Honors Chemistry Midterm

Accuracy

How close you are to the actual value

Precision

How consistent you are with you measurments

Significant Figures Counting Rules

1. All non-zero digits are counted as significant figures

2. All zeroes in the middle are counted

3. Trailing zeroes only count if your measurement contains a decimal point

4. Leading zeroes never count

Adding/Subtracting with Significant FIgures

Round the answer to have the same number of decimal places as the least precise measurement. Units must match.

Multiplying/Dividing with Significant Figures

The final answer should be rounded to have the same number of significant figures as the least precise measurement. Units do not have to match, they are combined.

Metric

Length = meters, Mass = Kilograms (grams), Time = seconds, Volume = liters (milliliters), Amount = moles (mol)

King Henry D(a)oesn’t Usually Drink Chocolate Milk

Density

• Measures in g/mL

  • Physical, intensive property of matter

  • Mass/Volume

Density of a Solid

• Very ordered

• Slow moving

• Typically highest density

Density of a Liquid

• Less ordered

• Move faster

• Slightly lower density

Density of a Gas

• Move very fast

• Basically no attraction

• Very low density

Heat (q)

• Measured in Joules

• q can be positive if energy is gained

• q can be negative if energy is lost

Calorimeter

Measures heat involved in chemical changes.

Specific Heat (c)

• Intensive physical property

• Measures how much energy in Joules is necessary to raise the temperature of 1 gram of a substance by 1 degree celsius

Heat Equation

q=mcdeltaT

Also

m_m c_m (T_F - T_i ) = m_w c_w (T_F - T_i )

Note: q water = -q system

Dalton’s Atomic Theory

1. All matter is made up of tiny invisible particles called atoms.

2. Atoms of the same element are identical. Atoms of different elements are different.

3. Atoms cannot be divided, created, or destroyed.

4. Atoms of different elements combine in whole number ratios to form compounds

5. Chemical reaction involve the rearrangement of atoms. No new atoms are created or destroyed.

Dalton’s Law of Constant Composition

All chemical compounds exist as a fixed mass ratio of elements.

Dalton’s Law of Multiple Proportions

When two elements can make more than one compound the ratio of the mass is sed as a whole number

Dalton’s Law of Conservation of Mass

Cannot create or destroy atoms

Electron Discovered

Discovered by J.J. THomson in the early 1900s.

Cathode Ray Tube Experiment

• Magnet bent light inside of tube, which doesn’t happen to light usually. Must be a small charged particle.

  • Discovery of the electron.

Thomson’s Model of the Atom

• Plum pudding model

• Sphere itself (atom) was positively charged

• Had negatively charged electrons in it

Ernest Rutherford

• Discovered nucleus

• His experiment was having a radioactive source constantly admitting alpha particles. Those went to very thin gold foil, and he expected them to go through, but they ricocheted back.

• Discovered proton

Rutherfords Model

• Nucleus is positive in the middle

• Empty space with electrons

Chadwik

• Discovered neutron in 1932

Isotope

More than one possible mass for the element

Niels Bohr

• Danish Physicist

• Early 1900s

• Clarified structure of electron cloud

Core Electrons

Electrons filling lower energy levels

Valence Electrons

Electrons on the highest energy level used.

Octet Rule

All atoms want 8 valence electrons

Particles to Moles

6.02 × 10²³ Particles = 1 mol

Grams to Moles

1 mole= “molar mass” g

Wave-PArticle Duality

Certain properties are best described by thinking of light as a wave or a particle

Amplitude

• Height of light wave

• Determines the brightness or intensity

Wavelength

• Distance between two crests of a wave (in meters)

  • Determines lights color

Frequency

• Number waves that pass by a point in a given number of time

• Measured in cycles/s, s^-1 or hertz

Photoelectric Effect

• Light can cause electrons to be emitted from metal

• Needs to have a high energy, a certain frequency

Ground State

Loest energy state for electrons in an atom

Excited State

• Any higher energy state for an atom

• Not permanent

Relaxation

• The process of releasing energy to go to a lower energy state

Quantum

The minimum amount of energy that an atom can absorb or release.

Frequency of electron

Frequency = h/mv

Order of Quantum Mechanical Model

Shells → subshells → orbitals

Aufbau Principle

FIll electrons into low-energy orbitals first

Hunds Rule

One electron in each orbital of a p,d, or f before pairing

Pauli Exclusion Principle

No two electrons can have an identical position

Quantum Numbers

• Describe the properties of an electron in an atom

• n, l, ml, ms

n

• Shell of the electron

• Can be any number

l

• describes the subshells (s, p, d, f…)

• Can be any number up to (n-1) for a particular shell

ml

• Describes the orbital within the subshell

• whole numbers that go from -l to +l

ms

• Describes the spins in the orbitals

• +1/2 spin (up) or -1/2 spin (down)

Atomic Radius

• Radius gets bigger down a group

• Radius gets smaller across a period

• More protons more attraction

Ionization energy

• The energy needed to remove an electron

• IE gets smaller down a group

• IE gets bigger across a period

• More attraction, harder to pull out electrons

Electron Affinity

• Energy to add an electron to an atom. Is going to be more negative when closer to fluorine

• EA less negative down a group

• EA more negative across a period

Metallic Character

• How easily a metal loses electrons

• MC more metallic down a group

• MC more metallic across a period

Electronegativity

• How much an atom attracts electrons to itself in a covalent bond

• less EN down a group

• More EN across a period

Weighted Average Equation

avg mass= f(percentage as a decimal)1 m(mass)1 + f2 m2…

Overall Reactivity of a Metal

• Metals lose electrons in reactions

• Reactivity increases towards Francium

Overall Reactivity of a Nonmetal

• Nonmetals gain electrons in reactions

• Reactivity increases towards Fluorine

Physical Properties

Examples include: Color, smell, freezing point, boiling point, melting point, infra-red spectrum, attraction or repulsion to magnets, opacity, viscosity, and density.

Chemical Properties

Examples include: Heat of combustion, flammability and corrosion/oxidation resistance, reactivity with alter, PH, and electromotive force.