Biology Chapter 2

Life depends on

chemistry

atom

the study of chemistry begins with the basic unit of matter

1 centimeter long / width of a finger

100 million atoms would be

protons, neutrons, and electrons

the subatomic particles that make up atoms

protons and neutrons

have about the same mass

protons

are positively charged

neutrons

carry no charge

nucleus

center of the atom

the nucleus

protons and neutrons bind together to bind

electron

have a mass much higher than protons and neutrons, is negatively charged with 1/1840 the mass of a proton

electrons are

in constant motion in the space surrounding the nucleus; are attracted to the positively charged nucleus but remain outside the nucleus because of the energy of their motion

atoms have

equal numbers of electrons and protons

subatomic particles have

equal but opposite charges

atoms are always

neutral

a chemical element is

a pure substance that consists entirely of one type of atom

are found in living organisms

two dozen elements

elements are represented by

one or two letter symbols

atomic number

the number of protons in an atom of an element

atoms of an element can

have different numbers of neutrons

isotopes

atoms of the same element that differ in the number of neutrons they contain

mass number

the sum of protons and neutrons in the nucleus of the atom

isotopes are

identified by their mass numbers

atomic mass

the weighted average of the masses of an elements isotopes

weighted

the abundance of each isotope in nature is considered when the average is calculated

isotopes of an element

have the same chemical properties because they have the same number of electrons

some isotopes

are radioactive, meaning that their nuclei are unstable and break down at a constant rate over time

geologists

can determine the ages of rocks and fossils by analyzing the isotopes found in them

radioactive isotopes

can also be used as label or tracers to follow the movements of substances within organisms

in nature

most elements are found combined with other elements in compounds

compound

is a substance formed by the chemical combination of two or more elements in definite proportions

chemical formula

the composition of compounds

water

contains two atoms of hydrogen for each atom of oxygen, with the chemical formula H2O.

the physical and chemical properties of a compound

are usually very different from those of the elements from which it is formed

hydrogen and oxygen

are gases at room temperature and can form liquid water

chlorine is

reactive

sodium chloride

is not poisonous and essential for the survival of most living things

atoms in compounds

are held together by chemical bonds

much of chemistry is

devoted to understanding how and when chemical bonds form

bond formation

involves the electrons that surround each atomic nucleus

electrons that are available

to form bonds are called valence electrons

the main types of chemical bonds are

ionic bonds and covalent bonds

ionic bond

formed when one or more electrons are transferred from one atom to another

atoms are

electrically neutral because they have equal numbers of protons and electrons

an atom that loses electrons

has a positive charge

an atom that gains electrons

has a negative charge

ions

positively and negatively charged atoms

attraction between oppositely charged ions is

also an ionic bond

sometimes electrons are

shared by atoms instead of being transferred

to share electrons means

the moving electrons actually travel in the orbitals of both atoms

covalent bond

forms when electrons are shared between atoms

single covalent bond

when the atoms share two electrons

double covalent bond

when the atoms share four electrons

triple covalent bond

when the atoms share six electrons

called a molecule

the structure that results when atoms are joined together by covalent bonds

molecule

the smallest unit of most compounds

atoms of different elements

do not all have the same ability to attract electrons

some atoms have

a stronger attraction for electrons then do other atoms

when the atoms in a covalent bond share electrons

the sharing is not always equal

even when the atoms sharing of electrons in a covalent bond are equal

the rapid movement of electrons can create regions on a molecule that have a positive or negative charge

processes that sustain life

digestion of food and gas exchange

living things are

composed of chemicals

chemicals are

composed of atoms

understanding life depends

on understanding atoms

atoms share

a fundamental structure

atoms are composed of

smaller particles

protons are found in

the nucleus of the atom

chemical bonds

the atoms of a compound are held together by

when the atoms in a covalent bond share electrons, the sharing is

not always equal

van der Waals forces

a slight attraction that develops between the oppositely charged regions of nearby molecules

atoms of different elements

do not have the same ability to attract electrons

van der waals forces are not

as strong as ionic or covalent bonds

life is impossible

without water

solid water is

less dense than liquid water (ex. ice floats)

water molecules are

neutral / carry no charge

a water molecule is polar because

there is an uneven distribution of electrons between the oxygen and hydrogen atoms

the negative pole is

near the oxygen atom

the positive pole is

between the hydrogen atoms

polar molecule

a molecule in which the charges are unevenly distributed

water is a

polar molecule, so you can say it has polarity

water molecules can attract one another

because of their partial charge

hydrogen bonds are not as strong as

ionic or covalent bonds

hydrogen bond

molecules attracting one another due to their partial charges

a single water molecule may be involved in as many as

four hydrogen bonds at a time

cohesion

the attraction of molecules of the same substance

because of water bonding

water is extremely cohesive, causing water to bead up on a small surface

adhesion

an attraction between molecules of different substances

an example of adhesion is

the menisus in a graduated cylinder

the adhesion with the walls of the cylinder is greater than

the cohesion of the molecules of the liquid

capillary action

one of the actions that draw water out of the roots of a plant and up into its stems and leaves

water is not always pure, it is often

apart of a mixture

mixture

a material composed of two or more elements or compounds that are physically mixed together but not chemically combined

examples of a mixture are

salt and pepper; sand and sugar

the two types of mixtures that can be made with water are

solutions and suspensions

if crystalline salt is placed in warm water, the sodium and chloride ions are

pulled apart by the polarity of the water molecules

solution

mixture of two or more substances in which the molecules of the substances are evenly distributed

solute

substance that is dissolved in a solvent to make a solution

solvent

substance in which a solute is dissolved to form a solution

true

in salt and water, water is the solvent and salt is the solute

some material _________ when placed in water but _________ so small that they do not settle out

do not dissolve; separate into small pieces

suspension

mixture of water and nondissolved materials