Ionic and Molecular Compounds Flashcards
how do chemical bonds form?
when atoms lose gain or share valence electrons to acquire a close shell of valence electrons
ionic bonds
when valence electrons of a metal atom are transferred to the atom of a nonmetal and the resulting ions attract each other
covalent bonds
occur when nonmetal atoms share electrons to attain a noble gas arrangement
Na + ion
principle cation outside the cell: highest concentration outside the cell
K+ ion
principle cation inside teh cell
Ca2+ ion
cation found in bones
Mg2+ ion
cation found in bones
ionic compounds
consist of positive or negative charges held together by strong electrical attractions between oppositely charged ions
when do ionic compounds form
if the overall energy of the system decreases: we can obtain this through the born-haber cycle
allows us to understand if a compound will form spontaneously or not
the crystalline state
it is characterized by the arrangement of the ions in the 14 Bravais lattices
which transition metals cannot form 2 or more positive ions
Zn2+ , Cd2+ and Ag+
nomenclature used for metals with variable charge
- the ion with the lower oxidation state gains the suffix -ous
- the ion with the higher oxidation state gains the suffix -ic
which is the only polyatomic ion that does not have a negative charge
NH4 +
how are polyatomic ions derived?
from the loss of hydrogen ions by a molecule with an acid character
how to tell if a compound is ionic or covalent
ionic: if the first element in the formula is a metal or the ammonium ion
covalent: the first element in the formula is a nonmetal
describe how the covalent bond of a hydrogen molecules is formed
-forms as the atoms move closer and the positive charge of the nucleus attracts the electron of the other atom
-has a shared pair of electrons, a covalent bond, to give a noble gas arrangement of He to each H atom
- forms, when the molecule formed, is more stable than the 2 individual H atoms
which elements do not form octets
hydrogen and boron
which is the central atom in Lewis structure
the least electronegative
what is the importance of molecule structures?
molecules like drugs can be designed based on Lewis’s Theory eg thalidomide
why is the octet rule not right?
- hydrogen requires just 2e to form a noble gas arrangement
- nonmetals P, S, Cl, Br and I can form compounds with 10 or 12 valence electrons
- sulfur in SF6 are 12 valence electrons: 6 bonds
- in BCl3 the B atom has only 3 valence electrons to share.
electronegativity
ability to attract shared electrons by the nucleus
describe the changes of electronegativity along a period
increases from left to right: increasing the positive charge of the nucleus therefore stronger attraction for electrons
describe the changes of electronegativity down a group
increases from top to bottom as there is a decreasing distance of the valence electrons from the nucleus
why is the polarity of the bonds important
because polarity affects reactivity and solubility
what can be used to predict the polarity of a bond?
the difference in electronegativity of bonding atoms can be used
nonpolar covalent bond
occurs between nonmetals: it is an equal or almost equal sharing of electrons by the 2 bonding atoms and has a very small electronegativity difference between atoms
polar covalent bond
occurs between nonmetal atoms: it is an unequal sharing of electrons and has a moderate electronegativity difference
dipole
segregation of charges in a polar bond
electronegativity difference between 0 and 0.4
nonpolar covalent bond