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Biology Chapter 2
Chapter 2 Biology
29
Biology
Undergraduate 1
10/04/2011

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Term
Matter
Definition
anything that takes up space and has mass
Term
element
Definition
basic substances that cannot be broken down to substances with different properties;  composed of only one type of atom
Term
atom
Definition

tiny particles;

smallest particle of an element that displays the properties of the element

 

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Term
atomic symbol
Definition
One or two letters create this symbol, which stands for it's name
Term
mass number
Definition
mass number of an atom is just about equal to the sum of its protons and neutrons
Term
protons, neutrons
Definition

located within the nucleus of an atom

 

proton:  positive subatomic particle located in the nucleus and assigned one atomic mass unit

 

neutrons:

neutral subatomic particle located in the nucleus and assigned one atomic mass unit

Term
electrons
Definition
subatomic particle that moves about the nucleus
Term
atomic number
Definition
all atoms of an element have the same number of protons.  This is the atom's atomic number.
Term
isotopes
Definition
atoms of the same element that differ in the number of neutrons.  They have the same number of protons, but have different mass numbers.
Term
tracer
Definition
substance having an attached radioactive isotope that allows a researcher to track its whereabouts in a biological system.
Term
orbital
Definition

particular volume of space where an electron is most apt to be found most of the time

 

Orbitals near the nucleus are circular or dumbbell shaped.  Other shapes occur in more distant orbitals. 

 

Orbitals contain no more than two electrons

Term
octet rule
Definition
states than an atom other than hydrogen tends to form bonds until it has eight electrons in its outer shell;  an atom that already has eight electrons in its outer shell does not react and is inert.
Term
compound
Definition
when atoms of two or more different elements bond together, the product is called a compound.
Term
molecule
Definition
smallest part of a compound that  still has the properties of the compound.
Term
ionic bond
Definition
Ionic compounds are held together by an attraction between negatively and positively charged ions called an ionic bond.
Term
salt
Definition
sodium chloride is an ionic compound formed when sodium reacts with chlorine
Term
covalent bonding
Definition

chemical bond in which atoms share one pair of electrons

 

results when two atoms share electrons in such a way that each atom has an octet of electrons in the outer shell (or two electrons in the case of hydrogen)

Term
nonpolar covalent bond
Definition
when the sharing of electrons between two atoms is fairly equal.
Term
electronegativity
Definition

the attraction of an atom for the electrons in a covalent bond.

 

oxygen atom is more electronegative than the hydrogen atom, so the oxygen atom can attract the electron pair to a greater extent than each hydrogen atom can.

Term
polar covalent bond
Definition

bond in which sharing of electrons between atoms is unequal.

 

in the case of water, the molecule itself is a polar molecule.

Term
hydrogen bond
Definition

polarity within a water molecule causes the hydrogen atoms in one molecule to be attracted to the oxygen atoms in other water molecules.  this attraction, although weaker than ionic or covalent bonds, is called a hydrogen bond.

 

because it is easily broken, it is often represented by a dotted line

Term
hydrophilic
Definition
when ions and molecules disperse in water, they move about and collide, allowing reactions to occur.  those molecules that can attract water are said to be hydrophilic
Term
hydrophobic
Definition
nonionized and nonpolar molecules that cannot attract water
Term
solution
Definition
contains dissolved substances, called solutes
Term
solutes
Definition
dissolved substances
Term
acids
Definition
substances that dissociate in water, releasing hydrogen ions (H+)
Term
bases
Definition
substances that either take up hydrogen ions (H+) or release hyroxide ions (OH-)
Term
pH scale
Definition

used to indicate the acidity and basicity (alkalinity) of a solution.

 

pH of 7 is neutral

Term
buffer
Definition
help keep the pH within normal limits because they are chemicals or combinations of chemicals that take up excess hydrogen ions (H+) or hydroxide ions (OH-)
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