The Science of Matter

8/29/12

Objective:

Understand the composition and their impact on the properties of matter.

Be able to classify chemical vs. physical changes

(How things change)

Chemistry is the study of the composition of matter and the changes that matter undergoes.

List 5 chemicals

Exit Ticket: What did you learn today?

8/30/12

Water, bleach, toothpaste, hairspray and deodorant are examples of chemicals that we use everyday

Remember:

Chemistry is the science that investigates the structure and properties of matter.
Matter is anything that takes up space and has mass
Mass is the measure of the amount of matter that an object contains

(Heat, light and radiowaves are not matter.)

Properties describe the characteristics and behavior of matter including the change it undergoes.

Behavior of matter is determined by the elements it contains and the arrangement of those elements

Examples: (contain different elements and properties)

Salt (Sodium and Chlorine)
/ Water (Hydrogen and Oxygen)

9/4/12

Physical change vs. Chemical change

Physical change / Chemical change
Does not change the substance / A new substance is formed and energy is either given off or absorbed
Can be reversed / Cannot be reversed. The substance cannot be turned back into its initial state.

Density:

Density is an important property of matter

It is used to identify substances

It is used to separate mixtures

Density is the mass of specific unit of volume

Density = mass/volume (D= M/V)

Volume =mass/density (V= M/D)

Mass = density x volume (M=DV)

In solids density is usually expressed grams per cubic centimeter (g/cm³) and kilograms per cubic centimeter (kg/cm³)

In liquids density is usually expressed as grams per liter (g/L) or grams per cubic centimeter (g/cm³)

Example: If a piece of rock has a mass of 14g and a volume of 5cm³,what is its density?

Steps:

Identify and write the givens:

M=14g, V= 5cm³, D=?

Write the formula:

D= M/V

Substitute:

D= 14g/5cm³

Solve: divide 14 by 5

D= 2.8 g/cm³

Homework : complete the density problems

9/19/12

Classifying Matter

Substance is matter with constant composition

Element made of only one type of atom
Compound is 2 or more elements that are chemically combined

Mixture is matter with variable composition

Heterogeneous is a mixture made up of more than one phase
Homogeneous is also called solutions made up of only one phase

Chemical change and energy

All chemical changes involve some sort of energy

Many chemical changes (reactions) release energy

Exothermic- release energy- HOT
Endothermic - absorb energy-COLD

9/24/12

Objective:

Students will be able to identify those scientists who were beneficial to the atomic theory

Early model of the atom:

The atom is the smallest particle of an element

Democritus: (460BC-370BC), Greek Philosopher

He was the first to suggest the existence of atoms. . He belied that atoms are indivisible (cannot be cut) and indestructible

His ideas was not based on experiments just philosophy

Lavoisier: (1700’s) French

“Conservation of Mass.” He changed chemistry to a quantitative science.

He measured the mass of a system before and after a reaction in a closed system

Stoichiometry

He isolated and named hydrogen and oxygen

He discovered how respiration and combustion are related

His major experiment involved cinnabar: red mercury oxide

Proust: (1800’s)

“The Law of Definite Proportions”

Tested Dalton’s 3rd postulate

Copper carbonate from a variety of sources

A compound always contains the same proportion of elements in definite proportions

Dalton’s Atomic Theory (1803), English, chemistry teacher

2000 years passed before more was known about the atom
Thought the atom looked like a marble/ball bearing (round, solid, sphere)
His findings were based on scientific experiments, not philosophy
Elements are composed of elements
Atoms of the same elements are identical and differ from the other elements
Atoms chemically combine in whole number ratios
Atoms cannot be created or destroyed
Atoms are extremely small

A penny containing pure copper contains 2,400,000,000,000,000,000,000,000,000 atoms

These can be observed using a scanning tunneling (electron) microscope

9/25/12

Dalton (1803)

Dalton is known as the founder of the atomic theory

He stated that the word atom is the basic unit of matter

Dalton also claimed that all atoms of a given element are identical

He discovered that the atoms of different elements have different properties and masses

He found that combining atoms of different elements formed compounds

Dmitri Mendeleev (1869)

He arranged elements into 7 groups with similar properties. He discovered that the properties of elements were periodic functions of their atomic weight. This became known as the Periodic Law

Cathode Ray:

Vacuum tube, all gasses pumped out
Metal piece called electrodes sticking out each end
Become charged when attached to strong electrical current
Rays travel in the tube from negative electrode (cathode) to the positively charged electrode (anode)
A magnet will deflect the cathode ray
Particles in the cathode ray are negatively charged.

JJ Thompson (1897)

While using the cathode ray tube, he discovered that the ray was deflected due to a magnetic electrical field

From this discovery he concluded that atoms contain small negatively charged particles called electrons.

Plum Pudding theory: Electrons are embedded within the structure of the atom just like raisin bread

The mass of the rest of the atom (besides the electrons) was thought to be evenly distributed and positively charged.

9/28/12

1916 Robert Millikan

Determined the mass of the electron to be 1/1840 the the mass of the proton or 9.11 X 1028. He used an oil drop apparatus.

1886 Eugen Goldstein

Discovered the proton, the subatomic particle with a positive charge and a mass of 1

1932 James Chadwick

Discovered the neutron, which is a subatomic particle with no charge but a mass equal to a proton (1).

Subatomic particles:

Particle / Charge / Mass / Location
Electron / -1 / Nothing / Electron cloud
Proton / +1 / 1 / Nucleus
Neutron / 0 (no charge) / 1 / Nucleus

1911 Ernest Rutherford

In 1911 he designed the Gold Foil Experiment
He aimed a beam of alpha (α) particles at a thin piece of gold foil (only a few atoms thick)
Most (α) particles passed through the foil
A small amount of the (α) particles were deflected.
To their surprise, some alpha particles bounced straight back
1/8000 did not go through the foil
He determined that the nucleus was a part of the atom

10-1-12:

Power point due Oct. 12:

Background of the science
Describe the experiment
How is it related to the atom?
How does it effect future scientist ?
75% slides
25% oral presentation

Rutherford’s Atom:

Conclusions:

There is a nucleus in the center of the atom where most of its mass is
The nucleus is positive
Atoms are mostly empty space
Disproved JJ Thompson’s Plum Pudding Model
If an atom is the size of a football field stadium, the nucleus is the size of a marble.

Niels Bohr 1885-1962

Planetary model 1913
Nucleus surrounded by orbiting electrons at different energy levels
Electrons have definite orbits
Utilized Planck’s Quantum energy theory
Worked on the Manhattan Project (US Atomic bomb)

10-2-12

Atomic Number: Element are different because they contain different number of protons

Atomic # = the number of protons in the nucleus

Mass number: Number of protons and neutrons in the nucleus

Element / P+ / N0 / E- / Mass #
Oxygen / 8 / 8 / 8 / 16
Arsenic / 33 / 42 / 33 / 75
Phosphorous / 15 / 16 / 15 / 31

Nuclide symbols contain the symbol of the element, the mass number and the atomic number:

10-4-12

Isotopes

Isotopesare atoms of the same element can have different number of neutrons

Isotopes have different mass numbers

Isotopes change the number of neutrons and the mass number for an atom.

10/11/12

Frederick Soddy proposed the idea of isotopes in 1912

Isotopes of the same element having different masses due to varying numbers of neutrons

Elements occur in nature as mixturesof isotopes.

10/22/12

Wed. Binder check

Objective: Students will be introduced to nuclear chemistry and radioactivity

Nuclear chemistry:

Types of Radioactivity:

By the end of this section you will be able to:

Observe nuclear changes and explain how they change an element
Express alpha and beta decay in nuclear equations
Model the half-life of an isotope
Explain how half-life is used to date materials

Vocabulary:

Radioactivity

Alpha particle

Beta particle

Alpha decay

Beta decay

Gamma decay

Half life

Radioactivity dating

Radioactive decay

Radioactivity is the spontaneous emission of radiation by an unstable atomic nucleus

Chemical reaction / Nuclear reaction
Occur when bonds are broken and formed / Occurs when nuclei combine, split and emit radiation
Involve only valence electrons / Can involve protons, neutrons and electrons
Atoms keep the same identity / Atoms of one element are often converted into atoms of another element
Associated with small changes in energy / Associated with large changes in energy
Temperature, pressure, concentration and catalysts affect reaction rates / Temperature, pressure, concentration do not affect reaction rates

10-23-12

Nuclear Reactions

Remember that the number of protons determined the identity of an element
Changing the number of protons will change the element into another element

During nuclear reactions atoms of one element are changed into atoms of another element.

Nuclear Notation:

Different isotopes of atoms can be represented using nuclear notation:

Nuclear reactions involve the protons and neutrons found in the nucleus.
During nuclear reactions a nucleus can gain or lose protons and neutrons

10-31-12

Radiation causes Radioactive Decay

Radioactive decay is the release of radiation by radioactive isotopes
Not all radioactive isotopes decay in the same way. Different types of decay change the nucleus in different ways
3 Types of decay

Alpha

Beta

Gamma

Radioactive alpha decay

Alpha decay is the release of alpha particles (2 protons and 2 neutrons)
Alpha particles are Helium nuclei consisting of 2 protons and 2 neutrons
Alpha particles which are large in size, collide with objects around them. They do not penetrate very deeply. They are stopped by a thin layer of material.
Alpha decay causes the decaying nucleus to lose 2 protons and 2 neutrons.

The mass number decreases by 4 (2 protons and 2 neutrons)

The atomic numberdecrease by 2

11-1-12

Radioactive Beta Decay

Beta decay is the release of beta particles from a decaying nucleus

A beta particle is a high energy electron with a 1- charge
Beta particles are written as :

Beta particles pass more easily through matter than alpha particles and require sheets of metal, blocks of wood or specialized clothing to be stopped
The electron released during beta decay is not one of the original electrons that existed outside the nucleus.
The beta particle (electron) is produced by the change of a neutron into a proton and an electron

Equation for radioactive beta decay: The parent nucleus turns into a daughter with an atomic number 1 greater. The mass number stays the same

Beta emission:

A neutron becomes a proton which stays in the nucleus and the electron is ejected from the atom

Add a proton and lose an electron /

11-2-12

Radioactive Gamma Decay

Gamma decay is the release of gamma rays from a nucleus

A gamma ray is a high energy form of electromagnetic radiation without a change in mass or charge

Gamma rays have high penetrating ability and are very dangerous to living cells

To stop gamma rays thick blocks of lead or concrete are needed

During gamma decay only energy is released

Gamma decay does not generally occur alone, it occurs with other modes of decay (alpha or beta)

When gamma decay is expressed in an equation it is expressed as

The following equation shows both gamma and alpha decay:

11/5/12

Half-Life

Radioactive Decay:

Radiation can be detected with Geiger counters and scintillation counters.

Quarter 2

11-13-12

Do Now: Complete the following problems

Sodium 24 has a half-life of 15 hours. How much Na-24 will remain in an 18.0g sample after 60 hours?

After 42 days a 2.0g sample of P-32 contains only .025g of the isotope. What is the half life of P-32?

Po-214 has a half life of 164 seconds. How many seconds would it take for 8.0g to decay to 0.25g?

11-14-12

The Power of the Nucleus

Vocabulary:

Nuclear Fission
Chain reaction
Nuclear reactor
Nuclear Fusion

E=mc2:

E= energy

M= mass

C= speed of light (3.0x 108m/s)

Nuclear reactions involve enormous changes in energy. During a nuclear reaction a small amount of mass can be converted into a large amount of energy.

Nuclear fission is the process of splitting a nucleus into 2 or more smaller fragments. This is accompanied by release of energy. Protons and neutrons are in the nucleus and are split. Energy is released.

Nuclear fission using Uranium

The sums of the mass numbers on the left and right are equal

As World War II (1939-1945) started, scientists were trying to find a way to sustain nuclear fission in a chain reaction.

Chain Reaction is a continuing series of reactions in which each produces a product that can react again and again.

11/15/12

In Fission of uranium, each neutron produced has the potential to cause the fission of another atom of Uranium 235.

In order for a chain reaction to occur there must be enough of a sample of the material for the neutrons to collide with other atoms

Critical mass: the point where the chain reaction becomes self-sustaining.

Supercritical mass: If the amount of fissionable material is much greater than critical mass the chain reaction escalates out of control and an explosion results.

11/16/12

All of the energy is released at once. This is what happens when an atomic bomb explodes

Nuclear Fission and Nuclear energy

In order for nuclear energy to be useful the reaction must be controlled so that the energy can be released slowly.

Nuclear power plants generate electrical energy through the controlled fission of Uranium.

This is done in a nuclear reactor. A nuclear reactor is a device that is used to extract energy from radioactive fuel.

11-19-12

Nuclear reactors and Pollution:

Nuclear reactors do not produce CO2 and other pollutants
They do not produce radioactive waste that is difficult to safely dispose of
New technologies allow much of the waste to be decayed, reducing the amount of hazardous waste produced
There is some risk of the release of this nuclear waste into the environment

Problems with nuclear reactors:

Nuclear energy costs more to produce than energy produced through the burning of fossil fuel
It is more expensive than using fossil fuels

Nuclear Fusion:

Nuclear fusion is the process of combining 2 or more nuclei to form a larger nucleus

Nuclear fusion is the process that occurs in the sun and other stars to produce energy

Nuclear fusion….. Hydrogen to Helium

11/20/12

The fusion of hydrogen to produce helium produces 20 X more energy than the fission of the same amount of uranium.

It does not produce any radioactive waste
Fusion reactions are easier to control than fission reaction

Problems with nuclear fusion:

Difficulty initiating and containing a fusion reaction has prevented its use as a practical energy source.
Nuclear fusion reactions require a large amount of energy to start the fusion reaction
In order to initiate a fusion reaction on earth a temperature greater than 100 million Kelvins would be required.
No material exists on earth that could contain the reaction.
A great goal for the future

Fission / Fusion
Splitting of an atomic nuclei caused by a neutron / Combining 2 or more nuclei
Chain reaction / Multi-step process
Produces radioactive waste / Does not produce radioactive waste
Used in nuclear plants and bombs / Not able to be initiated and contained because it requires a great deal of energy to start
Can generate a great deal of energy / Occurs on the sun with a tremendous amount of energy released

12/3/12

Periodic Table Geography

What information does the periodic table tell me?

The horizontal rows of the periodic table are called periods

The vertical columns of the periodic table are called groups or families. The elements in any group of the periodic table have similar physical and chemical properties

There are 18 groups and 7 periods

Periodic Law:

When elements are arranged in order of increasing atomic number, there is a periodic pattern in their physical and chemical properties

Elements are arranged based on similar properties

Elements are arranged based on increasing atomic number

Atomic number is the number of protons

Atom mass is the number of protons + number of neutrons

Most elements are metals

Metals:

Good conductors of heat and electricity
Malleable and able to be bent
Ductile
Loose electrons becoming positive ions

Metalloids:

Elements that touch the staircase
Metalloids have properties of both metals and nonmetals
More brittle than metals but less brittle than nonmetals
Semiconductors of electricity (anything that’s computerized or uses radio waves depends on semi conduction. Today, most semiconductor chips and transistors are created with silicon (14) is the heart of any electron device).
High tensile strength
Loose and gain electrons to get to eight

Non-metals

Poor conductors of heat and electricity

Tend to be brittle

Many are gaseous at room temperature

12-6-12

Alkali metals: Group 1

Alkaline Earth metals: Group 2