Physical Science for Armed Services Vocational Aptitude Battery (ASVAB) Study Guide

Electronic Structure of Atoms

According to the periodic table, the atomic number of hydrogen (H) is 1, because it has one proton in its nucleus. The number of protons in an atom determines its atomic nucleus. The atomic number of nitrogen (N) is 7; nitrogen has seven protons in its nucleus.

Niels Bohr, a Danish physicist, proposed a model of the atom that had a nucleus surrounded by concentric orbits

Electrons are found in the orbits. When electrons become excited, they absorb energy and move to an orbit farther from the nucleus. When they release energy, they fall to an orbit with lower energy closer to the nucleus. The energy level (also called electron shell) is a region of space in which electrons move around the nucleus.

Chemical Equations

Chemical equations are used to show the result of a physical or chemical change in matter. A physical change is when the shape or size of matter is changed, but the molecules remain unchanged. Steam from a boiling pot of water is an example of a physical change. A chemical change is one in which two or more molecules interact to form new molecules. Paper burning is an example of a chemical change—the paper changes to carbon.

The sum of the atomic weights of all the atoms in a formula is called the formula weight. A mole is the amount of substance containing Avogadro's number of particles, 6.02 × 1023 atoms of an element. The abbreviation is mol.

Use the following rules in balancing equations:

1. All reactants (starting materials) and products must be known, and their formulas must be correctly written.
2. The formulas are never changed in order to balance an equation.
3. The number of atoms of each element in the reactants must be equal to the number of atoms of the element in the products.
4. The numbers to the left of each formula (coefficients) must be reduced to the smallest possible whole numbers.

Types of chemical reactions include:

• Combination or synthesis reactions: two chemicals combine to form a new substance
• Decomposition reactions: one substance breaks down to create two or more substances

Concentration, Acids, Bases, and pH

Concentration is a measure of how much solute is in a solution. A solute is a substance that is dissolved in a medium, and a solvent is a medium in which a solute is dissolved. For instance: salt water is a solution—a homogenous mixture consisting of the solute (salt) and the solvent (water).

Acids are proton donors; they release hydrogen ions (protons). Acids have a sour taste. Bases are proton acceptors; they take up hydrogen ions. Bases have a bitter taste and feel slippery. Strong bases take up more hydrogen ions than weak bases.

The relative concentration of hydrogen ions is measured in concentration units called pH units. The pH scale runs from 0 to 14. A substance with a pH of 7 is neutral. Substances such as vinegar and orange juice, with a pH of less than 7, are considered acidic. Substances such as soaps and ammonia, with a pH of more than 7, are considered alkaline.

Measurement

Although you may be more familiar with the English system of measurement (inches, pounds, and so on), the metric system is the standard system of measurement in science. The metric system is a decimal system based on multiples and fractions of ten. The meter (m) is the standard unit of length in the decimal system:

1 meter = 100 centimeters (cm)

1 kilometer (km) = 1,000 meters

The gram (g) is the metric system unit of mass:

1 gram = 1,000 milligrams (mg)

1 kilogram (kg) = 1,000 grams

Volume, the amount of space occupied by a fluid or body, is usually measured using the liter. The cubic meter (cm3) is actually the standard metric unit of volume, but it is infrequently used.

1 liter (L) = 1,000 milliliters (ml)

1 cm3 = 1 ml

In science, temperature is most often measured using degrees Celsius (°C). On the Celsius scale, the freezing point for water is 0° and the boiling point for water is 100°. This makes it much easier to use than the Fahrenheit scale, which has a freezing point of 32° and a boiling point of 212°. The two equations below show how to convert a temperature measurement from one scale to the other.

Other important equations are as follows:

• Speed is the distance covered or traveled by an object per a certain unit or amount of time:

Speed = distance/time

• Momentum is the tendency of an object to continue moving in the same direction: Momentum = mass × speed
• Work is a force applied to an object which, in turn, results in movement:

Work = force × distance

• Power is the rate at which work is done. It is measured in joules (J):

Power = work/time

Note: Mass should not be confused with weight. Mass is the measurement of the amount of matter in an object. Weight is the force by which gravity attracts a body to Earth.

Energy

Energy, the capacity to do work, is never created or destroyed—it may only be changed in form. There are many forms of energy, including light, sound, heat, chemical, mechanical, and electrical. Energy, like power, is measured in joules.

The two forms of energy are potential and kinetic energy. Potential energy is the energy stored in a body or system as a consequence of its position, shape, or state. Kinetic energy is the energy of motion, and is usually defined as the work that will be done by the body possessing the energy when it is brought to rest.

Sound and light are measured by their wavelength. A wave is a periodic disturbance in a medium or space. Sound is a vibration at a frequency and intensity audible to the normal human ear (20–20,000 Hertz). Vibrations that have a lower frequency are called infrasounds, and those with a higher frequency are called ultrasounds. Light is a form of electromagnetic radiation. Light can pass through a vacuum, but sound cannot. The electromagnetic spectrum is displayed in the following diagram.

Refraction is the bending of light, especially when it moves from one material to another. The refraction of sunlight results in a spectrum of colors, such as a rainbow. The colors in a spectrum are red, orange, yellow, green, blue, indigo, and violet.

Another form of energy—heat—may be transferred via conduction, convection, or radiation. Conduction is the transmission of heat from a region of high temperature to a region of lower temperature. Putting a cool kettle of water on a stove to boil is a good example. Convection is the process by which parts of a fluid or gas change density due to the uneven application of heat. For instance, as a stove heats a cool room, the warmer (less dense) air rises and the cold air remains lower. Radiation is heat transmitted via electromagnetic waves. The sun's heat warming the petals of a flower is an example of radiation.