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Molecules
a neutral group of atoms joined together by covalent bonds
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covalent bonds
- atoms held together by sharing of electrons
- -tug of war between aroms over the elecrtons
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diatomic molecule
- B2, I2, N2, Cl2, H2, O2, F2
- -a molecule of consisting of 2 atoms
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molecular compound
- compound made of molecular (covalent) bonds
- -low melting and boiling points
- -gases or liquids at room temp.
- -made of 2 or more non-metals**
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molecular formulas
- the chemical formula of a molecular compound
- -show actual quantity of each element a molecule contains
- -not always in lowest terms
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octet rule in covalent bonding
- electrons sharing in covalent bonding allows for noble gas configuration
- -various element groups 4A,5A,6A,7A of ten form covalent bonds
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single covalent bonds
two atoms held together by sharing 1 pair of electrons
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structural formula
shows shared electrons by a single dash
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unshared pair
other valence electrons not shared, also called lone pair or nonbonding pair
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double and triple covalent bonds
bonding by sharing more than 1 pair of electrons
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double covalent bond
bond formed by sharing of 2 pairs of electrons
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triple covalent bond
bond formed by sharing of three pairs of electrons
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coordinate covalent bonds
a covalent bond in which one atom contributes both bonding electrons
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polyatomic ion
a tightly bound group of atoms that has a positive or negative charge and behaves as a unit
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how to draw lewis structure
- 1. determine position
- 2. find the total number of electrons available for bonding
- 3. place a single covalent bond between all pairs of atoms
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bond dissociation energy
- the energy required to break a bond between to covalently bonded atoms
- -expressed as the energy needed to break 1 mole of bonds
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large dissociation energy means..
a very strong bond
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resonance structure
two or more valid electron dot structures that have the same number of electron pairs for a molecule or ion
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exceptions to the octet rule
- -cant work in molecules whose total number of valence electrons is an odd #
- - some molecules have fewer than or more than a complete octet
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binary molecular compounds (naming them)
- prefixes are used to indicate the number of atoms of each type that are present in a compound
- 1-mono 2-di 3-tri 4-tetra 5-penta 6-hexa 7-hepta 8-octa 9-nona 10-deca
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molecular orbitals
- overlapping atomic orbitals of different elements that apply to the whole new molecule
- -each molecular orbital will hold up to 2 electrons
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molecular bonding results from..?
an imbalance between attractions and repulsions of nuclei and electrons of bonded atoms
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bonding orbital
the orbital holding electrons of a covalent bond
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sigma bonds
- molecular orbital formed when two atomic orbitals combine to form a summetrical orbital around the 2 nuclei
- -p atomic orbitals can also overlap end to end and form sigma bonds
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pi bonds
- bonding electrons found in irregular ovals above and below the nuclei of the bonding atoms
- -weaker than sigma bonds
- -atomic orbitals overlap less so less attraction
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how do p atomic orbitals make pi bonding orbitals?
from side by side overlapping p orbitals
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VSEPR
- valence shell electron pair repulsion
- -gives shape and bond angles to molecules so that valence electrons pair stay as far apart as possible.
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tetrahedral
all bond angles are 109.5 degrees
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pyramidal
bond angles are 107 degrees
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hybridization
several atomic orbitals mix to form the same total number of equivalent hybrid orbitals; gives info. about bonding and shape.
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nonpolar covalent bond
bonding electrons equally shared
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polar covalent bond
- bonding electrons are not shared equally
- -also called polar bond
- -one of the atoms pulls harder
- -the electrons are more likely to be found orbiting the one that pulls harder
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electronegativity
- relative ability to attract an electron while it is bonded
- -ranked on a scale of 0-0.4
- -in polar bond the more electronegative atom attracts electrons more strongly, gains slight negative charge
- -less electronegative atom has a slight positive charge.
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polar molecules
a molecule having one end slightly negative and one end slightly positive
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dipole
a molecule with two poles of charge; also called dipolar; orient themselves in an electric field
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polarity of a molecule is affected by....
bond polarity and shape
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intermolecular forces are weaker than...
ionic or covalent bonds
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van der waals forces
weakest attractions between molecules; named for dutch chemist Johannes van der waals
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dipole interactions (2 kinds)
- dipole-dipole: occur when polar molecules are attracted to one another; electrical attraction between oppositely charged regions of polar molecules; similar to but much weaker than ionic bonds
- dispersion forces:caused by the motion of electrons creating a temporary dipole as they orbit an atom; weakest of all molecular interactions
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hydrogen bonds
- a hydrogen covalently bonded to a very electronegative atom is also weakly bonded to an unshared pair of electrongs in another electronegative atom
- -bonding occurs with N,O, and F
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molecular solids
- solids held together by intermolecular forces such as dipole-dipole, dispersion, hydrogen bonding, etc.
- EX. fats, waxes
- -properties: soft, low MP
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covalent network solids
- solids held together by extended network of covalent bonds
- EX. diamond, quartz
- -properties: hard, high MP
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