Modern Chemistry Chapter 6
The percentage of ionic character and the type of bond in Br2 (electronegativity 2.8) is
0%; nonpolar covalent
A bond's character is more than 50% ionic if the electronegativity difference between the two atoms is greater than
1.7
Which of the following is not an example of a molecular formula
B
Which of the following molecules is nonpolar?
C2H4
ionic compound
NaCl
The ions in most ionic compounds are organized into a
crystal
The B--F bond in BF3 (electronegativities 2.0 and 4.0) is
ionic
Molecular Geometry
• VSEPR theory is used to predict the shapes of molecules based on the fact that electron pairs strongly repel each other and tend to be oriented as far apart as possible. • Hybridization theory is used to predict the shapes of molecules based on the fact that orbitals within an atom can mix to form orbitals of equal energy. • Intermolecular forces, such as dipole-dipole forces and London dispersion forces, exist between certain types of molecules. Hydrogen bonding is a special case of dipole-dipole forces. dipole - created by equal but opposite charges that are separated by a short distance dipole-dipole forces - The forces of attraction between polar molecules hybrid orbitals - orbitals of equal energy produced by the combination of two or more orbitals on the same atom. hybridization - the mixing of two or more atomic orbitals of similar energies on the same atom to produce new orbitals of equal energies. hydrogen bonding - The intermolecular force in which a hydrogen atom that is bonded to a highly electronegative atom is attracted to an unshared pair of electrons of an electronegative atom in a nearby molecule intermolecular forces - The forces of attraction between molecules London dispersion forces - The intermolecular attractions resulting from the constant motion of electrons and the creation of instantaneous dipoles molecular polarity - the uneven distribution of molecular charge. VSEPR theory - states that repulsion between the sets of valence-level electrons surrounding an atom causes these sets to be oriented as far apart as possible
How many extra electrons are in the Lewis structure of the phosphate ion, PO4^3-?
3
The electron configuration of aluminum, atoms number 13, is [Ne] 3s2 3p1. Aluminum is in Period
3
The electron configuration of nitrogen is 1s2 2s2 2p3. How many more electrons does nitrogen need to satisfy the octet rule?
3
How many electrons must be shown in the Lewis structure of the hydroxide ion, OH-
8
In a molecule of fluorine, the 2 shared electrons give each fluorine atoms how many electrons in the out energy level?
8
In drawing a Lewis structure, each nonmetal atom except hydrogen should be surrounded by
8 electrons
How is a hydrogen bond different from an ionic or covalent bond?
A hydrogen bond is a dipole-dipole attraction between a partially positive hydrogen atom and the unshared electron pair of a strongly electronegative atom such as O, N, or F. Unlike ionic or covalent bonds, in which electrons are given up or shared, the hydrogen bond is a weaker attraction. Hydrogen bonds are generally intermolecular, while ionic and covalent bonds occur between ions or atoms respectively.
Describe how a covalent bond holds two atoms together.
A pair of electrons is attracted to both nuclei of the two atoms bonded together
Mobile electrons in the metallic bond are responsible for
All of the above
Use the concept of potential energy to describe how a covalent bond forms between two atoms.
As the atoms involved in the formation of a covalent bond approach each other, the electron-proton attraction is stronger than the electron-electron and proton-proton repulsions. The atoms are drawn to each other and their potential energy decreases. Eventually, a distance is reached at which the repulsions between the like charges equals the attraction of the opposite charges. At this point, potential energy is at a minimum and a stable molecule forms.
The Lewis structure of which of the following compounds does not _____ follow the octet rule?
BF3
VSEPR theory predicts that the shape of which of the following compounds is not trigonal pyramidal?
BF3
Which of the following substances has the lowest boiling point?
CO
Name two elements that form compounds that can be exceptions to the octet rule.
Choose from hydrogen, boron, beryllium, phosphorus, sulfur, and xenon.
Which statement is true about a molecule of H2?
Each atom has an electron configuration like that of helium, The electrons from both atoms travel within the molecular orbital.
The elements whose electron configurations end with s2 p5 in the highest occupies energy level belong to
Group 17
nonpolar covalent compound
H2
The structure of which of the following compounds suggests that it has the highest melting point?
H2O
VSEPR applied to the unshared pairs of electrons around the central atom of which compound would suggest that the molecule has a bent shape?
H2O
Which of the following molecules is polar?
H2O
The structure of which of the following compounds suggests that it has the highest boiling point?
H2S
polar covalent compound
HCl
Which compound most likely has the greatest bond energy?
HF; H⎯F bond length = 92 pm
The lattice energy of compound A is greater in magnitude than that of compound B. What can be concluded from this fact?
It will be more difficult to break the bonds in compound A than those in compound B.
types of attractions in order of increasing strength
London dispersion, dipole-dipole, hydrogen bonding, ionic
The pair of elements that forms a bond with the least ionic character is
Mg and Cl
Use the concept of electron configurations to explain why the number of valence electrons in metals tends to be less than the number in most nonmetals.
Most metals have their outer electrons in s orbitals, while nonmetals have their outer electrons in p orbitals.
A example of a molecule that cannot be represented adequately by a single Lewis structure is
O3-
H2S and H2O have similar structures and their central atoms belong to the same group. Yet H2S is a gas at room temperature and H2O is a liquid. Use bonding principles to explain why this is.
Oxygen has higher electronegativity than sulfur, which creates a highly polar bond. Increased polarity in H2O bonds means a stronger intermolecular attraction, making water a liquid at room temperature. Hydrogen bonding exists between water molecules, but not between hydrogen sulfide molecules.
Identify the major assumption of the VSEPR theory, which is used to predict the shape of atoms.
Pairs of valence electrons repel one another.
Bonds that possess between 5% and 50% ionic character are considered to be
Polar covalent
Choose from hydrogen, boron, beryllium, phosphorus, sulfur, and xenon.
Resonance structures show that one Lewis structure cannot correctly represent the location of electrons in a bond. Resonance structures show delocalized electrons, while Lewis structures depict electrons in a definite location.
What is the relationship between the enthalpy of vaporization of a metal and the strength of the bonds that hold the metal together?
The amount of energy required to vaporize a metal is a measure of the strength of the bonds that hold the metal together. The greater a metal's enthalpy of vaporization, the stronger the metallic bond.
What types of bonds are present in an ionic compound that contains a polyatomic ion?
The atoms in a polyatomic ion are held together with covalent bonds, but polyatomic ions combine with ions of opposite charge to form ionic compounds.
How can electronegativity be used to distinguish between an ionic bond and a covalent bond?
The difference between the electronegativity of the two atoms in a bond will determine whether the bond is ionic or covalent. If the difference in electronegativity is greater than 1.7, the bond is considered ionic.
Describe the electron distribution in a polar-covalent bond and its effect on the partial charges of the compound.
The electron density is greater around the more electronegative atom, giving that part of the compound a partial negative charge. The other part of the compound has an equal partial positive charge.
In water, two hydrogen atoms are bonded to one oxygen atom. Why isn't water a linear molecule?
The electron pairs that are not involved in bonding also take up space, creating a tetrahedron of electron pairs and making the water molecule angular or bent.
Describe the force that holds two ions together in an ionic bond.
The force of attraction between unlike charges holds a negative ion and a positive ion together in an ionic bond.
How does the behavior of electrons in metals contribute to the metal's ability to conduct electricity and heat?
The mobility of electrons in a network of metal atoms contributes to the metal's ability to conduct electricity and heat.
In what way is a polar-covalent bond similar to an ionic bond?
There is a difference between the electronegativities of the two atoms in both types of bonds that results in electrons being more closely associated with the more electronegative atom.
How are dipole-dipole attractions, London dispersion forces, and hydrogen bonding similar?
They are all forces of attraction between molecules. In all cases there is an attraction between the slightly negatively-charged portion of one molecule and the slightly positively charged portion of another molecule.
The concept that electrostatic repulsion between electron pairs surrounding an atoms causes these pairs to be separated as far as possible is the foundation of
VSEPR Theory
A covalent bond consists of
a shared electron pair
As light strikes the surface of a metal, the electrons in the electron sea
absorb and re-emit the light
In metals, the valence electrons
are shared by all of the atoms
As independent particles, most atoms are
at relatively high potential energy
The melting points of ionic compounds are higher than the melting _____ points of molecular compounds because
attractive forces between ions are greater than the attractive forces between molecules.
To draw a Lewis structure, it is not necessary to know
bond energies
The energy required to break a chemical bond and form neutral isolated atoms is called
bond energy
An ionic bond results from electrical attraction between
cations and anions
A mutual electrical attraction between the nuclei and valence electrons of different atoms that binds the atoms together is called a
chemical bond
The fact that metals are malleable and ionic crystals are brittle is best explained in terms of their
chemical bonds
In the 3 molecules, O2, HCl, and F2, which atoms would have a partial negative charge?
chlorine
As the electronegativity difference between bonded atoms decreases, _____ the bond becomes more
covalent
As atoms bond with each other, they
decrease their potential energy, thus creating more stable arrangements of matter.
As atoms bond with each other, they
decrease their potential energy, thus creating more-stable arrangements of matter
When a stable covalent bond forms, the potential energy of the atoms
decreases
A molecule containing 2 atoms is called a
diatomic molecule
The equal but opposite charges present in the 2 regions of a polar molecule create a
dipole
When a metal is drawn into a wire, the metallic bonds
do not break
A covalent bond between 2 atoms produced by sharing 2 pairs of electrons is called a
double bond
The property of being able to be drawn, pulled, or extruded through a small opening to produce a wire is called
ductility
the charge of an ion is
either positive or negative
In metallic bonds, the mobile electrons surrounding the positive ions are called
electron sea
The degree to which bonding between atoms of 2 different elements is ionic or covalent can be determined from the differences in the
electronegativities of the elements
A nonpolar covalent bond is unlikely when 2 atoms of different elements join because the atoms are likely to differ in
electronegativity
What property of the two atoms in a covalent bond determines whether or not the bond will be polar?
electronegativity
What two factors determine whether or not a molecule is polar?
electronegativity difference and molecular geometry or unshared electron pairs
What are shared in a covalent bond?
electrons
The notation for sodium chloride, NaCl, stands for one
formula unit
The simplest collection of atoms from which the formula of an ionic compound can be established is called a
formula unit
Compared with ionic compounds, molecular compounds
have lower melting points
Atoms with a strong attraction for electrons they share with another atom exhibit
high electronegativity
Ionic compounds are brittle because the strong attractive forces
hold the layers in relatively fixed positions
If two covalently bonded atoms move closer than a distance of the _____ bond length, the potential energy of the atoms
increases
If two covalently bonded atoms move closer than a distance of the bond length, the potential energy of the atoms
increases
In general, the strength of the metallic bond moving from left to right on any row of the periodic table.
increases
Name the type of energy that is a measure of strength for each of the following types of bonds:
ionic - lattice energy covalent - bond energy metallic bond - enthalpy of vaporization
If a bond's character is more than 50% ionic, then the bond is called a(n)
ionic bond
The greater the electronegativity difference between 2 bonded atoms, the greater the percentage of __ in the bond
ionic character
The greater the electronegativity difference between two atoms bonded together, the greater the bond's percentage of
ionic character
What type of energy best represents the strength of an ionic bond?
lattice energy
In drawing a Lewis structure, the central atoms is generally the
least electronegative atom
According to VSEPR theory, what is the shape of a molecule of CS _____ 2?
linear
The shape of molecules that contain only two atoms is
linear
Use VSEPR theory to predict the shape of the hydrogen chloride molecule HCl
linear
carbon dioxide
linear
According to VSEPR theory, which of the following shapes is possible for a molecule with the molecular formula of AB2?
linear, bent
According to the octet rule, a calcium atom has a tendency to
lose two electrons.
Compared with the neutral atoms involved in the formation of an ionic compound, the crystal lattice that results is
lower in potential energy
If a material can be shaped or extended by physical pressure, such as hamming, which property does the material have
malleability
A chemical bond formed by the attraction between positive ions and surrounding mobile electrons is a
metallic bond
A chemical bond that results from the attraction between metals atoms and the surrounding sea of electrons is called a
metallic bond
Malleability and ductility are characteristic of substances with
metallic bonds
The chemical formula for water, a covalent compound, is H2O. This is an example of a
molecular formula
A neutral group of atoms held together by covalent bonds is a
molecule
A neutral group of atoms held together by covalent bonds is called a
molecule
The boiling point of water, H _____ 2O, is higher than the boiling point of hydrogen sulfide, H2S, because water molecules are
more polar and form hydrogen bonds
In a crystal of an ionic compound, each cation is surrounded by a number of
negative ions
What group of elements satisfies the octet rule without forming compounds?
noble gases
How many double bonds are in the Lewis structure for hydrogen _____ fluoride, HF?
none
A bond that is less than 5% ionic is considered
nonpolar covalent
If 2 covalently bonded atoms are identical, the bond is
nonpolar covalent
If two covalently bonded atoms are identical, the bond is identified as
nonpolar covalent
A chemical bond between atoms results from the attraction between the valence electrons and of different atoms.
nuclei
Nonpolar covalent bonds are not common because
one atom usually attracts electrons more strongly than the other
Nonpolar covalent bonds are not common because
one atoms usually attracts electrons more strongly than the other
A covalent bond in which there is an unequal attraction for the shared electrons is
polar
If the atoms that share electrons have an unequal attraction for the electrons, the bond is called
polar
If electrons involved in bonding spend most of the time closer to one atom rather than polar covalent the other, the bond is
polar covalent
A covalent bond in which the bonded atoms have an unequal attraction for the shared electrons is called
polar covalent bond
A charged group of covalently bonded atoms is called a
polyatomic _
VSEPR theory
predicts the shape of some molecules, assumes that pairs of valence electrons surrounding an atom repel each other
Elements in a group or column in the periodic table can be expected to have similar
properties
Bond energy is the energy
required to break a chemical bond and form separate, neutral atoms.
Bonding molecules or ions that cannot be correctly represented by a single Lewis structure is
resonance
Bonding in molecules or ions that cannot be represented adequately by _____ a single Lewis structure is represented by
resonance structures
A covalent bond is formed when two atoms
share one or more pairs of electrons with each other.
In metals, the valence electrons are considered to be
shared by all surrounding atoms
Compared with nonmetals, the number of valence electrons in metals is generally
smaller
Lattice energy is an indication of the
strength of an ionic bond
Use VSEPR theory to predict the shape of the carbon tetraiodide molecule, Cl4
tetrahedral
VSEPR theory predicts that the shape of carbon tetrachloride, CCl4, is
tetrahedral
methane
tetrahedral
What are the radioactive elements with atomic numbers from 90 to 103 called
the actinides
What orbitals combine together to form sp3 hybrid orbitals around a carbon atom?
the s orbital and all three p orbitals from the second energy level
Bond length between two bonded atoms is
the separation at which their potential energy is minimum
required to break a chemical bond and form separate, neutral atoms.
the separation at which their potential energy is minimum.
VSEPR theory is a model for predicting
the shape of molecules
Bond length is the distance between 2 bonded atoms at
their minimum potential energy
Atoms naturally move
toward low potential energy
nitrate ion
trigonal planar
According the VSEPR theory, the structure of the ammonia molecule, NH3, is
trigonal-pyramidal
According to VSEPR theory, what is the shape of a molecule of NBr _____ 3?
trigonal-pyramidal
In a double covalent bond,
two atoms share two pairs of electrons.
A single covalent bond involves the sharing of
two electrons
The electrons involved in the formation of a chemical bond are called
valence electrons
The electrons involved in the formation of a covalent bond are
valence electrons
The forces of attraction between molecules in a molecular compound are generally
weaker than the attractive forces among formula units in ionic bonding
Ionic Bonding and Ionic Compounds
• An ionic compound is a three-dimensional network of positive and negative ions mutually attracted to one another. • Connect metals and nonmetals • Because of the strong attraction between positive and negative ions, ionic compounds tend to be harder and more brittle and to have higher boiling points than materials containing only covalently bonded atoms. • Polyatomic ions are charged groups of atoms held together by covalent bonds. formula unit - is the simplest collection of atoms from which an ionic compound's formula can be established. ionic compound - is composed of positive and negative ions that are combined so that the numbers of positive and negative charges are equal lattice energy - is the energy released when one mole of an ionic crystalline compound is formed from gaseous ions. polyatomic atom - A charged group of covalently bonded atoms
Covalent Bonding and Molecular Compounds
• Atoms in molecules are joined by covalent bonds. • The bond length between two atoms in a molecule is the distance at which the potential energy of the bonded atoms is minimized. • The octet rule states that many chemical compounds tend to form bonds so that each atom, by gaining, losing, or sharing electrons, shares or has eight electrons in its highest occupied energy level. • A single bond is a covalent bond in which a pair of electrons is shared between two atoms. Covalent bonds in which more than one pair of electrons is shared are called multiple bonds. • Bonding within many molecules and ions can be indicated by a Lewis structure. Molecules or ions that cannot be correctly represented by a single Lewis structure are represented by resonance structures. bond energy - the energy required to break a chemical bond and form neutral isolated atoms. bond length - The distance between two bonded atoms at their minimum potential energy, that is, the average distance between two bonded atoms chemical formula - indicates the relative numbers of atoms of each kind in a chemical compound by using atomic symbols and numerical subscripts. diatomic molecule - a molecule containing only two atoms. double bond - a covalent bond produced by the sharing of two pairs of electrons between two atoms electron-dot notation - an electron-configuration notation in which only the valence electrons of an atom of a particular element are shown, indicated by dots placed around the element's symbol. Lewis structures - formulas in which atomic symbols represent nuclei and inner-shell electrons, dot-pairs or dashes between two atomic symbols represent electron pairs in covalent bonds, and dots adjacent to only one atomic symbol represent unshared electrons. lone/unshared pair - a pair of electrons that is not involved in bonding and that belongs exclusively to one atom molecular compound - A chemical compound whose simplest units are molecules molecular formula - shows the types and numbers of atoms combined in a single molecule of a molecular compound molecule - a neutral group of atoms that are held together by covalent bonds multiple bond - Double and triple bonds octet rule - Chemical compounds tend to form so that each atom, by gaining, losing, or sharing electrons, has an octet of electrons in its highest occupied energy level. resonance - e refers to bonding in molecules or ions that cannot be correctly represented by a single Lewis structure. single bond - a covalent bond produced by the sharing of one pair of electrons between two atoms. structural formula - a indicates the kind, number, arrangement, and bonds but not the unshared pairs of the atoms in a molecule. triple bond - a covalent bond produced by the sharing of three pairs of electrons between two atoms.
Metallic Bonding
• Metallic bonding is a type of chemical bonding that results from the attraction between metal atoms and a surrounding sea of mobile electrons. • The electron sea formed in metallic bonding gives metals their properties of high electrical and thermal conductivity, malleability, ductility, and luster. ductility - the ability of a substance to be drawn, pulled, or extruded through a small opening to produce a wire malleability - the ability of a substance to be hammered or beaten into thin sheets metallic bonding - The chemical bonding that results from the attraction between metal atoms and the surrounding sea of electrons
Introduction to Chemical Bonding
• Most atoms are chemically bonded to other atoms. • The three major types of chemical bonding are ionic, covalent, and metallic. • In general, atoms of metals bond ionically with atoms of nonmetals, atoms of metals bond metallically with each other, and atoms of nonmetals bond covalently with each other. chemical bond - a mutual electrical attraction between the nuclei and valence electrons of different atoms that binds the atoms together covalent bonding - results from the sharing of electron pairs between two atoms ionic bonding - Chemical bonding that results from the electrical attraction between large numbers of cations and anions non-polar covalent bond - a covalent bond in which the bonding electrons are shared equally by the bonded atoms, resulting in a balanced distribution of electrical charge. polar - bonds that have an uneven distribution of charge. polar-covalent bond - a covalent bond in which the bonded atoms have an unequal attraction for the shared electrons