Unit 1 and Unit 2 Chem 103 Exam 1

Science + Chemistry is

a way of seeing and understanding the world

Science + Chemistry is a process

of discovery

Science + Chemistry relies

relies on a shared language and observation

Science + Chemistry prefers

quantitative over qualitative measurements

Discovery Cycle

Observation→Hypothesis—>Experiment

Natural Laws

a statement of what happens with no exceptions ex. energy is conserved

Theory

Logical model that explains why things occur

Understanding cycle

Theory→Prediction→Experiment

What is the study of matter

composition, structure, changes, properties, interaction with/ energy

Matter has

mass and occupies space

When classifying matter by physical state, divide into what categories

State, fixed shape, and fixed volume attM

Matter can also be classified by

fundamental composition

elements

composed of atoms (one type) and cannot be broken into simpler chemical substances

Compounds

composed of molecules with 2 or more different kinds of atoms.

Compounds are bonded in _____ proportions

fixed

Mixtures

readily separable combinations of elements and or compounds. (proportions are not fixed)

Mixture types

homogenous and heterogeneous

homogenous

visibly uniform(solutions, gas mixtures, colloids)

heterogenous

visibly non-uniform (suspension, mixtures of solids)

Accuracy

agreement with the value

Precision

reproducibility of measurement

Law of conversation of mass

total reactants = total mass of product

laws of definite + multiple properties (definite definition)

compounds are always composed of same elements in same proportions

laws of definite + multiple properties (multiple definition)

2 elements can combine in different ratios to form two or more different compounds

ratios of element “A” mass combined w/const mass of element “B”

reduce to whole #s

elements are composed of

indivisible atoms

atoms of different elements have

different properties

compounds are formed when atoms are

combined in fixed proportions

atoms do not change identity during chemical reactions they….

reorganize to produce new compounds

atoms are __________ of element

ultimate constituents

Atoms are not

indivisible

How was the electron discovered?

• The setup: Thomson used a sealed glass tube with most of the air removed, known as a cathode ray tube. When high voltage was applied, a glowing beam of energy (a cathode ray) traveled from the negative side (cathode) to the positive side (anode).

• Deflection by fields: Thomson placed charged electric plates and magnets around the tube. The ray bent toward the positive electric plate and away from the negative plate.

• The conclusion: Because opposite charges attract, Thomson proved the ray consisted of moving, negatively charged particles.

Proving Particles Were Universal

• Universal building blocks: Thomson tested different types of metals for the electrodes inside the tube. He found that the same negative particles appeared every time.

• Mass-to-charge ratio: By measuring how much the beam bent, Thomson calculated the mass-to-charge ratio of the particles. He found they were roughly 1,800 times lighter than a hydrogen atom.

How was the nuclei discovered

• fire tiny, positively charged alpha particles at an extremely thin sheet of gold foil.

• The tracking: They used a fluorescent zinc sulfide screen that flashed a spark of light whenever an alpha particle hit it, allowing them to track where the particles went after passing through the foil.

The Surprising Results

• Most went straight through: The vast majority of the alpha particles passed straight through the gold foil without changing direction, proving that atoms are mostly empty space.

• Some deflected: A tiny fraction of the alpha particles were deflected sideways at sharp angles.

• A few bounced back: An even smaller number of particles bounced straight back toward the source A dense core: Rutherford deduced that these dramatic deflections could only be caused by a tiny, hard, and intensely dense core of positive charge at the center of the atom. [1, 2]

• Overturning the old model: This disproved the widely accepted "plum pudding" model (which imagined positive charge spread out like a uniform pudding) and established the nuclear model of the atom

Nucleus

100,000times smaller than the atoms

The nucleus is

very dense (pea worth would weigh 250 million tons)

Isotopes

different number of neutrons for the same atom.

Atomic number

number of protons/identification of atom type(element)

Atomic mass is equal to

protons + neutrons

Atomic mass identifies the

isotope

if we change the number of protons

we get a new element

if we change the number of electrons

then we get an ion of the same element

if we change the number of neutrons

then we get an isotope of the same element

protons =

atomic number

electrons=

atomic number - ionic charge

neutrons=

atomic mass-atomic number

amu (the units ) is defined as

1/12 mass of carbon-12

atomic masses are weighted averages of

naturally occurring isotopes

Isotopes=

exact mass * percentage abundance = contribution to average mass

Molecular mass

the sum of atomic masses from periodic table

Mole and Avogadro’s number

instead of dealing w/atoms individually, use a grouping of atoms- scaling factor

Mass(g,mg)→_____→Particles (atoms, molecules, ions)

to move from mass to moles (g/mol), to move from moles to particles use Avogadro’s number

Elemental analysis gives % by

mass of elements in a compound (convert using moles)

empirical formula

most mathematically reduced formula (might be the same as molecular formula sometimes)