Chapter Two: The Chemical Context of Life

Question 1

How are matter and mass related? (Define these two)

Answer 1

Matter is anything that takes up space & has mass; Mass is the amount of matter in an object

Question 2

What is an element? Where do their symbols come from?

Answer 2

A substance that cannot be broken down to other substances by chemical reactions (92 recognized)
Element symbols are the first 1-2 letters of the name (some from Latin or German).

Question 3

Compounds v.s. Molecules

Answer 3

Compound: A substance consisting of at least two different elements; they have characteristics different of its elements.
Molecules: at least 2 atoms held together by covalent bonds

Question 4

What is the difference (if there is any) between an essential element and a trace element? State everything you know about these two.

Answer 4

An essential element is an element essential to life, which are 25/92 of the recognized elements. A trace element is an essential element but only required in extremely minute amounts.

Question 5

What does 96% of living matter consist of? Hint: elements

Answer 5

Carbon, oxygen, hydrogen, & nitrogen

Question 6

Definition of atom

Answer 6

the smallest unit of matter that still retains the properties of an element (different in every element); subatomic particles make it up.

Question 7

Electrons v.s Protons v.s. Neutrons

Answer 7

Electron: A subatomic particle with a single negative electrical charge & a mass of about 1/2000 that of a neutron or proton (which is why it doesn’t affect the atomic mass). At least one moves around the nucleus of an atom.
Proton: A subatomic particle with a single positive electrical charge, with a mass of about 1.7 x 10 ^-24 grams, and is found in the nucleus of an atom
Neutron: A subatomic particle having no electrical charge, with a mass of about 1.7 x 10 ^-24 grams, and is found in the nucleus of an atom.

Question 8

Definition of Atomic Nucleus

Answer 8

The center of an atom with protons & neutrons

Question 9

Definition of Dalton

Answer 9

A measure of mass for atoms & subatomic particles; the same as the atomic mass unit (amu).

Question 10

Atomic number v.s. Mass number

Answer 10

Atomic number: The number of protons in the nucleus of an atom, unique for each element & designated by a subscript to the left of an elemental symbol (v2He)
Mass number: the sum of protons & neutrons in an atom’s nucleus, written as a superscript to the left of an element’s symbol (^4He)

Question 11

What is an isotope? Are all atoms of an element an isotope? What is the difference in behavior in chemical reactions between each isotope?

Answer 11

Isotope: 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;
Yes they are all isotopes, elements occur as a mixture of isotopes;
Isotopes behave identically in chemical reactions

Question 12

What is a radioactive isotope? Is it safe?

Answer 12

A radioactive isotope is one in which the nucleus decays spontaneously, giving off particles & energy. It changes the atom to another element;
They are used as important diagnostic tools in medicine, thus making it safe, however, radiation form decaying isotopes poses a hazard to life by damaging cellular molecules.

Question 13

Which part of an atom is involved in chemical reactions?

Answer 13

Electrons, which vary in the amount of energy they possess

Question 14

Energy v.s. Potential Energy

Answer 14

Energy: the capacity to cause change (do work)
Potential energy: the energy that matter possesses because of its location or structure. Matter usually moves to the lowest possible state of potential energy.

Question 15

How does potential energy relate to electrons?

Answer 15

The farther away an electron is from a nucleus, the greater its potential energy. It is determined by energy levels

Question 16

What is an electron shell? Can electrons change which shell they are in?

Answer 16

Electron shell: An energy level of electrons at a characteristic average distance from the nucleus of an atom.
Electrons can change shells, but only by absorbing or losing an amount of energy equal to the difference in potential energy between the shells its switching from
Absorb -> move farther out
Lose -> falls back, heat is released

Question 17

The chemical behavior of an atom is determined by/ depends on……

Answer 17

is determined by the distribution of electrons in the atom’s electron shells
depends on the number of electrons in the valence shell

Question 18

Define:
Valence
Valence electrons
Valence shell

Answer 18

Valence: an atom’s bonding capacity
Valence electrons: electrons in the last shell of an atom
Valence shell: outermost electron shell

Question 19

What happens when atoms have the same number of valence electrons? What happens when their valence shell is complete?

Answer 19

When the atoms have the same number of valence electrons, they exhibit similar chemical behavior. When their valence shell is complete, they become unreactive, or inert.

Question 20

State what you know about orbitals

Answer 20

Orbital: The three dimensional space where an electron is most likely to be found (90% of the time). There are two electrons per orbital.
The first shell has one orbital called 1s (s for shape, which is sphere)
The second shell has four orbitals called 2s and 2p (2px, 2py, 2pz); the 2p ones are shaped like dumbells
Other shells have more complex shapes for orbitals

Question 21

What do atoms do with valence electrons (when their shell isn’t full)?

Answer 21

They either share or transfer valence electrons

Question 22

Definition of chemical bonds

Answer 22

An attraction between 2 atoms, resulting from a sharing of valence electrons/ the presence of opposite charges on atoms.

Question 23

Define:
Covalent bonds
Ionic bonds
Hydrogen bonds
Van Der Waals Interactions

Answer 23

Covalent bonds: The sharing of a pair of valence electrons by 2 atoms; can have single or double bonds
Ionic bonds: when cations & anions attract each other (electron transfers can allow this bond to form)
Hydrogen bonds: 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
Van Der Waals Interactions: + and - attract, and nonpolar covalent bonds have these regions; this occurs only when atoms and molecules are very close together

Question 24

Structural formula v.s. Molecular formula

Answer 24

Structural: H-H O=O
Molecular: (H20)

Question 25

Definition of electronegativity

Answer 25

the attraction of a particular kind of atom for the electrons of a covalent bond
more electronegative means more stronger pull to shared electrons

Question 26

Nonpolar covalent bonds v.s Polar covalent bonds

Answer 26

Nonpolar: a type of covalent bond in which electrons are shared equally between 2 atoms of similar electronegativity
Polar: a covalent bond between 2 atoms differing in electronegativity. Shared electrons are pulled closer to more electronegative atoms; one is slightly + and the other slightly negative.

Question 27

What is an ion? What are ionic compounds?

Answer 27

Ion: a charged molecule or atom. Cations are + charged, anions are - charged
Ionic compounds (salts): compounds formed by ionic bonds

Question 28

Why is molecular shape crucial in biology?

Answer 28

Molecular shape is crucial in biology because it determines how biological molecules recognize & respond to one another

Question 29

What are chemical reactions? What is chemical (dynamic) equilibrium?

Answer 29

Chemical reactions: the making & breaking of chemical bonds, leading to changes in the making of matter
Chemical equilibrium: the point at which reactions offset one another exactly; reactions still go on, but with no effect on the concentrations of reactants & products.