Chem 101 Midterm 1

Intensive Property

A property that doesn’t change with the amount of the substance present (ex. density)

Extensive Property

A property that changes with the amount of substance present (ex. mass, volume).

Chemical property

A property having to do with a chemical change, if it says “reacts,” it’s probably a chemical property (ex. flammability, acidity)

Physical property

A property that can be observed or measured without changing the substance's chemical identity (ex. color, melting point).

Elements vs Compounds

Elements are pure substances that cannot be broken down into simpler substances, while compounds are substances formed when two or more elements chemically bond together.

Atoms vs Molecules

Atoms are the smallest unit of an element, while molecules are two or more atoms bonded together, representing the smallest unit of a compound.

Diatomic elements

Elements that are found as two of the same element bonded together (Ex. H2, N2, O2, etc). Neumonic: Have No Fear Of Ice CoLd Beer. Hydrogen, Nitrogen, Fluorine, Oxygen, Iodine, Chlorine, Bromine.

Physical Change

A type of change that alters the form or appearance of a substance but does not change its chemical composition. (Ex. Evaporation, melting, freezing)

Chemical Change

A process that involves the transformation of one or more substances into different substances, resulting in a change in chemical properties (Ex. combustion, rusting, digestion)

Energy

The capacity to do work

Kinetic Energy

The energy of motion

Potential Energy

Energy by virtue of position or composition

Law of Conservation of Energy

Energy cannot be created or destroyed, but it can be converted from one form to another. (physical and chemical changes have changes in energy)

Potential Energy as a Measure of Stability

• Oppositely-charged particles attract, PE is negative

  • More Stable

• Like-charged particles repel, PE is positive

  • Less Stable

Which is more favorable, negative PE or 0 PE

Negative

Sublimation

Going from solid to gas, sublime → lifts you up (Ex. water vapor coming off ice)

Deposition

Going from gas to solid (In back of freezer)

Energy Absorption

From lower energy to higher energy (Ex. Solid → Liquid, Liquid → Gas)

Energy Release

From higher energy to lower energy (Ex. Gas → Liquid, Liquid → Solid)

Does physical or chemical changes require more energy?

Chemical changes

Dimensional Analysis

How we analyze units

cm compared to mL

1cm³ = 1mL = 1cm x 1cm x 1cm

Relative mass of an electron (e^-)

~0 amu or 0.0005 amu

Relative mass of a proton (p^+)

~1 amu or 1.007 amu

Relative mass of a neutron (n^0)

~1 amu or 1.009 amu

Thompson’s Plum Pudding Model (blueberry muffin)

Idea that an atom was a positive sphere of matter (muffin) with negative electrons (blueberries) embedded in it

Rutherford’s Experiment

He shone a beam of alpha particles on a thin sheet of gold foil, a.k.a. what should’ve been the blueberry muffin. They saw that most of the particles went through, but some veered off and bounced back in different directions at large angles, showing that there is a nucleus. This disproved Thomson’s model

Nucleus

Region of concentrated mass and positive charge

If you increase thickness of gold in Rutherford’s experiment what will happen?

More alpha particles would be scattered at large angles, more nuclei more likely the particles are to hit the nuclei

What size would the atom be if the nucleus was the size of a blueberry

The size of Kenan Stadium

What is most of the mass of an atom?

Protons and Neutrons

Most of atoms are _____

Empty Space

Atoms are defined by the number of _____

Protons

Most of the volume in an atom is accounted for by _______

The electron cloud

Group 1 in the periodic table

Alkali Metals

Group 2 in the periodic table

Alkaline earth metals

Group 16 in the periodic table

Chalcogens

Group 17 in the periodic table

Halogens

Group 18 in the periodic table

Noble gases

Metals

• White section

• Shiny, solid, conductor

• Malleable and ductile

• Solid at room temp (except mercury)

Nonmetals

• Light gray section

• Solids (brittle), liquids, and gases

• Nonconductors

Metalloids

• Dark gray section

• Shiny (like metals) but brittle (like nonmetals)

• Semiconductors

Relationship between density, mass, and volume

Units to measure speed

length/time: u (speed/velocity) = m/s

Units to measure volume

length³: V = m³

Units to measure density

mass/volume: D = kg/m³

Units to measure energy

Joule: J = kg x m² / s²

Units to measure power

Watt: W = Joule/s

Relationship between Celsius and Kelvin

Celsius is shifted 273 to become Kelvin (K=C+273). Melting point of ice is 0C and 273K

Temperature

A measure of the average kinetic energy of the particles in a sample

What are celsius and kelvin based off of

Celsius is based on the properties of water, Kelvin is based on the properties of gas

Accuracy

Proximity of a measurement to the true value (bullseye)

Precision

Proximity of several measurements to each other (shooting darts at the same place every time)

Measurement

The comparison between a known and unknown value

Uncertainty

The smallest measurable difference between measured properties. More decimal places means less uncertainty and more precision. Determines the limits of precision of a measurement

Significant figures

The measured digits in a number

How many significant figures

• 0s after a number with no decimal point don’t count (12000 has only 2 sig figs)

• A decimal point means all 0s after it are significant (1.2000 and 12000. have 5 sig figs)

• 0s on the left of a number are not significant (0.0012 has 2 sig figs)

• Exact numbers have infinite precision (2 iclickers)

• Sig figs from conversion factors within one system are not counted (1 m = 100 cm, 1ft = 12in)

• Conversion factors between systems need to follow rules (2.2 lb = 1.0 kg)

  • Exception: 1in = 2.54 cm exactly

Sig figs for multiplication and division

Same as number with fewest sig figs

Sig figs for addition and subtraction

Same as number with fewest decimal places

Why is a mole so large?

So we can interact with the amount of the substance bc atoms are so small

Molar Mass

The mass (in grams) of one mole of a substance, same as atomic mass (u/atom)

One mole of an element has a mass of:

That element’s atomic mass

Relationship between wavelength and energy and frequency

Shorter wavelength is more energy less frequency

Frequency ν (measured in Hz)

How often the wave (λ (measured in meters)) happens

Speed of light (c)

c=λν or ν=c/λ

Energy of a photon

E=hc/λ or λ=hc/E

How do photons interact with atoms?

1 photon hits 1 atom to eject 1 electron

Does the difference between Bohr model steps change?

The energy difference between two steps is always a set difference. Energy levels are described by quantum numbers (n = 1, 2, 3, etc)

Electron moves to higher energy level

When photon is absorbed

Electron moves to a lower energy level

When photon is emitted, more energy between levels means photon emitted is higher energy

Wavelength of an electron (de Broglie wavelength)

λ = h/mu

In what way do electrons behave like waves?

They experience interference in a double slit experiment

Constructive interference

When two waves in phase (building something together, in line with each other) add to give a wave with twice the amplitude

Destructive interference

When two waves out of phase with each other add to cancel each other out

Standing waves

Waves constructively interfering with itself. They need to be integers because non-integer wavelengths don’t match up when wrapped around themselves.

Wave-particle Duality

Since electromagnetic radiation (EMR) can have particle behavior (photons), particles can have wave behavior

How does wave-particle duality have do do with electrons

Electrons (and any object with mass) are moving in a wave-like pattern

Hertz (Hz)

# of cycles per second (1s^-1)

Why is it hard to observe wavelength of large objects

Their wavelength is very small compared to their size

Implications of de Broglie wavelength

• Large object = large mass and speed = smaller wavelength

• Smaller wavelength (relative to object) = no observed wave-like movement

• Larger wavelength (relative to object) = object moves as wave

Uncertainty Principle

We cannot simultaneously define the position and momentum of a quantum mechanical particle. With electrons we define energy (proportional to momentum) exactly but accept limitation that we do not know exact position

• (Δx)(Δmu) ≥ h/4π → Uncertainty of position and Uncertainty of momentum

  • If you measure one precisely, the uncertainty of the other increases

Schrodingers Equation

Shows a 3D wave function Ψ (how we define orbitals) that shows where the electron with that set of quantum numbers is most likely found. Most will be in the middle though some on the sides like spraying ink onto a paper. Solving the wave equation gives a set of wave functions or orbitals

Orbitals

Describes the volume around the nucleus where the electron is most likely to be found, described as quantum numbers (n, l, m sub l)

Quantum number “n”

The principal quantum number describes the energy level (shell) on which the orbital resides. The values are integers greater than or equal to 1. As the energy level increases, so does the number of nodes; orbital size increases, and it is easier to remove an electron (a greater distance from the nucleus makes the connection weaker)

The # of nodes

n - 1

Radial Probability

The likelihood of finding an electron at some distance from the nucleus. At zero, the radius is zero, so the radial probability function (Ψ²r²) goes to zero. Even as n increases there is still a probability that there are electrons close to nucleus, even though small probability

Why isn’t the nucleus a node?

To be a node the phase must switch

Quantum number “l”

• Defines the shape of the orbital

• Values between 0 to n-1

• Value of l and corresponding designation:

  • 0,s

  • 1,p

  • 2,d

  • 3,f

  • 4,g

Quantum number “m sub l”

• Describes the 3D orientation of the orbital (along which axis)

• Values between -l and +l (Ex. l=2 msubl=-2,-1,0,1,2)

An orbital is a 3d representation of a ______

Wave

S Orbital

• l = 0

• msubl has 1 value: 0

• Looks like a sphere

• No nodes

p orbitals

• Value of l=1

• msubl has 3 values: -1,0,1

• Dumbell shape (2 lobes) with a node between

d orbitals

• Value of l=2

• msubl has 5 values

• (4/5 orbital shapes) 4 lobes, one orbital looks like dumbell with donut on it

• 4 lobes with 2 nodes

f orbitals

• 6 lobes

• 3 nodes

• msubl has 7 values

Orbitals vs electrons

n,l,msubl describe orbitals, all those plus msubs describe electrons. There can be 2 electrons in 1 orbital but without describing the spin of the electron, all that is described is the orbital

Spin Quantum Number “msubs”

• 2 values (+1/2 or -1/2)

• Spin up vs spin down

Degenerate orbitals

for one-electron atoms or ions, orbitals with the same n value have the same energy

Non-Degenerate Orbitals

• As the number of electrons increases so does the number of interactions between them

• In many-electron atoms, orbitals with the same n-value are not degenerate

Subshells and the periodic table

*note that helium (at top right of p block) is in the s block technically*

Aufbau Principle

Fill lower energy orbitals first, in ground state