Chapter 2 - Chemical Bonding Flashcards
Bonding
bond = forces of attraction balanced against forces of repulsion (nuclei to nuclei), connects atoms together in some matter, long term
chemical bond = force within a fundamental particle, covalent or ionic
physical bond = force between fundamental particles
Bond types
covalent = EN between 0 and 0.4, both ends of the bond are neutral
polar covalent = EN between 0.4 and 1.7 (approximately), bond has partial positive and negative ends
ionic = EN greater than 1.7 (approximately), metal and a nonmetal, high melting point, hard, brittle
Ionic bonding
electrostatic attraction between oppositely charged ions (charged atoms)
ionization = gain/loss of electrons to/from other atoms
ionic bond formation = the attraction due to ionization
Ionic substances and electricity
ionic substances are not conductive in a solid state due to the organized arrangement of ions in a crystal lattice shape
they are conductive in a dissolved, liquid, or gas state due to the motion of charges which produce an electrical current
the ions of a substance do not experience attraction in a solution because they are surrounded by hydration spheres
Formula for ionic substances
ionization process (transfer of electrons) determines the charge of the ions
the criss-cross method determines the resulting ratio of the ions to form a substance
go to lowest terms, as this is only a ratio
Covalent bonding
shared pair of electrons, mutual attraction between nuclei and shared electrons
when all atoms have a full valence shell, no more sharing is needed, unless in the case of a free radical or boron and beryllium
when deriving a formula, you cannot go to lowest terms because the substances exhibit different properties
covalent connection can be single bonded, double bonded, or triple bonded
Molecular structure diagram
formula displays the number of atoms of each element in the molecule
expanded formula displays which atom is connected to which, which helps to distinguish the difference between compounds with the same formula
a molecular structure diagram can then be created from an expanded formula
Forces on particles
there are always attractive forces between fundamental particles in substances
intramolecular forces = holds atoms of a molecule together, affect chemical properties (covalent)
intermolecular forces = attract adjacent molecules together due to oppositely charged poles, affect physical properties (ionic)
types of covalent bonds and geometry of the bonds determine the intermolecular forces, and therefore determine physical properties
Bond angles
bond angles are determined by the number of lone pairs and bonds
bonds and lone pairs are mutually repulsive, lone pairs more so than bonds, and therefore adopt the maximum angle between bonds
in a 2D drawing, it may appear as if there are several versions of molecules, however in a 3D version, there is one molecule due to bond angles
Shape names
straight = AX2E0 bent = AX2E2, AX2E1 flat triangle = AX3E0 triangular pyramid = AX3E1 tetrahedral = AX4E0
Determining polarity
are any of the bonds polar (yes = continue, no = non)
is the shape symmetrical (yes = continue, no = polar)
are all the bonds the same (yes = non, no = polar)
Dipole-dipole forces
dipole = structure with two pole
attractive force acting between polar molecules, positive end of one is attracted to the negative end of another
London dispersion forces
electrostatic forces of attraction between adjacent molecules due to temporary dipoles created by random motion of electrons
affected by number of electrons in the molecule
Hydrogen bonding
not a function of electron dispersion
attraction between hydrogen proton and nearby lone pairs on other molecules (oxygen, fluorine, nitrogen)
forms a very strong intermolecular force
mutual attraction of 2 electron pairs for the same nucleus, inverse covalent bond
10% as strong as a covalent bond
Ranking of forces
ionic bonds
hydrogen bonds
dipole-dipole
London dispersion forces
Physical properties related to bonds
the stronger the intermolecular bonds, the more energy must be used to break them, thermal energy is required
hardness = must separate the molecules
malleability = state of spatial organization in intermolecular bonds
odour = inversely related to intermolecular bond strength
melting point = directly related in intermolecular bond strength
Solubility
solution = homogeneous mixture, same properties all the way down to particle size
polar molecules dissolve in polar
non polar dissolves in non polar
ionic can dissolve in polar depending on the charges
Nomenclature
naming of pure substances = one substance has one name
naming of molecular substances = one structure has one name
regulated by IUPAC
Ionic nomenclature
binary ionic compound = cation (roman numeral) anion
elements that require roman numerals = copper, tin, lead, iron
cation = name of element or of polyatomic ion, positive
anion = name of polyatomic ion, or of element, change ending to “ide”, negative
eg. copper (II) chloride
Molecular nomenclature
list of element names, change ending to “ide”
inorganic molecules = order of the periodic table
organic molecules = alphabetical order
use greek prefixes to indicate number of atoms in formula
Prefixes
mono, di, tri, tetra, penta, hexa, hepta, octa, nona, deca
omit prefix “mono” always for the first name in the list, or when ambiguity is not created
eg. carbon monoxide vs carbon dioxide
Acid nomenclature
named as if ionic with hydrogen as the cation
eg. aqueous hydrogen sulfate, aqueous hydrogen chloride
Coordinate covalent bonds
coordinate covalent bond = covalent bond made from a lone pair, once made, they are no different from a non coordinate bond
Physical vs. chemical
physical change = any change not producing a new substance
chemical change = any process that produces a new substance
physical property = a trait that helps identify a substance
chemical property = description how a substance interacts with other substances in chemical changes
Types of substances
pure substance = only one type of particle, cannot be broken down into other substances by physical processes
element = pure substance with only one type of atom, cannot be physically or chemically broken down
compound = pure substance with more than one type of atom, more than one element, can be chemically broken down
Types of mixtures
mechanical mixture = a non-uniform mixture, different characteristics in different regions
homogenous mixture = uniform mixture, a solution
