Chemistry

Question 1

Element

Answer 1

a substance composed of only one type of atom

Question 2

Molecule

Answer 2

a unit composed of two or more atoms joined together by chemical bonds

Question 3

Compound

Answer 3

a substance composed of 2 or more elements that have been joined by chemical bonds

Question 4

Mixture

Answer 4

a combination of 2 or more substances that do NOT chemically bond

Question 5

Ionic Bonds

Answer 5

• atoms sometimes strip electrons from their bonding partners
• an example is the transfer of an electron from sodium to chlorine
• after the transfer of an electron, both atoms have charges
• a charged atom for molecules is called an ion
• an ionic bond is an attraction between an anion(-) and a cation(+) - oppositely charged ions

Question 6

Ions and Ionic Compounds

Answer 6

• When at atom or molecule loses electrons, it becomes positively charged
• positively charged ions are called cations
• when an atom molecule gains electrons, it becomes negatively charged
• negatively charged ions are called anions
• an atom or molecule can lose more than one electron
• when molecules loose electrons, polyatomic ions are formed

Question 7

Ionic Compounds

Answer 7

• compounds formed by ionic bonds are called ionic compounds

- salts, such as sodium chloride are often found in nature as crystals

Question 8

Covalent Bonds

Answer 8

• molecules are formed by covalent bonds
• a covalent bond is when two atoms share one or more parts of outer-shell electrons
• in a covalent bond, the shared electron counts as part of each atom’s valence shell
• much stronger than ionic bonds - holds lots of energy
• a single covalent bond or double bond is sharing of two parts of valence electrons
• covalent bonds can form between atoms of the same element of atoms of different elements

Question 9

Electronegativity

Answer 9

• outer orbital determines reactivity of atom - electronegativity
• electronegativity is an atom’s attraction for the electrons in a covalent bond
• the more electronegativity an atom, the more strongly it pulls shared electrons toward itself

Question 10

Polar Covalent Bond

Answer 10

• in a nonpolar covalent bond, the atoms share the electron equally
• in a polar covalent bond, one atom is more electronegative and the atoms do not share the electron equally

Question 11

The structure of water

Answer 11

Its two hydrogen atoms are joined to one oxygen atom by single covalent bonds.
But the electrons of the covalent bonds are not shared equally between oxygen and hydrogen.
This unequal sharing makes water a polar molecule.

Question 12

Weak Chemical Bonds

Answer 12

• most of the strongest bonds in organisms are covalent bonds that form a cell’s molecules
• weak chemical bonds, such as ionic bonds and hydrogen bonds, are also important
• weak chemical bonds reinforce shapes of large molecules and help molecules adhere to each other.

Question 13

2 types of compounds exist in living things

Answer 13

inorganic and organic compounds

Question 14

Inorganic Compounds

Answer 14

Water - living things consists of 60% to 90% water, which acts as a way for transport and chemical activities within the cell
Salts - they are important for maintaining osmotic balance in the cell and for many of the cells chemical reactions
acids and bases - these compounds are important for maintaining the proper balance of acidity and alkalinity in the cell

Question 15

Organic Compounds

Answer 15

• all organic compounds contain the elements carbon and hydrogen
• larger than inorganic compounds

Question 16

Elements in Organisms

Answer 16

• the most frequently occurring chemical elements in living things are carbon, hydrogen, and oxygen
• however, a variety of other elements are needed by living organisms these include: sulfer, calcium, phosphorus, iron and sodium

Question 17

Role of elements

Answer 17

sulfer- essential element in variable group of amino acids

calcium- is necessary for bone and tooth formation, blood clotting, and nerve impulse transmission

phosphorus- is also used for bone and tooth formation, essential element in nucleotides, including ATP

iron- is a part of hemoglobin, a molecule needed to carry oxygen in the blood

Sodium- balances both water in the body and acid/base concentration. It also functions in nerve function

Question 18

General Properties of Aqueous Solutions

Answer 18

Acids- substances to ionize in solution to form hydrogen and increase the concentration of H+ in the solution
Bases- are substances that can react with or accept H+ ions.
Salts- are ionic compounds that can be formed by replacing one or more of the hydrogen ions of an acid by a different positive ion

Question 19

Acids, Bases and pH

Answer 19

• dissociation of water molecules leads to acidic and basic conditions that affect living organisms
• water dissociates into hydronium ions and hydroxide ions
• charges in the concentration of these ions can have a great affect on living organisms

Acid- a chemical compound that dissociates into one or more hydrogen ions and one or more negative ions. An acid donates H+ ions to solutions.
Base- dissociates into one or more positive ions and one or more hydroxide ions. A base accepts H+ ions and removes them from solution, reducing the hydrogen ion concentration of a solution

Question 20

Strong and Weak Acids

Answer 20

• strong acids ionize or dissociates completely in water

- weak acids ionize slightly (less than 5%) in water

Question 21

pH

Answer 21

• to describe the activity of a solution we use the pH scale
• is a measure of the concentration of H+ ions in a solution
• is determined by the relative concentration of H+

Question 22

pH Scale

Answer 22

• a logarithmic scale used to express the amount of H+ ions in a solution
• pH is determined as the negative log of the (H+) of a solution
• a change of one whole number represents a tenfold change in the number of H+ ions
• a solution with pH 3 has ten times as many H+ ions as a solution with pH 4

Question 23

Buffers

Answer 23

• a buffer is a substance that helps minimize the change in the pH of a solution when acids or bases are added
• consist of acid-base pair that reversibly combines with hydrogen ions
• buffers work by releasing H+ when their concentration falls, and absorbing H+ when their concentration rises
• are important to living organisms because most cells can survive and function normally only within a relatively narrow range