chapter 9 Flashcards by Maya T

why do chemical bonds form?

Chemical bonds form in
order to lower the
potential energy of an
atom

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when does a chemical bond form?

A chemical bond forms
when the potential
energy of the bonded
atoms is lower than the
potential energy of the
atoms alone

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when do bonds form?

Bonds form when
electrons are
simultaneously attracted
to two nuclei

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what is lewis theory based on?

-Simplest of bonding theories
-Based on the filling of valence shell by sharing
electrons

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what 2 things does valence bond theory consider?

Considers orbital overlap

- Hybridization of molecular orbitals

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what is molecular orbital theory based on?

Most complex

- Based on the mixing of molecular orbitals from atoms

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types of atoms for ionic bonds? characteristic?

metal and nonmetal

- electrons transferred

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types of atoms for covalent bonds? characteristic?

nonmetal and nonmetal

electrons shared

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types of atoms for metallic bonds? characteristic?

metal and metal

electrons pooled

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how does lewis theory describe bonding?

Chemical bonds form to share or transfer electrons to
attain a stable electron configuration
• We need to consider valence electrons, those in the
outermost principle energy level

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how are valence electrons represented in lewis models?

We represent valence electrons with dots surrounding

the atom

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what is the octet rule?

The octet rule states that bonded atoms want to have a
stable electron configuration with 8 electrons in the
outermost shell to lower their potential energy

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how do lewis structures exist for ionic compounds?

Electrons are not shared in ionic compounds

• Need to transfer the electron(dot) to the non-meta

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what is lattice energy?

There is energy associated with forming a crystalline

lattice of alternating cations and anions

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how can we calculate lattice energy?

the Born-Haber cycle

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ion size trend in lattice energy

Lattice energies become less exothermic with increasing

ionic radius

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ion charge trend in lattice energy?

Lattice energies become more exothermic with

increasing magnitude of ionic charge

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coloumbs law is

the reason for these trends

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compare ions by size etc

qualitative

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what is the relationship between q1q2 and lattice energy?

as q1q2 increases, lattice energy becomes more exothermic

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melting and boiling points of ionic bonds? tendency to conduct?

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!high melting and boiling points
!tendency to not conduct electricity when solid
!tendency to conduct electricity when dissolved

what is a bonding pair?

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Bonding pair: shared pair of electrons

non bonding pair?

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Non-bonding pair: lone pair, pair of electrons associated

with only one atom - non-bonding electrons

how can two atoms attain an octet?

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Two atoms can share more than one electron pair to
attain an octet
!can form single, double, triple bonds (2,4,6 shared
electrons or 1,2,3 shared pairs)

what does the length of a bond depend on?

atoms involved and type of bond

bond lengths for bonds. what can we predict from bond length?

triple bond

which bonds are stronger?

!Generally, the shorter the bond, the stronger it is

5 steps to draw lewis structures

1. Calculate the total number of electrons by summing the valence electrons of each atom in the molecule 2. Write the correct skeletal structure for the molecule drawing a single bond between each bonding atom • Central atom is generally the one with lower group number 3. Distribute the remaining unaccounted-for electrons in pairs, giving octets to as many atoms as possible (except hydrogen) • Start with the terminal atoms first 4. If any non-hydrogen atoms do not have an octet form double or triple bonds 5. Charged molecules have square brackets around them with the net charge as the superscript

3 guidelines for drawing lewis structures

!Hydrogens are always in terminal positions ! More electronegative atoms are also terminal ! Less electronegative atoms are in central positions

which element is the most electronegative?

what bond type has small (0-0.4) electronegativity difference?

covalent

what bond type has medium (0.4-2.0) electronegativity difference?

polar covalent

what bond type has large (2.0+) electronegativity difference?

ionic

what are resonance structures?

have more than one Lewis structure, which has the same connectivity, but different electron arrangements

what is formal charge?

charge an atom would have if all | electrons were shared equally

why do we need to determine formal charges?

Need to determine the formal charge if you are to | predict the correct Lewis structure

formal charge formula

Formal Charge= # of valence e- | in free atom - (number of nonbonding e - + 1/2 # of bonding e -)

what is electronegativity?

- the ability of an element to draw electrons to itself in a covalent bond • Electronegativity is measured on a scale, where 4.0 is the most electronegative (F) and all other elements are measured relative to it

are electrons shared equally between atoms? what is a polar covalent bond?

no Polar covalent bond - a bond with unequally shared electrons

how many electrons can an expanded octet have? which elements are likely to have one? what orbitals are used?

up to 12 electrons • Usually elements in the 3rd period and below • Use empty d-orbitals

what are the exceptions to the octet rule?

Odd electron species | Incomplete octets

describe an odd electron species

will have one unpaired electron, | called a radical

describe an incomplete octet

When elements have less than 8 | valence electrons they may not form a complete octet

formal charge rules

1. The sum of all formal charges in a neutral molecule must be zero 2. The sum of all formal charges in an ion must be equal to the charge of the ion 3. Small (or zero) formal charges on atoms are better than large ones 4. When formal charge cannot be avoided, negative formal charges should reside on the most electronegative atom 5. Structures having formal charges of the same sign on adjacent atoms are unlikely

are all resonance structures equal?

all resonance structures are equally good. equally contribute to the actual bonding structure of NO3-

what is the rule for the sum of all formal charges in a neutral molecule

The sum of all formal charges in a neutral | molecule must be zero

what is the rule for the sum of all formal charges in an ion?

The sum of all formal charges in an ion must be | equal to the charge of the ion

which charges on atoms are better?

Small (or zero) formal charges on atoms are | better than large ones

what happens when formal charge cannot be avoided?

When formal charge cannot be avoided, negative formal charges should reside on the most electronegative atom

which structures having formal charges are unlikely?

Structures having formal charges of the same | sign on adjacent atoms are unlikely

chapter 9 Flashcards

(50 cards)