CHEM101: Chapter 9: Chemical Bonding I: The Covalent Bond
what elements are most likely to form cations in ionic compounds
- alkali metals - alkaline earth metals
what is a key component of the expanded octet exception
- atom period 3 and beyond can form compounds in which more than eight electrons surround the central atom *also have 3d orbitals that can be used in bonding*
ionic bonds are generally between metals and nonmetals, why?
- because they have such differing electronegativities
electronegativity is related to.....
- electron affinity - ionization energy
what elements are most likely to form anions
- halogens - oxygen
what are the names of the three exceptions to the octet
- incomplete octet - odd number electrons - more than eight electrons around the central atom
electronegativity increase how when going through a group
- increase going up a group *electronegativity decreases with increasing atomic number*
electronegativity increase how when going across a period?
- increases as one goes left to right *this is because metallic character of the element decreases*
what is a key component of the odd number electron exception
- it simple has an odd number of valence electrons
define ionic bond
- the electrostatic force that holds ions together in an ionic compound
what is the equation for the enthalpy of reaction
- total energy input minus total energy released
a polar covalent bond forms when electronegativity difference is in the range of _____ -_____
0.3-2.0
an ionic bond forms when the electronegativity difference between atoms is _____ or more
2.0
define covalent compounds
compounds that contain only covalent bonds
describe lewis dot symbol
consists of the symbol of an element and one dot for each valence electron in an atom of an element
sometimes in expanded octets the octet rule is satisified for all atoms but there are still valence electrons left to place, simple place them as _____ _____ around the central atom
lone pairs
single bonds are the ________ bonds in terms of bond length
longest
most covalent bonds involve ________ atoms
nonmetallic
define resonance structure
one of two or more lewis structures for a single molecule that cannot be represented accurately by only one lewis structure
define lone pairs
pairs of valence electrons that are not involved in covalent bond formation
atoms of elements with similar electronegativities tend to form ______ ______ _____ because the shift in electron density is so small
polar covalent bonds
lattice energy is always ________, because the separation of ions in a solid into ions in the gas phase is an endothermic process by coulombs law
positive
odd electrons are sometimes referred to as _________
radicals
what is the Born-Haber cycle
relates lattice energies of ionic compounds to ionization energies, electron affinities, and other atomic and molecular properties
electronegativity is a ________ concept, only in reference to the atoms it is around
relative
the octet rule works mainly for element in what period
second
triple bonds are the ______ bonds in terms of bond length
shortest
having short bonds makes a molecule more _________
stable
the greater the lattice energy the more ________ the ionic compound
stable
define electronegativity
the ability of an atom to attract towards itself the electrons in a chemical bond
define bond length
the distance between nuclei of two covalently bonded atoms in a molecule
define formal charge
the electrical charge difference between the valence electrons in an isolated atom and the number of electrons assigned to that atom in a lewis structure
define polar covalent bond
the electrons spend more time in the vicinity of one atom than the other
define lattice energy
the energy required to completely separate one mole of solid ionic compound into gaseous ions
define bond enthalpy
the enthalpy change required to break a particular bond in 1 mole of gaseous molecules
what is a key component of the incomplete octet exception
the molecule simple has less than 8 valence electrons
what is coulombs law
the potential energy between two ions is directly proportional to the product of their charges and inversely proportional to the distance of separation between them
define single bond
two atoms are held together by one electron pair
define triple bond
two atoms share three pairs of electrons
define double bond
two atoms share two pairs of electrons
covalent bonding between many electron atoms involves only the __________ _________
valence electrons
what is maximum stability
when an atom is isoelectronic with a noble gas
what is the only pure covalent bond
when the same atoms bind to eachother because their electronegativities are the same
define covalent bond
a bond in which two electrons are shared by two atoms
define coordinate covalent bond
a covalent bond in which one of the atoms donates both electrons
define lewis structure
a representation of covalent bonding in which shared electron pairs are shown either as lines or as pairs of dots between two atoms and lone pairs are shown as pairs of dots on individual atoms
in resonance structure, the same atoms must be bonded to one another for _____ the resonance strutures of a given species
all
describe the octet rule
an atom other than hydrogen tends to form bonds until it is surrounded by eight valence electrons
define multiple bonds
bonds formed when two atoms share two or more pairs of electrons
