Chem 161Chapter 1: Matter, Energy,

and the Origins of the Universe

Problems: 1.1-1.10, 1.14-1.22, 1.24-1.93, 1.96

Chapter 1: Matter, Energy, and the Origins of the

Universe• Science: study of nature that results in a

logical explanation of the observations

• Chemistry: study of matter, its properties, and the changes it undergoes

• In what fields is chemistry used today? How is it used? 

1.2 Matter: An Atomic View• We study matter at different levels:

– macroscopic: the level which we can observe with the naked eye (geologists study rocks at the macroscopic level)

– microscopic: the level which we can observe using a microscope (scientists study tiny animals, plants, or crystals at the microscopic level)

– atomic or molecular (also called particulate): • at the level of atoms and molecules• can only be “observed” using the most

powerful microscopes• most atoms and molecules are a few

nanometers in size The term “nanotechnology” refers to materials created or developed by manipulating atoms and/or molecules

1.1 Classes of Matter• matter: anything that has

mass and occupies volume

• Types of matter we deal with:– pure substances

(elements & compounds): a single chemical consisting of only one kind of matter

– mixtures (homogeneous & heterogeneous): Two or more pure substances can combine to form mixtures

Pure Substances• Two types of pure substances:

– elements:• consist of only one type of atom• atoms cannot be broken down into smaller

components by chemical reaction– Examples: copper wire (Cu), sulfur powder

(S8), sodium (Na), barium (Ba), hydrogen gas (H2), oxygen gas (O2), and chlorine gas (Cl2).

– compounds:• consist of more than one type of atom and have

a specific chemical formula– Examples include hydrogen chloride (HCl),

water (H2O), sodium chloride (NaCl) [table salt], barium chloride (BaCl2)

Mixtures• Two or more pure substances can combine

to form mixtures.– mixtures:

• consist of many compounds and/or elements, with no specific formula

• matter having variable composition with definite or varying properties can be separated into component elements and/or compounds

• Examples: Any alloy like brass, steel, 10-K to 18-K gold (anything less than 24K gold); course mixtures like sea water, carbonated soda; air is a mixture consisting of nitrogen (~78%), oxygen (21%), and other trace gases.

Mixtures

• Mixtures can be homogeneous or heterogeneous:– Homogeneous mixtures have a

uniform appearance and composition. • e.g. solutions (salt water, soda,

etc.), metallic alloys, homogenized milk

– Heterogeneous mixtures do not have a uniform composition• e.g. chocolate chip cookie, coarse

mixture of sand and iron filings, raw (non-homogenized) milk

1.6 States of Matter• Matter exists in one of three physical states:

solid, liquid, gas– Example 1: A few drops of food coloring is

added to a beaker of water. How would you expect the water to appear after a few minutes? Why?

– Example 2: If you add a drop of food coloring on top of an ice cube, would you expect the same result? Why?

To understand matter, we must recognize how particles behave at the molecular level.

States of Matter

Gas

• Volume is variable, particles are widely spaced

• Takes the shape of the container because particles are moving– If container volume expands,

particles move apart to fill container

– If container volume decreases, particles move closer together

• Particles are in constant random motion

Liquid

• Fixed (or constant) volume, but shape can change

• Takes the shape of the container because particles are moving

• Particles are packed closely together but move around each other

Solid

• Has definite shape, rigid volume• Particles can only vibrate in

place

Dep

ositio

nGas

Liquid

Solid

Vaporization

Freezing

Changes of State

Melting

Condensation

Su

blim

ati

on

Properties of Matter

• Intensive Properties: properties independent of quantity– Density– Boiling point– Freezing point

• Extensive Properties: properties that depend on quantity– Mass– Volume

Physical and Chemical Properties and Changes

• Physical Properties:– physical state (solid, liquid, gas)– electrical and heat conductivity– color– solubility (amount of solid that dissolves in

liquid)– density– hardness– melting and boiling points– odor

• Chemical Properties: how a substance reacts with other substances– e.g. hydrogen reacts explosively with oxygen

Chemical vs. Physical Changes

Physical Change:• a process that does not alter the chemical

makeup of the starting materials– changing shape, changing physical state,

dissolving– boiling water, melting ice, hammering gold

into foil, dissolving salt in water

Note: In the images here, the chemical makeup of H2O does not change as it goes from a solid to a liquid and to a gas.

Chemical Change:• a process that does changes the chemical

makeup of the starting materials • We can use space-filling models to show what

happens at the molecular-level when H2 and O2 react to form water (H2O) of each molecule.

Notice that the H2O has a different chemical makeup than H2 and O2.

Chemical vs. Physical Changes

The following examples are all chemical changes that convert the reactants to completely different compounds and/or elements.

Chemical vs. Physical Changes

release of gas bubbles(fizzing)

formation of insoluble solid (precipitation) oxidation of matter

(burning or rusting)

Example Problem 1Consider the following molecular-level representations of different substances:

A B C

D F

E

For each figure above, indicate if it represents an element, a compound, or a mixture AND if it represents a solid, liquid, or gas.

Example Problem 2Match the following substances with the correct molecular-level representation.

_____ ammonia (NH3) _____ air _____hydrogen_____ sodium chloride _____ mercury _____ copper

A B C

D F

E

Example Problem 3

Which of the following are chemical changes?

burning condensing dissolving

melting vaporizing rusting

Making Measurements and Expressing Results

Accuracy vs. Precision• accuracy: indicates how close a

measurement is to the true value• precision: refers to how closely two or more

measurements agree with one another

For each diagram (above), what is the level of accuracy and precision?

accurate inaccurate precise imprecise

Testing a Hypothesis – The Big Bang Revisited

• In the 1960s, the US launched the first communication satellites, called Echo and Telstar, which were basically reflective spheres that bounced microwave signals from transmitters to receivers back on Earth.

• Bell Labs in NJ had built an antenna to receive such signals, and two Bell Lab scientists, Robert W. Wilson and Arno A. Penzias, were trying to improve the antenna’s reception.

• But they kept picking up a background signal, no matter where they directed the antenna.

• Assuming the signal was just an artifact, even attributing it to pigeons roosting on the antenna, the pair continued testing the equipment until they finally realized their original hypothesis must have been wrong, that the nuisance signal was not an artifact but actually significant.

Testing a Hypothesis – The Big Bang Revisited

• Wilson and Penzias learned that a Princeton University physicist named Robert Dicke had predicted residual energy left over from the Big Bang.

• Their nuisance signal matched Professor Dicke’s predicted Big Bang microwave echo Wilson and Penzias shared the Nobel Prize in Physics in 1978 for discovering the cosmic microwave background radiation of the universe.

Testing a Hypothesis – The Big Bang Revisited