Chem 151 Exam 3

Front 1

Define: Enthalpy

Back 1

a property of a system that reflects its capacity to exchange heat (q) with the surroundings so that ∆H = q for a constant pressure process

Front 2

Define: Enthalpy change

Back 2

∆Hreaction = ∆Hproducts - ∆Hreactants

Endothermic reactions increase in enthalpy via the diagram

Exothermic reactions have a negative enthapy that releases heat into surroundings

Front 3

Thermochemical equation rules

Back 3

4 rules for using ∆H in thermochemical equations:

1.The magnitude of H is directly proportional to the amount of reactant or product used.

2.H for a reaction is equal in magnitude but opposite in sign to H for the reverse reaction.

3.The enthalpy change for a reaction depends on the state of the reactants and products.

4.The value of H for a reaction is the same whether it occurs in one step or in a series of steps (Hess’s Law).

Front 4

define enthalpy of formation

Back 4

An enthalpy of formation (Hf) is the enthalpy change for the reaction in which a compound is made from its constituent elements in their elemental forms.

Front 5

Main components of electron configuration notation

Back 5

Principle quantum number: Size and energy level

Angular momentum: Shape and Sublevel (S,P,D,F)

Magnetic: orientation in sublevel

Spin: Either positive or negative, clockwise or counterclockwise.

Front 6

Properties of wavelength and frequency

Back 6

Frequency: How many waves passing a given point per unit. A shorter frequency has a higher energy.

Wavelength: Wavelength is the actual wave from crest to crest.

Front 7

Bohr Constant

Back 7

2.18 x 10^(-18) J

Front 8

Know the equation

Back 8

Speed of light (C) = (wavelength) L x (Frequency) V

E=h (planks constant 6.63x10^-34) x (frequency)

Front 9

The electromagnetic spectrum in order

Back 9

gamma ray, Xray, ultraviolet rays, visible light, infared, microwave, radio.

Front 10

What is the photoelectric effect

Back 10

The photo electric effect is the production of electrons when light is shone on a material

Front 11

what is plancks quantum theory

Back 11

Max Planck suggested that the energy of light is proportional to its frequency, also showing that light exists in discrete quanta of energy.

Front 12

What is a line spectra

Back 12

a line spectra exist because electrons can only emit allowed energy from specific orbitals, and depending on the element the energies are different. That is why we get independent and unique line spectra

Front 13

Limitations of bohrs model?

Back 13

(1) Electrons exist only in certain discrete energy levels described by quantum numbers.

(2) Energy is involved in the transition of an electron from one energy level to another.

Front 14

Bohrs 3 postulates

Back 14

1. The electron of a hydrogen atom can only be incertain locations. Those locations are orbits,each one with a specific radius. Each orbitcorresponds to a definite amount of energy.(The greater the radius of the orbit, the higherthe energy of that orbit.)

2. An electron in a permitted orbit has the energythat is associated with that orbit. It has an“allowed” energy state.An electron will not radiate energy, so it does notslowly lose energy such that it would eventuallyfall into the nucleus.

3. The electron will only absorb or emit an amountof energy such that it can move from one orbit toanother orbit. That is to say that it can onlychange from one “allowed” energy state toanother. It will not absorb or emit energy lessthat the amount needed to move to anotherpermitted energy state/orbit.The energy is absorbed/emitted in the form of aphoton, E = hv.

Front 15

what is the heisenburg uncertainty principle

Back 15

Heisenberg uncertainty principle – tells us the we cannot know the location and momentum of an electron at the same time so we literally have no idea where it is, only the probability of where might be at any given time.

Front 16

what is the use of schrodinger equations in quantum mechanics

Back 16

Schrodinger equations – gave us the ability to quantify and estimate a region where the electrons are most likely to be “most of the time” – blue clouds.

Front 17

What is quantum mechanics

Back 17

Quantum mechanics is a field of study that deals with things on the near atomic scale, it was developed to further understand the atom and the differing light spectrum emitted by different elements.

Front 18

What is the conflict with light

Back 18

Light is considered to act in a wave. Waves dont have mass but light acts as a particle sometimes.

Particles are generally considered to have mass whereas waves are not considered to have mass – see the conflict? (wave – particle duality nature of light)

Front 19

Wavelike movement of matter?

Back 19

Matter only has wavelike properties on a small scale, the object itself has to be small

Front 20

What Ψ

Back 20

Ψ = the amplitude of the electron wave

Ψ 2 = is a probability function

Ψ 2 dx = the probability of finding the electron particle in the region of space dx.

Front 21

Probability density

Back 21

The density of the electron cloud around a nucleus. the orbitals have differing densities, and make it simpler or harder to determine the position of an electron

Front 22

Observing orbitals what do we find.

Back 22

1. Number of peaks increases with ↑ n

2. Number of nodes increases with ↑ n

3. Electron density ↔increases with ↑ n

Front 23

How is bohrs model similar to schrodingers

Back 23

Bohr's model depicts differing lines and energy levels which is right, and the Schrodinger model expands on this by demonstrating orbital clouds, where the electron position is uncertain, and various energy levels that an electron position can be determined at.

Front 24

S,p,d orbital shapes

Back 24

S orbitals are simply spheres

P orbitals look like dumbbells

D orbitals look like four leaf clovers when laid flat or given a z axis, it looks like a dumbbell shoved into a doughnut

Front 25

Ionization energy compared to atomic radii

Back 25

As atomic size increases, ionization energy decreases.Ionization energy is the amount of energy needed to remove the most loosely held electron from a single atom (in the gaseous state), resulting in a positively charged ion and a free electron.Atomic size is the essentially the distance from the center of the atom to the outermost electron, which is the most loosely held electron.

Front 26

Metallic and nonmetallic patterns

Back 26

Metallic patterns increase going diagnolly down to the left from carbon and nonmetalic is the exact inverse of that

Front 27

What are condensed electrons

Back 27

Elements in a group have the outer shell electrons.

• The electron configurations for these elements only differ by the previous noble gas and energy level.

Front 28

What are the three basic kinds of bonds

Back 28

Covalent

Ionic

Metallic

Front 29

What are the different electrostatic interactions

Back 29

Attractions

Repulsions

Repulsions between nucleii

Front 30

6N + 2

Back 30

6N + 2 Rule

• “N” = the number of atoms in the molecule except hydrogen.

1.If 6N + 2 calculation = number of valence electrons, then all single bonds. (SF2)

2.If 6N + 2 calculation > number of valence electrons by 2, then one double bond. (O2)

3.If 6N + 2 calculation > number of valence electrons by 4, then two double bonds or one triple bond. (CO2 or N2)

Front 31

What is polarity

Back 31

Bond polarity is a measure of how equally or unequally the electrons in any covalent bond are shared.

• Nonpolar covalent bond – electrons are shared equally.

• Polar covalent bond – one of the atoms exerts a greater attraction for the bonding electrons than the other atoms so the electrons are unequally shared.

Front 32

What is resonance

Back 32

Differing structures that are all equated.