Chapter 2

Question 1

what do animals have

Answer 1

structures n mechanisms that defend them from attack

Question 2

describe how science works in real life

Answer 2

e. Unlike college courses, nature is not neatly packaged into
individual sciences—biology, chemistry, physics, and so forth. Biologists specialize
in the study of life, but organisms and their environments are natural systems to
which the concepts of chemistry and physics apply. Biology is multidisciplinary.

Question 3

matter

Answer 3

which is anything that

takes up space and has mass

Question 4

element n how many

Answer 4

is a substance
that cannot be broken down to other substances by chemical
reactions. 92

Question 5

compound n ex

Answer 5

d is a substance consisting of two or more
different elements combined in a fixed ratio. Table salt, for
example, is sodium chloride (NaCl), a compound composed
of the elements sodium (Na) and chlorine (Cl) in a 1:1 ratio.

Question 6

emergent properties

Answer 6

These are simple examples of organized matter having

emergent properties: A compound has characteristics different from those of its elements

Question 7

weight v mass

Answer 7

*In everyday language we tend to substitute the term weight for mass, although
the two are not identical. Mass is the amount of matter in an object, whereas the
weight of an object is how strongly that mass is pulled by gravity. The weight of
an astronaut walking on the moon is approximately 1⁄
6 the astronaut’s weight on
Earth, but his or her mass is the same. However, as long as we are earthbound,
the weight of an object is a measure of its mass;

Question 8

essential elements

Answer 8

Of the 92 natural elements, about 20–25% are essential
elements that an organism needs to live a healthy life and
reproduce

Question 9

what four elements make up 96% of living orgx

Answer 9

Just four elements—oxygen (O), carbon (C), hydrogen (H),
and nitrogen (N)—make up approximately 96% of living
matter.

Question 10

trace elements

Answer 10

required in only minute quantities

Question 11

Some naturally occurring elements are …

Answer 11

toxic to organisms.

Question 12

atom

Answer 12

is the
smallest unit of matter that still retains the properties of an
element. Atoms are so small that it would take about a million
of them to stretch across the period printed at the end of this
sentence.

Question 13

subatomic particles

Answer 13

Using high-energy
collisions, physicists have produced more than 100 types of
particles from the atom, but only three kinds of particles are
relevant here: neutrons, protons, and electrons

Question 14

protons n electrons…

Answer 14

s. Protons
and electrons are electrically charged. Each proton has one
unit of positive charge, and each electron has one unit of
negative charge. A neutron, as its name implies, is electrically neutral.

Question 15

atomic nucleus

Answer 15

Protons and neutrons are packed together tightly in a dense
core, or atomic nucleus, at the center of an atom; protons
give the nucleus a positive charge.

Question 16

mass of a proton and neutron alone?

Answer 16

1.7 x 10^-24 g

Question 17

dalton

Answer 17

since g is too big, we use a unit of measurement called
the dalton, in honor of John Dalton, the British scientist who
helped develop atomic theory around 1800. we use it for atoms ad molecules and subatomic particles.

Question 18

atomic number

Answer 18

. This number of protons, which is unique to that element, is called the atomic
number and is written as a subscript to the left of the symbol for the element

Question 19

atoms charge and subatomic particles balanace

Answer 19

. Unless otherwise indicated, an atom is neutral in
electrical charge, which means that its protons must be balanced by an equal number of electrons. Therefore, the atomic
number tells us the number of protons and also the number
of electrons in an electrically neutral atom

Question 20

mass no.

Answer 20

We can deduce the number of neutrons from a second
quantity, the mass number, which is the total number of
protons and neutrons in the nucleus of an atom.

Question 21

how to find the number of neutrons

Answer 21

. Because the atomic number indicates
how many protons there are, we can determine the number
of neutrons by subtracting the atomic number from the mass
number.

Question 22

simplest atom?

Answer 22

1 1 H

Question 23

atomic mass

Answer 23

total mass of an atom

Question 24

isotope

Answer 24

diff atomic forms of an elemnt

Question 25

radioactive isotope

Answer 25

. A radioactive isotope is one in which
the nucleus decays spontaneously, giving off particles and
energy. When the radioactive decay leads to a change in
the number of protons, it transforms the atom to an atom
of a different element. For example, when an atom of
carbon-14 (14C) decays, it loses a proton, becoming an atom
of nitrogen (14N). Radioactive isotopes have many useful
applications in biology.

Question 26

tracers

Answer 26

Cells can use radioactive atoms just as they would
use nonradioactive isotopes of the same element. The radioactive isotopes are incorporated into biologically active
molecules, which are then used as tracers to track atoms during metabolism, the chemical processes of an organism. diagnostic medical tool.

Question 27

half life

Answer 27

fixed rate, expressed as the half-life of the isotope—the

time it takes for 50% of the parent isotope to decay

Question 28

half lifes are unaffected by…

Answer 28

temp, pressure or any other environmental vble

Question 29

radiometric dating

Answer 29

. Using a process called radiometric dating, scientists measure the ratio of different isotopes and calculate how
many half-lives (in years) have passed since an organism was
fossilized or a rock was formed

Question 30

each isotope can best…

Answer 30

“measure” a particular range of

years:

Question 31

. When two atoms approach each other during a

chemical reaction…

Answer 31

, their nuclei do not come close enough to
interact. Of the three subatomic particles we have discussed,
only electrons are directly involved in chemical reactions.

Question 32

energy

Answer 32

is defined as the capacity to cause change—

for instance, by doing work

Question 33

pot en and example

Answer 33

Potential energy is the energy
that matter possesses because of its location or structure. For
example, water in a reservoir on a hill has potential energy
because of its altitude. When the gates of the reservoir’s dam
are opened and the water runs downhill, the energy can be
used to do work, such as moving the blades of turbines to generate electricity. Because energy has been expended, the water
has less energy at the bottom of the hill than it did in the reservoir. Matter has a natural tendency to move toward the lowest
possible state of potential energy; in our example, the water
runs downhill. To restore the potential energy of a reservoir,
work must be done to elevate the water against gravity.

Question 34

electron shells

Answer 34

Electrons are found in different
electron shells, each with a characteristic average distance
and energy level. In diagrams, shells can be represented by
concentric circles

Question 35

how can elecrons move between shells?

Answer 35

An electron can move from one shell to another,
but only by absorbing or losing an amount of energy equal
to the difference in potential energy between its position
in the old shell and that in the new shell.

Question 36

photosynthesis n this process

Answer 36

For example, light energy can excite an electron
to a higher energy level. (Indeed, this is the first step taken
when plants harness the energy of sunlight for photosynthesis, the process that produces food from carbon dioxide and water. You’ll learn more about photosynthesis in
Chapter 10.) When an electron loses energy, it “falls back”
to a shell closer to the nucleus, and the lost energy is usually
released to the environment as heat.

Question 37

what state of pot en do electrons reside in

Answer 37

Electrons, like all matter, tend to exist in the

lowest available state of potential energy.

Question 38

The chemical behavior of an atom depends mostly on 1. We call those outer
electrons 2 and the outermost electron
shell the 3

Answer 38

1. the
   number of electrons in its outermost shell.
2. valence e
3. valence shell

Question 39

Atoms with the same number of electrons in their valence shells
exhibit …

Answer 39

similar chemical behavior

Question 40

orbital

Answer 40

. Accordingly, the concentric-circle
diagrams do not give a real picture of an atom. In reality,
we can never know the exact location of an electron. What
we can do instead is describe the space in which an electron
spends most of its time. The three-dimensional space where
an electron is found 90% of the time is called an orbital.

Question 41

how many e to an orbital? how many e can fit in the first electron shell?

Answer 41

No more than 2 electrons can occupy a single orbital. The
first electron shell can therefore accommodate up to 2 electrons
in its s orbital

Question 42

how do atoms interact

Answer 42

As you will see in the next section, atoms interact in a way that completes their valence shells. When they
do so, it is the unpaired electrons that are involved.

Question 43

how do atoms interact part 2

Answer 43

Atoms with
incomplete valence shells can interact with certain other atoms
in such a way that each partner atom completes its valence
shell: The atoms either share or transfer valence electrons

Question 44

chemical bonds

Answer 44

These
interactions usually result in atoms staying close together, held
by attractions called chemical bonds

Question 45

strongest kinds of chemical bonds?

Answer 45

. The strongest kinds of
chemical bonds are covalent bonds and ionic bonds in dry ionic
compounds. (Ionic bonds in aqueous, or water-based, solutions
are weak interactions, as we will see later.)

Question 46

covalent bond

Answer 46

A covalent bond is the sharing of a pair of valence electrons
by two atoms

Question 47

hydrogen and overlapping?

Answer 47

s. When the two hydrogen atoms come close enough

for their 1s orbitals to overlap, they can share their electrons

Question 48

molecule

Answer 48

two or more atoms held together by covalent bonds

Question 49

single bond

Answer 49

a pair of shared e

Question 50

valence

Answer 50

Each atom that can share valence electrons has a bonding
capacity corresponding to the number of covalent bonds the
atom can form. When the bonds form, they give the atom
a full complement of electrons in the valence shell. The
bonding capacity of oxygen, for example, is 2. This bonding capacity is called the atom’s valence and usually equals
the number of unpaired electrons required to complete the
atom’s outermost (valence) shell.

Question 51

see graph of the diff kinds of covalent bonds

Answer 51

ok lol

Question 52

why are h2 and o pure

Answer 52

The molecules H2 and O2 are pure elements rather than
compounds because a compound is a combination of two or
more different element

Question 53

electronegativity

Answer 53

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

Question 54

This type of bond

is called a polar covalent bond

Answer 54

unequal charge distribution. d. Such bonds vary in their
polarity, depending on the relative electronegativity of the two
atoms. For example, the bonds between the oxygen and hydrogen atoms of a water molecule are quite polae

Question 55

Oxygen is one of the most electronegative elements…

Answer 55

attracting shared electrons much more strongly than hydrogen does.

Question 56

describe the bonding of o n h

Answer 56

In a covalent bond between oxygen and hydrogen, the electrons spend more time near the oxygen nucleus than near the
hydrogen nucleus. Because electrons have a negative charge
and are pulled toward oxygen in a water molecule, the oxygen
atom has two regions of partial negative charge (each indicated
by the Greek letter δ with a minus sign, δ-, “delta minus”), and
each hydrogen atom has a partial positive charge (δ+, “delta
plus”)

Question 57

. Note that the transfer of an electron

is not, by itself, the formation of a bond; …

Answer 57

rather, it allows a

bond to form because it results in two ions of opposite charge.

Question 58

what happens when socium n chlorine bond

Answer 58

When
these two atoms meet, the lone valence electron of sodium
is transferred to the chlorine atom, and both atoms end up
with their valence shells complete. (Because sodium no longer
has an electron in the third shell, the second shell is now the
valence shell.)

Question 59

what happens when sodium binds to chlorine in terms of electrons

Answer 59

The electron transfer between the two atoms
moves one unit of negative charge from sodium to chlorine.
Sodium, now with 11 protons but only 10 electrons, has a net
electrical charge of 1+; the sodium atom has become a cation.
Conversely, the chlorine atom, having gained an extra electron,
now has 17 protons and 18 electrons, giving it a net electrical
charge of 1- ; it has become a chloride ion—an anion.

Question 60

how are salts found in nature

Answer 60

Salts are
often found in nature as crystals of various sizes and shapes.
Each salt crystal is an aggregate of vast numbers of cations
and anions bonded by their electrical attraction and arranged
in a three-dimensional lattice

Question 61

formula for an ionic compound indiates what

Answer 61

The formula for an ionic
compound, such as NaCl, indicates only
the ratio of elements in a crystal of the
salt. “NaCl” by itself is not a molecule.

Question 62

magnesium and choride bonding pattern

Answer 62

n. Magnesium (12Mg) must
lose 2 outer electrons if the atom is to
have a complete valence shell, so it has a
tendency to become a cation with a net
charge of 2+ (Mg2+
). One magnesium
cation can therefore form ionic bonds
with two chloride anions (Cl-
)

Question 63

reread pg 86, the question mark

Answer 63

ok lol

Question 64

why are ionic bonds weak in water

Answer 64

r, however,
the ionic bonds are much weaker because each ion is partially
shielded by its interactions with water molecules

Question 65

why is the reversibility of weak interactions an advantage sometimes

Answer 65

The reversibility of weak interactions can
be an advantage: Two molecules can come together, affect one
another in some way, and then separate.

Question 66

hydrogen bond

Answer 66

. When a hydrogen atom is covalently bonded to an
electronegative atom, the hydrogen atom has a partial positive
charge that allows it to be attracted to a different electronegative atom nearby. This attraction between a hydrogen and an
electronegative atom is called a hydrogen bond

Question 67

who are the electronegative partners usually in bio

Answer 67

o or n

Question 68

vanderwalls attractions

Answer 68

These van der Waals interactions are individually weak and occur only when atoms and molecules are
very close together. When many such interactions occur
simultaneously, however, they can be powerful

Question 69

how are the shapes of molecules with more than two atoms determined

Answer 69

These shapes are determined by the positions of the atoms’

orbitals

Question 70

For water molecules (H2O), two of the hybrid orbitals in

the oxygen’s valence shell are shared with…

Answer 70

hydrgoen

Question 71

The methane molecule (CH4) has the shape of a completed tetrahedron because …

Answer 71

all four hybrid orbitals of the
carbon atom are shared with hydrogen atoms (see Figure
2.15b). The carbon nucleus is at the center, with its four
covalent bonds radiating to hydrogen nuclei at the corners
of the tetrahedron. Larger molecules containing multiple
carbon atoms, including many of the molecules that
make up living matter, have more complex overall shapes.

Question 72

endorphins

Answer 72

n. Endorphins are signaling molecules
made by the pituitary gland that bind to the receptors, relieving pain and producing euphoria during times of stress, such
as intense exercise.

Question 73

chemical rxn

Answer 73

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

Question 74

rxn of water

Answer 74

This reaction breaks the covalent bonds of H2 and O2 and

forms the new bonds of H2O.

Question 75

photosynthesis

Answer 75

The raw materials of photosynthesis are carbon dioxide
(CO2) and water (H2O), which land plants absorb from the air
and soil, respectively. Within the plant cells, sunlight powers
the conversion of these ingredients to a sugar called glucose
(C6H12O6) and oxygen molecules (O2), a by-product that can be
seen when released by a water plant (Figure 2.17). Although
photosynthesis is actually a sequence of many chemical reactions, we still end up with the same number and types of
atoms that we had when we started. Matter has simply been
rearranged, with an input of energy provided by sunlight.

Question 76

All chemical reactions are theoretically …

Answer 76

reversible, with
the products of the forward reaction becoming the reactants
for the reverse reaction

Question 77

chemical equilibrium

Answer 77

s. As products accumulate,
collisions resulting in the reverse reaction become more frequent. Eventually, the forward and reverse reactions occur
at the same rate, and the relative concentrations of products
and reactants stop changing. The point at which the reactions
offset one another exactly is called chemical equilibrium.

Question 78

when only can electrons move from one shell to another?

Answer 78

An electron can move from one shell to another only if the energy
it gains or loses is exactly equal to the difference in energy between
the energy levels of the two shells.

Question 79

during formation of a covalent bond (in H in the following example…)…

Answer 79

When two hydrogen
atoms approach each
other, the electron of
each atom is also
attracted to the proton
in the other nucleus.

Question 80

what is a valence?

Answer 80

Valence is typically the number of electrons needed to fill the outermost shell of an atom