Chapter 2 The Molecules of Cells
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78 Terms
What is matter?
Anything that takes up space and has mass.
3 states of matter
Solid, liquid, and gas.
What is a element
A substance that cannot be broken down by ordinary chemical means.
How many naturally occurring elements are there?
92
What six elements make up 95% of organisms?
Oxygen, carbon, hydrogen, nitrogen, phosphorus, and sulfur.
what’s a atom
smallest part of an element that has the element’s properties
What are the three subatomic particles
Protons, neutrons, and electrons.
charge does a proton have?
Positive (+).
charge does a neutron have?
No charge (neutral)
charge does an electron have?
Negative (−)
Where are protons and neutrons found?
in nucleus
Where are electrons found?
Around the nucleus in electron shells.
What is the atomic number?
The number of protons.
What is the mass number?
Protons + neutrons.
What are groups on the periodic table?
Vertical columns.
What are periods on the periodic table?
Horizontal rows.
What are isotopes?
Atoms of the same element with different numbers of neutrons.
What are radioactive isotopes?
sotopes that release energy as they decay.
What are some uses of low-level radiation?
Medical scans, such as thyroid scans and PET scans.
What are some uses of high-level radiation?
Killing bacteria/fungi and treating cancer.
What is an electron shell?
An energy level around the nucleus.
How many electrons can the first shell hold?
2 electrons.
How many electrons can most other shells hold?
8 electrons.
What is the octet rule?
Atoms are stable with 8 electrons in their outer shell.
What is a molecule?
Two or more atoms bonded together.
What is a compound?
Two or more different elements bonded together.
What happens to energy during a chemical reaction?
Energy may be released or absorbed.
What is an ion?
A charged atom formed by gaining or losing electrons.
What happens when an atom loses electrons?
It becomes positively charged.
What happens when an atom gains electrons?
It becomes negatively charged.
What is an ionic bond?
Attraction between oppositely charged ions.
What happens in ionic bonding?
Electrons are transferred from one atom to another.
What is a covalent bond?
A bond formed when atoms share electrons
What is a single covalent bond?
Sharing one pair of electrons.
What is a double covalent bond?
Sharing two pairs of electrons.
Why is the shape of a molecule important?
Its shape affects its biological function.
What shape do molecules with two atoms have
linear
What shape does methane have?
Tetrahedral
What is a nonpolar covalent bond?
Electrons are shared equally.
What is a polar covalent bond?
Electrons are shared unequally.
What is electronegativity?
An atom’s attraction for electrons
Why is water a polar molecule?
Oxygen attracts electrons more strongly than hydrogen.
What charge does oxygen have in water?
Partial negative
What charge does hydrogen have in water?
Partial positive
What is a hydrogen bond?
An attraction between partially charged molecules.
Are individual hydrogen bonds strong or weak?
Weak individually, but strong collectively
What percentage of organisms is water?
About 70–80%
Why is water liquid at Earth’s surface temperatures?
Hydrogen bonding
What is water’s heat capacity?
Its ability to absorb heat without a large temperature change.
Why is high heat capacity important to organisms?
It helps maintain stable body temperatures.
What is a calorie?
Heat needed to raise 1 g of water by 1°C.
What is water’s heat of vaporization?
The energy needed to turn water into gas.
How does sweating cool the body?
Evaporation removes heat from the skin
What is a solvent?
A substance that dissolves other substances.
What is a solute?
A substance dissolved in a solution.
Why is water a good solvent?
Because it is polar.
What does hydrophilic mean?
Attracted to water.
What does hydrophobic mean?
Not attracted to water.
What is cohesion?
Water molecules sticking to each other.
What is adhesion?
Water sticking to other polar surfaces.
What is surface tension?
The force that holds molecules together at a liquid’s surface.
Why can some insects walk on water?
Water has high surface tension.
Is ice more or less dense than liquid water?
Less dense.
At what temperature is water most dense?
4°C.
Why does ice float?
Ice is less dense than liquid water.
Why is ice less dense than liquid water?
Hydrogen bonds form an open crystal structure.
What ions does water produce when it ionizes?
H⁺ and OH⁻.
What is an acid?
A substance that releases H⁺ in water
What is a base?
A substance that releases OH⁻ or takes up H⁺.
What does a high H⁺ concentration mean?
The solution is acidic
What does a low H⁺ concentration mean?
The solution is basic.
What does pH measure?
Acidity or basicity.
What pH is acidic?
Below 7.
What pH is neutral?
7
What pH is basic?
Above 7.
What is a buffer?
A chemical that helps keep pH within normal limits.
What elements are always found in organic molecules?
Carbon and hydrogen.
Why is carbon important?
It can form many different organic molecules.