Chapter 5

Steps to drawing a correct Lewis Structure.

1.) Count the total number of valence electrons and draw the skeletal structure of the molecule. 2.) Complete the octets of the terminal atoms using available electrons. Count each existing bond in the skeletal structure as two atoms. 3.) Place any remaining electrons on the central atom. 4.) If necessary to satisfy the octet rule, convert lone pairs on outlying atoms into one or more multiple bonds.

ionic electronegativity difference

2.0 or more

C H O F

4 bonds 3 bonds 2 bonds 1 bond

The percent ionic character of the H-F bond is 41.5% and the observed dipole moment is 1.82 D. What would be the calculated dipole moment of the bond, based on a complete separation of charge?

4.39 D

Certain molecules are electron deficient, having fewer than ________ electrons around the central atom. Elements that commonly form electron deficient compounds are beryllium and ________.

8 boron

non polar covalent bond

A bond between atoms whose electronegativities differ by less than 0.5.

covalent bond

A chemical bond that involves sharing a pair of electrons between atoms in a molecule

pure covalent bond

A covalent bond with equal sharing of electrons between atoms.

Facts about Lewis structures

A lewis structure shows the number of covalent bonds between bonded atoms. Lone pair electrons are represented as pairs of dots A covalent bond is represented as a line or as dots between atoms.

Free radical

An atom or molecule with an odd number of electrons.

Examples of incomplete octets

BeCl2 BH3

Which of the following statements correctly describe the "normal" bonding pattern for a neutral atom of each elements, assuming that the octet rule is obeyed?

C forms four covalent bond. F forms a single covalent bond. H forms one covalent bond and generally not found as a central atom in covalent species.

In general, electronegativity ____________ as atomic size increases bc a shared electron pair is closer to the nucleus of a smaller atom, which therefore attracts these electrons _________ strongly. Thus, electronegaticity tends to ___________ from left to right across a period of the periodic table and tends to __________ down a group.

Decreases more increases decreased

Polar covalent bond

Density is highest near the more electronegative atom.

Electronegativity

Electronegativity describes the relative ability of an atom in a covalent bond to attract the shared electron pair(s) Electronegativity is a relative frequency

Electronegativity

Electronegativity describes the relative ability of an atom in a covalent bond to attract the shared electrons. Electronegative is a relative quantity.

Elements that do not obey the octet rule because they have more than eight valence electrons are said to have an _________ valence shell. This is only possible for elements that have available ______ orbitals, which are the elements found from period _________ of the periodic table onward.

Expanded d 3

All of the electrons in a many -electron atom can participate in covalent bonding.

False

BeF2

Fewer than eight valence electrons due to a shortage of valence electrons.

NO2

Fewer than eight valence electrons due to an odd number of valence electrons.

Select all the statements that correctly describe the relationships between bond order, bond length, and bond energy.

For a given pair of atoms, a triple bond is stronger than a double bond. The shorter the bond, the greater the bond strength.

Describe formal charge

Formal charge is the comparison of an atom's associated electrons with its isolated valence electrons. Formal charge can be used to determine the most plausible Lewis structure for a given compound.

ionic bond

Formed when one or more electrons are transferred from one atom to another

Resonance Structure

Lewis structures for the same species that differ in the placement of electrons.

General trends in electronegativity

Metals tend to have lower electronegativities than nonmetals. Fluorine is the most electronegative element. Electronegativity tends to decrease down a group of the periodic table.

SCl6

More than eight valence electrons due to an expanded octet.

Molecule(s) that contain an odd number of valence electrons.

OH NO NO2

A lewis structure will usually require one or more multiple bonds if there is an atom present that does not have a full ______ after all available electrons have already been placed. The multiple bond is formed by exchanging one ____ electron pair for each new brand.

Octet lone

A covalent bond in which electrons are shared unequally is

Polar covalent bond

The bonded atoms that have partial negative and positive _____ due to unequal electron distribution.

Poles

Which of the following statements correctly describe resonance structures?

Resonance structures differ only in the arrangement of electrons. An individual resonance structure does not accurately represent the structure of the species.

Octet rule

States that when atoms bond they may lose, gain, or lose electrons in order to attain in an outer level containing eight electrons.

chemical formula

Symbols that show the elements in a compound and the ratio of atoms

ionic bonding

The electrostatic attraction between oppositely charged ions

Electron affinity

The energy released when an electron is added to an atom of a given element in the gas phase.

Electronegativity

The tendency of an atom of a given element to attract shared electrons to itself in a covalent bond.

Resonance structures are Lewis structure that have the same relative placement of _____ but a difference arrangement of ____.

atoms electrons

Polar covalent electronegativity difference

between 0.5 and 2.0

A pair of electrons shared between two atoms in a covalent bond is called a shared or _______ electron pair, whereas an outer-level electron wait that i snot involved in bonding is called an unshared or _____ pair.

bonding lone

length of covalent bond is the distance between the ____________ of the two covalently bonded atoms.

centers

A covalent bond in which both electrons are contributed by one of the two bonded atoms is called a __________ covalent bond.

coordinate

ionic bond

electrons have been transferred from one atom to another

Nonpolar electronegativity difference

less than 0.5

"Percent ionic character" is a means of comparing the ____________ dipole moment of a bond to the calculated value based on a complete separation of charges.

observed

Atoms bond in order to attain in a full _______ level or shell of electrons. Elements in period 2 seek a total of _ such electrons while period 1 elements such as hydrogen seek a total of _.

outer 8 2

Bond order, bond length, and bond energy are closely related. For a given pair of atoms, the greater the number of electron pairs shared between the atoms, the ______ and _______ the bond will be.

shorter stronger

lattice energy

the energy required to separate 1 mol of the ions of an ionic compound

polar covalent bond

unequal sharing of electrons

In a Lewis structure of a molecule, only the ________ electrons are shown.

valence