Chapter 2 Lecture Notes

Matter and Energy

Matter

Mass: Mass is a property of physical objects which, roughly speaking, measure the amount of matter contained in an object. It is a central concept of classical mechanics and related subjects. In the SI system of measurement, mass is measured in kilograms.

Mass vs. Weight

Weight: Weight is the vertical force exerted by a mass as a result of gravity. In the SI system of measurement, weight is measured in Newton's.

Matter: Matter is anything that has mass and occupies space. One contemporary view on matter takes it as all scientifically observable entities whatsoever. Matter can more accurately be defined as the energy that has a low vibratory rate, a compressed energy state.

Combinations of Atoms

Atom: An atom is the smallest component of an element having the chemical properties of the element

Molecule: A molecule is the smallest particle of a pure substance that still retains its chemical composition and properties. Molecules can be either polyatomic (composed of several atoms) or monoatomic (as in noble gases which are composed of single-atom molecules). Polyatomic molecules are electrically neutral clusters of two or more atoms joined by shared pairs of electrons (covalent bonds) that behave as a single particle.

Compound: A compound is a substance formed from two or more elements, with a fixed ratio determining the composition. For example, dihydrogen monoxide (water, ) is a compound composed of two hydrogen atoms for every oxygen atom.

A molecule is formed when two or more atoms join together chemically. A compound is a molecule that contains at least two different elements. All compounds are molecules but not all molecules are compounds.

A molecule is what you get when any atoms join together.

A compound is what you get when atoms of two or more different elements join together.

All compounds are molecules, but not all molecules are compounds.

Water is a molecule because it is made from atoms that have been chemically combined. It is also a compound because the atoms that make water are not all the same - some are oxygen and some are hydrogen.

Oxygen in the atmosphere is a molecule because it is made from two atoms of oxygen. It is not a compound because it is made from atoms of only one element - oxygen. This type of molecule is called a diatomic molecule, a molecule made from two atoms of the same type.

Molecular hydrogen (), molecular oxygen () and molecular nitrogen () are not compounds because each is composed of a single element. Water (), carbon dioxide () and methane () are compounds because each is made from more than one element. The smallest bit of each of these substances would be referred to as a molecule. For example, a single molecule of molecular hydrogen is made from two atoms of hydrogen while a single molecule of water is made from two atoms of hydrogen and one atom of oxygen.

Energy: Energy is a fundamental quantity that every physical system possesses; it allows us to predict how much work the system could be made to do, or how much heat it can exchange. In the SI system of measurement, energy is measured in joules or electron volts (eV).

Types of Energy:

Mechanical Energy: Mechanical energy is the energy which an object possesses due to its motion or its stored energy of position.

Potential Energy: Potential energy is the energy of a system associated with the spatial configuration of the system's components and their interaction(s) with each other. Or in other words the energy associated where the object is compared to where there would be zero energy.

Kinetic Energy: Kinetic energy is the portion of energy associated with the motion of a body.

Chemical Energy: Energy released as a result of chemical reactions. For example, by burning hydro carbons in the presence of oxygen, chemical energy would occur. It can also be thought of the energy stored in the chemical bonds of molecules.

Electrical Energy: Electrical energy is a form of energy related to the position of an electric charge in an electric field. It is also the energy made available by the flow of electric charge through a conductor.

Thermal Energy (Heat): Thermal energy is kinetic energy due to disordered motions and vibrations of microscopic particles such as molecules and atoms, usually associated with temperature.

Nuclear Energy: The energy released in a nuclear reaction, such as fission or fusion.

Electromagnetic Energy: A wave characterized by variations of electric and magnetic fields (for example, short wavelengths such as X-rays through the ultraviolet, visible and infrared regions to longer wavelengths such as radar and radio waves).

Einstein's Mass-Energy Equivalence:

where E is energy, m is mass and c is the speed of light in a vacuum ().

Example

What is the rest energy of a 1.00 g particle traveling at ?

Solution:

Since, it is asking for the rest energy the speed that it is traveling does not matter. Now we will use Einstein's equation.

Radiation: Radiation is energy that comes from a source and travels through some material or through space. Light, heat and sound are types of radiation. A person exposed to radiation is said to be irradiated.

Ionizing Radiation: Radiation that has enough energy to eject electrons from electrically neutral atoms, leaving behind charge atoms or ions. There are four basic types of ionizing radiation: Alpha particles (helium nuclei), beta particles (electrons), neutrons, and gamma rays (high frequency electromagnetic waves, x-rays, are generally identical to gamma rays except for their place of origin.) Neutrons are not themselves ionizing but their collisions with nuclei lead to the ejection of other charged particles that do cause ionization.

Fundamental Particles

The fundamental particles of the atom are the electron, proton, and neutron.

 Particle Mass amu charge charge symbol Electron 0.000549 -1 Proton 1.00728 1 Neutron 1.00867 none none

Atomic Mass Units (amu): A unit of mass equal to 1/12 the mass of an atom of the carbon isotope with mass number 12; approximately .

The Atom

Wikipedia-This is a link to the Wikipedia entry on the atom.

Vision Learning Atomic Theory I - This is the first part of how the atomic theory developed.

Vision Learning Atomic Theory II - This is the second part of how the atomic theory developed.

Greek Atom

Dalton Atom

John Dalton, (1766-1844) wrote New System of Chemical Philosophy in 1808.

Dalton's atomic theory rests on the following postulates.

1. All matter consists of tiny particles.

2. Atoms are indestructible and unchangeable.

3. Elements are characterized by the mass of their atoms.

4. When elements react, their atoms combine in simple, whole-number ratios.

Dmitri Mendeleev - Periodic Table, Period Table 2

Thomson Atom

J. J. Thomson (1856 - 1940) with others discovered the electron in the late 1890's.

Bohr Atom

Neils Bohr (1885-1962), put forth the planetary model of the atom. Bohr simulation.

Atom Video

Atomic Structure

Chemical Elements: The number of protons in the atoms of an element is known as the atomic number of the element. For example, all atoms with 6 protons in their nuclei are atoms of the chemical element carbon, and all atoms with 92 protons in their nuclei are atoms of the element uranium.

Isotopes: Isotopes are atoms of a chemical element whose nuclei have the same atomic number, Z, but different atomic weights, A. The word isotope, meaning at the same place, comes from the fact that isotopes are located at the same place on the periodic table. The atomic number corresponds to the number of protons in an atom. Thus, isotopes of a particular element contain the same number of protons. The difference in atomic weights results from differences in the number of neutrons in the atomic nuclei.

Atomic Nomenclature

The protocol for representing elements:

Examples:

Barium

Ruthenium

Aluminum Ion

Aluminum Oxide

Ionization: Any process by which a neutral atom gains or loses electrons, thus acquiring a net charge. High temperatures, electrical discharges or nuclear radiations can cause ionization.

1. Cosmic Rays: Highly energetic sub-atomic particles, mostly protons and helium nuclei, which travel across space at close to the speed of light. The lowest energy cosmic rays originate in the Sun; higher energy ones from supernovae and pulsars within the Galaxy, while those with the highest energy of all may be extra galactic in origin, possibly from quasars and active galactic nuclei.

2. Terrestrial Radiation: Long wave radiation that is emitted by the earth back into the atmosphere. Most of it is absorbed by the water vapor in the atmosphere, while less than ten percent is radiated directly into space

3. Internally Deposited Radionuclides: Internal radiation comes from radioactive materials that occur naturally in the human body. Isotopes of potassium and carbon are the primary sources of internal radiation exposures.