CHM 2050

Hypothesis

 tentative explanation of observations that acts as a guide for gathering and checking information

Laws of science

summarize a vast number of observations, describe/predict some facet of natural world

Scientific theory

used to explain why natural phenomena occur, testable explanation of aspects of nature

Macroscopic domain

things large enough to be sensed by human sight or touch

Microscopic domain

too small to be seen with naked eye (cells, molecules, atoms, electrons, protons, neutrons)

Symbolic domain

 chemical symbols/formulas/equations

Matter

anything that occupies space and has mass

States of matter

• Solid: rigid, possesses definite shape

• Liquid: flows and takes the shape of its container 

• Gas: takes both the shape and volume of its container

• Plasma: gaseous state of matter containing electrically charged particles

• Aqueous: dissolved

Mass

measure of amount of matter in an object

Weight

 the force that gravity exerts on an object

Law of conservation of matter

 there is no change in total quantity of matter when an object changes phases (solid to liquid etc.)

Pure substance

constant composition

Elements

pure substances that cannot be broken down into simpler substances by chemical changes (ex. aluminum, gold)

Compounds

pure substances comprised of two or more elements, can be broken down by chemical changes to form elements or other compounds

Mixture

composed of two or more types of matter that can be present in varying amounts and can be separated by physical changes (like evaporation)

Heterogeneous mixture

composition of mixture varies from point to point (ex. italian dressing)

Homogenous mixture (solution)

uniform composition and looks the same throughout (ex. sports drink, air, maple syrup, gasoline, salt water)

Atom

smallest particle of an element that has the properties of that element and can enter into a chemical combination

Democritus atomic theory

all matter is made of atoms, atoms are indestructible, are in constant motion, and the space between atoms is empty/void

Today’s atomic theory

Atoms are composed of smaller elemental particles (protons, neutrons, electrons) and can only be changed by nuclear reactions

Molecule

consists of two or more atoms joined by chemical bonds (can be the same atom or different atoms)

Physical property

• characteristic of matter that is not associated w/ change in chemical composition

  • Ex. density, color, hardness, melting and boiling point, electrical conductivity

Physical change

• change in the state or properties of matter with no change in chemical identity

  • Ex. ice melts, sugar dissolves in coffee, wax melts

Chemical property

• ability to change from one type of matter into another

  • Ex. flammability, toxicity, acidity, and other types of reactivity

Chemical change

• produces one or more types of matter that are different from the original matter (requires a chemical reaction)

  • Ex. rust is a new type of matter than the original matter (water, iron, oxygen), reactions performed in labs

Extensive properties

• depend on the amount of matter present

  • Ex. mass, volume, length

Intensive properties

• do not depend on the amount of matter present

  • Ex. Temperature, color

Base Units of the SI System

• Length: meter (m)

• Mass: kilogram (kg)

• Time: second (s)

• Temperature: kelvin (K)

• Electric current: ampere (A)

• Amount of substance: mole (mol)

• Luminous intensity: candela (cd)

Unit prefixes to memorize

Prefix	Symbol	Factor
femto	f	10-15
pico	p	10-12
nano	n	10-9
micro	µ	10-6
milli	m	10-3
centi	c	10-2
deci	d	10-1
kilo	k	103
mega	M	106
giga	G	109
tera	T	1012
peta	P	1015

Temperature conversions

• Fahrenheit

  • Freezing point: 32

  • Boiling point: 212

• F = (9/5 C) + 32

• C = (F - 32) * 5/9

• K = C + 273.15

Dalton’s Atomic Theory

1. Matter is composed of very small particles called atoms. Atoms are the smallest unit of an element that can participate in a chemical change

2. Elements consist of only one type of atom, which has a mass that is characteristic of the element and is the same for all atoms of the element. A macroscopic sample of an element contains MANY atoms which have identical chemical properties

3. Atoms of one element have different properties than atoms of another element

4. Compounds consist of 2+ elements combined in a small, whole-number ratio. In a given compound, the elements exist in the same ratio.

5. Atoms are neither created nor destroyed during a chemical change, but are rearranged to form different substances

Law of mass conservation

the mass of an isolated system remains unchanged by any chemical reaction or physical change

Open system

can exchange energy and matter

Closed system

can exchange energy, but not matter

Isolated system

cannot exchange energy or matter

Law of definite composition

no matter its source, a chemical compound is always composed of the same elements in the same proportions by mass

Law of multiple proportions

when 2 elements react to form more than one compound, a fixed mass of one element will react w/ masses of the other element in a ratio of small, whole numbers

Mass percentage

• what percentage of the total mass is made up of one specific element

Mass ratio

• the ratio of masses between two different elements in a mixture or compound

Thompson

• Cathode ray tube showed that atoms contain small, negatively charged particles called electrons

  • Plum-pudding model: developed by Lord Kelvin, JJ Thompson where electrons were swimming in a “pudding” of positively charged matter

Millikan

• Millikan Oil Drop experiment discovered that there is a fundamental electric charge: the charge of an electron

Rutherford

• gold foil scattering experiment showed that atoms have a small, dense, positively charged nucleus (positive charge comes from particles called protons)

  • Alpha particle: 2 protons, 2 neutrons

Chadwick

• nucleus contains neutral particles called neutrons

Soddy

• atoms of the same element can differ in mass (isotopes)

Atomic number (Z)

 # of protons in the nucleus, defines elemental identity

Mass number (A)

# of protons + neutrons

Isotopes

versions of the same element with different numbers of neutrons (therefore different atomic masses)

• Periodic table shows mass number as the average atomic mass of all naturally occurring isotopes (molar mass)

• Natural abundance: if you have a mole of a material, the natural abundance is the probability that you have a particular isotope

• All elements have isotopes