Chapter 2 - The Chemical Context of Life

Question 1

Element

Answer 1

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

Question 2

Compound

Answer 2

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

Question 3

Trace elements

Answer 3

An element indispensable for life but required in extremely minute amounts.

Question 4

Atom

Answer 4

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

Question 5

Neutrons

Answer 5

A subatomic particle with no electrical charge.

Question 6

Protons

Answer 6

A subatomic particle with a positive electrical charge.

Question 7

Electrons

Answer 7

A subatomic particle with a negative electrical charge. Form a cloud around the nucleus.

Question 8

Atomic nucleus

Answer 8

Contains protons and neutrons. Almost the same mass and are measured in Daltons.

Question 9

Daltons

Answer 9

A measure of mass for atoms and subatomic particles; the same as the atomic mass unit, or amu.

Question 10

Atomic number

Answer 10

The number of protons in an atom, unique for each element and designated by a subscript to the left of the elemental symbol.

Question 11

Atomic mass

Answer 11

The total mass of an atom, which is the mass in grams of 1 mole of the atom.

Question 12

Mass number

Answer 12

The sum of the number of protons and neutrons in an atoms nucleus.

Question 13

Isotope

Answer 13

One of several atomic forms of an element, each with the same number of protons but a different number of neutrons, thus differing in atomic mass.

Question 14

Radioactive Isotope

Answer 14

An isotope that is unstable; the nucleus decays spontaneously, giving off detectable particles and energy.

Some applications of radioactive isotopes in biological research are

• Dating fossils
• Tracing atoms through metabolic processes
• Diagnosing medical disorders

Question 15

Potential energy

Answer 15

The energy that matter has because of its location or structure

Question 16

Electron shell

Answer 16

An electron’s state of potential energy. Also called energy level.

Question 17

The chemical behavior of an atom is determined by…

Answer 17

valence electrons.

Question 18

Valence electrons

Answer 18

Electrons in the outermost electron shell, or valence shell.

Question 19

Elements with a full valence shell are…

Answer 19

Chemically inert

Question 20

Orbital

Answer 20

the three-dimensional space where an electron is found 90% of the time.

Question 21

Chemical bond

Answer 21

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.

Question 22

Covalent Bond

Answer 22

A type of strong chemical bond in which two atoms share one or more pairs of valence electrons. Can form between atoms of the same element or atoms of different elements

Question 23

Molecule

Answer 23

Two or more atoms held together by covalent bonds.

Question 24

Single (covalent) bond

Answer 24

The sharing of one pair of valence electrons.

Question 25

Double (covalent) bond

Answer 25

The sharing of two pairs of valence electrons.

Question 26

Structural formula

Answer 26

The notation used to represent atoms and bonding. For example, Hydrogen with its single bonded two valence electrons: H—H or H:H

Question 27

Compound

Answer 27

A combination of two or more different elements.

Question 28

Valence

Answer 28

The bonding capacity of a given atom; usually equals the number of unpaired electrons required to complete the atoms outermost (valence) shell.

Question 29

Electronegativity

Answer 29

An atom’s attraction for the electrons in a covalent bond.

Question 30

The more electronegative an atom, the more ________ it pulls shared electrons toward itself.

Answer 30

strongly

Question 31

Nonpolar covalent bond

Answer 31

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

Question 32

Polar covalent bond

Answer 32

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

Question 33

Ionic Bond

Answer 33

A chemical bond resulting from the attraction between oppositely charged ions. (One atom steals an electron from the other atom so that both have completed valence shells).

Question 34

Ion

Answer 34

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

Question 35

Cation

Answer 35

A positively charged ion.

Question 36

Anion

Answer 36

A negatively charged ion.

Question 37

Ionic bond

Answer 37

An attraction between an anion and a cation. Compounds formed by ionic bonds are called ionic compounds, or salts .

Question 38

Weak chemical bonds

Answer 38

Reinforce shapes of large molecules and help molecules adhere to each other. Examples are ionic bonds and hydrogen bonds.

Question 39

Hydrogen bond

Answer 39

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

Question 40

Van der Waals Interactions

Answer 40

Weak attractions between molecules or parts of molecules that result from transient local partial charges. Collectively, such interactions can be strong, as between molecules of a gecko’s toe hairs and a wall surface.

Question 41

A molecule’s shape is determined by...

Answer 41

The positions of its atoms’ valence orbitals. In a covalent bond, the s and p orbitals may hybridize, creating specific molecular shapes. Biological molecules recognize and interact with each other with a specificity based on molecular shape, so molecules with similar shapes can have similar biological effects.

Question 42

Chemical reactions

Answer 42

The making and breaking of chemical bonds. All chemical reactions are reversible: products of the forward reaction become reactants for the reverse reaction.

Question 43

Reactants

Answer 43

The starting molecules of a chemical reaction.

Question 44

Products

Answer 44

The final molecules of a chemical reaction.

Question 45

Chemical equilibrium

Answer 45

Reached when the forward and reverse reaction rates in chemical reactions are equal.