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Chapter 2 Notes I. Boylan/Earth Science Atoms- the smallest part of an element that still has all the characteristics of the element A. The building blocks of matter 1. Matter is anything that takes up space and has mass. All matter is composed of atoms. The arrangement and types of atoms give matter its properties. 2. Some forms of matter contain only one type of atom. Such substances are elements. B. The Structure of Atoms- atoms are so small that they cannot be seen (even with a microscope; our models of an atom are mental models, which means that they are ideas of how an object might look Ex. atoms; dinosaurs; cavemen 1. nucleus- center of the atom and contains the protons and neutrons of the atom (protons are positively charged and neutrons are neutral-no charge) 2. electron cloud- surrounds the outside of the nucleus and contains the electrons of the atom (electrons are negatively charged particles) 3. diagram of an atom: C. Mass Numbers and Atomic Numbers 1. atomic numbers = the number of protons in an atoms nucleus; this number is also equal to the number of electrons in the same atom; atoms tend to be neutral (protons (+) = electrons (-)); all atoms of the same element have the same atomic number 2. mass number = to the number of protons and neutrons found in the nucleus of an atom of an element; the more protons and neutrons, the higher the mass number; electrons are not a part of the mass because they are so tiny 3. figuring number of subatomic particles (protons, electrons, and neutrons) II. a. atomic number indicates the number of protons in an atom b. number of electrons is usually the same as protons (protons = electrons); atoms tend to be neutral c. to find the number of neutrons, subtract the atomic number from the mass number 4. isotopes = when an element has a change in the number of neutrons Ex. Carbon-14 is used to determine the age of ancient objects 5. ions = when an atom gains or loses electrons; the atom is then either negatively or positively charged (loses electrons = positively charged; gains electrons = negatively charged) Combinations of Atoms A. How Atoms Combine 1. molecules- 2 or more atoms combined; atoms share electrons in the outermost portion of their electron clouds; example: (H2O) 2. compounds- when 2 or more substances combine chemically; has properties different from the properties of each of the elements in it; example: water (H2O) 3. chemical properties = describe how one substance changes when it reacts with other substances; example: iron changes to rust when it reacts to water and oxygen ***may indicate a chemical reaction: a. color change b. gas produced c. temperature change 4. Ions- electrically charged atoms; atom either gains or loses electrons; Example: Na loses an electron and is a positive ion; Cl gains an electron and is a negative ion; the 2 join to become a neutral molecule (NaCl) B. Mixtures =substances which are mixed, but each retains its own properties; the components of a mixture can be separated by physical means; Examples are soil, salad, sweetened tea; a kind of mixture is a solution (when one substance is dissolved in another substance); the only way to separate the components of a compound is through a chemical reaction III. Matter A. Physical Properties of Matter = things you can observe without changing a substance; Examples: color; measurements; texture B. Density = measure of the mass of an object divided by its volume; usually given in grams per cubic centimeter (g/cm ); Example: average density of liquid water is 1 g/cm Density formula: Density = mass volume ***An object that is more dense than water will sink, whereas one that’s less dense than water will float. III. C. States of Matter- on Earth matter occurs in 4 physical states 1. solids- molecules are in a fixed position relative to each other; atoms or molecules may vibrate, but do not switch positions; a solid resists changes in shape and volume 2. liquids- atoms or molecules remain close to one another but are free to change positions; this allows liquids to flow; liquids take the shape of their container, but resist changes in volume 3. gases- atoms or molecules have very little attractive force; they move freely and independently; they do not resist changes in volume or shape 4. plasma- the most common state of matter in the universe; composed of ions and electrons; Examples: stars are composed of matter in the plasma state along with fluorescent lights and lightning bolts D. Changing the State of Matter 1. matter is changed from a liquid to a solid at its freezing point; Example: water’s freezing point is 0 degrees Celsius 2. matter changes from a liquid to a gas at its boiling point; Example: water’s boiling point is 100 Degrees Celsius 3. pressure changes can also affect the state of matter; different substances have different freezing and boiling points E. Changes in Physical Properties- some physical properties may change when the matter changes state; Example: density of water changes as it changes state Superconductors = any material that allows electricity to pass through it without resistance to the flow of electrons A. no electricity is wasted B. electric currents can be stored in a super conducting ring C. extremely low temperatures are needed to make materials into superconductors E. Examples: titanium, zinc, lead, and mercury