Biology Chapter 2

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The Chemical Basis of Life Campbell Biology concepts and connections

Element

A subsctance that cannot be broken down to other substance by ordinary chemcial means.

Matter

Anything that occupies space and has mass.

Compound

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

Trace elements

an element that is essential for life but required in extremely minute amounts.

Atom

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

Proton

A subatomic particle with a single positive electrical charge, found in the nucleus of an atom.

Electron

A subatomic particle with a single negative electrical charge. One or more electrons move around the nuclues of an atom.

Neutron

A subatomic particle having no electrical charge, found in the nucleus of an atom.

Nucleus

An atom's central core, containing protons and neutrons.

Mass Number

The sum of the number of protons and neutrons in an atom's nucleus.

Atomic Mass

The total mass of an atom; also called atomic weight. Given as a whole number, the atomic mass approximately equals the mass number.

Isotopes

One of several atomic forms of an element, each with teh same number of protons but different number of neutrons.

Radioactive Isotope

An isotope whose nucleus decays spontaneously, giving off particles and energy.

Atomic Number

The number of protons in each atom of a particular element.

Electron Shells

An energy level representing the distance of an electron from the nucleus of an atom.

Chemical Bonds

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.

Covalent Bond

A strong chemical bond in which two atoms share one or more pairs of outer-shell electrons.

Molecule

Two or more atoms held together by covalent bonds.

Electronegativity

The attraction of a given atom for the electrons of a covalent bond.

Nonpolar Covalent Bonds

A covalent bond in which electrons are shared equally between two atoms of similar electronegativity.

Polar Covalent Bond

A covalent bond between atoms that differ in electronegativity. The shared electrons are pulled closer to the more electornegative atom, making it slightly negative and the other atom slightly positive.

Polar Molecule

A molecule containing polar covalent bonds and having an unequal distribution of charges.

Ion

An atom or group of atoms that has gained or lost one or more electrongs, thus acquiring a charge.

Ionic Bond

A chemical bond resulting from the attraction between oppositely charged ions.

Salt

A compound resulting from the formation of ionic bonds; also called an ionic compound.

Hydrogen Bonds

A type of weak chemical bond formed when the partially positive hydrogen atom participating in a polar covalent bond in one molecule is attracted to the partially negative atom participating in a polar covalent bond in another molecule (or in another region of the same molecule).

Chemical Reaction

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

Reactants

A starting material in a chemical reaction.

Product

An ending material in a chemical reaction.

Cohesion

The sticking together of molecules of the same kind, often by hydrogen bonds.

Adhesion

The attraction between different kinds of molecules.

Surface Tension

A measure of how difficult it is to stretch or break the surface of a liquid. Water has a high surface tension because of the hydrogen bonding of surface molecules.

Heat

The amount of energy associated with the movement of atoms and molecules in a body of matter.

Temperature

Measures the intensity of heat.

Evaporative Cooling

occurs because the molecules with the greates energy leave.

Solution

A liquid that is a homogeneous mixture of two or more substances.

Solvent

The dissolving agent of a solution. Water is the most versatile solvent known.

Solute

A substance that is dissolved in a solution.

Aqueous Solution

A solution in which water is the solvent.

Acid

A substance that increases the hydrogen ion concentration in a solution. 0 on pH scale is a strong acid.

Base

A substance that decreases the hydrogen ion concentration in a solution. 14 is a strong base on the pH scale.

pH Scale

A scale we used to describe how acidic or basic a solution is. The scale ranges from 0-14, 0 being the most acidic and 14 being the most basic. 7 is neutral (pure water)

Buffers

A chemical substance that resists changes in pH by accepting hydrogen ions from or donating hydrogen ions to solutions.

substance that minimize changes in pH.

Acid Precipitation

Rain, snow or fog that is more acidic than pH 5.2.

Ocean Acidification

Decreasing pH of ocean waters due to absoprtion of excess atmospheric CO2 from the burning of fossil fuels.

What 4 elements make up about 96% of living matter?

Oxygen, carbon, hydrogen, and nitrogen.

The nucleus of an atom contains...??

Neutrons and protons.

First shell of an atom can contain how many electrons?

2

Second shell of an atom can contain how many electrons?

8

Third shell of an atom can contain how many electrons?

8

Fourth shell of an atom can contain how many electrons?

18

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