Download Chapter 2 Notes

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