Chemistry Midterm

Chemistry

The study of matter and the changes it undergoes

Organic Chemistry

Study of compounds containing carbon

Inorganic chemistry

Study of compounds not containing carbon

Biochemistry

Study of the processes that take place in living organisms

Analytical Chemistry

Study of the composition of matter

Physical chemistry

Study of reaction mechanisms (rates and energy transfer occurring in a reaction)

Pure Chemistry

• Pursuit of chemical knowledge for its own sake

• Ex. sticky notes

Applied chemistry

research directed toward a practical goal

Steps of Scientific Method

1. Observation

2. hypothesis

3. controlled experiment

4. theory (explanation for what happened)

5. scientific law (summary of the results of many observations)

6. collaborate and communicate

steps of numeric problem solving

1. Analyze

2. calculate

3. evaluate

accuracy

a measure of how close a measurement is to the actual, true, or theoretical value

precision

a measure of how close a series of measurements are to one another

error

accepted value - experimental value

percent error

sig figs when looking at a physical measurement

all known digits + 1 estimated digit

adding or subtracting sig figs

sum/difference rounded to the same number of decimal points as the number with the least number of decimal points in the equation

International System of Units (SI)

Standards of measurement used in science based on the metric system

SI Base Units

• Length: meter (m)

• Mass: kilogram (kg)

• temp: kelvin (K)

• time: seconds (s)

• Amount of a substance: mole (mol)

• luminous intensity: candela (cd)

• Electric current: ampere (A)

1 Liter

1 dm³, 1000 cm³

energy

force (N) x distance (m)

force

acceleration

velocity

Joule

Newton

Calorie

• non-SI unit for energy

• quantity of heat that raises one gram of pure water by 1 C

• 1 cal = 4.184 J

Celsius

• Uses freezing point of water (0 C) and boiling point of water (100 C)

• C = 5/9(F-32)

Kelvin

• aka absolute scale

• freezing point of water: 273.15 K

• boiling point of water: 373.15 K

• degree sign is not used

• K = C + 273.15

• No negative temps

Density

• D = g/cm³

• D = g/mL

extensive properties

a property that depends on the amount of matter in a sample

Intensive properties

properties that depend on the type of matter, not how much

Pure substance

matter that has uniform and definite composition

physical property

quality or condition of a substance that can be observed without changing the composition of a substance

solid

definite shape and volume, incompressible

liquid

indefinite shape, definite volume, particles not rigid or orderly but flow past each other

gas

indefinite shape and volume, particles flow past each other, compressible

fluid

any substance that has particles able to flow past each other

vapor

the gaseous state of a substance that is generally a liquid or solid at room temperature

physical change

properties of a material change but the composition does not, reversible or irreversible

heterogenous mixture

a mixture in which the composition is not uniform throughout

homogenous mixture

a mixture in which the composition is uniform throughout, also called a solution

phase

describes any part of a sample within uniform composition and properties

filtration

separated solid from liquid due to particle size

distillation

separates two liquids due to their volatility (readiness to become gas)

chromatography

separates a mixture due to phase mobility

centrifuge and separation funnels

separates mixtures based on density

chemical change

produces matter with different composition than its original

2 ways to break down compounds

Heating and electrolysis

distinguishing substances and mixtures

if the composition of a material is fixed, it is a substance. If the composition can vary, it is a mixture

atomic number

# of protons, unique to each element

period

• horizontal row on a periodic table

• properties differ from one to the next

• 7

group

• vertical column

• properties similar

• 18

metals

• 80% of the periodic table

• generally good heat and electricity conductors

• high sheen or luster (reflect light)

• solid at room temp (except Hg)

• ductile (can be drawn into a wir3e)

• malleable (can be formed into foil)

• like to form cations (atoms with a positive charge)

• metallic character increases from top right to bottom left on the periodic table, with exceptions

nonmetals

• located in the top-right corner of the periodic table, except for H

• most are gases at room temp, some solids, 1 liquid (Br)

• poor conductors, good insulators

• solids are brittle

• like to form anions (atoms with a negative charge)

metalloids

• staircase that borders metals and nonmetals on the periodic table

• semi-conductors (conduct heat and electricity efficiently between a metal and nonmetal)

• solid at room temp

chemical properties

• the ability of a substance to undergo a specific chemical change

• can only be observed when going through a chemical change

chemical reaction

when one or more substances change into one or more new substances

reactant

substance present at the start of a reaction

product

substance formed during the reaction

4 clues of a chemical change

• transfer of energy: energy used or produced in the form of light or heat

• change in color

• formation of a gas

• precipitate forms: a solid that forms and settles out of a liquid mixture

model

representation of a theory using words, diagrams, or mathematical expressions

atom

the smallest particle of an element that retains its identity and properties in a chemical reaction

Democritus

• said everything is made form indivisible and indestructible particles (atoms)

• no experimental support

Dalton

Turned Democritus’s ideas into scientific theory by studying ratios in which elements combine in chemical reactions

Dalton’s first postulate

all elements are composed of tiny indivisible particles called atoms. (Not valid)

Dalton’s second postulate

atoms of the same element are identical. (Not valid)

Dalton’s third postulate

Atoms of different elements can be physically mixed together or chemically combined in simple whole-number ratios to form compounds. (Valid)

Dalton’s fourth postulate

Chemical reactions occur when atoms are separated from each other, joined, or rearranged in different combinations. Atoms of one element cannot change into atoms of another element as a result of a chemical reaction. (Valid)

Size of Atom

Radius of an atom ranges from 5 × 10^-11 m to 2 × 10^-10 m

observing atoms

through scanning electron microscopes. A beam of electrons is focused on the sample

Dalton’s model of an atom

a dense sphere

Cathode Ray Experiment

• Conducted by JJ Thompson

• Cathode ray is a glowing beam that travels from the cathode to the anode

• Cathode is a negatively charged electrode

• Anode is positively charged electrode

• Thomspon took most of the pressure out of the system and ran the Cathode Ray

• Measured the mass to charge ratio of the tiny negative particles in the ray using a magnetic field and the beam deflected a lot

Cathode Ray conclusions

• All substances contain negatively charged particles (capusuls/electrons) because the beam was always attracted to the positive side of the magnetic field

• particles must have a very great charge, be very small, or both

Robert Millikan

• Oil drop experiment to find the charge of an electron

• Suspended negatively charged oil droplets between two charged plates

• Adjusted the voltage to see how the oil fell

• Discovered the charge of an electron

charge of an electron

1.60 × 10^-19 coulomb

Eugene Goldstein

• anode ray experiment

• discovered the proton

• anode ray deflected much less than cathode ray

James Chadwick

• Realized that the mass of an atom was much larger than the mass of protons and electrons

• called the extra particle a neutron

Mass of an electron

9.11 × 10^-31 kg

mass of a proton

1.67 × 10^-27 kg

Ernest Rutherford

Conducted an experiment using gold foil. According to Thompson, alpha particles (helium atoms without their electrons) should pass straight through the foil, but 1 in 20,000 shot back at him. So, he proposed that the atom is mostly empty space with a nucleus containing the protons and neutrons. Called this the nuclear atom.

Atomic number

number of protons, gives elements unique properties.

mass number

protons + neutrons

hydrogen isotopes

• Hydrogen-1

• Hydrogen-2 (Deuterium)

• Hydrogen-3 (Tritium)

Mass spectrometer

allows us to calculate the masses of atoms

relative mass

one AMU is 1/12 the mass of a Carbon-12 atom.

Weighted atomic mass

(mass x abundance) + (mass x abundance)

nuclear atom

protons and neutrons are in the positively charged nucleus, electrons distributed around the nucleus.

Bohr Atom model

• Planetary model

• electrons exist in specific paths called energy levels

• predicted the behavior of hydrogen

• didn’t account for repulsion between electrons

quantum

• the amount of energy needed to climb an energy level

• explains why elements emit different colors

atomic emission spectrum

different frequencies of light emitted by different elements

photoelectric effect

the phenomenon that when light shines on metal, electrons are emitted from the metal if there is sufficient energy. discovered by Einstein

spectroscopy

• measurements of spectra produced when radiation from the electromagnetic spectrum interacts with matter

• matter absorbs and emits electromagnetic radiation

Wavelength and frequency relation

inversely proportional

frequency and energy relation

directly proportional through Planck’s constant

Energy when a photon is absorbed or emitted

when a photon is absorbed or emitted by an atom or molecule, energy is increased or decreased by the amount equal to the energy of the photon

quantum mechanical model

• Erwin Schrodinger worked from Bohr’s planetary model to develop equations to determine the properties of an electron as a wave and particle

• Photoelectric effect + Heisenberg uncertainty principle = quantum mechanical model

• determined allowed regions where electrons could exist (probabilities)

• no specific paths or orbits in this model

Heisenberg uncertainty principle

it is impossible to know the position and momentum (trajectory) of quantum particles

electron cloud

the darker the cloud, the higher the probability an electron is there

atomic orbital

the region of space with the highest probability of finding an electron

Principle energy levels (n)

Bohr’s energy levels