electricity Many are soluble in water All water solutions of salts conduct
electricity
Representing Ions The Lewis dot structure of positive
metal ions is the same as the atom minus the valence electrons, and a charge is added.
Na+ Mg+2 Al+3 Sn+4
The Lewis dot structure of nonmetal ions is the same as the atom except that the gained valence electrons and a negative charge are added.
Representing Ions Examples of nonmetal (negative)
ions:
F:
:
:: - O:-2::
:For most purposes the dots can be left off.
Formulas of Ionic Compounds
Ionic compounds are electrically neutral Ionic compounds are made of charged ions
K+ + Br- KBrThe sum of the negative charges must equal the sum of the positive charges
Formulas of Ionic Compounds
Na+ + O-2 ?
2 Na+ + O-2 Na2O
(two positive charges, two negativecharges)
Names of Ionic Compounds
Metal ions are named after the metal – Na+ is the sodium ion
Nonmetal ions are named after the nonmetal, with the ending changed to “-ide” – Cl- is the chloride ion
Salts are named with the metal first, then the nonmetal with the “-ide” ending – CdS is called “cadmium sulfide”.
Covalent Bonds Covalent bonds are formed by atoms (two
nonmetals) sharing two more valence electrons.• A single bond contains two electrons (one
pair), a double bond consists of two pair of electrons, and a triple bond is made of three pairs of electrons.
In Lewis structures a single bond (two electrons) is represented by a line.
H-H (same as H2)
Covalent Bonds A double bond is two lines, and a
triple bond is three lines.
O=O::
::O2, or oxygen gas
:NN:N2, or nitrogen gas
Octet Rule Atoms share enough electrons to fulfill the
octet rule. Shared electrons count for both bonded atoms.
H. O:
H.
:
.. H:O:
H.
:
. H:O: H
::
Octet RuleLewis Structures
Lewis dot structure for water – every atom has a complete valence shell (8 electrons for O and 2 electrons for H)
Octet RuleLewis Structures
The electrons in the bonds can be replaced with lines.
The extra electrons on oxygen are called “lone pairs”.
Properties of covalent compounds
Covalent compounds form molecules – small groups of atoms bonded together
When solid molecular compounds (having covalent bonds) melt, boil or dissolve, the covalent bonds do not break.
Instead, the molecules separate from each other.