Unit 9: Chapter 12 - Bonding

Resonance

A molecule shows this when more than one Lewis structure can be drawn for the molecule

What is the difference between a polar bond and a polar molecule (one that has a dipole moment)?

A polar bond is covalent but electrons are more attracted to the atom with the higher electronegativity. A polar molecule has positive and negative regions due to the molecule's shape as well as the polarity of the bonds.

How does the polarity of a bond depend on the difference in electronegativities of the two atoms participating in the bond? If two atoms have exactly the same electronegativity, what type of bond will exist between the atoms? If two atoms have vastly different electronegativity, what type of bond will exist between them?

A slight difference in electronegativity will lead to a slightly polar covalent bond. A very large difference in electronegativity will lead to a very polar covalent bond; if the difference is too large (metals and nonmetals) an ionic bond will form with the metal giving its electron to the nonmetal.

What is the geometric structure of the water molecule? How many pairs of valence electrons are there on the oxygen atom in the water molecule? What is the approximate H-O-H bond angle in the water?

Angular; 4; angular; 109.5

Determine the polarity of bonds

Arrow points towards the negative charge center (more electronegative element), and tail indicates the positive center of charge. Any diatomic molecule that has a polar bond has a dipole moment. Some polyatomic molecules also do.

Covalent bond

Between atoms that are nonmetallic and involves the sharing of electrons

nonpolar covalent bond

Between atoms that are nonmetallic and involves the sharing of electrons

Describe the type of chemical bonding that exists between the atoms in the hydrogen fluoride molecule, HF.

By bonding with eachother, H and F atoms share valence electrons because atoms have different attractions for electrons, not equal. Polar covalent.

Why are cations smaller than their parent atoms? Why are anions larger?

Cations are smaller in size because they are formed by loss of electrons and anions are larger in size because they are formed by the gain of electrons. cation than in its parent atom. ... The remaining electrons are, therefore held more tightly by the protons in the nucleus and thus their radii.

What is special about the arrangement of electrons in novel gases?

Filled s and p electron shells - full valence shells

Ionic bond

Formed when one or more electrons are transferred from one atom to another (metal to nonmetal)

READ TEXTBOOK

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REVIEW WHOLE PACKET

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Understand table 12.4

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Electronegativity

the relative ability of an atom in a molecule to attract shared electrons to itself. Increases going from left to right across a period and decrease going down a group for the representative elements. The higher the atom's electronegativity value, the closer the shared electrons tend to be to that atom when it forms a bond. Directly related to ionization energy.

What is the geometric structure of boron trifluoride molecule, BF3? How many pairs of valence electrons present on boron atom? What is the approximate F-B-F bond angles in BF3?

trigonal planar; 3; 120

What is the geometric structure of ammonia? How many pairs of valence electrons surround the nitrogen atom in NH3? What is the approximate H-N-H bond angles in ammonia?

trigonal pyramidal; 4; 109.5

After writing an electron configuration, how do you tell how many covalent bonds (sharing of electrons) each could form?

unfufilled subleves indicate space to share electrons to complete valence shells

atom pair

Indicates a pair of atoms that will create a bond

Polar covalent bond

Intermediate cases in which the atoms are not so different that electrons are completely transferred but are different enough so that unequal sharing of electrons results

How are ionic bonds and covalent bonds different?

Ionic bonds occur between a positive metal and a negative nonmetal, and electrons are transferred from the metal to the nonmetal. Covalent bonds occur between two nonmetals, which share electrons.

What types of elements react to form ionic compounds? Give an example of the formation of an ionic compound from its elements.

Ionic compounds generally form between elements that are metals and elements that are nonmetals. For example, the metal calcium (Ca) and the nonmetal chlorine (Cl) form the ionic compound calcium chloride (CaCl2). In this compound, there are two negative chloride ions for each positive calcium ion.

What type of bonding requires the complete transfer of an electron from one atom to another? What type of bonding involves the sharing (either equally or unequally) of electrons between atoms?

Ionic; covalent

Explain what the different symbols in a Lewis dot structure represent.

Letters represent elements, dots represent valence electrons, and lines represent bonds

Determine the shape of a molecule using VSEPR theory

Linear (180) if 2 electron pairs, trigonal planar (triangular) (120) if 3 electron pairs, tetrahedral (109.5) if 4 electron pairs, trigonal pyramid (109.5 - tetrahedral) if 4 electron pairs but one lone pair, bent or v-shaped (109.5 - tetrahedral) if 4 electron pairs but two lone pairs (refer to 12.4)

Describe the type of chemical bonding that exists between the atoms in the hydrogen molecule, H2.

The bond joining two hydrogen atoms in a hydrogen gas molecule is a classic covalent bond. The bond is easy to analyze because the hydrogen atoms only have one proton and one electron each. The electrons are in the hydrogen atom's single electron shell, which has room for two electrons.

Explain how you can use the periodic table to predict relative polarity of bonds. For example how do you know by looking at the periodic table that a C-O bond is more polar than a N-O bond?

The closer the atoms are to each other on the periodic table, the less polar the bond is between the, Thus, comparing C-O and N-O for example, N and O are closer on the periodic table than C and O, sot he N-O bond is not as polar as the C-O bond.

Define a chemical bond

The force that holds atoms together

What is the main idea in the Valence Shell Electron Pair Repulsion theory?

The main idea is that electrons repel each other and therefore the structure of a molecule coms from bonding electrons and lone pairs of electrons are positioned as far apart as possible from each other.

Implications of electronegativity on bonding type

The polarity of a bond depends on the difference between the electronegativity values of the atoms forming the bonds. If atoms have very similar electronegativities, electrons are shared almost equally and the bond shows little polarity. If atoms have very different electronegativity values, a very polar bond is formed. In extreme cases one or more electrons are actually transferred, forming ions and an ionic bond. In general, if the difference between the electronegativities of two elements is about 2.0 or greater, the bond is considered to be ionic.

Lewis Structure octet rule

all other elements - they require 8 electrons to fill their valence electrons

Lone pairs or unshared pairs

electrons not involved in bonding

what do other elements do to acquire a noble gas configuration

gain, lose, or share electrons and exist in pairs

What is meant by nitrogen fixation?

getting nitrogen directly from atmosphere

What does the shape of a crystal tell you about its internal structure?

ion ratios and charges are different

Lewis Structure duet rule

only hydrogen and helium - they require 2 electrons to fill their valence shell

Using the VSEPR theory, predict molecular structure of: CCl4, H2S, GeI4

tetrahedral, bent, tetrahedral

What is the geometric structure of CH4 molecule? How many pairs of valence electrons on CH4? What is the estimated H-C-H bond angles in CH4?

tetrahedral; 4; 109.5

How do electronegativity values help us determine the polarity of a bond?

the charge distribution in a polar covalent bond? the more electronegative atom attracts electrons more strongly and gains a slightly negative charge. The less electronegative atom has a slightly positive charge.

Draw a Lewis dot structure for any given element or compound.

1. Obtain the sum of the valence electrons for all elements involved in the molecule 2. Arrange the valence electrons to satisfy the octet or duet rule (some pairs may be unbonded) 3. Draw lines for each shared pair of electrons; show dots for unbonded electrons *Practice

Single bond

2 atoms sharing 1 electron pair

Double bond

2 atoms sharing 2 pairs of electrons

Triple bond

3 electron pairs are shared

What circumstance must exist for a bond to be purely covalent? How does a polar covalent bond differ from an ionic bond?

A bond is purely covalent when there is no difference in the electronegativities of the atoms involved In the bond. Therefore, diatomic elements have purely covalent bonds. A polar covalent bond occurs when elements of differing electronegativities bond, creating a dipole moment. The electrons are still shared, but the more electronegative atom has a larger "portion".

Explain what is meant by the term "chemical bond."

A chemical bond is a force that holds atoms together in a molecule.

What tests can be done to determine if a substance contains ionic bonds?

Conduct electricity when melted?

Which compounds is VSEPR applicable to and why?

Covalent bonds because covalent bonds form lewis structures.

When atoms of a metal react with atoms of a nonmetal, what type of electron configuration do the resulting ions attain? Explain how the atoms in a covalently bonded compound can attain noble gas electron configurations.

Metals and nonmetals react to form ionic compounds, with the metal donating its electron to the nonmetal and the atoms being held together by electrostatic attraction (a very strong bond). Atoms in covalent compounds achieve noble gas configuration by sharing valence electrons so that both atoms have eight electrons.

Why do metals lose electrons to form ions? When does a metal stop losing ions?

Metals tend to lose electrons to attain Noble Gas electron configuration. Groups 1 and 2 (the active metals) lose 1 and 2 valence electrons, respectively, because of their low Ionization energies. ... The sodium atom gives up an electron to form the Na+ ion and the chorine molecule gains electrons to form 2 Cl- ions.

Which of the following molecules contain polar covalent bonds? P4, O2, O3, HF

Not phosphorus bc same element, not oxygen because same element, not ozone because same element, yes hydrogen fluoride.

How does a polar covalent bond differ from a nonpolar covalent bond?

Polar covalent bonding is a type of chemical bond where a pair of electrons is unequally shared between two atoms. ... If the electronegativity of two atoms is basically the same, a nonpolar covalent bond will form, and if the electronegativity is slightly different, a polar covalent bond will form.

What does it mean to say that a bond is polar? What are the conditions that give rise to a bond's being polar? Does the fact that a molecule possesses polar bonds necessarily mean that the molecule itself will also be polar?

Polar if shared electron pair is attracted more strongly by one of the bonded atoms than another. Polarity due to differences in electronegativity values. May have polar bond but not a polar molecule. Polarity must be determined by overall shape.

Why must a Lewis Structure for a molecule be drawn before we can determine its molecular structure?

The structure depends on the number of atoms and lone pairs of electrons around the central atom. While BF3 and NF3have the same number of atoms around the central atoms, there is a lone pair of electrons on the nitrogen in NF3. Thus, the molecular structure of NF3 is trigional pyramidal and BF3 is trigional planar. In order to determine the molecular structure we must know the number of atoms and lone pairs around the central atom. To know this, we must draw the Lewis structure.

Why are the valence electrons of an atom the only electrons likely to be involved in bonding the other atoms?

The valence electrons are involved in bonding one atom to another. The attraction of each atom's nucleus for the valence electrons of the other atom pulls the atoms together. ... Atoms covalently bonded as a molecule are more stable than they were as separate atoms.

Why do we only consider the valence electrons in drawing a Lewis structure?

The valence electrons are the other shell electrons, and only these electrons are involved in bonding atoms of the molecules. Because Lewis structures represent bonds in a molecule, only the valence electrons are considered.

How many electrons are involved when two atoms in a molecule are connected by a "double bond"?

Two oxygen atoms must share 2 electrons each to complete each other's shells, making a total of 4 shared electrons. Because twice as many electrons are shared, this is called a 'double covalent bond'. Double bonds are much stronger than single bonds, so the bond length is shorter and the bond energy is higher.

Explain what the "duet" and "octet" rules are and how they are used to describe the arrangement of electrons in a molecule.

When atoms form covalent bonds, they try to attain a valence - electron configuration similar to nearest noble gas element. Hydrogen has 2 electrons (like Helium, duet rule) and others 8 (like Neon and Argon, octet rule)

Lewis Structure

a representation of a molecule that shows how the valence electrons are arranged among the atoms in the molecule