1.1. Water

Question 1

The Earth was formed…
Water was created…
First living organism was created…

Answer 1

…app. 4.6 billion years ago.
…app. 4,5 billion years ago (when Earth solidified and cooled, steam condensated).
…app. 3.8 billion years ago.

Question 1

Why is water the major medium for life?

Answer 1

All living substances, when dissolved in a liquid solvent, start moving more rapidly, creating more collisions, and chemical reactions to occur between them (result in a product - called metabolical reactions).

Question 1

Metabolical reactions

Answer 1

Chemical reactions between two living substances in a liquid solvent in which a product is made.

Question 2

Life likely occurred spontaneously in…

Answer 2

…swamps, ponds, hydrothermal pools, the sea…

Question 3

Hydrogen atom

Answer 3

• atomic number: 1
• mass number: 1
• 1st period
• 1st column
• 1 electron
• 1 proton
• 0 neutrons
• 1 shell

Question 4

Oxygen atom

Answer 4

• atomic number 8
• mass number 16
• 2nd period
• 16th column
• 8 electrons
• 8 protons
• 8 neutrons
• 2 shells

Question 5

Why is oxygen reactive?

Answer 5

Two of the six electrons in its outer shell are separated and are looking for other electrons to form an electron pair.

Question 6

How are covalent bonds in water created?

Answer 6

Electron shells of different atoms (O and H) will spontaneously draw near each other because of the attraction between them. When they get close enough, they’ll overlap and their lone electrons will form shared electron pairs.

Question 7

another name for covalent bonds

Answer 7

shared electron pairs

Question 8

Why is the water molecule polar?

Answer 8

Because covalent bonds (shared electrons) are more attracted to the side that contains more protons (that is, which is more electronegative) which is the side on which oxygen’s nucleus is, so they will lean towards that side. So one pole has a more negative “charge” than the other, making it polar.

Question 9

How is water polar but not charged?

Answer 9

The overall sum of protons and electrons creates a 1:1 ratio making the overall molecule neutral, but the unequal distribution of particles (e-) creates polarity.

Question 10

hydrogen bond

Answer 10

an attraction force (not a chemical bond) between atoms of oxygen and hydrogen of different water molecules

Question 11

What is the state of hydrogen bonds in different states of matter?

Answer 11

• gaseous: completely broken, molecules float freely
• liquid: partially broken up because of more mol. movement but can be remade
• solid: completely solid/stable and they keep water mol. as far away from each other as possible creating a permanent structure (crystal lattice)

Question 12

Which molecules are polar and which are not?

Answer 12

The ones whose atoms’ electronegativities differ by a lot are polar (H2O, NH3) and those whose atoms have similar values of electronegativity are non-polar (CO2).

Question 13

The most electronegative elements are situated…

Answer 13

…in the right upper corner of the PTE.

Question 14

hydrophilic molecules

Answer 14

molecules attracted to water

Question 15

hydrophobic molecules

Answer 15

molecules repulsed by water

Question 16

What type of substances does water dissolve?

Answer 16

Either polar or charged (MgSO4 example - attracted, surrounded, overpowered ionic bonds, split, hydrated ions) - both are hydrophilic.

Question 17

cohesion

Answer 17

the binding of same molecules by H-bond (attraction between molecules of the same kind)

Question 18

adhesion

Answer 18

the binding of different molecules by (weak) H-bonds (hydrogen-negatively charged ends of other molecules) (attraction between different molecules)

Question 19

What are molecules which are both hydrophilic and hydrophobic called?

Answer 19

Amphipathic molecules.

Question 20

lipoproteins

Answer 20

transport all (hydrophobic) substances through blood - they are both hydrophilic and hydrophobic

Question 21

Are the following molecules charged or polar?:
- glucose (the simplest sugar)
- amino acids
- urea
- ethanol

Answer 21

• polar (soluble in water)
• charged (negatively)
• polar (dissolves in urine, kidneys get urea from blood)
• polar

Question 22

How was water (most likely) delivered to Earth?

Answer 22

By colliding asteroids (more often collided in the past and contained more water).

Question 23

Why is there life only on Earth?

Answer 23

• the distance of Earth from Sun keeps temp. on Earth below water’s boiling point
• Earth’s gravity keeps water in its atmosphere (planet)

Question 24

Goldilocks principle

Answer 24

planet orbiting its sun at just the right distance for liquid water to exist on its surface - not too cold or too hot = Goldilocks zone