Physical Science Review

Elements (a substance that cannot be broken down into other substances) are substances composed of only one type of atom. All matter is composed of a relatively small number of elements, alone (example O₂ : Oxygen gas) or in various combinations (example: H₂O: water). The atoms of all the elements are composed of protons (positive charged; located in the nucleus), neutrons (no charge; located in the nucleus; to find the number of neutrons it’s the atomic mass minus the atomic number), and electrons (negative charged; located around the nucleus). When the elements were first organized by atomic mass, chemical properties ( example: reactivity, radioactivity, and valence) and physical properties (such as density, boiling point, melting point, and conductivity), it was found that repeating patterns could be identified. The modern periodic table arranges elements by atomic number (which represents the number of protons/electrons in the atom) and groups elements with similar chemical properties into vertical columns called families or groups. Families that are included in the periodic table are: Alkali metals, alkaline earth metals, transition metals, halogen gases, and noble gases.

There are 3 states of matter: solids, liquids, and gases. Solids have a definite shape and volume; Liquids has no definite shape but has a volume; and a gas has no definite shape or volume. Factors that can change the change of these states of matter are temperature, pressure, and concentration.

The evolution of the periodic table reflects the tentative nature of scientific knowledge. Our understanding of the periodic law has been refined as new information was discovered (e.g., the existence of protons and electrons). Our increasing understanding of the nature of matter has led to the development of new materials (e.g., plastics) and processes that have profoundly impacted society in ways both good, such as the development of new drugs, and bad, such as pollution.

Chemical reactions occur all around us and within our bodies. The rates of these reactions range from very fast to very slow, and those rates are affected by many variables (temperature, surface area, catalysts), some of which we can control. While chemical reactions combine or break apart reactants (your initial chemicals before the reaction) , the total mass of the products (the chemicals after the reactions) remains the same as the total mass of the reactants – this is the conservation of mass. You must have the same amount of each element on each side of the reaction, they can be in different combinations but they all must be there.

Balancing a chemical equation… Subscripts are the small numbers in a chemical equation. It is found after the element symbol. It tells us the number of that element in one group. Subscripts remain the same when you balance an equation. Coefficients are the big numbers in a chemical equation. It is found un the front of the chemical compound. It tells us how many compounds or groups we have. Note: groups are not connected.

Most of the moving objects students encounter in their everyday life have multiple forces acting upon them. If more than one force acts on an object along a straight line, then the forces will reinforce or cancel one another depending upon their direction and magnitude (the amount of force). Forces can change the direction and speed of an object’s movement. Forces work together to affect the motion of objects.

Newton’s Laws of Motion—

Newton’s 1^st Law: Law of Inertia

An object that is at rest will remain at rest or an object that is moving will continue to move in a straight line with constant speed, if and only if the net force acting on that object is zero.

Newton’s 2^nd Law: F=ma

The total force is equal to the mass of the object times the acceleration. If a force is applied to an object, the force will cause the object to have either a deceleration (if the force on the object is going in the opposite direction of its current motion) or an acceleration (if the force on the object is going in the same direction of its current motion), which is a change in speed.

Newton’s 3^rd Law: Action and Reaction

When one object exerts a force on a second object, the second object exerts an equal and opposite force on the first object.

Gravitation is a universal force that all masses exert on other masses. The strength of the gravitational attraction is decreased when the distance between masses is increased.

Waves have common characteristics such as frequency ( the number of cycles per one second) , amplitude (the height of the wave) , wavelength ( the length of the wave; usually measured from crest to crest) and energy. Larger amplitude waves carry more energy. Because the speed of waves within a given medium (or environment) is constant, increasing the frequency of a wave causes a decrease in the wavelength. The equation to find the speed of a wave is : speed of the wave = frequency times wavelength.

A basic law of nature is that energy is constant in the universe; it can be transformed, but not created or destroyed. When energy is used to move an object, that object’s energy is increased equivalently. The increase may be in kinetic energy( the energy of motion), or in potential energy (stored energy) or some combination of the two. When a moving object slows down due to friction, its kinetic energy is being transformed into heat energy, the random kinetic energy of the atoms and molecules that make up the object and its surroundings. Energy transformations always involve some transfer of heat energy to the environment. During chemical reactions, energy may be transformed from chemical potential energy to heat, light, and other forms of energy, or vice versa. During nuclear reactions, energy is transformed into matter or matter is transformed into energy.