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