Water - 3.2 (1) Flashcards
Page 44 & a bit of 45
How do atoms form molecules?
they join together by making bonds with each other
In ionic bonds, what do atoms do?
they give or receive electrons
What do the atoms form?
negative or positive ions that are held together by the attraction of the opposite charges
When do covalent bonds occur?
when atoms share electrons
What is not always shared equally by the atoms of different elements?
the negative electrons
In covalent bonds, what will the electrons spend more time closer to?
one of the atoms than to the other
What will the atom with more negative electrons be in comparison with the other atom in the bond?
slightly negative (delta negative) and the other atom will therefore be slightly positive (delta positive)
The molecules where this occurs in are..
polar
What is meant by polar?
this means that they have regions of negativity and regions of positivity
What are oxygen and hydrogen examples of?
elements that don’t share electrons equally in a covalent bond
Oxygen always has a much greater share of what?
the electrons in an O-H bond
What do many organic molecules contain?
oxygen and hydrogen bonded together which are called hydroxyl (OH) groups (so they are then slightly polar)
What is water (H2O) an example of?
a molecule that is polar
What does water contain?
two of the hydroxyl groups
How do polar molecules, including water, interact with each other?
as the positive and negative regions of the molecule attract each other and form bonds
What are these bonds called?
hydrogen bonds
What are hydrogen bonds?
weak interactions which break and reform between the constantly moving water molecules
Although hydrogen bonds are weak interactions, they occur in…
high numbers
What gives water its unique characteristics which are essential for life on this planet?
hydrogen bonding
What kind of boiling point does water have?
a high boiling point
Is water a small molecule that is much lighter than the gases carbon dioxide or oxygen?
yes
Unlike oxygen and carbon dioxide, water is a liquid at…
room temperature, and this is due to the hydrogen bonding between water molecules
What does it take a lot of to increase the temperature of water and to cause water to become gaseous (or to evaporate)?
a lot of energy
When water freezes, what happens?
it turns to ice
How are most substances in their solid state than in their liquid state?
more dense
When water turns into ice, what happens?
it becomes less dense
Why does water become less dense when it turns into ice?
because of the hydrogen bonds that are formed
As water is cooled below 4 degrees celsius, what do the hydrogen bonds do?
they fix the positions of the polar molecules slightly further apart than the average distance in the liquid state
What does this produce?
a giant, rigid, but open structure, with every oxygen atom at the centre of a tetrahedral arrangement of hydrogen atoms
What does this result in?
a solid that is less dense than liquid water
