Chemistry A- Unit 4: Molecules
Lesson 16
Bond Properties
Which image is a space-filling model of water?
D
Based on the electronegativity difference of the elements in each compound, which has the highest boiling point?
KCl has the highest boiling point.
Lesson 15
Molecular Shapes
Lesson 14
Shapes of Molecules
How can the VSEPR model be used to determine the shape of a covalent molecule?
Since molecular shape is based on the electrons surrounding the central atom, the VSEPR theory predicts the shape of the molecule based on the bonding electron pairs and lone electron pairs around the central atom.
Which statement describes a space-filling model of a molecule?
The radii of the spheres in a space-filling model are proportional in size to the radii of the atoms they represent.
Water (H2O) is a polar molecule. Ethane (C2H6) is nonpolar. What is true about water and ethane?
Water is likely to have a higher boiling point because it is polar.
What does the valence bond theory describe?
how the valence orbitals of different atoms overlap to create a covalent bond
Examine the molecular geometry models. What molecular shape has three electron groups where all three groups are shared by the central atom?
iii, because the three bonded atoms will form a straight bond with the nucleus of the central atom, forcing the other bonded atoms' nuclei to be equidistant from each other
What is a bond angle?
the angle between two bonded pairs of atoms that share at least one atom
What cannot be determined using the Lewis structure of the ammonia (NH3) molecule?
the three-dimensional arrangement of atoms in the molecules
What is the molecular geometry of a compound?
the three-dimensional structure of the nuclei of atoms in a molecule or polyatomic ion
How does the octet rule apply to ionic and covalent bonds? Select all that apply.
Atoms with covalent bonds satisfy the octet rule by sharing electrons. Nonmetals with ionic bonds satisfy the octet rule by gaining electrons.
Which image is a ball-and-stick model of methane (CH4)?
B
Alexa says that the molecular geometry of a compound is a three-dimensional structure, while Echo says that it is a two-dimensional structure. Alexa also thinks that this structure of the nuclei of atoms is only for ionic compounds. Echo thinks that the structure is for covalent compounds. Who is right?
Both are partially correct; the molecular geometry of a compound is a three-dimensional structure of the nuclei of atoms in a molecule. Molecules are covalently-bonded.
Why does a trigonal pyramid molecule have a different shape than a trigonal planar molecule?
Both molecules have three bonding pairs of electrons. A trigonal pyramid molecule has four angles of 107° because there is also a lone pair of electrons around the central atom. However, a trigonal planar molecule has three angles of 120° because there are no lone pairs of electrons around the central atom.
Review the information. In Compound A, Element W has an electronegativity of 2.8, and Element X has an electronegativity of 2.5. In Compound B, Element Y has an electronegativity of 2.0, and Element Z has an electronegativity of 3.8. Which statement correctly identifies the ionic compound and describes the use of electronegativity in determining this?
Compound B is ionic. The electronegativity difference is 1.8, which can be determined by subtracting the electronegativity of Element Y from that of Element Z. Electronegativity differences greater than 1.7 indicate ionic bonds.
What must happen to break a chemical bond?
Energy must be provided.
Ethane (C2H6) has one C-C bond and six C-H bonds. The electronegativity difference between carbon and hydrogen is less than 0.4. What is a property of ethane?
Ethane is nonpolar because it has an even distribution of charge across the entire molecule, which results from the small electronegativity difference between the carbon and hydrogen atoms.
Using the VSEPR theory, what is the shape of a water molecule (H2O)?
It is bent because the oxygen atom has four pairs of valence electrons. Since only two pairs of the oxygen atom's valence electrons are shared with the hydrogen atoms, the lone electron pairs have a greater repulsive effect than the shared pairs of electrons. Thus, the oxygen atom is in the center and the hydrogen atoms are moved closer together to form a bond angle of 104.5°.
If two atoms have the same number of bonds, why would a compound with a lone pair of electrons on the central atom have smaller bond angles than a compound without a lone pair?
Lone electron pairs cause greater repulsion than bonding pairs; therefore, angles between the bonding pairs are reduced.
Which molecule is a trigonal planar structure?
Molecule with 3 angles at 120 degrees.
Sulfur has six valence electrons and potassium has one valence electron. The electronegativity difference between the two elements is 1.76. How can the octet rule be used to explain the bonding of potassium and sulfur?
Sulfur needs to lose six electrons to reach a full octet. Each potassium atom needs access to seven electrons to achieve a full octet. Sulfur and potassium share six electrons, forming a covalent bond.
What happens when bonds are broken?
The attraction between atoms weakens, so they separate into elements or simpler compounds.
What must happen to break a bond?
The electrostatic attraction between atoms must be overcome by a sufficient amount of energy.
Using VSPER theory, what are the approximate bond angles of a compound that has a central atom bonded to three other atoms and no lone electron pairs?
The molecule will form 120° bond angles because the lack of lone electron pairs means there will be no additional repulsion forces acting upon the atoms. Therefore, atoms will lie on a trigonal plane.
A white, powdered substance quickly melted over a low heat source. When in molten form, it did not conduct electricity. What can be said about the nature of this compound?
This compound is covalent because it does not conduct electricity in molten form.
How does the valence bond theory describe a covalent bond formation?
XXX The valence bond theory explains that covalent bonds are formed in the region of the inner orbital when inner orbitals overlap with the valence orbitals of another atom.
What is bond length?
XXX the average of the multiple ways electrons can be shared between two atoms XXX the distance between the valence electrons of an atom and the nucleus of the other atom in a bond
What type of bond would be formed between nitrogen (N) and nitrogen (N)? Why?
a nonpolar covalent bond because there is less than a 0.4 difference in electronegativity between the atoms
What is the angle between two bonded pairs of atoms that share at least one atom?
bond angle
In what type of bond are electrons shared to satisfy the octet rule?
covalent bonds
What is the molecular geometry of a molecule made of two atoms that share one pair of electrons and have no lone electrons pairs?
linear
Which theory states that orbitals extend around multiple nuclei over the entire molecule?
molecular orbital theory
What atomic orbitals are involved in the formation of sp2 hybrid orbitals?
one s and two p orbitals
Water is a polar compound. What kinds of substances can dissolve easily in water?
polar substances
Based on the VSEPR theory, what molecular shape can be predicted if a molecule has three bonding pairs of electrons and no lone electron pairs around the central atom?
trigonal planar