Matter

and

Change P Squires

General Chemistry

2005-2006

Observing Chemical Change

• Open book to page 55 and conduct Discovery Lab

• (50 pts)

Properties of Matter

•What is a substance?

• Physical Properties

• Chemical Properties

Physical States

Solid

Liquid

Gas

Plasma

What are some characteristics

of each?

Give the physical state of each of these:

1. Silver

2. Gasoline

3. Helium

4. Rubbing alcohol

5. Air

6. Glass

7. Lightning

Solid

Liquid

Gas

Liquid

Gas

Solid or liquid

Plasma

Plasma

Physical Changes

• Physical changes only involve changes in state or

appearance.

• What are some examples of physical change?

Catch words for Physical Change

• Boil

• Freeze

• Melt

• Condense

• Break

•Split

•Grind

•Cut

•Crush

•Bend

Chemical Changes

• Chemical changes and chemical properties always produce new substances.

Chemical or physical change ???

• Food spoiling• Nail rusting• Oil burning• Sugar dissolving• Water boiling• Firefly flashing• Egg cooking• Snowflake melting

Chemical

Chemical

Chemical

Physical

Physical

Chemical

Chemical

Physical

Percent mass

Percent mass (%) = mass of element_ mass of compound

x 100

Calculations

1. A 78.0 g sample of an unknown compound contains 12.4 g of hydrogen. What is the percent by mass of hydrogen in the compound?

2. If 1.0 g of hydrogen reacts completely with 19.0 g of fluorine, what is the percent by mass of hydrogen in the compound that is formed?

Pure Substances

• Elements are the building blocks of matter.

• Atoms are the smallest part of an element.

Mixtures

… do not have a definite composition

… are either heterogeneous, with clearly visible components… or homogeneous,

which are uniform in appearance

Solutions

• Solutions are homogeneous mixtures containing a solute which is dissolved in a solvent.

Classify as heterogeneous, or homogeneous (solution)

• Blood

• Choc. chip ice cream

• Brass (Cu-Zn alloy)

• Homogenized milk

• Hummingbird food

Homogeneous

Heterogeneous

Homogeneous

Homogeneous

Homogeneous (solution)

We separate mixtures …

… based on differences in the chemical and physical

properties of the components in the mixture.

Separating Mixtures

• Quick Lab Handout

• (50 points)

How would you separate the following?

Aluminum filings and iron filings?

Saw dust and sand?

Salt and powdered charcoal?

Water and alcohol?

Elements

• A pure substance that can not be separated into simpler substance by physical or chemical means.

Compounds

• A combination of two or more different elements that are combined chemically.

• What are some examples of compounds?

The Law of Conservation of Mass

Matter can neither be created or destroyed

during a chemical reaction.

Law of Definite Proportions

Elements comprise compounds in definite proportions by mass.

Law of Multiple Proportions

When different compounds are formed, they combine in whole number ratios.

H2O H2O2

ChemLab

• Read and complete ChemLab

page 78. (100 points)

• Answer Questions at end:

Analyze and Conclude.

Structure of the Atom

Part of the Atom

• Electron

• Proton

• NeutronWhat charge does each have?

Where are they found?

Which ones make up the mass of the atom?

Which ones make up the size of the atom?

How Do Atoms Differ?•Atomic Number

•Atomic Mass

Element Atomic Number

Protons Electrons Atomic Mass

He 2

Pb 82

8

30

Mass Number

Number of neutrons = mass number – atomic number

Isotopes …

Therefore, isotopes of the same element have different masses.

…of the same element have the same number of protons and electrons but different numbers of neutrons.

Symbols for Isotopes

EA

Z

Symbol of Element

Mass number

Atomic number

A is the symbol for mass number

Z is the symbol for atomic number

MiniLab

• Do modeling isotope lab on page 102.

Energy and

Electrons

Light and Energy

• Frequency = f or f with units of Hertz (Hz)

• Wavelength = with units of meters (m)

What is the relationship between frequency and

wavelength?

For electromagnetic energy, the equation is:

c is the speed of light c = 3.00 x 108 m/sec

fc

Electromagnetic Spectrum

• Electromagnetic waves carry energy.

• Light is part of the electromagnetic spectrum

The Electromagnetic Spectrum

radi

o

TV

rada

r

mic

row

aves

infr

ared

visi

ble

ligh

t

ultr

avio

let

X-r

ays

gam

ma

rays

Shorter wavelengthHigher frequencyHigher energy

Longer wavelengthLower frequencyLower energy

The Electromagnetic Spectrum

radi

o

TV

rada

r

mic

row

aves

infr

ared

visi

ble

ligh

t

ultr

avio

let

X-r

ays

gam

ma

rays

400 nm 700 nm

Increasing energy

The visible spectrum was discovered by …

Dr. Roy G. Biv

Red Orange Yellow Green Blue Indigo Violet

700 nmLower energy

400 nmHigher energy

Niels Bohr

Bohr said that electrons could exist only in certain discrete energy levels …

… and that electrons can only change energy levels when they absorb or give off a certain amount of energy. (1913)

Hydrogen atom

nucleus

Discrete energy levels for electrons

electron

Hydrogen atom

Electrons can exist in this orbit,

Hydrogen atom

…or in this orbit,

Hydrogen atom

…or in this orbit,

Hydrogen atom

…but not in between the orbits.

Hydrogen atom

Unless the electron is absorbing energy, or …

Giving off energy

When high voltage is connected to the hydrogen discharge tube, a bluish light is given off.

When observed through a diffraction grating, specific lines of color are observed.

The electron in a hydrogen atom gains energy from the electricity passing thru the tube and …

… the electron moves up to a higher energy level.

The electron in the excited state is “unstable”.

The electron drops to a lower energy level, and …

… gives off light of a certain energy and wavelength.

Hydrogen atom

Hydrogen atom

energy

The electron absorbs energy and …

Hydrogen atom…the

electron is elevated

to the next energy level

The electron is unstable and

“wants” to return to a lower

energy level

Hydrogen atom

Hydrogen atom

Light of a particular wavelength is given off

HeliumHelium

NeonNeon

HydrogenHydrogen

“Regardless of it’s shortcomings and the

modifications that were later applied, Bohr’s model of the atom was the first successful attempt to make the internal structure of the atom agree with spectroscopic data.”

Asimov, 1964

Quantum Mechanical Model of the Atom

1. A small, dense positively charged nucleus which contains protons and neutrons.

2. Electrons which exist outside of the nucleus at …

– various distances from the nucleus, and at …

– various energy levels.

The Electrons

3. The electrons can have both a mass, as does matter, and a wavelength, as does light energy.

4. The electrons themselves are not little solid spheres in orbit around the nucleus, but exist as a “fog” of half-energy, half-matter. The electrons can behave as either matter or energy, depending on the experiment.

Energy Levels

5. Based on the ideas of Bohr, the electrons are located …

– … in major energy levels,– … in energy sublevels within major

energy levels, – … in orbitals within each sublevel.

Next up….

The Periodic Table