Chemistry Chapter 10

Front 1

Lewis Theory chemical principle

Back 1

Lewis theory is a model for chemical bonding. In L:ewis theory, chemical bonds are formed when atoms transfer valence electrons (ionic bonding) or share valence electrons (covalent bonding) to attain noble gas electron configurations. Inn lewis theory, valance electrons are represented as dots surrounding the symbol for an element. When two or more elements bond together, the dots are transferred or shared so that every atom gets eight dots (an octet), or two dots (a duet) in the case of hydrogen.

Front 2

Molecular shapes chemical principle

Back 2

The shapes of molecules can be predicted by combining Lewis theory with valence shell electron pair repulsion (VSEPR) theory. In this model, electron groups--lone pairs, single bonds, double bonds, and triple bonds--around the central atom repel one another and determine the geometry of the molecule.

Front 3

Electronegativity and polarity chemical principle

Back 3

Electronegativity refers to the relative ability of elements to attract electrons within a chemical bond. Electronegativity increases as you move to the right across a period in the peeriodic table and decreases as you move down a column. When two nonmetal atoms of different electronegativities form a covalent bond, the electrons in the bond are not evenly shared and the bond is polar. In diatomic molecules, a polar bond results in a polar molecule. In multi-atom molecules, polar bonds may cancel, forming a nonpolar molecule, or they may sum, forming a polar molecule.

Front 4

Lewis theory relevance

Back 4

bonding theories predict what combinations of elements will form stable compoiunds they can also be used to predict the properties of those compounds. For example, pharmaceutical companies use bonding theories when they are designing drug molecules that must interact with a specific part of a protein molecule.

Front 5

Molecular shapes relevance

Back 5

Molecular shapes determine many of the properties of compounds. Water's bend geometry, for example, causes it to be a liquid at room temp instead of a gas. It also causes ice to float on water and is responsible for the hexagonal patterns in snow flakes.

Front 6

Electronegativity and polarity relevance

Back 6

The polarity of a molecule influences many of its properties such as whether it will be a solid, liquid, or gas at room temp and whether it will mix with other compounds. Oil and water, for example, do not mix because water is polar while oil is nonpolar.

Front 7

Bonding pair electrons

Back 7

electrons that are shared between two atoms are bonding pair electrons.

Front 8

bondint theories

Back 8

Models that predict how atoms bond together to form molecules.

Front 9

Chemical bond

Back 9

involves the sharing or transfer of electrons to attain stable electron configurations for the bonding atoms.

Front 10

Covalent bond

Back 10

If the electrons are shared, the bond is a covalent bond.

Front 11

Double bond

Back 11

When two electron pairs are shared between two atoms, the resulting bond is a double bond. In general doiuble bonds are shorter and stronger than single bonds.

Front 12

Electron geometry

Back 12

the geometrical arrangement of electron groups.

Front 13

Electronegativity

Back 13

The ability of an element to attract electrons within a covalent bond is called electronegativity.

Front 14

Dipole moment

Back 14

The result of unequal electron sharing is a dipole moment, a separation of charge within the bond. Covalent bonds with a dipole moment form polar covalent bonds.

Front 15

Ionic bond

Back 15

If the electrons are transferred it is an ionic bond.

Front 16

Nonpolar

Back 16

If two elements with identical electronegativities form a covalent bond, they equally share the electrons. There is no dipole moment. The molecule is now nonpolar.

Front 17

Resonance structure

Back 17

We can draw the dot structures different ways and they are still correct.

Front 18

Linear

Back 18

Molecular geometry linear
angle: 180
electron geometry: linear
Lone pairs: 0
Bonding groups:2
Electron groups: 2

Front 19

Trigonal planar

Back 19

Molecular geometry: trigonal planar
Bond angle: 120
Electron geometry: trigonal planar
Lone pairs: 0
Bonding groups: 3
Electron Groups: 3

Front 20

bent

Back 20

Molecular geometry: Bent
angle: 120
Electron geometry: trigonal planar
Lone pair: 1
Bonding groups: 2
Electron groups: 3

Front 21

Tetrahedral

Back 21

Molecular geometry: tetrahedral
Angle: 109.5
Geometry: tetrahedral
Lone Pair: 0
Bonding groups: 4
Electron Groups: 4

Front 22

Trigonal pyramidal

Back 22

Molecular geometry: trigonal pyramidal
Angle: 109.5
Geometry: tetrahedral
Lone pair: 1
Bonding groups: 3
Electron Groups: 4

Front 23

Bent

Back 23

Molecular geometry: bent
angle: 109.5
Electron Geometry: tetrahedral
Lone pairs: 2
Bonding groups: 2
Electron Groups: 4

Front 24

Why are bonding theories important?

Back 24

Bonding theories predict how atoms bond together to form molecules, and they also predict what combinations of atoms form molecules and what combinatioins do not. Likewise, bonding theories explain the shapes of molecules, which in turn determine many of their physical and chemical properties.

Front 25

Give some examplles of what bonding theories can predict?

Back 25

They predict how atoms bond together to form compounds, predict why water is H2O and not H3O. They explain the shapes of molecules which in turn determines many of their physical and chemical properties.

Front 26

In Lewis theory what is an octet? What is a duet?

Back 26

The number of valance electrons in an atom. Atoms with 8 valance electrons are considered stable. For Helium 2 paired dots represents a stable electron config.

Front 27

According to Lewis Theory, what is a chemical bond?

Back 27

In Lewis theory, a chemical bond involves the sharing or transfer of electrons to attain stable electron configuration for the bonding atoms.

Front 28

What is the difference between ionic bonding and covalent bonding?

Back 28

in an ionic bond the electron is transferred. In a covalent bond the electron is shared.

Front 29

How can lewis theory be used to determine the formula of ionic compounds? You may explain this with an example.

Back 29

The lewis structure for potassium has1 valance electron whereas the lewis structure for monatomic chlorine has 7 valance electrons. From these structures we can determine that if potassium gives up its one valence electron to chlorine, K+ and Cl- are formed; therefore teh formula must be KCl.

Front 30

What is the difference between a lone pair and a bonding pair?

Back 30

A long pair is not bonded to another atom. A bonding pair is a pair that connects one atom to anotehr.

Front 31

how are double and triple bonds physically different from single bonds?

Back 31

Double and triple bonds are shorter and sstronger than single bonds.

Front 32

how do you determine the number of electrons that go into the Lewis structure of a molecule?

Back 32

The number of valance electrons for any main group element is equal to its group number on the periodic table. If you are writing it for a polyatomic ion the charge of the ion must be considered when calculating the total number of electrons. Add one electron for each negative charge and subtract one electron for each positive charge.

Front 33

Why does the octet rule have exceptions?

Back 33

The octet rule is not complex enough to be correct every time. For example, some molecules in nature have an odd number of valance electrons and thus will not have octets on all their constituent atoms. Some elements tend to form compounds in nature in which they have more siulfer or less boron than 8 valance shell electrons.

Front 34

What are resonance structures? Why are they necessary?

Back 34

When we can write two or more equivalent lewis structures for the same molecule we find that the average or intermediate between the two lewis strucctures is correct.

Front 35

Explain how VSEPR predicts the shapes of molecules.

Back 35

It is based on the idea that lone pairs, single bonds, or multiple bonds repel each other. This repulsion because of the negative charge determines the geometry of the molecule.

Front 36

If all of the electron groups around a central atom are bonding (that is, there are no lone pairs), what is the molecular geometry for: 2 electron groups? Three electron groups? 4 electron groups? And Bond angles:

Back 36

2 electrons: linear 180
3 electrons: trigonal planar 120
4 electrons: Tetrahedral 109.5

Front 37

What is the difference between electron geometry and molecular geometry in VSEPR?

Back 37

Electron geometry: The geometrical arrangement of the electron groups.
Molecular geometry: the geometrical arrangement of the atoms.

Front 38

What is electronegativity?

Back 38

Electronegativity is the ability of an element to attract electrons within a covalent bond.

Front 39

What is a polar covalent bond?

Back 39

A polar covalent bond is a bond that has a dipole moment.

Front 40

Why is it important to know if a molecule is polar or nonpolar?

Back 40

It is important to know if a molecule is polar or nonpolar in order to determine how it will react with other molecules.

Front 41

If a molecule has polar bonds, will the molecule itself be polar? Why or why not?

Back 41

If a molecule contains a polar bond then the molecule is polar.