Chemical Basis of Life

Question 1

Matter

Answer 1

anything that occupies space and has mass Rock, wood, air, metal, water, and animals are all matter

Question 2

Element

Answer 2

pure substance that cannot be broken down into other substances by chemical means Elements are often described as the “basic ingredients” of matter.

Question 3

Number of elements important to life

Answer 3

25

Question 4

Four important elements to life

Answer 4

oxygen (O), carbon (C), hydrogen (H), and nitrogen (N)—make up about 96 percent of the living matter in your body

Question 5

Elements composing most of remaining 4 %

Answer 5

Calcium (Ca), phosphorus (P), potassium (K), sulfur (S)

Question 6

Compound

Answer 6

substance containing two or more elements that are chemically combined in a fixed ratio

water (H2O) is a compound that always contains the same ratio of hydrogen combined with oxygen

Question 7

Atom

Answer 7

smallest possible particle of an element

a carbon atom is the smallest possible “piece” of the element carbon

Question 8

Subatomic Particles

Answer 8

all elements are made up of even smaller components called subatomic particles – proton, electron, neutron

Question 9

Proton

Answer 9

subatomic particle with a single unit of positive electrical charge (+)

Question 10

Electron

Answer 10

subatomic particle with a single unit of negative electrical charge (-)

Question 11

Neutron

Answer 11

A third type of subatomic particle, the neutron, is electrically neutral, meaning it has no electrical charge

Question 12

Physical and Chemical Properties of Elements

Answer 12

An element’s physical and chemical properties depend on the number and arrangement of its subatomic particles

Question 13

Nucleus

Answer 13

An atom’s protons and neutrons are tightly packed together, forming a central core called the nucleus

Electrons, which have much less mass than neutrons and protons, continually move about the outside of the nucleus at great speed

The attraction between the negatively charged electrons and the positively charged protons keeps the electrons close to the nucleus

Question 14

Atomic Number

Answer 14

number of protons in their atoms

a helium atom, with 2 protons, has an atomic number of 2

Question 15

Electrons Not Constant

Answer 15

Left alone, an atom tends to hold as many electrons as protons

Certain atoms can lose one or more electrons, while some atoms can gain one or two electrons

The number of electrons determines how the atom interacts with other atoms

Question 16

Isotopes

Answer 16

Isotopes of an element have the same number of protons in their atoms but different numbers of neutrons

Carbon-12 (usually written ¹²C), which has atoms containing 6 neutrons, makes up about 99 percent of all naturally occurring carbon

Question 17

Stable Isotopes

Answer 17

Both 12C and 13C are stable isotopes, meaning their nuclei do not change with time

Question 18

Radioactive Isotope

Answer 18

Nucleus decays (breaks down) over time, giving off radiation in the form of matter and energy

Radioactive isotopes are useful as “biological spies” for observing what happens to different atoms within organisms

Though radioactive isotopes have many beneficial uses, the particles and energy they give off can also damage cells

Question 19

Atom’s Structure Affects Reaction with other Elements

Answer 19

The key is the atom’s electrons. Electrons differ in the amount of energy they have and how tightly they are held by the protons in the nucleus. Based on these properties, chemists describe an atom’s electrons as belonging to certain energy levels.

Question 20

Ionic Bond

Answer 20

an atom transfers an electron to another atom

Table salt, or sodium chloride (NaCl), is a compound formed as a result of electron transfer between sodium (Na) atoms and chlorine (Cl) atoms

When the two atoms collide, the chlorine atom strips away sodium’s outer electron. In the process, chlorine’s highest energy level, now with 8 electrons, becomes filled. In losing an electron, the sodium atom’s second energy level, which already has 8 electrons, becomes the highest. It, too, is filled

Losing an electron leaves the sodium ion with a charge of 1+, while gaining an electron gives chlorine (now called chloride) a charge of 1-. The attraction holding the oppositely charged Na+ and Cl- ions together is the ionic bond

Question 21

Covalent Bond

Answer 21

a covalent bond forms when two atoms share electrons

an oxygen atom (O) shares a pair of electrons with each of two hydrogen atoms, forming two covalent bonds

Question 22

Number of Bonds

Answer 22

Number of bonds an atom can form usually equals the number of additional electrons that will fill its highest energy level

A hydrogen atom can accept one additional electron, so it can form one bond. In contrast, an oxygen atom can accept two electrons in its highest energy level, so it can form two bonds

Question 23

Molecules

Answer 23

Two or more atoms held together by covalent bonds form a molecule

Question 24

Chemical Formula

Answer 24

A chemical formula tells you the number and types of atoms in a molecule.

For example, the chemical formula H₂O indicates that a water molecule contains two atoms of hydrogen and one atom of oxygen. (The absence of a subscript after the oxygen symbol is understood to mean “1.”)

Question 25

Structural Formula

Answer 25

Indicates how atoms in a molecule are linked by bonds

Question 26

Space-Filling Model

Answer 26

Color-coded spheres symbolize atoms, is a drawing that depicts a three-dimensional model of a molecule

Question 27

Chemical Reactions

Answer 27

Within your cells certain molecules constantly become rearranged into other molecules as existing chemical bonds break (absorbing energy from the surroundings) and new ones form (releasing energy to the surroundings). Such changes, which result in the formation of one or more new substances, are called **chemical reactions** Chemical reactions do not create or destroy atoms, but only rearrange them

Question 28

Chemical Equation

Answer 28

is a convenient way to describe a chemical reaction. Just like a math equation, such as 1 + 1 = 2, you read this equation from left to right. It states that two molecules of hydrogen (2 x H₂) react with one molecule of oxygen (O₂), forming two molecules of water (2 x H₂O)

Question 29

Reactants

Answer 29

starting material for a chemical reaction

Question 30

Products

Answer 30

material created as a result of a chemical reaction

Question 31

Structure of Water

Answer 31

the key to water's unusual properties is that the electrons of each covalent bond are not shared equally between oxygen and hydrogen atoms. Oxygen pulls electrons much more strongly than does hydrogen. The unequal sharing of electrons causes the oxygen end of the molecule to have a slight negative charge, while the end with the two hydrogen atoms is slightly positive.

Question 32

Polar Molecule

Answer 32

A molecule in which opposite ends have opposite electric charges.

Question 33

Hydrogen Bond

Answer 33

Weak attraction between the hydrogen atom of one molecule and a slightly negative atom within another molecule is a type of chemical bond called a hydrogen bond.

Question 34

Cohesion

Answer 34

Tendency of molecules of the same kind to stick to one another is called cohesion. Cohesion is much stronger for water than for most other liquids.

Question 35

Adhesion

Answer 35

Attraction that occurs between unlike molecules.

Question 36

Water and Cohesion and Adhesion

Answer 36

Trees depend on cohesion and adhesion to help transport water from their roots to their leaves.

Question 37

Thermal Energy

Answer 37

Total amount of energy associated with the random movement of atoms and molecules in a sample of matter.

Question 38

Temperature

Answer 38

Temperature is a measure of the average energy of random motion of the particles in a substance. When two substances differ in temperature, thermal energy in the form of heat is transferred from the warmer substance to the cooler one. One result of this property is that it causes oceans and large lakes to moderate the temperatures of nearby land areas.

Question 39

Density

Answer 39

Density is the amount of matter in a given volume. A high-density substance is more tightly "packed" than a low-density substance. In most substances, the solid state is more dense than the liquid state. Water is just the opposite—its solid form (ice) is less dense than the cold liquid form. How is the fact that ice floats important to living things? If ice sank, it would form on the bottom of a body of water as the water was cooling. Ponds and lakes would freeze from the bottom up, trapping the fish and other organisms in a shrinking layer of water without access to the nutrients from the muddy bottom. Instead, when a deep body of water cools, the floating ice insulates the liquid water below, allowing life to persist under the frozen surface.

Question 40

Solution

Answer 40

When you stir table salt into a glass of water, you are forming a solution, a uniform mixture of two or more substances.

Question 41

Solvent

Answer 41

The substance that dissolves the other substance and is present in the greater amount is the solvent (in this case, water).

Question 42

Solute

Answer 42

The substance that is dissolved and is present in a lesser amount is the solute (in this case, salt).

Question 43

Aqueous Solution

Answer 43

When water is the solvent, the result is called an aqueous solution. Water is the main solvent inside all cells, in blood, and in plant sap. Water dissolves an enormous variety of solutes necessary for life.

Question 44

Acid

Answer 44

A compound that donates H+ ions to a solution is called an acid.

Question 45

Base

Answer 45

A compound that removes H+ ions from an aqueous solution is called a base.

Question 46

pH Scale

Answer 46

The pH scale describes how acidic or basic a solution is. The scale ranges from 0 (most acidic) to 14 (most basic).

Question 47

Buffers

Answer 47

Many biological fluids contain buffers, substances that cause a solution to resist changes in pH. An example of the importance of buffers is their role in regulating the pH of the blood. Human blood normally has a pH of about 7.4. Certain chemical reactions within your cells can lead to an increase in the amount of H+ ions. When these ions move into the blood, buffers take up some of them, preventing the blood from becoming acidic enough to endanger cell function.