Glossary of Chemistry - Bonding and Chemical Structure

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What can atoms of many elements combine to form?
What are the atoms in most molecules held together by?
They are held together by strong attractive forces called chemical bonds
How are these bonds formed?
They are formed via the interaction of the valence electrons of the combining atoms
What are intermolecular forces?
They are the weaker forces between molecules
What are atoms bonded according to?
The octet rule
What does it say?
It says that an atom tends to bond with other atoms until it has eight electrons in its outermost shell, thereby forming a stable electron configuration similar to that of the Group VIII elements
What are exceptions to the rule?
Hydrogen can only have two valence electrons, lithium and beryllium, can bond to attain two and four valence electrons, respectively, boron, which bonds to attain six, and elements beyond the second row, such as phosphorus and sulfur, can expand their octets to include more than eight electrons by incorporating d orbitals
What are the two types of bonds?
There are ionic bonds and covalent bonds
What is ionic bonding?
It is when electrons from an atom with smaller ionization energy are transferred to an atom with a greater electron affinity, and the resulting ions are held together by electrostatic forces
What happens in covalent bonding?
An electron pair is shared between two atoms
What is it called when the bond is partially covalent and partially ionic?
They are called polar covalent bonds
What happens when two atoms with large differences in electronegativity react?
There will be a complete transfer of electrons from the less electronegative atom to the more electronegative atom
What is the atom called that loses electrons and becomes a positively charged ion?
It is called a cation
What is the atom called that gains electrons and becomes a negatively charged ion?
It is called an anion
For this transfer to occur, what does the difference in electronegativity need to be?
It needs to be 1.7
In general, what do elements of Groups I and II bond ionically to?
They unusually bond to elements of Group VII
What is an example of this?
Na + Cl forms Na+Cl-
What is the electrostatic force of attraction between the charged ions called?
Ionic bond
What do ionic compounds have for characteristic physical properties?
They have high melting and boiling points due to the strong electrostatic forces between the ions. They can conduct electricity in the liquid and aqueous states, though not in the solid state
What do ionic solids form?
They form crystal lattices consisting of infinite arrays of positive and negative ions in which the attractive forces between ions of opposite charge are maximized, while the repulsive forces between ions of like charge are minimized
What happens when two or more atoms with similar electronegativities attract?
The energy required to form ions is greater than the energy that would be released upon the formation of an ionic bond (the process is not energetically favorable)
If they don’t make ionic bonds, how do they achieve a noble gas electron configuration?
They gain one by sharing electrons in a covalent bond
What does the binding force between the two atoms result from?
It results from the attraction that each electron of the shared pair has for the two positive nuclei
What are their characteristics?
They are low-melting solids, and do not conduct electricity in the liquid or aqueous states
What is the number of shared electron pairs between two atoms called?
It is called bond order
What does a single bond have?
It has a bond order of one
What about three?
It has a bond order of three
What two features can a covalent bond be characterized by?
Bond length and bond energy
What is bond length?
It is the average distance between the two nuclei of the atoms involved in the bond
What happens as the number of shared electron pairs increases?
The two atoms are pulled closer together, leading to a decrease in bond length
Is a triple bond shorter than a double bond?
What is bond energy?
It is the energy required to separate two bonded atoms
What does the strength of the bond increase with?
It increases as the number of shared electron pairs increases
What are the shared valence electrons of a covalent bond called?
They are called the bonding electrons
What are the valence electrons not involved in the covalent bond called?
They are called nonbonding electrons
What are lone electron pairs?
They are just another name for nonbonding electrons
What is a Lewis structure?
It is used to represent the bonding and nonbonding electrons
What is the formal charge?
The Formal charge is what exists when the number of electrons officially assigned to an atom in a Lewis structure does not always equal the number of valence electrons of the free atom
What is the equation for formal charge?
It is equal to the number of valence electrons in the free atom minus one half the number of bonding electrons, minus the number of nonbonding electrons
Is a Lewis structure with a small or no formal charge preferable to one with a large formal charge?
Is a Lewis structure more stable when the negative formal charges are placed on the more electronegative atom?
When does polar covalent bonding occur?
It occurs between atoms with small differences in electronegativity, generally in the range of .4 to 1.7 Pauling units
What is a molecule called that has a separation of positive negative charge called?
It is called one with a dipole moment
When does a nonpolar covalent bond occur?
It occurs between atoms that have the same electronegativies
What is a coordinate covalent bond?
It is a bond that the shared electron pair comes from the lone pair of one of the atoms in the molecule
What happens once a bond like that forms?
It is indistinguishable from any other covalent bond
What is a Lewis acid?
It is a compound that can accept an electron pair
What is a Lewis base?
It is a compound that can donate an electron pair to form a covalent bond
What is VSEPR Theory?
It uses Lewis structures to predict the molecular geometry of covalently bonded molecules
What is the angle between linear molecules?
180 Degrees
What is the angle between a trigonal planar molecules?
120 Degrees
What is the angle between a tetrahedral molecule?
109.5 Degrees
What are the angles between a trigonal bipyramidal molecule?
90, 120, and 180 Degrees
What are the angles between an octahedral molecule?
90 and 180 Degrees
What is a molecule with a net dipole moment called?
It is called polar
What are the attractive forces that exist between molecules known as?
They are known as intermolecular forces
What are dipole-dipole interactions?
They are the interactions that occur when polar molecules tend to orient themselves such that the positive region of one molecule is close to the negative region of another molecule
What is hydrogen bonding?
It is a specific, unusually strong form of dipole-dipole interaction
When does it occur?
It happens when hydrogen is bound to a highly electronegative atom such as fluorine, oxygen, or nitrogen, the hydrogen atom carries little of the electron density of the covalent bond
What are characteristics of substances which display hydrogen bonding?
They tend to have unusually high boiling points compared with compounds of similar molecular formula that do not hydrogen bond
What are dispersion or London forces?
They occur when the electron clouds of two molecules interact
How strong are dispersion forces?
They are generally weaker than other intermolecular forces
Do they extend over long distances?
Why do large molecule have greater dispersion forces?
Because they have electrons that are far from the nucleus, and this makes them easy to polarize

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