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General Chemistry MCAT > Bonding and Chemical Interactions > Flashcards

Bonding and Chemical Interactions Flashcards

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1
Q

Are the chemical and physical properties of a molecule the same as those of the constituent elements that make up the molecule?

A

The chemical and physical properties of a compound are usually very different that those of its constituents

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2
Q

Can Hydrogen follow the octet rule?

A

-Hydrogen is an exception to the octet rule
- Hydrogen can only have 2 valence electrons

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3
Q

Octet Rule

A

The desire of all atoms to achieve noble gas configuration

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4
Q

What is a simple way to remember all the exceptions to the octet rule?

A

1) Incomplete octet: elements that are stable with fewer than 8 electrons in valence shell

2)Expanded octet: Any element in period 3 and greater can hold more than 8 electrons.

3) Odd numbers of electrons: Any molecule with an odd number of valance electrons cannot distribute those electrons to give eight to each atom. (Nitric Oxide has eleven valence electrons total)

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5
Q

What are the elements that are stable with an incomplete octet?

A

1) Hydrogen( stable with 2 electrons)

2)Helium (stable with 2 electrons)

3)Lithium (stable with 2 electrons)

4)Beryllium (stable with 4 electrons)

5) Boron (stable with 6 electrons)

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6
Q

What are the elements that are stable with an expanded octet?

A

1) any element in period 3 and greater.
EX: phosphorus (10), Sulfur (12), Chlorine (14) ect.

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7
Q

What are the common elements that almost always abide by the octet rule?

A

1) carbon

2)nitrogen

3)Oxygen

4)Flourine

5)Sodium

6)Magnesium

Remember, nonmetals gain electrons to achieve their respective complete octet and Metals lose electrons to achieve their respective complete octet

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8
Q

What are the 2 classifications for chemical bonds?

A

1) ionic

2) Covalent

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9
Q

Chemical bonds

A

An attraction between two atoms resulting from a sharing of outer-shell electrons.
-results in the formation of a compound.

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10
Q

Ionic bonding

A

-A type of bond that results in 2 oppositely charged ions

-typically a metal loses electrons and a nonmetal accepts those electrons.

-The resulting electrostatic attraction between opposite charges is what holds the ions together.

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11
Q

What type of structure does the type of attraction created through ionic bonding form?

A

-Lattice structure consisting of repeating rows of cations and anions rather than individual molecular bonds.

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12
Q

What is covalent bonding?

A

when atoms share one or more pairs of electrons with another atom.

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13
Q

What kind of atoms usually exhibit covalent bonding?

A

-Usually non-metals that have a relatively similar values of electronegativity.

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14
Q

What determines the degree of polarity in a covalent bond?

A

-The degree to which the pair of electrons are shared.
-this will determine if the covalent bond is polar or non polar

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15
Q

coordinate covalent

A

a covalent bond in which one atom contributes both bonding electrons

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16
Q

What type of chemical bond forms between atoms that have significantly different electronegativities?

A

-Ionic bonds

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17
Q

What are the characteristics for ionic compounds.

A

1) ionic compounds have a very high melting and boiling point.

2) Many ionic compounds dissolve readily in water and other polar solvents.

3) ionic compounds are very good conductors in the molten or aqueous state.

4) Ionic compounds form a crystalline lattice in the solid state.

-consists of repeating positive and negative ions.

-This arrangement the attractive forces between oppositely charged ions are maximized and the repulsive forces between ions of like charge are minimized.

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18
Q

Why do ionic compounds tend to form between metals and nonmetals?

A

This is due to:
-differences in electronegativity
-metals have low ionization energies while nonmetals have high electron affinities.

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19
Q

Why do covalent bonds occur?

A

-This is because the electronegativity values are relatively similar between 2 atoms.
-This allows for a stalemate where a covalent bond will allow a mostly equal sharing of electrons.

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20
Q

What are the characteristics of covalent compounds?

A

-contain discrete molecular units with relatively weak intermolecular interactions. because of this, covalent compounds have lower melting and boiling points.

-Covalent compounds do not break down into constituent ions and are therefore poor conductors of electricity in the liquid state or in aqueous solutions.

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21
Q

What are the 3 characteristics of a covalent bond?

A

1) bond length :
as the number of shared electron pairs increase, the 2 atoms that make up the covalent bond are pulled closer together.

2)Bond energy:
-The greater the number of pairs, the more energy is required to break the bonds holding the atoms together.

3) Polarity:
The atom with the higher electronegativity get the larger share of the electron density.

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22
Q

dipole

A

a polar covalent bond that has a separation of charges

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23
Q

non polar covalent bond

A

a covalent bond in which the bonding electrons are shared equally by the bonded atoms, resulting in a balanced distribution of electrical charge.

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24
Q

What kind of atoms can come together to form a nonpolar covalent bond?

A

–Only bonds between atoms of the same element will have exactly the same electronegativity.
-therefore only atoms of the same element can have nonpolar covalent bonds.
-there can be nonpolar covalent bonds between atoms with a difference of electronegativity of less than .5

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25
Q

polar covalent bonds

A

A covalent bond between atoms that differ in electronegativity. The shared electrons are pulled closer to the more electronegative atom, making it slightly negative and the other atom slightly positive.

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26
Q

dipole moment

A

a property of a molecule whose charge distribution can be represented by a center of positive charge and a center of negative charge

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27
Q

Electronegativity values for polar and non polar covalent bonds?

A

1) polar covalent: .5 to 1.7

2) nonpolar covalent: 0 to .5

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28
Q

What are bonding and nonbonding electrons

A

1) Bonding electrons: valence electrons involved in a covalent bond.

2) nonbonding electrons: valence electrons no incolved in covalent bonds/

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29
Q

Lewis structure

A

A structural formula in which electrons are represented by dots; dot pairs or dashes between two atomic symbols represent pairs in covalent bonds.

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30
Q

formal charge

A

The number of valence electrons in an isolated atom minus the number of electrons assigned to the atom in the Lewis structure

31
Q

What is the equation used to find the formal charge of a compound?

A

Formal charge= (#valence electrons)-(#bonds)-(#nonbonding electrons)

32
Q

What is the differences between that formal charge and oxidation number

A

-Formal charge: hypothetical charge that would result if all bonding electrons are shared equally in a covalent bond.

-Oxidation number: The hypothetical charge that would result if all bonding electrons are assigned to the more electronegative atom in the bond (ionic)

The distribution of electron density between the carbon and oxygen atoms lies somewhere between the extremes predicted by the formal charges and the oxidation states.

33
Q

Resonance structures

A

Lewis structures that have the same arrangement of atoms in a molecule but differ in the distribution of electrons among the atoms.

-The actual electron distribution in the compound is a hybrid of all the resonance structures.

34
Q

resonance hybrid

A

the actual structure of a molecule that is intermediate between two or more resonance structures

35
Q

How does one access the stability of a resonance structure?

A

1) a lewis structure with small or no formal charge is preferred over one with a large charge.
2) A lewis structure with less separation between opposite charges is preferred over a structure with a large separation.
3) A lewis structure in which a negative formal charge are placed on more electronegative atoms is more stable than the opposite.
The more stable a lewis structure, the more the structure is a contributor to the resonance hybrid

36
Q

VSEPR

A

valence shell electron pair repulsion theory

37
Q

What is the VSEPR theory?

A

-Predicts the molecular geometry of covalently bonded molecules based on their lewis dot structure.

-States the the 3D arrangement of atoms surrounding a central atom is determined by the repulsion between bonding and nonbonding electron pairs in the valance shell of the central atom.

38
Q

What are the steps used to predict the geometrical structure of a molecule using the VSEPR theory?

A

1) draw lewis structure of molecule.

2) Count the total number of bonding and nonbonding electron pairs in the valance shell of the central atom.

3) arrange the electron pairs around the central atom so that they are as far apart as possible.

39
Q

electron geometry (VSEPR)

A
40
Q

What are the criteria for a linear molecular geometry

A

1) Number of electron groups: 2

2) Number of Lone Pairs: 1

3) Ideal Bond Angles: 180°

41
Q

What are the criteria for a trigonal planar electron geometry

A

1) Number of electron groups: 3

2) Number of Lone Pairs: 0 or 1

3) Ideal Bond Angles: 120°

42
Q

What are the criteria for a Tetrahedral electron geometry

A

1) Number of electron groups: 4

2) Number of Lone Pairs: 0, 1, or 2

3) Ideal Bond Angles: 109.5°

43
Q

What are the criteria for trigonal bipyramidal electron geometry

A

1) Number of electron groups: 5

2) Number of Lone Pairs: 0, 1, 2, or 3

3) Ideal Bond Angles: 90°, 120° , 180°

44
Q

What are the criteria for a Octahedral electron geometry

A

1) Number of electron groups: 6

2) Number of Lone Pairs: 0, 1, or 2

3) Ideal Bond Angles: 90°, 180°

45
Q

bent electron geometry

A

The central atom is surrounded by 2 shared electron domains and 1 (or 2) unshared electron domain.

120°

46
Q

trigonal pyramidal electron geometry

A

The central atom is surrounded by 3 shared electron domains and 1 unshared electron domain

109.5°

47
Q

Seesaw electron geometry

A

4 bonding domains, 1 non-bonding domain

90°, 120°

48
Q

T-shaped electron geometry

A

3 bonding domains, 2 non-bonding domains

90°

49
Q

linear (trigonal bipyramidal)

A

180°

50
Q

squared pyramidal electron geometry

A

90°

51
Q

square planar electron geometry

A

90°

52
Q

What is the difference between electron geometry and molecular geometry?

A

1) Electron geometry: describes the spacial arrangement of all pairs of electrons around a central atom, including both bonding and lone pairs of electrons.

2) Molecular Geometry: Describes the spacial arrangement of only the bonding pairs of electrons.

53
Q

What shapes can molecular geometry be?

A

1) linear

2)trigonal planar

3) Tetrahedral

4) Trigonal bopyramidal

5) octahedral

54
Q

ideal bond angle

A

-determined by electronic geometry

-lone pairs of e- are closer to the nucleus so they exert more repulsion

-presence of lone pairs of e- makes ideal angle smaller

EX: a tetrahedral shape should have angles of 109.5° however the lone pair of electrons in the oxygen atom exert more repulsion than bonding pairs and the angle will be 104.5° instead

55
Q

How can the molecular geometry effect the polarity of a molecule?

A

-First we must remember that a compound with non polar bonds is always non-polar but a compound with polar bonds may be polar or nonpolar, depending upon the spatial orientation of the polar bonds in the molecule.

-this means that a compound made up of polar bonds can have those bonds arranged in a way that the polarity of each bond cancels the polarity of each bond.

EX: CCl4 has four polar C-Cl bonds, but because the molecular geometry of carbon tetrachloride is tetrahedral, the four bond dipoles point to the vertices of the tetrahedron and cancel each other out. this results in a non polar compound.

56
Q

must a compound with non polar bonds always be non-polar?

A

-Yes, a non-polar compound must always be non-polar

-BUT
-A compound made up of polar bonds can be polar or non-polar depending on the arrangement of the molecules molecular geometry.

57
Q

What happens to the orbitals when 2 atoms bond to form a compound?

A

The atomic orbital interact to form a molecular orbital.

58
Q

molecular orbital

A

an orbital that applies to the entire molecule and that describes the probability of finding the bonding electrons in a given space.

59
Q

How does one obtain a molecular orbital?

A

-By combining the wave functions of the atomic orbitals.

-Qualitatively, the overlap of 2 atomic orbitals describes this molecular orbital.

60
Q

bonding orbital

A

A molecular orbital that is obtained if the signs of the 2 atomic orbitals are the same.

61
Q

antibonding orbital

A

-A molecular orbital that is obtained when the signs of the atomic orbitals that make up the molecular orbital are not the same

62
Q

What happens then the atomic orbitals that make up a molecular orbital overlap head to head?

A

The resulting bond is a Sigma bond

63
Q

sigma bond characteristics

A

-Formed when atomic orbitals overlap head to head.

-this type of bond allows for free rotation about their axes because the electron density of the bonding orbital is a single linear accumulation between the atomic nuclei.

64
Q

What happens then the atomic orbitals that make up a molecular orbital overlap in a way that there are 2 parallel electron cloud densities?

A
  • A pi bond is formed
65
Q

Pi bond characteristics

A
  • pi bonds do not allow for free rotation because electron densities are parallel and cannot be twisted in a way that allows continuous overlapping of the clouds of electron densities.
66
Q

intermolecular forces

A

the forces which mediate interaction between molecules
-these forceds can impact certain physical characteristics such as melting point and boiling points.

67
Q

types of intermolecular forces

A

1) London dispersion forces

2) Dipole-dipole interactions

3) Hydrogen bonds

Weakest : London - Dipole - Hydrogen : Strongest

68
Q

London Dispersion Forces (LDF)

A

is a temporary attractive force that results when the electrons in two adjacent atoms occupy positions that make the atoms form temporary dipoles. This force is sometimes called an induced dipole-induced dipole attraction.

69
Q

Characteristics of LDF

A

-The weakest of all intermolecular forces.

-only significant when molecules are in close proximity

-strength depends on ease that molecules can be polarized to induce a dipole.

-Larger molecules possess larger LDF

70
Q

dipole-dipole interactions

A

attractive forces between polar molecules

-result when two dipolar molecules interact with each other through space. When this occurs, the partially negative portion of one of the polar molecules is attracted to the partially positive portion of the second polar molecule

71
Q

Hydrogen bond

A

A type of weak chemical bond formed when the slightly positive hydrogen atom of a polar covalent bond in one molecule is attracted to the slightly negative atom of a polar covalent bond in another molecule.

72
Q

What elements must hydrogen be bonded to to exhibit hydrogen bonding?

A

FON

-Flourine

-Nitrogen

-Oxygen

-Hydrogen bond is formed only by the three highly electronegative elements- fluorine, oxygen and nitrogen. So, hydrogen bonding is possible only in those compounds in which the hydrogen atom is directly bonded to fluorine, oxygen or nitrogen.

73
Q

Is a hydrogen bond stronger than a covalent bond?

A

-A covalent bond is stronger
-Hydrogen bonding is only 10% as strong as a covalent bond.

General Chemistry MCAT (7 decks)

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