Dacey's Essays and Outlines

Mr. Dacey’s Matter and Energy Essays 

 

1. Describe the modern scientific model of the atom.

 

The atom consists of a small central nucleus containing protons and neutrons, surrounded by a cloud of orbiting electrons. The protons and neutrons have almost all of the atom’s mass. Electrons weigh almost nothing, so the atom’s atomic mass is determined by adding the protons to the neutrons. Atoms of an element always have the same number of protons, which is also known as the atom’s atomic number. Every natural element exists as a mix of isotopes, which are atoms with different numbers of neutrons. If an atom has too many or too few neutrons, it will eventually decay (break apart). These unstable isotopes are called radioactive. Virtually every element has at least one radioactive isotope. Radioactive carbon-14 for example, has 2 more neutrons than stable carbon-12, which makes C-14 unstable over time. 

 

Electrons have a negative charge which is equal and opposite to the positive charge of the proton. Neutrons have no charge. When an atom gains one or more electrons it becomes a negative ion, and when it loses electrons it becomes a positive ion.

 

2. Compare physical and chemical properties of matter, including examples of both.

 

Physical properties of a substance describe the way the substance always behaves. Examples include color, melting and boiling points, reflectivity, conductivity, magnetism, and the way the substance breaks or scratches. Chemical properties involve the way the substance reacts with other substances. When testing chemical properties, new substances are produced. An example would be how aluminum reacts with iron oxide to produce aluminum oxide and iron in a thermite reaction. Other examples include acid dissolving marble or digesting your food, a pumpkin rotting on the porch, and anything that's burning.

 

3. Compare the 4 common states of matter in terms of how they appear to us, and explain why they appear as they do in terms of atoms.

 

Solids have a definite shape and a definite volume. This is because their atoms are held in a 3-dimensional structure called a crystal lattice. The atoms vibrate in place more and more as heat is added, but they are not free to move around. Increased heat and vibration causes thermal expansion. If the atoms vibrate too much, they break free of the crystal lattice and the solid melts.

Liquids have a definite volume but no definite shape. They take the shape of the container. In liquids, the atoms are somewhat free to move around, but are still loosely held together. If the atoms move fast enough as heat is added, they break free of the attraction from the other atoms and become gas.

Gases have no definite shape or volume. A sample of gas will expand to fill the container its in, an elevator fart for example. The atoms move about freely. 

Plasma is a lot like a gas except that the atoms are stripped of some of their electrons. Plasma is a chaotic mixture of atoms, ions, and electrons, that gives off light, emits an electric field, and is influenced by magnetic fields.

 

4. Discuss how energy is transferred from one form to another throughout the hydrologic cycle. Begin with water in a lake on a sunny day, and end with a rainy day later in the week on another lake a few hundred kilometers away. Your discussion should include types of energy like thermal, gravitational, and electromagnetic, and how they affect matter (especially water molecules).

 

The hydrologic cycle begins with electromagnetic radiation from the sun. When solar radiation (mostly visible light) hits the Earth, the land and water absorb the visible light and re-emit the energy as infrared radiation, which then heats the atmosphere. The absorbed radiation causes water to evaporate and thermal expansion causes the air to rise, carrying the water vapor with it. The rising water vapor, mostly from seawater, gains more and more gravitational potential energy. The air rises and continues to expand as the pressure around it decreases. This spreads out the heat in the air, causing the temperature to drop in a process called adiabatic cooling. Eventually the air cools to the point where water vapor condenses into tiny droplets or ice crystals, and clouds form. The condensation process releases the heat that it took to evaporate it in the first place, which heats the atmosphere within the clouds. When the droplets or crystals in the cloud stick together they eventually become heavy enough to fall, due to gravity, as precipitation. The precipitated water flows as runoff and groundwater into distant lakes, and eventually back to the sea.


Outlines

 

1. Describe the modern scientific model of the atom.

• nucleus contains protons and neutrons

• protons

            • positive charge

            • mass of 1 AMU

            • number of protons is element’s atomic number

• neutron

            • no charge

            • mass of 1 AMU

            • different numbers of neutrons cause different isotopes 

            • some isotopes are unstable (radioactive)

                        ex: C-12 stable, C-14 not stable w/2 extra neutrons

• electron

            • orbit nucleus

            • negative charge

            • create negative ions when gained, positve when lost

            • almost no mass

 

 

2. Compare physical and chemical properties of matter, including examples of both.

• physical

            • how substance behaves

                        ex: color, melting & boiling points, magnetism, how it breaks, scratches

• chemical

            • how substance reacts with other substances

            • testing chem. properties always makes new substances

            ex:  Al + rust makes molten iron (thermite)

                   burning, decay, acid on calcite

 

 

3. Compare the 4 common states of matter in terms of how they appear to us, and explain why they appear as they do in terms of atoms.

• solid

            • definite shape and volume           

            • atoms in 3-d crystal lattice

            • atoms vibrate in place

• liquid

            • definite volume, no definite shape

            • atoms held together but free to move around

• gas

            • no definite shape or volume

            • atoms move about freely

• plasma

            • like gas, but many atoms stripped of electrons

            • mixture of atoms, ions, and electrons

            • produces light and electric field

            • influenced by magnetism