Bellringer Answer the following questions “How do you think the words molecules, elements, and atoms are related?” “What does water look like?” Bellringer

Properties of Water Chapters 2.1 & 2.2

Water is essential Everything that makes you up depends on water. All life processes take place in a watery environment (aqueous solution) How water is shaped plays a role in why it is used in your body. Water is essential

Atomic Structure

Atomic Structure Atoms are made up of Protons – positively charged Neutrons – neutrally charged Electrons – negatively charged The protons and neutrons are found in the center of the atom (called the nucleus) Electrons are found on the outside in the electron cloud (or shell) Atomic Structure

More simplistic, but still helpful Better represents reality

Covalent bonds – atoms share electrons and hold together this way (very strong bond) Ionic bonds – atoms give up or take an electron from another atom, this causes a change in charge and makes them hold together Types of bonds

Covalent bond

Ionic bond

Polarity Water is a polar molecule This means one end of the molecule is negative and one end is positive Oxygen is negative Hydrogen is positive This means water is attracted to similar polar molecules So, water likes other water molecules Polarity

Non-polar There are also non-polar molecules. This means they do not have differently charged regions on them. Fats are common non-polar molecules What happens when you try to mix water and oil? “Like dissolves like” Non-polar

Water and Oil Notice the separation between the two fluids. The oil is hydrophobic, so it is repulsed by the water. This causes the oil to stick together and separate itself from the water in a dramatic fashion. This can also be noticed if you’ve ever had oil and vinegar. If you wanted to use that on a salad, you would have to shake it up first so the oil and vinegar infuses together more easily.

Hydrogen bonds are attractions between slightly positive hydrogen atoms and slightly negative oxygen atoms (sometimes nitrogen) These are so important that they are even used to support your DNA as well as protein folding. Hydrogen Bonds

Hydrogen bond H O H  –  +  –  +  –  +  –  + —— —— Fig. 3-2 Figure 3.2 Hydrogen bonds between water molecules The charged regions of a polar water molecule are attracted to oppositely charged parts of neighboring molecules. Each molecule can hydrogen-bond to multiple partners, and these associations are constantly changing.  –  +

An individual hydrogen bond is much weaker than a covalent bond. These bonds are the reason why water is liquid much of the time. There are important properties of hydrogen bonds (which you need to remember) Hydrogen Bonds

Properties of hydrogen bonds High Specific Heat Water resists change in temperature. This means water has to absorb heat to rise in temperature Think about cells – why would this be really important? Properties of hydrogen bonds

Properties of hydrogen bonds Cohesion Attraction among molecules of the same substance. Water likes other water molecules, so they stick to each other easily This is why water beads on windows, forms droplets. Gives surface of water (called surface tension) Properties of hydrogen bonds

Figure 3.4 Walking on water The high surface tension of water, resulting from the collective strength of its hydrogen bonds, allows he water strider to walk on the surface of a pond

Properties of hydrogen bonds Adhesion Attraction of water molecules to different substances. This is why water “climbs” up the edge of a test tube. What about plants? You will need to be able to distinguish the differences between all 3 of these properties. Make sure you never forget them! Properties of hydrogen bonds

Adhesion Water-conducting cells Cohesion 150 µm Fig. 3-3 Adhesion Water-conducting cells Direction of water movement Cohesion Figure 3.3 Water transport in plants Adhesion of the water to cell walls by hydrogen bonds helps resist the doward pull of gravity. Cohesion due to hydrogen bonds between water molecules helps hold together the column of water within the cells Evaporation from leaves pulls water upwards from the roots through water-conducting cells. Because of the properties of cohesion and adhesion, the tallest tress can transport water more than 100m upward – approximately one-quarter the height of the Empire State Building. 150 µm

Properties of hydrogen bonds When water freezes, it expands. This is because the energy within the molecules has slowed down, allowing for longer lasting hydrogen bonds. Helps protect and insulate organisms in water systems (e.g. lakes, rivers,) from cold air Properties of hydrogen bonds

Hydrogen bonds are stable Hydrogen bonds break and re-form Fig. 3-6 Hydrogen bond Ice Hydrogen bonds are stable Liquid water Hydrogen bonds break and re-form Figure 3.6 Ice: crystalline structure and floating barrier In ice, each molecule is hydrogen-boded to four neighbors in a three-dimensional crystal. Because the crystal is spacious, ice has fewer molecules than an equal volume of liquid water. In other words, ice is less dense than liquid water. Floating ice becomes a barrier that protects the liquid water below from the colder air. The marine organisms shown here is a type of shrimp called krill; it was photographed beneath floating ice in the Antarctic Ocean.

Properties of hydrogen bonds Water is considered the most common solvent in biology Molecules and ions can’t form in a non-water environment. Big molecules have to be dissolved before they can move. This is why water is considered to be the closest thing to a “universal solvent” on Earth. Properties of hydrogen bonds

Solutions 3 parts What are these components in a can of soda? Solution – mixture of substances that is uniform throughout Solvent – substance in the greatest amount that dissolves something else (like water) Solute – the substance that dissolves What are these components in a can of soda? What about in a glass of sweet tea? Solutions

Since substances sometimes break down into ions in water, we can have some free floating protons in a solution Higher amount of protons = acid Lower amounts of protons = base Strongest acid = zero on the pH scale. Strongest base = 14 on the pH scale. The closer a substance gets to the number 7 on the scale, the more neutral (or less reactive) it becomes. Acids and Bases

More acidic 1 2 3 Acid rain Acid rain 4 5 Normal rain 6 7 8 9 10 11 12 Fig. 3-10 More acidic 1 2 3 Acid rain Acid rain 4 5 Normal rain 6 7 8 9 10 Figure 3.10 Acid precipitation and its effects on a forest Acid rain is thought the be responsible for killing trees in many forests, including the fir forest shown here in the Czech Republic 11 12 13 More basic 14