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Bio Chap. 2
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29
Biology
Undergraduate 1
02/15/2009

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Term

Element

Definition

a substance that cannot be broken down to other substances by chemical reactions.

Term
Compound
Definition

a substance consisting of two or more different elements combined in a fixed ratio.

Term
trace elements
Definition

Elements required by an organism in only minute quantities.

 

Ex: Iron

Term
Atom
Definition

The smallest unit of matter that still retains the properties of an element

Term
Neutrons
Definition

electrically neutral subatomic particles

Term
Electrons
Definition

electrically negative subatomic particles

Term

Protons

Definition

Electrically positive subatomic particles

Term
Atomic Nucleus
Definition

consists of protons and neutrons; at center of atom

Term
Dalton
Definition

a unit of measurement for atoms and subatomic particles; named after John Dalton who developed atomic theory.

 

1 Dalton = 1 amu (atomic mass unit)

 

Protons/neutrons have mass of 1 amu

Term
Atomic Number
Definition

the number of protons in the nucleus (and consequently the number of electrons in the atom unless otherwise specified)

Term
Mass Number
Definition

sum of protons and neutrons in the nucleus of an atom

Term
Atomic mass
Definition

the total mass of an atom - equal to the mass number

Term
Isotopes
Definition

An atom that has more neutrons than other atoms of the same element (and therefore a greater mass)

 

These atoms still have the same number of protons though.

Term
Radioactive Nuclei
Definition

an isotope in which the nucleus decays spontaneously, giving off particles and energy.

 

used in bio to date fossils, follow atoms through metabolism 

 

EX: Carbon-14

Term
Energy
Definition

the capacity to cause change

Term
Potential Energy
Definition

The energy that matter possesses because of its location or structure.

 

The more distant an electron is from the nucleus, the greater its potential energy. An electron's potential energy is determined by its energy level (NOTE: electrons can't exist b/w energy levels)

 

EX: water in a reservoir on a hill has potential energy because of its altitude.  When gates of reservoir are opened, the water  runs downhill and the energy can be used to do work.

Term
Valence Electrons
Definition

electrons in the outermost shell (valence shell) that mostly contribute to the chemical behavior of an atom.

Term
Orbital
Definition
Term
Chemical Bonds
Definition

an attraction between two atoms, resulting from a sharing of outer-shell electrons or the presence of opposite charges on the atoms.  The bonded atoms gain complete outer electron shells (an octet)

Term
Molecule
Definition

two or more atoms held together by covalent bonds

Term

Molecular Formula

Definition

indicates what atoms the molecule consists of.

 

EX: H2

Term
Structural Formula
Definition

Represents both the atoms and bonds that the molecule consists of.

 

EX: H-H

Term
electronegativity
Definition

The attraction of a particular kind of atom for the electrons of a covalent bond; the more electronegative an atom, the more it pulls shared electrons toward itself.

Term
ion
Definition

charged atom (or molecule)

 

cation = positive

anion = negative

Term
ionic bond
Definition

when cations and anions attract each other;

 

formed by ionic compounds, or salts (bonds are lattice like)

Term

Hydrogen Bond

Definition

forms when a hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom

Term
Van der Waals Interactions
Definition

Weak attractions between molecules or parts of molecules that result from localized charge fluctuations.

Term
Chemical Reactions
Definition

The making and breaking of chemical bonds, leading to changes in the composition of matter

 

EX: 2H2 + O2 --> H2O

Term
Chemical Equilibrium
Definition

In a chemical reaction, the state in which the rate of the forward reaction equals the rate of the reverse reaction, so that the relative concentrations of the reactants and products do not change with time.

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