PPT #1 Chapter 2 Chemistry review, properties of water and pH 2014 HHS AP Biology Eggers

Chemistry vocab terms Matter Element Compound Atom: neutrons, protons, electrons Atomic number Mass number Isotopes

Of what are we made? Everything around us is composed of matter. Matter is anything that has mass and volume. An atom is the smallest particle of matter that cannot be subdivided and still have the same properties. It is the basic unit of matter. Atoms with unique characteristics are called elements. Atoms are composed of even smaller components called subatomic particles.

Label the parts of this atom

Protons, neutrons & electrons Protons: Located in the nucleus, have a mass of 1, and a single positive charge. Neutrons: Located in the nucleus, have a mass of 1 and have no charge. Electrons: Located in energy shells surrounding the nucleus, have almost no mass, and have a single negative charge. Generally, atoms have the same number of electrons as protons and since the opposite charges cancel each other out, atoms are neutral.

Protons What happens if you change the number of protons in the nucleus? The number of protons tells you which element this atom is – and this number is called the atomic number. If you change the number of protons then you’re dealing with a different element. All atoms of the same element have the same atomic number.

Neutrons What happens if you change the number of neutrons in the nucleus of an atom? The element stays the same, but… If you change the number of neutrons then you change the mass number, which is equal to the number of protons plus the number of neutrons. If you change the number of neutrons in an atom then you have an isotope of that element.

Isotopes Isotopes are different forms of the same element. Each isotope has the same number of protons but different number of neutrons. Each isotope of a given element has a different mass number.

Symbols for elements Mass number Atomic number

Isotopes of hydrogen and carbon

How about the electrons? Electrons exist around the nucleus of an atom in electron shells. There are some simple rules about these shells. These are: The first shell will hold up to two electrons. The second shell will hold up to eight electrons. The third shell will also hold up to eight electrons – later shells can hold more but we don’t encounter these elements in biological molecules very often. A full outer shell makes an atom very stable!

Atoms with electron shell diagrams

Naturally occurring elements in the human body

Why do we care about electron shells?

Four major elements in biology and their valance electrons…

Full electron shells are stable – not full shells are reactive Atoms react with each other when their outer electron shells are not full. They can react by sharing electrons, forming covalent bonds, or by stealing electrons, forming ionic bonds.

Covalent bonds

Atoms can share more than one pair of electrons

Types of bonds Nonpolar covalent – when electrons are shared equally between two atoms Polar covalent – when electrons are unequally shared between two atoms Electronegativity: a measure of the tendency of an atom to attract or pull electrons toward itself Ionic – involves the complete transfer of valance electrons between atoms to form two charged atoms called ions Cation Anion Hydrogen bond – electromagnetic attractive interaction between polar molecules Van der Waals interactions – induced electrical interactions between two or more atoms or molecules that are very close to one another

STOP FOR CHECK IN… https://www.youtube.com/watch?v=QXT4OVM4vXI https://www.youtube.com/watch?v=a8LF7JEb0IA

The chemical properties of the water molecule shape all of biology Chemical formula: H2O Two hydrogen atoms covalently bonded to one oxygen molecule But what type of covalent bond is it?

Why is it drawn in a V-shape? Oxygen has an atomic number of 8. Two electrons fill the first shell, leaving 6 in the second shell. Oxygen therefore makes two covalent bonds. The two electron pairs force the unpaired electrons together – these form the covalent bonds with the hydrogen atoms.

The bond between an oxygen and a hydrogen atom is not equal! Oxygen is more electronegative – that means that it has a greater pull on the shared electrons than does hydrogen. Since the electrons are pulled closer to hydrogen, oxygen has a partial negative charge and hydrogen has a partial positive charge.

Polar molecules attract each other This attraction between adjacent water molecules is called hydrogen bonding. It’s a different type of attraction than magnets, but you can use that idea to help conceptually understand how water molecules interact. The partially negative oxygen is attracted to the partially positive hydrogen on a neighboring water.

Hydrogen bonding… Makes water molecules “sticky”. This “stickiness” of water molecules to each other, and also to other polar molecules, results in the unique properties of water that make life as we know it possible.

Property 1: Cohesion Water molecules sticking to each other is called cohesion. Related to cohesion is surface tension.

Property 2: Adhesion Water molecules are attracted to other charged or polar molecules. Glass is charged… This results in the phenomenon of capillary action.

Property 3: High specific heat Heat is the amount of energy associated with movement of atoms and molecules in matter. Temperature measures the intensity of heat and represents the average kinetic energy of the molecules. Water can absorb an enormous amount of heat energy with very little temperature change. Even MORE energy is required when water changes phases – the heat of fusion refers to change from a solid to liquid and heat of vaporization when liquid water changes to gaseous vapor.

Significance of water’s high specific heat Heat of vaporization

Property 4: Water is less dense as a solid than as a liquid

Property 5: Water is a FABULOUS solvent Water readily interacts with any charged or polar molecules. The water molecules that surround the solute are called its hydration shell Molecules that interact well with water are called hydrophilic (water-loving)

…water does not interact well with non-polar molecules Molecules that contain mainly carbon and hydrogen are non-polar – like fats an oils Non-polar molecules cannot interact well with the polar water molecules. They are referred to as hydrophobic (water-hating).

Soap is amphipathic!

STOP FOR CHECK IN… Crash Course Water: Liquid Awesome https://www.youtube.com/watch?v=HVT3Y3_gHGg

Molarity: a measure of the solute concentration of an aqueous solution Calculate molecular mass, which is the sum of the masses of all of the atoms present in a molecule This number is equal to the number of grams in 6.02 x 1023 of that molecule – or one mole (mol) A one molar solution is equal to 1 mol/L. Eg The molecular mass of sucrose is 342 daltons. Therefore, adding 342 g of sucrose to one liter of water would give you a one molar, or 1 M, solution of sucrose. How much sucrose would you add to 1L to make a 0.5M solution of sucrose?

Water can ionize Or break from H2O into OH- and H+ The concentration of H+ in pure water at 25oC due to ionization is 1 x 10-7 M This means that the concentration of OH- must also be 1 x 10-7 M

The pH scale The pH scale is the negative log of the concentration of H+ ions in a solution. In pure water, [H+] = 10-7 which corresponds to pH=7.0 Note that pH declines as [H+] increases – a pH from 0 to 7 is acidic and greater than 7 is basic.

Buffers Buffer: a substance that minimizes changes in the concentration of H+ and OH- by accepting and donating H+ from solution.https://www.youtube.com/watch?v=8Fdt5WnYn1k

STOP… Bozeman science – pH video https://www.youtube.com/watch?v=Xeuyc55LqiY